Journal articles
O'Sullivan M (In Press). Climate-driven variability and trends in plant productivity over recent decades based on three global products. Global Biogeochemical Cycles
Mercado LM, Medlyn BE, Huntingford C, Oliver R, Clark D, Sitch S, Zelazowski P, Kattge J, Harper A, Cox PM, et al (In Press). Large sensitivity in land carbon storage due to geographical and temporal variation in the thermal response of photosynthetic capacity. New Phytologist
Zhang L, Jiang F, He W, Wu M, Wang J, Ju W, Wang H, Zhang Y, Sitch S, Walker AP, et al (2023). A Robust Estimate of Continental‐Scale Terrestrial Carbon Sinks Using GOSAT XCO2 Retrievals. Geophysical Research Letters, 50(6).
Cox AJF, Hartley IP, Meir P, Sitch S, Dusenge ME, Restrepo Z, González-Caro S, Villegas JC, Uddling J, Mercado LM, et al (2023). Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change.
New Phytol,
238(6), 2329-2344.
Abstract:
Acclimation of photosynthetic capacity and foliar respiration in Andean tree species to temperature change.
Climate warming is causing compositional changes in Andean tropical montane forests (TMFs). These shifts are hypothesised to result from differential responses to warming of cold- and warm-affiliated species, with the former experiencing mortality and the latter migrating upslope. The thermal acclimation potential of Andean TMFs remains unknown. Along a 2000 m Andean altitudinal gradient, we planted individuals of cold- and warm-affiliated species (under common soil and irrigation), exposing them to the hot and cold extremes of their thermal niches, respectively. We measured the response of net photosynthesis (Anet ), photosynthetic capacity and leaf dark respiration (Rdark ) to warming/cooling, 5 months after planting. In all species, Anet and photosynthetic capacity at 25°C were highest when growing at growth temperatures (Tg ) closest to their thermal means, declining with warming and cooling in cold-affiliated and warm-affiliated species, respectively. When expressed at Tg , photosynthetic capacity and Rdark remained unchanged in cold-affiliated species, but the latter decreased in warm-affiliated counterparts. Rdark at 25°C increased with temperature in all species, but remained unchanged when expressed at Tg. Both species groups acclimated to temperature, but only warm-affiliated species decreased Rdark to photosynthetic capacity ratio at Tg as temperature increased. This could confer them a competitive advantage under future warming.
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Author URL.
Wang H, Ciais P, Sitch S, Green JK, Tao S, Fu Z, Albergel C, Bastos A, Wang M, Fawcett D, et al (2023). Anthropogenic disturbance exacerbates resilience loss in the Amazon rainforests.
Glob Chang BiolAbstract:
Anthropogenic disturbance exacerbates resilience loss in the Amazon rainforests.
Uncovering the mechanisms that lead to Amazon forest resilience variations is crucial to predict the impact of future climatic and anthropogenic disturbances. Here, we apply a previously used empirical resilience metrics, lag-1 month temporal autocorrelation (TAC), to vegetation optical depth data in C-band (a good proxy of the whole canopy water content) in order to explore how forest resilience variations are impacted by human disturbances and environmental drivers in the Brazilian Amazon. We found that human disturbances significantly increase the risk of critical transitions, and that the median TAC value is ~2.4 times higher in human-disturbed forests than that in intact forests, suggesting a much lower resilience in disturbed forests. Additionally, human-disturbed forests are less resilient to land surface heat stress and atmospheric water stress than intact forests. Among human-disturbed forests, forests with a more closed and thicker canopy structure, which is linked to a higher forest cover and a lower disturbance fraction, are comparably more resilient. These results further emphasize the urgent need to limit deforestation and degradation through policy intervention to maintain the resilience of the Amazon rainforests.
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Author URL.
Dong G, Fan L, Fensholt R, Frappart F, Ciais P, Xiao X, Sitch S, Xing Z, Yu L, Zhou Z, et al (2023). Asymmetric response of primary productivity to precipitation anomalies in Southwest China. Agricultural and Forest Meteorology, 331
van der Woude AM, Peters W, Joetzjer E, Lafont S, Koren G, Ciais P, Ramonet M, Xu Y, Bastos A, Botía S, et al (2023). Author Correction: Temperature extremes of 2022 reduced carbon uptake by forests in Europe.
Nat Commun,
14(1).
Author URL.
Bittencourt P, Rowland L, Sitch S, Poyatos R, Miralles DG, Mencuccini M (2023). Bridging Scales: an Approach to Evaluate the Temporal Patterns of Global Transpiration Products Using Tree‐Scale Sap Flow Data. Journal of Geophysical Research Biogeosciences, 128(3).
Yu L, Fan L, Ciais P, Sitch S, Fensholt R, Xiao X, Yuan W, Chen J, Zhang Y, Wu X, et al (2023). Carbon dynamics of Western North American boreal forests in response to stand-replacing disturbances.
International Journal of Applied Earth Observation and Geoinformation,
122Abstract:
Carbon dynamics of Western North American boreal forests in response to stand-replacing disturbances
North American boreal forests are known to be an important carbon pool in boreal ecosystems, but have experienced extensive tree mortality and carbon loss due to multiple agents of stand-replacing disturbances in recent decades. However, the impacts of these stand-replacing disturbances on forest dynamics are still unknown. We used a recently developed remote-sensing based stand-replacing disturbance product, coupled with aboveground biomass (AGB), gross primary productivity (GPP) and leaf area index (LAI) datasets to estimate the impacts of stand-replacing disturbances (e.g. fires, logging and insect outbreaks) on the carbon balance of western North American boreal forests during 2000–2012. Our results showed that fire, logging and insect outbreaks resulted in AGB losses of 23.4, 16.6, and 4.7 Tg/yr, respectively. In the post-disturbance periods, AGB did not recover to its pre-disturbed levels in the 10th year, which is longer than the recovery time of GPP and LAI. Furthermore, the losses of AGB, GPP and LAI in fire events were the dominant factors for forest recovery after stand-replacing fire. Vapor Pressure Deficit (VPD), soil clay content, temperature and precipitation were the important factors for forest recovery after stand-replacing insect outbreaks and stand-replacing logging. When removing the impact of environmental factors, our results showed a smaller magnitude of AGB, GPP and LAI loss relative to the results including these factors, although similar recovery trajectories were observed among the two results. The results have important implications for understanding the effects of stand-replacing disturbances on the carbon dynamics of boreal forests, which is required to adopt effective forest management strategies after disturbance.
Abstract.
Niu Z, He H, Yu P, Sitch S, Zhao Y, Wang Y, Jain AK, Vuichard N, Si B (2023). Climate Change and CO2 Fertilization Have Played Important Roles in the Recent Decadal Vegetation Greening Trend on the Chinese Loess Plateau. Remote Sensing, 15(5).
Ito A, Li T, Qin Z, Melton JR, Tian H, Kleinen T, Zhang W, Zhang Z, Joos F, Ciais P, et al (2023). Cold-Season Methane Fluxes Simulated by GCP-CH<sub>4</sub> Models.
GEOPHYSICAL RESEARCH LETTERS,
50(14).
Author URL.
Fawcett D, Sitch S, Ciais P, Wigneron JP, Silva-Junior CHL, Heinrich V, Vancutsem C, Achard F, Bastos A, Yang H, et al (2023). Declining Amazon biomass due to deforestation and subsequent degradation losses exceeding gains.
Glob Chang Biol,
29(4), 1106-1118.
Abstract:
Declining Amazon biomass due to deforestation and subsequent degradation losses exceeding gains.
In the Amazon, deforestation and climate change lead to increased vulnerability to forest degradation, threatening its existing carbon stocks and its capacity as a carbon sink. We use satellite L-Band Vegetation Optical Depth (L-VOD) data that provide an integrated (top-down) estimate of biomass carbon to track changes over 2011-2019. Because the spatial resolution of L-VOD is coarse (0.25°), it allows limited attribution of the observed changes. We therefore combined high-resolution annual maps of forest cover and disturbances with biomass maps to model carbon losses (bottom-up) from deforestation and degradation, and gains from regrowing secondary forests. We show an increase of deforestation and associated degradation losses since 2012 which greatly outweigh secondary forest gains. Degradation accounted for 40% of gross losses. After an increase in 2011, old-growth forests show a net loss of above-ground carbon between 2012 and 2019. The sum of component carbon fluxes in our model is consistent with the total biomass change from L-VOD of 1.3 Pg C over 2012-2019. Across nine Amazon countries, we found that while Brazil contains the majority of biomass stocks (64%), its losses from disturbances were disproportionately high (79% of gross losses). Our multi-source analysis provides a pessimistic assessment of the Amazon carbon balance and highlights the urgent need to stop the recent rise of deforestation and degradation, particularly in the Brazilian Amazon.
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Author URL.
Fernández-Martínez M, Peñuelas J, Chevallier F, Ciais P, Obersteiner M, Rödenbeck C, Sardans J, Vicca S, Yang H, Sitch S, et al (2023). Diagnosing destabilization risk in global land carbon sinks.
Nature,
615(7954), 848-853.
Abstract:
Diagnosing destabilization risk in global land carbon sinks
Global net land carbon uptake or net biome production (NBP) has increased during recent decades1. Whether its temporal variability and autocorrelation have changed during this period, however, remains elusive, even though an increase in both could indicate an increased potential for a destabilized carbon sink2,3. Here, we investigate the trends and controls of net terrestrial carbon uptake and its temporal variability and autocorrelation from 1981 to 2018 using two atmospheric-inversion models, the amplitude of the seasonal cycle of atmospheric CO2 concentration derived from nine monitoring stations distributed across the Pacific Ocean and dynamic global vegetation models. We find that annual NBP and its interdecadal variability increased globally whereas temporal autocorrelation decreased. We observe a separation of regions characterized by increasingly variable NBP, associated with warm regions and increasingly variable temperatures, lower and weaker positive trends in NBP and regions where NBP became stronger and less variable. Plant species richness presented a concave-down parabolic spatial relationship with NBP and its variability at the global scale whereas nitrogen deposition generally increased NBP. Increasing temperature and its increasing variability appear as the most important drivers of declining and increasingly variable NBP. Our results show increasing variability of NBP regionally that can be mostly attributed to climate change and that may point to destabilization of the coupled carbon–climate system.
Abstract.
Wang Y, Liu J, Wennberg PO, He L, Bonal D, Köhler P, Frankenberg C, Sitch S, Friedlingstein P (2023). Elucidating climatic drivers of photosynthesis by tropical forests.
Glob Chang Biol,
29(17), 4811-4825.
Abstract:
Elucidating climatic drivers of photosynthesis by tropical forests.
Tropical forests play a pivotal role in regulating the global carbon cycle. However, the response of these forests to changes in absorbed solar energy and water supply under the changing climate is highly uncertain. Three-year (2018-2021) spaceborne high-resolution measurements of solar-induced chlorophyll fluorescence (SIF) from the TROPOspheric Monitoring Instrument (TROPOMI) provide a new opportunity to study the response of gross primary production (GPP) and more broadly tropical forest carbon dynamics to differences in climate. SIF has been shown to be a good proxy for GPP on monthly and regional scales. Combining tropical climate reanalysis records and other contemporary satellite products, we find that on the seasonal timescale, the dependence of GPP on climate variables is highly heterogeneous. Following the principal component analyses and correlation comparisons, two regimes are identified: water limited and energy limited. GPP variations over tropical Africa are more correlated with water-related factors such as vapor pressure deficit (VPD) and soil moisture, while in tropical Southeast Asia, GPP is more correlated with energy-related factors such as photosynthetically active radiation (PAR) and surface temperature. Amazonia is itself heterogeneous: with an energy-limited regime in the north and water-limited regime in the south. The correlations of GPP with climate variables are supported by other observation-based products, such as Orbiting Carbon Observatory-2 (OCO2) SIF and FluxSat GPP. In each tropical continent, the coupling between SIF and VPD increases with the mean VPD. Even on the interannual timescale, the correlation of GPP with VPD is still discernable, but the sensitivity is smaller than the intra-annual correlation. By and large, the dynamic global vegetation models in the TRENDY v8 project do not capture the high GPP seasonal sensitivity to VPD in dry tropics. The complex interactions between carbon and water cycles in the tropics illustrated in this study and the poor representation of this coupling in the current suite of vegetation models suggest that projections of future changes in carbon dynamics based on these models may not be robust.
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Author URL.
Kou-Giesbrecht S, Arora VK, Seiler C, Arneth A, Falk S, Jain AK, Joos F, Kennedy D, Knauer J, Sitch S, et al (2023). Evaluating nitrogen cycling in terrestrial biosphere models: a disconnect between the carbon and nitrogen cycles.
EARTH SYSTEM DYNAMICS,
14(4), 767-795.
Author URL.
Ruehr S, Keenan TF, Williams C, Zhou Y, Lu X, Bastos A, Canadell JG, Prentice IC, Sitch S, Terrer C, et al (2023). Evidence and attribution of the enhanced land carbon sink.
Nature Reviews Earth and Environment,
4(8), 518-534.
Abstract:
Evidence and attribution of the enhanced land carbon sink
Climate change has been partially mitigated by an increasing net land carbon sink in the terrestrial biosphere; understanding the processes that drive this sink is thus essential for protecting, managing and projecting this important ecosystem service. In this Review, we examine evidence for an enhanced land carbon sink and attribute the observed response to drivers and processes. This sink has doubled from 1.2 ± 0.5 PgC yr−1 in the 1960s to 3.1 ± 0.6 PgC yr−1 in the 2010s. This trend results largely from carbon dioxide fertilization increasing photosynthesis (driving an increase in the annual land carbon sink of >2 PgC globally since 1900), mainly in tropical forest regions, and elevated temperatures reducing cold limitation, mainly at higher latitudes. Continued long-term land carbon sequestration is possible through the end of this century under multiple emissions scenarios, especially if nature-based climate solutions and appropriate ecosystem management are used. A new generation of globally distributed field experiments is needed to improve understanding of future carbon sink potential by measuring belowground carbon release, the response to carbon dioxide enrichment, and long-term shifts in carbon allocation and turnover.
Abstract.
Farha MN, Daniells J, Cernusak LA, Ritmejerytė E, Wangchuk P, Sitch S, Mercado LM, Hayes F, Brown F, Cheesman AW, et al (2023). Examining ozone susceptibility in the genus Musa (bananas). Functional Plant Biology
Cui T, Fan L, Ciais P, Fensholt R, Frappart F, Sitch S, Chave J, Chang Z, Li X, Wang M, et al (2023). First assessment of optical and microwave remotely sensed vegetation proxies in monitoring aboveground carbon in tropical Asia. Remote Sensing of Environment, 293
Vieira I, Verbeeck H, Meunier F, Peaucelle M, Sibret T, Lefevre L, Cheesman AW, Brown F, Sitch S, Mbifo J, et al (2023). Global reanalysis products cannot reproduce seasonal and diurnal cycles of tropospheric ozone in the Congo Basin. Atmospheric Environment, 304
Li X, Piao S, Huntingford C, Peñuelas J, Yang H, Xu H, Chen A, Friedlingstein P, Keenan TF, Sitch S, et al (2023). Global variations in critical drought thresholds that impact vegetation. National Science Review, 10(5).
Grassi G, Schwingshackl C, Gasser T, Houghton RA, Sitch S, Canadell JG, Cescatti A, Ciais P, Federici S, Friedlingstein P, et al (2023). Harmonising the land-use flux estimates of global models and national inventories for 2000–2020.
Earth System Science Data,
15(3), 1093-1114.
Abstract:
Harmonising the land-use flux estimates of global models and national inventories for 2000–2020
Abstract. As the focus of climate policy shifts from pledges to implementation, there
is a growing need to track progress on climate change mitigation at the
country level, particularly for the land-use sector. Despite new tools and
models providing unprecedented monitoring opportunities, striking
differences remain in estimations of anthropogenic land-use CO2 fluxes
between, on the one hand, the national greenhouse gas inventories (NGHGIs) used to assess
compliance with national climate targets under the Paris Agreement and, on the other hand, the
Global Carbon Budget and Intergovernmental Panel on Climate Change (IPCC) assessment reports, both based on global
bookkeeping models (BMs). Recent studies have shown that these differences are mainly due to
inconsistent definitions of anthropogenic CO2 fluxes in managed
forests. Countries assume larger areas of forest to be managed than BMs do, due
to a broader definition of managed land in NGHGIs. Additionally, the
fraction of the land sink caused by indirect effects of human-induced
environmental change (e.g. fertilisation effect on vegetation growth due to
increased atmospheric CO2 concentration) on managed lands is treated as
non-anthropogenic by BMs but as anthropogenic in most NGHGIs. We implement an approach that adds the
CO2 sink caused by environmental change in countries' managed forests
(estimated by 16 dynamic global vegetation models, DGVMs) to the
land-use fluxes from three BMs. This sum is conceptually more comparable to
NGHGIs and is thus expected to be quantitatively more similar. Our analysis
uses updated and more comprehensive data from NGHGIs than previous studies
and provides model results at a greater level of disaggregation in terms of
regions, countries and land categories (i.e. forest land, deforestation,
organic soils, other land uses). Our results confirm a large difference (6.7 GtCO2 yr−1) in global
land-use CO2 fluxes between the ensemble mean of the BMs, which
estimate a source of 4.8 GtCO2 yr−1 for the period 2000–2020,
and NGHGIs, which estimate a sink of −1.9 GtCO2 yr−1 in the same
period. Most of the gap is found on forest land (3.5 GtCO2 yr−1),
with differences also for deforestation (2.4 GtCO2 yr−1), for fluxes
from other land uses (1.0 GtCO2 yr−1) and to a lesser extent for
fluxes from organic soils (0.2 GtCO2 yr−1). By adding the DGVM
ensemble mean sink arising from environmental change in managed forests
(−6.4 GtCO2 yr−1) to BM estimates, the gap between BMs and NGHGIs
becomes substantially smaller both globally (residual gap: 0.3 GtCO2 yr−1) and in most regions and countries. However, some discrepancies
remain and deserve further investigation. For example, the BMs generally
provide higher emissions from deforestation than NGHGIs and, when adjusted
with the sink in managed forests estimated by DGVMs, yield a sink that is
often greater than NGHGIs. In summary, this study provides a blueprint for harmonising the estimations
of anthropogenic land-use fluxes, allowing for detailed comparisons between
global models and national inventories at global, regional and country
levels. This is crucial to increase confidence in land-use emissions
estimates, support investments in land-based mitigation strategies and
assess the countries' collective progress under the Global Stocktake of the
Paris Agreement. Data from this study are openly available online via the Zenodo portal
(Grassi et al. 2023) at https://doi.org/10.5281/zenodo.7650360.
.
Abstract.
Li J, Bevacqua E, Wang Z, Sitch S, Arora V, Arneth A, Jain AK, Goll D, Tian H, Zscheischler J, et al (2023). Hydroclimatic extremes contribute to asymmetric trends in ecosystem productivity loss.
Communications Earth and Environment,
4(1).
Abstract:
Hydroclimatic extremes contribute to asymmetric trends in ecosystem productivity loss
Gross primary production is the basis of global carbon uptake. Gross primary production losses are often related to hydroclimatic extremes such as droughts and heatwaves, but the trend of such losses driven by hydroclimatic extremes remains unclear. Using observationally-constrained and process-based model data from 1982-2016, we show that drought-heat events, drought-cold events, droughts and heatwaves are the dominant drivers of gross primary production loss. Losses associated with these drivers increase in northern midlatitude ecosystem but decrease in pantropical ecosystems, thereby contributing to around 70% of the variability in total gross primary production losses. These asymmetric trends are caused by an increase in the magnitude of gross primary production losses in northern midlatitudes and by a decrease in the frequency of gross primary production loss events in pantropical ecosystems. Our results suggest that the pantropics may have become less vulnerable to hydroclimatic variability over recent decades whereas gross primary production losses and hydroclimatic extremes in northern midlatitudes have become more closely entangled.
Abstract.
Cheesman AW, Brown F, Farha MN, Rosan TM, Folberth GA, Hayes F, Moura BB, Paoletti E, Hoshika Y, Osborne CP, et al (2023). Impacts of ground-level ozone on sugarcane production.
Science of the Total Environment,
904Abstract:
Impacts of ground-level ozone on sugarcane production
Sugarcane is a vital commodity crop often grown in (sub)tropical regions which have been experiencing a recent deterioration in air quality. Unlike for other commodity crops, the risk of air pollution, specifically ozone (O3), to this C4 crop has not yet been quantified. Yet, recent work has highlighted both the potential risks of O3 to C4 bioenergy crops, and the emergence of O3 exposure across the tropics as a vital factor determining global food security. Given the large extent, and planned expansion of sugarcane production in places like Brazil to meet global demand for biofuels, there is a pressing need to characterize the risk of O3 to the industry. In this study, we sought to a) derive sugarcane O3 dose-response functions across a range of realistic O3 exposure and b) model the implications of this across a globally important production area. We found a significant impact of O3 on biomass allocation (especially to leaves) and production across a range of sugarcane genotypes, including two commercially relevant varieties (e.g. CTC4, Q240). Using these data, we calculated dose-response functions for sugarcane and combined them with hourly O3 exposure across south-central Brazil derived from the UK Earth System Model (UKESM1) to simulate the current regional impact of O3 on sugarcane production using a dynamic global vegetation model (JULES vn 5.6). We found that between 5.6 % and 18.3 % of total crop productivity is likely lost across the region due to the direct impacts of current O3 exposure. However, impacts depended critically on the substantial differences in O3 susceptibility observed among sugarcane genotypes and how these were implemented in the model. Our work highlights not only the urgent need to fully elucidate the impacts of O3 in this important bioenergetic crop, but the potential implications air quality may have upon tropical food production more generally.
Abstract.
Ma Y, Yue X, Sitch S, Unger N, Uddling J, Mercado L, Gong C, Feng Z, Yang H, Zhou H, et al (2023). Implementation of trait-based ozone plant sensitivity in the Yale Interactive terrestrial Biosphere model v1.0 to assess global vegetation damage. GMD
Yan R, Wang J, Ju W, Goll DS, Jain AK, Sitch S, Tian H, Benjamin P, Jiang F, Wang H, et al (2023). Interactive effects of the El Niño-Southern Oscillation and Indian Ocean Dipole on the tropical net ecosystem productivity. Agricultural and Forest Meteorology, 336
Heinrich V, House J, Gibbs DA, Harris N, Herold M, Grassi G, Cantinho R, Rosan TM, Zimbres B, Shimbo JZ, et al (2023). Mind the gap: reconciling tropical forest carbon flux estimates from earth observation and national reporting requires transparency.
Carbon Balance Manag,
18(1).
Abstract:
Mind the gap: reconciling tropical forest carbon flux estimates from earth observation and national reporting requires transparency.
BACKGROUND: the application of different approaches calculating the anthropogenic carbon net flux from land, leads to estimates that vary considerably. One reason for these variations is the extent to which approaches consider forest land to be "managed" by humans, and thus contributing to the net anthropogenic flux. Global Earth Observation (EO) datasets characterising spatio-temporal changes in land cover and carbon stocks provide an independent and consistent approach to estimate forest carbon fluxes. These can be compared against results reported in National Greenhouse Gas Inventories (NGHGIs) to support accurate and timely measuring, reporting and verification (MRV). Using Brazil as a primary case study, with additional analysis in Indonesia and Malaysia, we compare a Global EO-based dataset of forest carbon fluxes to results reported in NGHGIs. RESULTS: Between 2001 and 2020, the EO-derived estimates of all forest-related emissions and removals indicate that Brazil was a net sink of carbon (- 0.2 GtCO2yr-1), while Brazil's NGHGI reported a net carbon source (+ 0.8 GtCO2yr-1). After adjusting the EO estimate to use the Brazilian NGHGI definition of managed forest and other assumptions used in the inventory's methodology, the EO net flux became a source of + 0.6 GtCO2yr-1, comparable to the NGHGI. Remaining discrepancies are due largely to differing carbon removal factors and forest types applied in the two datasets. In Indonesia, the EO and NGHGI net flux estimates were similar (+ 0.6 GtCO2 yr-1), but in Malaysia, they differed in both magnitude and sign (NGHGI: -0.2 GtCO2 yr-1; Global EO: + 0.2 GtCO2 yr-1). Spatially explicit datasets on forest types were not publicly available for analysis from either NGHGI, limiting the possibility of detailed adjustments. CONCLUSIONS: By adjusting the EO dataset to improve comparability with carbon fluxes estimated for managed forests in the Brazilian NGHGI, initially diverging estimates were largely reconciled and remaining differences can be explained. Despite limited spatial data available for Indonesia and Malaysia, our comparison indicated specific aspects where differing approaches may explain divergence, including uncertainties and inaccuracies. Our study highlights the importance of enhanced transparency, as set out by the Paris Agreement, to enable alignment between different approaches for independent measuring and verification.
Abstract.
Author URL.
Ruehr S, Keenan TF, Williams C, Zhou Y, Lu X, Bastos A, Canadell JG, Prentice IC, Sitch S, Terrer C, et al (2023). Publisher Correction: Evidence and attribution of the enhanced land carbon sink (Nature Reviews Earth & Environment, (2023), 4, 8, (518-534), 10.1038/s43017-023-00456-3).
Nature Reviews Earth and EnvironmentAbstract:
Publisher Correction: Evidence and attribution of the enhanced land carbon sink (Nature Reviews Earth & Environment, (2023), 4, 8, (518-534), 10.1038/s43017-023-00456-3)
Correction to: Nature Reviews Earth & Environment, published online 25 July 2023. In the version of the article initially published, the y-axis labels in Fig. 7b, now reading “+” and “–”, read “234” and “254”, respectively. This has been corrected in the HTML and PDF versions of the article.
Abstract.
Gampe D, Zscheischler J, Reichstein M, O’Sullivan M, Smith WK, Sitch S, Buermann W (2023). Publisher Correction: Increasing impact of warm droughts on northern ecosystem productivity over recent decades. Nature Climate Change, 13(11), 1272-1272.
Heinrich VHA, Sitch S, Rosan TM, Silva-Junior CHL, Aragão LEOC (2023). RE:Growth—A toolkit for analyzing secondary forest aboveground carbon dynamics in the Brazilian Amazon. Frontiers in Forests and Global Change, 6
Fan L, Wigneron JP, Ciais P, Chave J, Brandt M, Sitch S, Yue C, Bastos A, Li X, Qin Y, et al (2023). Siberian carbon sink reduced by forest disturbances.
Nature Geoscience,
16(1), 56-62.
Abstract:
Siberian carbon sink reduced by forest disturbances
Siberian forests are generally thought to have acted as an important carbon sink over recent decades, but exposure to severe droughts and fire disturbances may have impacted their carbon dynamics. Limited available forest inventories mean the carbon balance remains uncertain. Here we analyse annual live and dead above-ground carbon changes derived from low-frequency passive microwave observations from 2010 to 2019. We find that during this period, the carbon balance of Siberian forests was close to neutral, with the forests acting as a small carbon sink of +0.02+0.01+0.03 PgC yr−1. Carbon storage in dead wood increased, but this was largely offset by a decrease in live biomass. Substantial losses of live above-ground carbon are attributed to fire and drought, such as the widespread fires in northern Siberia in 2012 and extreme drought in eastern Siberia in 2015. These live above-ground carbon losses contrast with ‘greening’ trends seen in leaf area index over the same period, a decoupling explained by faster post-disturbance recovery of leaf area than live above-ground carbon. Our study highlights the vulnerability of large forest carbon stores in Siberia to climate-induced disturbances, challenging the persistence of the carbon sink in this region of the globe.
Abstract.
Pellegrini AFA, Reich PB, Hobbie SE, Coetsee C, Wigley B, February E, Georgiou K, Terrer C, Brookshire ENJ, Ahlström A, et al (2023). Soil carbon storage capacity of drylands under altered fire regimes.
Nature Climate Change,
13(10), 1089-1094.
Abstract:
Soil carbon storage capacity of drylands under altered fire regimes
The determinants of fire-driven changes in soil organic carbon (SOC) across broad environmental gradients remains unclear, especially in global drylands. Here we combined datasets and field sampling of fire-manipulation experiments to evaluate where and why fire changes SOC and compared our statistical model to simulations from ecosystem models. Drier ecosystems experienced larger relative changes in SOC than humid ecosystems—in some cases exceeding losses from plant biomass pools—primarily explained by high fire-driven declines in tree biomass inputs in dry ecosystems. Many ecosystem models underestimated the SOC changes in drier ecosystems. Upscaling our statistical model predicted that soils in savannah–grassland regions may have gained 0.64 PgC due to net-declines in burned area over the past approximately two decades. Consequently, ongoing declines in fire frequencies have probably created an extensive carbon sink in the soils of global drylands that may have been underestimated by ecosystem models.
Abstract.
Metz E-M, Vardag SN, Basu S, Jung M, Ahrens B, El-Madany T, Sitch S, Arora VK, Briggs PR, Friedlingstein P, et al (2023). Soil respiration-driven CO2 pulses dominate Australia's flux variability.
Science,
379(6639), 1332-1335.
Abstract:
Soil respiration-driven CO2 pulses dominate Australia's flux variability.
The Australian continent contributes substantially to the year-to-year variability of the global terrestrial carbon dioxide (CO2) sink. However, the scarcity of in situ observations in remote areas prevents the deciphering of processes that force the CO2 flux variability. In this study, by examining atmospheric CO2 measurements from satellites in the period 2009-2018, we find recurrent end-of-dry-season CO2 pulses over the Australian continent. These pulses largely control the year-to-year variability of Australia's CO2 balance. They cause two to three times larger seasonal variations compared with previous top-down inversions and bottom-up estimates. The pulses occur shortly after the onset of rainfall and are driven by enhanced soil respiration preceding photosynthetic uptake in Australia's semiarid regions. The suggested continental-scale relevance of soil-rewetting processes has substantial implications for our understanding and modeling of global climate-carbon cycle feedbacks.
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Author URL.
Nagy L, Eller CB, Mercado LM, Cuesta FX, Llambí LD, Buscardo E, Aragão LEOC, García-Núñez C, Oliveira RS, Barbosa M, et al (2023). South American mountain ecosystems and global change – a case study for integrating theory and field observations for land surface modelling and ecosystem management. Plant Ecology & Diversity, ahead-of-print(ahead-of-print), 1-27.
van der Woude AM, Peters W, Joetzjer E, Lafont S, Koren G, Ciais P, Ramonet M, Xu Y, Bastos A, Botía S, et al (2023). Temperature extremes of 2022 reduced carbon uptake by forests in Europe.
Nat Commun,
14(1).
Abstract:
Temperature extremes of 2022 reduced carbon uptake by forests in Europe.
The year 2022 saw record breaking temperatures in Europe during both summer and fall. Similar to the recent 2018 drought, close to 30% (3.0 million km2) of the European continent was under severe summer drought. In 2022, the drought was located in central and southeastern Europe, contrasting the Northern-centered 2018 drought. We show, using multiple sets of observations, a reduction of net biospheric carbon uptake in summer (56-62 TgC) over the drought area. Specific sites in France even showed a widespread summertime carbon release by forests, additional to wildfires. Partial compensation (32%) for the decreased carbon uptake due to drought was offered by a warm autumn with prolonged biospheric carbon uptake. The severity of this second drought event in 5 years suggests drought-induced reduced carbon uptake to no longer be exceptional, and important to factor into Europe's developing plans for net-zero greenhouse gas emissions that rely on carbon uptake by forests.
Abstract.
Author URL.
Heinrich VHA, Vancutsem C, Dalagnol R, Rosan TM, Fawcett D, Silva-Junior CHL, Cassol HLG, Achard F, Jucker T, Silva CA, et al (2023). The carbon sink of secondary and degraded humid tropical forests.
Nature,
615(7952), 436-442.
Abstract:
The carbon sink of secondary and degraded humid tropical forests.
The globally important carbon sink of intact, old-growth tropical humid forests is declining because of climate change, deforestation and degradation from fire and logging1-3. Recovering tropical secondary and degraded forests now cover about 10% of the tropical forest area4, but how much carbon they accumulate remains uncertain. Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa5,6. On the basis of satellite data products4,7, our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20 years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107 Tg C year-1 (90-130 Tg C year-1) between 1984 and 2018, counterbalancing 26% (21-34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year-1 (44-62 Tg C year-1) across the main tropical regions studied.
Abstract.
Author URL.
Bian C, Xia J, Zhang X, Huang K, Cui E, Zhou J, Wei N, Wang Y, Lombardozzi D, Goll DS, et al (2023). Uncertainty and Emergent Constraints on Enhanced Ecosystem Carbon Stock by Land Greening. Journal of Advances in Modeling Earth Systems, 15(5).
Murray-Tortarolo G, Poulter B, Vargas R, Hayes D, Michalak AM, Williams C, Windham-Myers L, Wang JA, Wickland KP, Butman D, et al (2022). A Process-Model Perspective on Recent Changes in the Carbon Cycle of North America.
JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES,
127(9).
Author URL.
Kondo M, Sitch S, Ciais P, Achard F, Kato E, Pongratz J, Houghton RA, Canadell JG, Patra PK, Friedlingstein P, et al (2022). Are Land‐Use Change Emissions in Southeast Asia Decreasing or Increasing?. Global Biogeochemical Cycles, 36(1).
Seiler C, Melton JR, Arora VK, Sitch S, Friedlingstein P, Anthoni P, Goll D, Jain AK, Joetzjer E, Lienert S, et al (2022). Are Terrestrial Biosphere Models Fit for Simulating the Global Land Carbon Sink?. Journal of Advances in Modeling Earth Systems, 14(5).
Fawcett D, Cunliffe AM, Sitch S, O’Sullivan M, Anderson K, Brazier RE, Hill TC, Anthoni P, Arneth A, Arora VK, et al (2022). Assessing Model Predictions of Carbon Dynamics in Global Drylands.
Frontiers in Environmental Science,
10Abstract:
Assessing Model Predictions of Carbon Dynamics in Global Drylands
Drylands cover ca. 40% of the land surface and are hypothesised to play a major role in the global carbon cycle, controlling both long-term trends and interannual variation. These insights originate from land surface models (LSMs) that have not been extensively calibrated and evaluated for water-limited ecosystems. We need to learn more about dryland carbon dynamics, particularly as the transitory response and rapid turnover rates of semi-arid systems may limit their function as a carbon sink over multi-decadal scales. We quantified aboveground biomass carbon (AGC; inferred from SMOS L-band vegetation optical depth) and gross primary productivity (GPP; from PML-v2 inferred from MODIS observations) and tested their spatial and temporal correspondence with estimates from the TRENDY ensemble of LSMs. We found strong correspondence in GPP between LSMs and PML-v2 both in spatial patterns (Pearson’s r = 0.9 for TRENDY-mean) and in inter-annual variability, but not in trends. Conversely, for AGC we found lesser correspondence in space (Pearson’s r = 0.75 for TRENDY-mean, strong biases for individual models) and in the magnitude of inter-annual variability compared to satellite retrievals. These disagreements likely arise from limited representation of ecosystem responses to plant water availability, fire, and photodegradation that drive dryland carbon dynamics. We assessed inter-model agreement and drivers of long-term change in carbon stocks over centennial timescales. This analysis suggested that the simulated trend of increasing carbon stocks in drylands is in soils and primarily driven by increased productivity due to CO2 enrichment. However, there is limited empirical evidence of this 50-year sink in dryland soils. Our findings highlight important uncertainties in simulations of dryland ecosystems by current LSMs, suggesting a need for continued model refinements and for greater caution when interpreting LSM estimates with regards to current and future carbon dynamics in drylands and by extension the global carbon cycle.
Abstract.
Leung F, Sitch S, Tai APK, Wiltshire AJ, Gornall JL, Folberth GA, Unger N (2022). CO<sub>2</sub> fertilization of crops offsets yield losses due to future surface ozone damage and climate change.
ENVIRONMENTAL RESEARCH LETTERS,
17(7).
Author URL.
Deng Z, Ciais P, Tzompa-Sosa ZA, Saunois M, Qiu C, Tan C, Sun T, Ke P, Cui Y, Tanaka K, et al (2022). Comparing national greenhouse gas budgets reported in UNFCCC inventories against atmospheric inversions.
EARTH SYSTEM SCIENCE DATA,
14(4), 1639-1675.
Author URL.
Li S, Wang Y, Ciais P, Sitch S, Sato H, Shen M, Chen X, Ito A, Wu C, Kucharik CJ, et al (2022). Deficiencies of Phenology Models in Simulating Spatial and Temporal Variations in Temperate Spring Leaf Phenology. Journal of Geophysical Research Biogeosciences, 127(3).
Schwingshackl C, Obermeier WA, Bultan S, Grassi G, Canadell JG, Friedlingstein P, Gasser T, Houghton RA, Kurz WA, Sitch S, et al (2022). Differences in land-based mitigation estimates reconciled by separating natural and land-use CO2 fluxes at the country level. One Earth, 5(12), 1367-1376.
Liao C, Chen Y, Wang J, Liang Y, Huang Y, Lin Z, Lu X, Huang Y, Tao F, Lombardozzi D, et al (2022). Disentangling land model uncertainty via Matrix-based Ensemble Model Inter-comparison Platform (MEMIP).
ECOLOGICAL PROCESSES,
11(1).
Author URL.
Yang R, Wang J, Zeng N, Sitch S, Tang W, McGrath MJ, Cai Q, Liu D, Lombardozzi D, Tian H, et al (2022). Divergent historical GPP trends among state-of-the-art multi-model simulations and satellite-based products.
EARTH SYSTEM DYNAMICS,
13(2), 833-849.
Author URL.
Wang J, Jiang F, Ju W, Wang M, Sitch S, Arora VK, Chen JM, Goll DS, He W, Jain AK, et al (2022). Enhanced India-Africa Carbon Uptake and Asia-Pacific Carbon Release Associated with the 2019 Extreme Positive Indian Ocean Dipole.
Geophysical Research Letters,
49(22).
Abstract:
Enhanced India-Africa Carbon Uptake and Asia-Pacific Carbon Release Associated with the 2019 Extreme Positive Indian Ocean Dipole
The 2019 extreme positive Indian Ocean dipole drove climate extremes over Indian Ocean rim countries with unclear carbon-cycle responses. We investigated its impact on net biome productivity (NBP) and its constituent fluxes, using the Global Carbon Assimilation System (GCASv2) product, process-based model simulations from TRENDYv9, and satellite-based gross primary productivity (GPP). By distinguishing two separate regions, the India-Africa and Asia-Pacific, GCASv2 indicated enhanced terrestrial carbon uptake of 0.23 ± 0.20 PgC and release of 0.38 ± 0.15 PgC, respectively, during September–December (SOND) 2019. These NBP anomalies had comparable magnitudes to those following the 2015 extreme El Niño which, however, caused the consistent carbon release in both regions. The TRENDYv9 model ensemble confirmed these NBP responses, albeit with smaller magnitudes. These regional NBP anomalies were related to soil moisture variations with a dominant role of GPP. Understanding the impact of IOD provides new insights into mechanisms driving interannual variations in regional carbon cycling.
Abstract.
Yu Z, Ciais P, Piao S, Houghton RA, Lu C, Tian H, Agathokleous E, Kattel GR, Sitch S, Goll D, et al (2022). Forest expansion dominates China's land carbon sink since 1980.
Nat Commun,
13(1).
Abstract:
Forest expansion dominates China's land carbon sink since 1980.
Carbon budget accounting relies heavily on Food and Agriculture Organization land-use data reported by governments. Here we develop a new land-use and cover-change database for China, finding that differing historical survey methods biased China's reported data causing large errors in Food and Agriculture Organization databases. Land ecosystem model simulations driven with the new data reveal a strong carbon sink of 8.9 ± 0.8 Pg carbon from 1980 to 2019 in China, which was not captured in Food and Agriculture Organization data-based estimations due to biased land-use and cover-change signals. The land-use and cover-change in China, characterized by a rapid forest expansion from 1980 to 2019, contributed to nearly 44% of the national terrestrial carbon sink. In contrast, climate changes (22.3%), increasing nitrogen deposition (12.9%), and rising carbon dioxide (8.1%) are less important contributors. This indicates that previous studies have greatly underestimated the impact of land-use and cover-change on the terrestrial carbon balance of China. This study underlines the importance of reliable land-use and cover-change databases in global carbon budget accounting.
Abstract.
Author URL.
Rosan TM, Sitch S, Mercado LM, Heinrich V, Friedlingstein P, Aragão LEOC (2022). Fragmentation-Driven Divergent Trends in Burned Area in Amazonia and Cerrado. Frontiers in Forests and Global Change, 5
Friedlingstein P, Jones MW, O'Sullivan M, Andrew RM, Bakker DCE, Hauck J, Le Quéré C, Peters GP, Peters W, Pongratz J, et al (2022). Global Carbon Budget 2021.
Earth System Science Data,
14(4), 1917-2005.
Abstract:
Global Carbon Budget 2021
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and
their redistribution among the atmosphere, ocean, and terrestrial biosphere
in a changing climate is critical to better understand the global carbon
cycle, support the development of climate policies, and project future
climate change. Here we describe and synthesize datasets and methodology to
quantify the five major components of the global carbon budget and their
uncertainties. Fossil CO2 emissions (EFOS) are based on energy
statistics and cement production data, while emissions from land-use change
(ELUC), mainly deforestation, are based on land use and land-use change
data and bookkeeping models. Atmospheric CO2 concentration is measured
directly, and its growth rate (GATM) is computed from the annual
changes in concentration. The ocean CO2 sink (SOCEAN) is estimated
with global ocean biogeochemistry models and observation-based
data products. The terrestrial CO2 sink (SLAND) is estimated with
dynamic global vegetation models. The resulting carbon budget imbalance
(BIM), the difference between the estimated total emissions and the
estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a
measure of imperfect data and understanding of the contemporary carbon
cycle. All uncertainties are reported as ±1σ. For the first
time, an approach is shown to reconcile the difference in our ELUC
estimate with the one from national greenhouse gas inventories, supporting
the assessment of collective countries' climate progress. For the year 2020, EFOS declined by 5.4 % relative to 2019, with
fossil emissions at 9.5 ± 0.5 GtC yr−1 (9.3 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 0.9 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission of
10.2 ± 0.8 GtC yr−1 (37.4 ± 2.9 GtCO2). Also, for
2020, GATM was 5.0 ± 0.2 GtC yr−1 (2.4 ± 0.1 ppm yr−1), SOCEAN was 3.0 ± 0.4 GtC yr−1, and SLAND
was 2.9 ± 1 GtC yr−1, with a BIM of −0.8 GtC yr−1. The
global atmospheric CO2 concentration averaged over 2020 reached 412.45 ± 0.1 ppm. Preliminary data for 2021 suggest a rebound in EFOS
relative to 2020 of +4.8 % (4.2 % to 5.4 %) globally. Overall, the mean and trend in the components of the global carbon budget
are consistently estimated over the period 1959–2020, but discrepancies of
up to 1 GtC yr−1 persist for the representation of annual to
semi-decadal variability in CO2 fluxes. Comparison of estimates from
multiple approaches and observations shows (1) a persistent large
uncertainty in the estimate of land-use changes emissions, (2) a low
agreement between the different methods on the magnitude of the land
CO2 flux in the northern extra-tropics, and (3) a discrepancy between
the different methods on the strength of the ocean sink over the last
decade. This living data update documents changes in the methods and datasets used in this new global carbon budget and the progress in understanding
of the global carbon cycle compared with previous publications of this dataset (Friedlingstein et al. 2020, 2019; Le
Quéré et al. 2018b, a, 2016, 2015b, a, 2014, 2013). The
data presented in this work are available at https://doi.org/10.18160/gcp-2021 (Friedlingstein et al. 2021).
.
Abstract.
Friedlingstein P, O'Sullivan M, Jones MW, Andrew RM, Gregor L, Hauck J, Le Quéré C, Luijkx IT, Olsen A, Peters GP, et al (2022). Global Carbon Budget 2022.
Earth System Science Data,
14(11), 4811-4900.
Abstract:
Global Carbon Budget 2022
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and
their redistribution among the atmosphere, ocean, and terrestrial biosphere
in a changing climate is critical to better understand the global carbon
cycle, support the development of climate policies, and project future
climate change. Here we describe and synthesize data sets and methodologies to
quantify the five major components of the global carbon budget and their
uncertainties. Fossil CO2 emissions (EFOS) are based on energy
statistics and cement production data, while emissions from land-use change
(ELUC), mainly deforestation, are based on land use and land-use change
data and bookkeeping models. Atmospheric CO2 concentration is measured
directly, and its growth rate (GATM) is computed from the annual
changes in concentration. The ocean CO2 sink (SOCEAN) is estimated
with global ocean biogeochemistry models and observation-based
data products. The terrestrial CO2 sink (SLAND) is estimated with
dynamic global vegetation models. The resulting carbon budget imbalance
(BIM), the difference between the estimated total emissions and the
estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a
measure of imperfect data and understanding of the contemporary carbon
cycle. All uncertainties are reported as ±1σ. For the year 2021, EFOS increased by 5.1 % relative to 2020, with
fossil emissions at 10.1 ± 0.5 GtC yr−1 (9.9 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and ELUC was 1.1 ± 0.7 GtC yr−1, for a total anthropogenic CO2 emission
(including the cement carbonation sink) of 10.9 ± 0.8 GtC yr−1
(40.0 ± 2.9 GtCO2). Also, for 2021, GATM was 5.2 ± 0.2 GtC yr−1 (2.5 ± 0.1 ppm yr−1), SOCEAN was 2.9 ± 0.4 GtC yr−1, and SLAND was 3.5 ± 0.9 GtC yr−1, with a
BIM of −0.6 GtC yr−1 (i.e. the total estimated sources were too low or
sinks were too high). The global atmospheric CO2 concentration averaged over
2021 reached 414.71 ± 0.1 ppm. Preliminary data for 2022 suggest an
increase in EFOS relative to 2021 of +1.0 % (0.1 % to 1.9 %)
globally and atmospheric CO2 concentration reaching 417.2 ppm, more
than 50 % above pre-industrial levels (around 278 ppm). Overall, the mean
and trend in the components of the global carbon budget are consistently
estimated over the period 1959–2021, but discrepancies of up to 1 GtC yr−1 persist for the representation of annual to semi-decadal
variability in CO2 fluxes. Comparison of estimates from multiple
approaches and observations shows (1) a persistent large uncertainty in the
estimate of land-use change emissions, (2) a low agreement between the
different methods on the magnitude of the land CO2 flux in the northern
extratropics, and (3) a discrepancy between the different methods on the
strength of the ocean sink over the last decade. This living data update
documents changes in the methods and data sets used in this new global
carbon budget and the progress in understanding of the global carbon cycle
compared with previous publications of this data set. The data presented in
this work are available at https://doi.org/10.18160/GCP-2022 (Friedlingstein et al. 2022b).
.
Abstract.
Jones MW, Abatzoglou JT, Veraverbeke S, Andela N, Lasslop G, Forkel M, Smith AJP, Burton C, Betts RA, Werf GR, et al (2022). Global and Regional Trends and Drivers of Fire Under Climate Change. Reviews of Geophysics, 60(3).
Cunliffe AM, Anderson K, Boschetti F, Brazier RE, Graham HA, Myers-Smith IH, Astor T, Boer MM, Calvo LG, Clark PE, et al (2022). Global application of an unoccupied aerial vehicle photogrammetry protocol for predicting aboveground biomass in non-forest ecosystems.
REMOTE SENSING IN ECOLOGY AND CONSERVATION,
8(1), 57-71.
Author URL.
Crisp D, Dolman H, Tanhua T, McKinley GA, Hauck J, Bastos A, Sitch S, Eggleston S, Aich V (2022). How Well Do We Understand the Land‐Ocean‐Atmosphere Carbon Cycle?. Reviews of Geophysics, 60(2).
Lawal S, Sitch S, Lombardozzi D, Nabel JEMS, Wey H-W, Friedlingstein P, Tian H, Hewitson B (2022). Investigating the response of leaf area index to droughts in southern African vegetation using observations and model simulations.
HYDROLOGY AND EARTH SYSTEM SCIENCES,
26(8), 2045-2071.
Author URL.
Byrne B, Liu J, Yi Y, Chatterjee A, Basu S, Cheng R, Doughty R, Chevallier F, Bowman KW, Parazoo NC, et al (2022). Multi-year observations reveal a larger than expected autumn respiration signal across northeast Eurasia.
BIOGEOSCIENCES,
19(19), 4779-4799.
Author URL.
Crisp D, Dolman H, Tanhua T, McKinley G, Hauck J, Bastos A, Sitch S (2022). Mysteries of the Global Carbon Cycle. Eos, 103
Bruhn D, Newman F, Hancock M, Povlsen P, Slot M, Sitch S, Drake J, Weedon GP, Clark DB, Pagter M, et al (2022). Nocturnal plant respiration is under strong non-temperature control.
Nat Commun,
13(1).
Abstract:
Nocturnal plant respiration is under strong non-temperature control.
Most biological rates depend on the rate of respiration. Temperature variation is typically considered the main driver of daily plant respiration rates, assuming a constant daily respiration rate at a set temperature. Here, we show empirical data from 31 species from temperate and tropical biomes to demonstrate that the rate of plant respiration at a constant temperature decreases monotonically with time through the night, on average by 25% after 8 h of darkness. Temperature controls less than half of the total nocturnal variation in respiration. A new universal formulation is developed to model and understand nocturnal plant respiration, combining the nocturnal decrease in the rate of plant respiration at constant temperature with the decrease in plant respiration according to the temperature sensitivity. Application of the new formulation shows a global reduction of 4.5 -6 % in plant respiration and an increase of 7-10% in net primary production for the present-day.
Abstract.
Author URL.
Bastos A, Ciais P, Sitch S, Aragao LEOC, Chevallier F, Fawcett D, Rosan TM, Saunois M, Guenther D, Perugini L, et al (2022). On the use of Earth Observation to support estimates of national greenhouse gas emissions and sinks for the Global stocktake process: lessons learned from ESA-CCI RECCAP2 COMMENT.
CARBON BALANCE AND MANAGEMENT,
17(1).
Author URL.
O’Sullivan M, Friedlingstein P, Sitch S, Anthoni P, Arneth A, Arora VK, Bastrikov V, Delire C, Goll DS, Jain A, et al (2022). Process-oriented analysis of dominant sources of uncertainty in the land carbon sink.
Nature Communications,
13(1).
Abstract:
Process-oriented analysis of dominant sources of uncertainty in the land carbon sink
AbstractThe observed global net land carbon sink is captured by current land models. All models agree that atmospheric CO2and nitrogen deposition driven gains in carbon stocks are partially offset by climate and land-use and land-cover change (LULCC) losses. However, there is a lack of consensus in the partitioning of the sink between vegetation and soil, where models do not even agree on the direction of change in carbon stocks over the past 60 years. This uncertainty is driven by plant productivity, allocation, and turnover response to atmospheric CO2(and to a smaller extent to LULCC), and the response of soil to LULCC (and to a lesser extent climate). Overall, differences in turnover explain ~70% of model spread in both vegetation and soil carbon changes. Further analysis of internal plant and soil (individual pools) cycling is needed to reduce uncertainty in the controlling processes behind the global land carbon sink.
Abstract.
Wu C, Sitch S, Huntingford C, Mercado LM, Venevsky S, Lasslop G, Archibald S, Staver AC (2022). Reduced global fire activity due to human demography slows global warming by enhanced land carbon uptake.
Proc Natl Acad Sci U S A,
119(20).
Abstract:
Reduced global fire activity due to human demography slows global warming by enhanced land carbon uptake.
Fire is an important climate-driven disturbance in terrestrial ecosystems, also modulated by human ignitions or fire suppression. Changes in fire emissions can feed back on the global carbon cycle, but whether the trajectories of changing fire activity will exacerbate or attenuate climate change is poorly understood. Here, we quantify fire dynamics under historical and future climate and human demography using a coupled global climate–fire–carbon cycle model that emulates 34 individual Earth system models (ESMs). Results are compared with counterfactual worlds, one with a constant preindustrial fire regime and another without fire. Although uncertainty in projected fire effects is large and depends on ESM, socioeconomic trajectory, and emissions scenario, we find that changes in human demography tend to suppress global fire activity, keeping more carbon within terrestrial ecosystems and attenuating warming. Globally, changes in fire have acted to warm climate throughout most of the 20th century. However, recent and predicted future reductions in fire activity may reverse this, enhancing land carbon uptake and corresponding to offsetting ∼5 to 10 y of global CO2 emissions at today’s levels. This potentially reduces warming by up to 0.11 °C by 2100. We show that climate–carbon cycle feedbacks, as caused by changing fire regimes, are most effective at slowing global warming under lower emission scenarios. Our study highlights that ignitions and active and passive fire suppression can be as important in driving future fire regimes as changes in climate, although with some risk of more extreme fires regionally and with implications for other ecosystem functions in fire-dependent ecosystems.
Abstract.
Author URL.
Wang K, Bastos A, Ciais P, Wang X, Rödenbeck C, Gentine P, Chevallier F, Humphrey VW, Huntingford C, O'Sullivan M, et al (2022). Regional and seasonal partitioning of water and temperature controls on global land carbon uptake variability.
Nat Commun,
13(1).
Abstract:
Regional and seasonal partitioning of water and temperature controls on global land carbon uptake variability.
Global fluctuations in annual land carbon uptake (NEEIAV) depend on water and temperature variability, yet debate remains about local and seasonal controls of the global dependences. Here, we quantify regional and seasonal contributions to the correlations of globally-averaged NEEIAV against terrestrial water storage (TWS) and temperature, and respective uncertainties, using three approaches: atmospheric inversions, process-based vegetation models, and data-driven models. The three approaches agree that the tropics contribute over 63% of the global correlations, but differ on the dominant driver of the global NEEIAV, because they disagree on seasonal temperature effects in the Northern Hemisphere (NH, >25°N). In the NH, inversions and process-based models show inter-seasonal compensation of temperature effects, inducing a global TWS dominance supported by observations. Data-driven models show weaker seasonal compensation, thereby estimating a global temperature dominance. We provide a roadmap to fully understand drivers of global NEEIAV and discuss their implications for future carbon-climate feedbacks.
Abstract.
Author URL.
Nakhavali MA, Mercado LM, Hartley IP, Sitch S, Cunha FV, di Ponzio R, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al (2022). Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP).
Geoscientific Model Development,
15(13), 5241-5269.
Abstract:
Representation of the phosphorus cycle in the Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Abstract. Most land surface models (LSMs), i.e. the land components of Earth system models
(ESMs), include representation of nitrogen (N) limitation on ecosystem
productivity. However, only a few of these models have incorporated phosphorus
(P) cycling. In tropical ecosystems, this is likely to be important as N
tends to be abundant, whereas the availability of rock-derived elements, such as
P, can be very low. Thus, without a representation of P cycling, tropical
forest response in areas such as Amazonia to rising atmospheric CO2
conditions remain highly uncertain. In this study, we introduced P dynamics
and its interactions with the N and carbon (C) cycles into the Joint UK Land
Environment Simulator (JULES). The new model (JULES-CNP) includes the
representation of P stocks in vegetation and soil pools, as well as key
processes controlling fluxes between these pools. We develop and evaluate
JULES-CNP using in situ data collected at a low-fertility site in the
central Amazon, with a soil P content representative of 60 % of soils
across the Amazon basin, to parameterize, calibrate, and evaluate JULES-CNP.
Novel soil and plant P pool observations are used for parameterization and
calibration, and the model is evaluated against C fluxes and stocks and
those soil P pools not used for parameterization or calibration. We then
evaluate the model at additional P-limited test sites across the Amazon and in
Panama and Hawaii, showing a significant improvement over the C- and CN-only
versions of the model. The model is then applied under elevated
CO2 (600 ppm) at our study site in the central Amazon to quantify the impact
of P limitation on CO2 fertilization. We compare our results against the
current state-of-the-art CNP models using the same methodology that was used
in the AmazonFACE model intercomparison study. The model is able to
reproduce the observed plant and soil P pools and fluxes used for evaluation
under ambient CO2. We estimate P to limit net primary productivity
(NPP) by 24 % under current CO2 and by 46 % under elevated
CO2. Under elevated CO2, biomass in simulations accounting for CNP
increase by 10 % relative to contemporary CO2 conditions, although it
is 5 % lower compared to CN- and C-only simulations. Our results
highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon rainforest with low-fertility soils.
.
Abstract.
Hegglin MI, Bastos A, Bovensmann H, Buchwitz M, Fawcett D, Ghent D, Kulk G, Sathyendranath S, Shepherd TG, Quegan S, et al (2022). Space-based Earth observation in support of the UNFCCC Paris Agreement. Frontiers in Environmental Science, 10
Cunliffe AM, Boschetti F, Clement R, Sitch S, Anderson K, Duman T, Zhu S, Schlumpf M, Litvak ME, Brazier RE, et al (2022). Strong Correspondence in Evapotranspiration and Carbon Dioxide Fluxes Between Different Eddy Covariance Systems Enables Quantification of Landscape Heterogeneity in Dryland Fluxes. Journal of Geophysical Research Biogeosciences, 127(8).
Brown F, Folberth GA, Sitch S, Bauer S, Bauters M, Boeckx P, Cheesman AW, Deushi M, Dos Santos I, Galy-Lacaux C, et al (2022). The ozone-climate penalty over South America and Africa by 2100.
ATMOSPHERIC CHEMISTRY AND PHYSICS,
22(18), 12331-12352.
Author URL.
Wild B, Teubner I, Moesinger L, Zotta R-M, Forkel M, van der Schalie R, Sitch S, Dorigo W (2022). VODCA2GPP-a new, global, long-term (1988-2020) gross primary production dataset from microwave remote sensing.
EARTH SYSTEM SCIENCE DATA,
14(3), 1063-1085.
Author URL.
Rosan TM, Klein Goldewijk K, Ganzenmüller R, O’Sullivan M, Pongratz J, Mercado LM, Aragao LEOC, Heinrich V, Von Randow C, Wiltshire A, et al (2021). A multi-data assessment of land use and land cover emissions from Brazil during 2000–2019.
Environmental Research Letters,
16(7), 074004-074004.
Abstract:
A multi-data assessment of land use and land cover emissions from Brazil during 2000–2019
Abstract
. Brazil is currently the largest contributor of land use and land cover change (LULCC) carbon dioxide net emissions worldwide, representing 17%–29% of the global total. There is, however, a lack of agreement among different methodologies on the magnitude and trends in LULCC emissions and their geographic distribution. Here we perform an evaluation of LULCC datasets for Brazil, including those used in the annual global carbon budget (GCB), and national Brazilian assessments over the period 2000–2018. Results show that the latest global HYDE 3.3 LULCC dataset, based on new FAO inventory estimates and multi-annual ESA CCI satellite-based land cover maps, can represent the observed spatial variation in LULCC over the last decades, representing an improvement on the HYDE 3.2 data previously used in GCB. However, the magnitude of LULCC assessed with HYDE 3.3 is lower than estimates based on MapBiomas. We use HYDE 3.3 and MapBiomas as input to a global bookkeeping model (bookkeeping of land use emission, BLUE) and a process-based Dynamic Global Vegetation Model (JULES-ES) to determine Brazil’s LULCC emissions over the period 2000–2019. Results show mean annual LULCC emissions of 0.1–0.4 PgC yr−1, compared with 0.1–0.24 PgC yr−1 reported by the Greenhouse Gas Emissions Estimation System of land use changes and forest sector (SEEG/LULUCF) and by FAO in its latest assessment of deforestation emissions in Brazil. Both JULES-ES and BLUE now simulate a slowdown in emissions after 2004 (−0.006 and −0.004 PgC yr−2 with HYDE 3.3, −0.014 and −0.016 PgC yr−2 with MapBiomas, respectively), in agreement with the Brazilian INPE-EM, global Houghton and Nassikas book-keeping models, FAO and as reported in the 4th national greenhouse gas inventories. The inclusion of Earth observation data has improved spatial representation of LULCC in HYDE and thus model capability to simulate Brazil’s LULCC emissions. This will likely contribute to reduce uncertainty in global LULCC emissions, and thus better constrains GCB assessments.
Abstract.
O’Sullivan M, Zhang Y, Bellouin N, Harris I, Mercado LM, Sitch S, Ciais P, Friedlingstein P (2021). Aerosol–light interactions reduce the carbon budget imbalance.
Environmental Research Letters,
16(12), 124072-124072.
Abstract:
Aerosol–light interactions reduce the carbon budget imbalance
Abstract
. Current estimates of the global land carbon sink contain substantial uncertainties on interannual timescales which contribute to a non-closure in the global carbon budget (GCB) in any given year. This budget imbalance (BIM) partly arises due to the use of imperfect models which are missing or misrepresenting processes. One such omission is the separate treatment of downward direct and diffuse solar radiation on photosynthesis. Here we evaluate and use an improved high-resolution (6-hourly), gridded dataset of surface solar diffuse and direct fluxes, over 1901–2017, constrained by satellite and ground-level observations, to drive two global land models. Results show that tropospheric aerosol–light interactions have the potential for substantial land carbon impacts (up to 0.4 PgCyr-1 enhanced sink) at decadal timescales, however large uncertainties remain, with models disagreeing on the direction of change in carbon uptake. On interannual timescales, results also show an enhancement of the land carbon sink (up to 0.9 PgCyr-1) and subsequent reduction in BIM by 55% in years following volcanic eruptions. We therefore suggest GCB assessments include this dataset in order to improve land carbon sink estimates.
Abstract.
Silva Junior CHL, Carvalho NS, Pessoa ACM, Reis JBC, Pontes-Lopes A, Doblas J, Heinrich V, Campanharo W, Alencar A, Silva C, et al (2021). Amazonian forest degradation must be incorporated into the COP26 agenda.
NATURE GEOSCIENCE,
14(9), 634-635.
Author URL.
Teckentrup L, De Kauwe MG, Pitman AJ, Goll DS, Haverd V, Jain AK, Joetzjer E, Kato E, Lienert S, Lombardozzi D, et al (2021). Assessing the representation of the Australian carbon cycle in global vegetation models.
BIOGEOSCIENCES,
18(20), 5639-5668.
Author URL.
Qin Y, Xiao X, Wigneron J-P, Ciais P, Brandt M, Fan L, Li X, Crowell S, Wu X, Doughty R, et al (2021). Carbon loss from forest degradation exceeds that from deforestation in the Brazilian Amazon.
NATURE CLIMATE CHANGE,
11(5), 442-+.
Author URL.
MacBean N, Scott RL, Biederman JA, Peylin P, Kolb T, Litvak ME, Krishnan P, Meyers TP, Arora VK, Bastrikov V, et al (2021). Dynamic global vegetation models underestimate net CO<sub>2</sub> flux mean and inter-annual variability in dryland ecosystems.
ENVIRONMENTAL RESEARCH LETTERS,
16(9).
Author URL.
Wang S, Zhang Y, Ju W, Chen JM, Ciais P, Cescatti A, Sardans J, Janssens IA, Wu M, Berry JA, et al (2021). Erratum: Recent global decline of CO fertilization effects on vegetation photosynthesis (Science (2020) 370:6522 (1295-1300) DOI: 10.1126/science.abb7772).
Science,
371(6529).
Abstract:
Erratum: Recent global decline of CO fertilization effects on vegetation photosynthesis (Science (2020) 370:6522 (1295-1300) DOI: 10.1126/science.abb7772)
In the Research Article "Recent global decline of CO fertilization effects on vegetation photosynthesis, " there was a small error in the histogram in Fig. 1B in the main text and in fig. S9B in the supplementary materials caused by a data-processing bug (the x axis started from 0.2, not from zero as labeled), and the calculation of standard deviation (SD) was not fully explained in the figure caption (the caption did not state that the SD was calculated from the data within the range of the y axis). Figure 1B, fig. S9B, and their captions have been corrected accordingly. In the original figure, the authors chose the β range of -10 to 50 because this range is reasonable for CO fertilization effect (CFE) based on the meta-analysis results from free-air CO enrichment (FACE) experiments and on the results from Earth-system models (1). The authors have also prepared another figure in which they have changed the y axis range from [-10, 50] that covers more than 85% of all pixels to a wider range of -20 to 80 that covers more than 94% of all pixels (see fig. S1). The change of range only affects the SDs in Fig. 1 but not the global median that was used throughout the paper. The results and main findings of this article are not affected. The β distributions still differ significantly between 1982-1996 and 2001- 2015 (Fig. 1B), and the global declining trend of β remains significant (Fig. 1A).
Abstract.
Chen Z, Huntzinger DN, Liu J, Piao S, Wang X, Sitch S, Friedlingstein P, Anthoni P, Arneth A, Bastrikov V, et al (2021). Five years of variability in the global carbon cycle: comparing an estimate from the Orbiting Carbon Observatory-2 and process-based models.
ENVIRONMENTAL RESEARCH LETTERS,
16(5).
Author URL.
Gonsamo A, Ciais P, Miralles DG, Sitch S, Dorigo W, Lombardozzi D, Friedlingstein P, Nabel JEMS, Goll DS, O'Sullivan M, et al (2021). Greening drylands despite warming consistent with carbon dioxide fertilization effect.
Glob Chang Biol,
27(14), 3336-3349.
Abstract:
Greening drylands despite warming consistent with carbon dioxide fertilization effect.
The rising atmospheric CO2 concentration leads to a CO2 fertilization effect on plants-that is, increased photosynthetic uptake of CO2 by leaves and enhanced water-use efficiency (WUE). Yet, the resulting net impact of CO2 fertilization on plant growth and soil moisture (SM) savings at large scale is poorly understood. Drylands provide a natural experimental setting to detect the CO2 fertilization effect on plant growth since foliage amount, plant water-use and photosynthesis are all tightly coupled in water-limited ecosystems. A long-term change in the response of leaf area index (LAI, a measure of foliage amount) to changes in SM is likely to stem from changing water demand of primary productivity in water-limited ecosystems and is a proxy for changes in WUE. Using 34-year satellite observations of LAI and SM over tropical and subtropical drylands, we identify that a 1% increment in SM leads to 0.15% (±0.008, 95% confidence interval) and 0.51% (±0.01, 95% confidence interval) increments in LAI during 1982-1998 and 1999-2015, respectively. The increasing response of LAI to SM has contributed 7.2% (±3.0%, 95% confidence interval) to total dryland greening during 1999-2015 compared to 1982-1998. The increasing response of LAI to SM is consistent with the CO2 fertilization effect on WUE in water-limited ecosystems, indicating that a given amount of SM has sustained greater amounts of photosynthetic foliage over time. The LAI responses to changes in SM from seven dynamic global vegetation models are not always consistent with observations, highlighting the need for improved process knowledge of terrestrial ecosystem responses to rising atmospheric CO2 concentration.
Abstract.
Author URL.
Wu C, Venevsky S, Sitch S, Mercado LM, Huntingford C, Staver AC (2021). Historical and future global burned area with changing climate and human demography.
One Earth,
4(4), 517-530.
Abstract:
Historical and future global burned area with changing climate and human demography
Wildfires influence terrestrial carbon cycling and represent a safety risk, and yet a process-based understanding of their frequency and spatial distributions remains elusive. We combine satellite-based observations with an enhanced dynamic global vegetation model to make regionally resolved global assessments of burned area (BA) responses to changing climate, derived from 34 Earth system models and human demographics for 1860–2100. Limited by climate and socioeconomics, recent BA has decreased, especially in central South America and mesic African savannas. However, future simulations predict increasing BA due to changing climate, rapid population density growth, and urbanization. BA increases are especially notable at high latitudes, due to accelerated warming, and over the tropics and subtropics, due to drying and human ignitions. Conversely, rapid urbanization also limits BA via enhanced fire suppression in the immediate vicinity of settlements, offsetting the potential for dramatic future increases, depending on warming extent. Our analysis provides further insight into regional and global BA trends, highlighting the importance of including human demographic change in models for wildfire under changing climate.
Abstract.
Huntingford C, Sitch SA, O'Sullivan M (2021). Impact of merging of historical and future climate data sets on land carbon cycle projections for South America.
Climate Resilience and Sustainability,
1(1).
Abstract:
Impact of merging of historical and future climate data sets on land carbon cycle projections for South America
AbstractEarth System Models (ESMs) project climate change, but they often contain biases in their estimates of contemporary climate that propagate into simulated futures. Land models translate climate projections into surface impacts, but these will be inaccurate if ESMs have substantial errors. Bias concerns are relevant for terrestrial physiological processes which often respond non‐linearly (i.e. contain threshold responses) and are therefore sensitive to absolute environmental conditions as well as changes. We bias‐correct the UK Met Office ESM, HadGEM2‐ES, against the CRU–JRA observation‐based gridded estimates of recent climate. We apply the derived bias corrections to future projections by HadGEM2‐ES for the RCP8.5 scenario of future greenhouse gas concentrations. Focusing on South America, the bias correction includes adjusting for ESM estimates that, annually, are approximately 1 degree too cold, for comparison against 21st Century warming of around 4 degrees. Locally, these values can be much higher. The ESM is also too wet on average, by approximately 1 mm·day−1, which is substantially larger than the mean predicted change. The corrected climate fields force the Joint UK Land Environment Simulator (JULES) dynamic global vegetation model to estimate land surface changes, with an emphasis on the carbon cycle. Results show land carbon sink reductions across South America, and in some locations, the net land–atmosphere CO2 flux becomes a source to the atmosphere by the end of this century. Transitions to a CO2 source is where increases in plant net primary productivity are offset by larger enhancements in soil respiration. Bias‐corrected simulations estimate the rise in South American land carbon stocks between pre‐industrial times and the end of the 2080s is ∼12 GtC lower than that without climate bias removal, demonstrating the importance of merging historical observational meteorological forcing with ESM diagnostics. We present evidence for a substantial climate‐induced role of greater soil decomposition in the fate of the Amazon carbon sink.
Abstract.
Gampe D, Zscheischler J, Reichstein M, O’Sullivan M, Smith WK, Sitch S, Buermann W (2021). Increasing impact of warm droughts on northern ecosystem productivity over recent decades. Nature Climate Change, 11(9), 772-779.
Walker AP, De Kauwe MG, Bastos A, Belmecheri S, Georgiou K, Keeling RF, McMahon SM, Medlyn BE, Moore DJP, Norby RJ, et al (2021). Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2.
New Phytol,
229(5), 2413-2445.
Abstract:
Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2.
Atmospheric carbon dioxide concentration ([CO2 ]) is increasing, which increases leaf-scale photosynthesis and intrinsic water-use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2 ] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2 ]-driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2 ] (iCO2 ) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre-industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2 , albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.
Abstract.
Author URL.
Wiltshire AJ, Burke EJ, Chadburn SE, Jones CD, Cox PM, Davies-Barnard T, Friedlingstein P, Harper AB, Liddicoat S, Sitch S, et al (2021). Jules-cn: a coupled terrestrial carbon-nitrogen scheme (jules vn5.1).
Geoscientific Model Development,
14(4), 2161-2186.
Abstract:
Jules-cn: a coupled terrestrial carbon-nitrogen scheme (jules vn5.1)
Understanding future changes in the terrestrial carbon cycle is important for reliable projections of climate change and impacts on ecosystems. It is well known that nitrogen (N) could limit plants' response to increased atmospheric carbon dioxide and it is therefore important to include a representation of the N cycle in Earth system models. Here we present the implementation of the terrestrial nitrogen cycle in the Joint UK Land Environment Simulator (JULES)-the land surface scheme of the UK Earth System Model (UKESM). Two configurations are discussed-the first one (JULES-CN) has a bulk soil biogeochemical model and the second one is a development configuration that resolves the soil biogeochemistry with depth (JULES-CNlayer). In JULES the nitrogen (N) cycle is based on the existing carbon (C) cycle and represents all the key terrestrial N processes in a parsimonious way. Biological N fixation is dependent on net primary productivity, and N deposition is specified as an external input. Nitrogen leaves the vegetation and soil system via leaching and a bulk gas loss term. Nutrient limitation reduces carbon-use efficiency (CUE-ratio of net to gross primary productivity) and can slow soil decomposition. We show that ecosystem level N limitation of net primary productivity (quantified in the model by the ratio of the potential amount of C that can be allocated to growth and spreading of the vegetation compared with the actual amount achieved in its natural state) falls at the lower end of the observational estimates in forests (approximately 1.0 in the model compared with 1.01 to 1.38 in the observations). The model shows more N limitation in the tropical savanna and tundra biomes, consistent with the available observations. Simulated C and N pools and fluxes are comparable to the limited available observations and model-derived estimates. The introduction of an N cycle improves the representation of interannual variability of global net ecosystem exchange, which was more pronounced in the C-cycle-only versions of JULES (JULES-C) than shown in estimates from the Global Carbon Project. It also reduces the present-day CUE from a global mean value of 0.45 for JULES-C to 0.41 for JULES-CN and 0.40 for JULES-CNlayer, all of which fall within the observational range. The N cycle also alters the response of the C fluxes over the 20th century and limits the CO2 fertilisation effect, such that the simulated current-day land C sink is reduced by about 0.5 Pg C yr-1 compared to the version with no N limitation. JULES-CNlayer additionally improves the representation of soil biogeochemistry, includ ing turnover times in the northern high latitudes. The inclu sion of a prognostic land N scheme marks a step forward in functionality and realism for the JULES and UKESM mod els.
Abstract.
Chini L, Hurtt G, Sahajpal R, Frolking S, Goldewijk KK, Sitch S, Ganzenmueller R, Ma L, Ott L, Pongratz J, et al (2021). Land-use harmonization datasets for annual global carbon budgets.
EARTH SYSTEM SCIENCE DATA,
13(8), 4175-4189.
Author URL.
Heinrich VHA, Dalagnol R, Cassol HLG, Rosan TM, de Almeida CT, Silva Junior CHL, Campanharo WA, House JI, Sitch S, Hales TC, et al (2021). Large carbon sink potential of secondary forests in the Brazilian Amazon to mitigate climate change.
Nature Communications,
12(1).
Abstract:
Large carbon sink potential of secondary forests in the Brazilian Amazon to mitigate climate change
Tropical secondary forests sequester carbon up to 20 times faster than old-growth forests. This rate does not capture spatial regrowth patterns due to environmental and disturbance drivers. Here we quantify the influence of such drivers on the rate and spatial patterns of regrowth in the Brazilian Amazon using satellite data. Carbon sequestration rates of young secondary forests (
Abstract.
Chen Z, Liu J, Henze DK, Huntzinger DN, Wells KC, Sitch S, Friedlingstein P, Joetzjer E, Bastrikov V, Goll DS, et al (2021). Linking global terrestrial CO<sub>2</sub> fluxes and environmental drivers: inferences from the Orbiting Carbon Observatory 2 satellite and terrestrial biospheric models.
ATMOSPHERIC CHEMISTRY AND PHYSICS,
21(9), 6663-6680.
Author URL.
Obermeier WA, Nabel JEMS, Loughran T, Hartung K, Bastos A, Havermann F, Anthoni P, Arneth A, Goll DS, Lienert S, et al (2021). Modelled land use and land cover change emissions – a spatio-temporal comparison of different approaches.
Earth System Dynamics,
12(2), 635-670.
Abstract:
Modelled land use and land cover change emissions – a spatio-temporal comparison of different approaches
Abstract. Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle and, hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable and has to be inferred from models instead, such as semi-empirical bookkeeping models and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an important example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called loss of additional sink capacity (LASC). The LASC results from the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation and accumulates over time, which is not captured in bookkeeping models. The fLULCC from transient DGVM simulations, thus, strongly depends on the timing of land use and land cover changes mainly because LASC accumulation is cut off at the end of the simulated period. To estimate the LASC, the fLULCC from pre-industrial DGVM simulations, which is independent of changing environmental conditions, can be used. Additionally, DGVMs using constant present-day environmental forcing enable an approximation of bookkeeping estimates. Here, we analyse these three DGVM-derived fLULCC estimations (under transient, pre-industrial, and present-day forcing) for 12 models within 18 regions and quantify their differences as well as climate- and CO2-induced components and compare them to bookkeeping estimates. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0±0.6 PgC yr−1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8±0.3 PgC yr−1). From 1850 onward, the fLULCC accumulated to 189±56 PgC with 40±15 PgC from the LASC. Around 1960, the accumulating nature of the LASC causes global transient fLULCC estimates to exceed estimates under present-day conditions, despite generally increased carbon stocks in the latter. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, equatorial Africa, and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM compared to bookkeeping approaches. Our study unravels the strong dependence of fLULCC estimates on the time a certain land use and land cover change event happened to occur and on the chosen time period for the forcing of environmental conditions in the underlying simulations. We argue for an approach that provides an accounting of the fLULCC that is more robust against these choices, for example by estimating a mean DGVM ensemble fLULCC and LASC for a defined reference period and homogeneous environmental changes (CO2 only).
.
Abstract.
He W, Ju W, Jiang F, Parazoo N, Gentine P, Wu X, Zhang C, Zhu J, Viovy N, Jain AK, et al (2021). Peak growing season patterns and climate extremes-driven responses of gross primary production estimated by satellite and process based models over North America.
Agricultural and Forest Meteorology,
298-299Abstract:
Peak growing season patterns and climate extremes-driven responses of gross primary production estimated by satellite and process based models over North America
Representations of the seasonal peak uptake of CO2 and climate extremes effects have important implications for accurately estimating annual magnitude and inter-annual variations of terrestrial carbon fluxes, however the consistency of such representations among different satellite models and process-based (PB) models remain poorly known. Here we investigated these issues over North America based on a large ensemble of state-of-the-art gross primary production (GPP) models, including two solar-induced chlorophyll fluorescence (SIF)-based models (WECANN and GOPT), three remote sensing driven light-use efficiency (LUE) models, and 10 PB models. We found that the two SIF-based GPP estimates were bilaterally consistent in spatial patterns of peak growing season GPP (GPPPGS; with the largest uptake at the Corn-Belt area in the United States) and climate extremes-driven responses. The simulations from three LUE models showed relatively consistent spatial patterns of GPPPGS and climate extremes-driven responses, which agreed well with SIF-based estimates and satellite based metrics. Obviously differed from SIF and LUE based estimates, the simulations from PB models exhibited noticeable divergences and mostly failed to reasonably replicate the spatial pattern of GPPPGS. In addition, satellite models and PB models were comparably able to capture the effects of climate extremes on GPP, but showing obvious divergences in the magnitude of impacts among different models, and the former outperformed the latter in locating GPP changes caused by climate extremes. We discussed the possible origins of such discrepancies in state-of-the-art models with focus on PB models. Improving the parameterizations of critical variables (e.g. leaf area index) and better characterizing environmental stresses could lead to more robust estimates of large-scale terrestrial GPP with PB models, thus serving for accurately assessing global carbon budget and better understanding the impacts of climate change on the terrestrial carbon cycle. Our study offers a baseline for improving large-scale estimation of terrestrial GPP.
Abstract.
Wang S, Zhang Y, Ju W, Chen JM, Ciais P, Cescatti A, Sardans J, Janssens IA, Wu M, Berry JA, et al (2021). Recent global decline of CO<sub>2</sub> fertilization effects on vegetation photosynthesis (vol 370, pg 1295, 2020).
SCIENCE,
371(6529).
Author URL.
Hayman GD, Comyn-Platt E, Huntingford C, Harper AB, Powell T, Cox PM, Collins W, Webber C, Lowe J, Sitch S, et al (2021). Regional variation in the effectiveness of methane-based and land-based climate mitigation options.
EARTH SYSTEM DYNAMICS,
12(2), 513-544.
Author URL.
Nakhavali MA, Mercado L, Hartley IP, Sitch S, Cunha FV, Ponzio RD, Lugli LF, Quesada CA, Andersen KM, Chadburn SE, et al (2021). Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP).
Geoscientific Model Development DiscussionsAbstract:
Representation of phosphorus cycle in Joint UK Land Environment Simulator (vn5.5_JULES-CNP)
Most Land Surface Models (LSMs), the land components of Earth system models (ESMs), include representation of N limitation on ecosystem productivity. However only few of these models have incorporated phosphorus (P) cycling. In tropical ecosystems, this is likely to be particularly important as N tends to be abundant but the availability of rock-derived elements, such as P, can be very low. Thus, without a representation of P cycling, tropical forest response in areas such as Amazonia to rising atmospheric CO2 conditions remains highly uncertain. In this study, we introduced P dynamics and its interactions with the N and carbon (C) cycles into the Joint UK Land Environment Simulator (JULES). The new model (JULES-CNP) includes the representation of P stocks in vegetation and soil pools, as well as key processes controlling fluxes between these pools. We evaluate JULES-CNP at the Amazon nutrient fertilization experiment (AFEX), a low fertility site, representative of about 60 % of Amazon soils. We apply the model under ambient CO2 and elevated CO2. The model is able to reproduce the observed plant and soil P pools and fluxes under ambient CO2. We estimate P to limit net primary productivity (NPP) by 24 % under current CO2 and by 46 % under elevated CO2. Under elevated CO2, biomass in simulations accounting for CNP increase by 10 % relative to at contemporary CO2, although it is 5 % lower compared with CN and C-only simulations. Our results highlight the potential for high P limitation and therefore lower CO2 fertilization capacity in the Amazon forest with low fertility soils.
Abstract.
Liu J, you Y, Li J, Sitch S, Gu X, Nabel JEMS, Lombardozzi D, Luo M, Feng X, Arneth A, et al (2021). Response of global land evapotranspiration to climate change, elevated CO<sub>2</sub>, and land use change.
AGRICULTURAL AND FOREST METEOROLOGY,
311 Author URL.
Wang S, Zhang Y, Ju W, Chen JM, Cescatti A, Sardans J, Janssens IA, Wu M, Berry JA, Campbell JE, et al (2021). Response to Comments on "Recent global decline of CO2 fertilization effects on vegetation photosynthesis".
Science,
373(6562).
Abstract:
Response to Comments on "Recent global decline of CO2 fertilization effects on vegetation photosynthesis".
Our study suggests that the global CO2 fertilization effect (CFE) on vegetation photosynthesis has declined during the past four decades. The Comments suggest that the temporal inconsistency in AVHRR data and the attribution method undermine the results’ robustness. Here, we provide additional evidence that these arguments did not affect our finding and that the global decline in CFE is robust.
Abstract.
Author URL.
Winkler AJ, Myneni RB, Hannart A, Sitch S, Haverd V, Lombardozzi D, Arora VK, Pongratz J, Nabel JEMS, Goll DS, et al (2021). Slowdown of the greening trend in natural vegetation with further rise in atmospheric CO<sub>2</sub>.
BIOGEOSCIENCES,
18(17), 4985-5010.
Author URL.
Bastos A, Orth R, Reichstein M, Ciais P, Viovy N, Zaehle S, Anthoni P, Arneth A, Gentine P, Joetzjer E, et al (2021). Vulnerability of European ecosystems to two compound dry and hot summers in 2018 and 2019.
Earth System Dynamics,
12(4), 1015-1035.
Abstract:
Vulnerability of European ecosystems to two compound dry and hot summers in 2018 and 2019
In 2018 and 2019, central Europe was affected by two consecutive extreme dry and hot summers (DH18 and DH19). The DH18 event had severe impacts on ecosystems and likely affected vegetation activity in the subsequent year, for example through depletion of carbon reserves or damage from drought. Such legacies from drought and heat stress can further increase vegetation susceptibility to additional hazards. Temporally compound extremes such as DH18 and DH19 can, therefore, result in an amplification of impacts due to preconditioning effects of past disturbance legacies. Here, we evaluate how these two consecutive extreme summers impacted ecosystems in central Europe and how the vegetation responses to the first compound event (DH18) modulated the impacts of the second (DH19). To quantify changes in vegetation vulnerability to each compound event, we first train a set of statistical models for the period 2001-2017, which are then used to predict the impacts of DH18 and DH19 on enhanced vegetation index (EVI) anomalies from MODIS. These estimates correspond to expected EVI anomalies in DH18 and DH19 based on past sensitivity to climate. Large departures from the predicted values can indicate changes in vulnerability to dry and hot conditions and be used to identify modulating effects by vegetation activity and composition or other environmental factors on observed impacts. We find two regions in which the impacts of the two compound dry and hot (DH) events were significantly stronger than those expected based on previous climate-vegetation relationships. One region, largely dominated by grasslands and crops, showed much stronger impacts than expected in both DH events due to an amplification of their sensitivity to heat and drought, possibly linked to changing background CO2 and temperature conditions. A second region, dominated by forests and grasslands, showed browning from DH18 to DH19, even though dry and hot conditions were partly alleviated in 2019. This browning trajectory was mainly explained by the preconditioning role of DH18 on the impacts of DH19 due to interannual legacy effects and possibly by increased susceptibility to biotic disturbances, which are also promoted by warm conditions. Dry and hot summers are expected to become more frequent in the coming decades, posing a major threat to the stability of European forests. We show that state-of-the-art process-based models could not represent the decline in response to DH19 because they missed the interannual legacy effects from DH18 impacts. These gaps may result in an overestimation of the resilience and stability of temperate ecosystems in future model projections.
Abstract.
Leung F, Williams K, Sitch S, Tai APK, Wiltshire A, Gornall J, Ainsworth EA, Arkebauer T, Scoby D (2020). Calibrating soybean parameters in JULES 5.0 from the US-Ne2/3 FLUXNET sites and the SoyFACE-O3 experiment.
Geoscientific Model Development,
13(12), 6201-6213.
Abstract:
Calibrating soybean parameters in JULES 5.0 from the US-Ne2/3 FLUXNET sites and the SoyFACE-O3 experiment
Abstract. Tropospheric ozone (O3) is the third most important
anthropogenic greenhouse gas. O3 is detrimental to plant productivity,
and it has a significant impact on crop yield. Currently, the Joint UK Land
Environment Simulator (JULES) land surface model includes a representation
of global crops (JULES-crop) but does not have crop-specific O3 damage
parameters and applies default C3 grass O3 parameters for soybean that
underestimate O3 damage. Physiological parameters for O3 damage
in soybean in JULES-crop were calibrated against leaf gas-exchange
measurements from the Soybean Free Air Concentration Enrichment (SoyFACE)
with O3 experiment in Illinois, USA. Other plant parameters were
calibrated using an extensive array of soybean observations such as crop
height and leaf carbon and meteorological data from FLUXNET sites near
Mead, Nebraska, USA. The yield, aboveground carbon, and leaf area index (LAI)
of soybean from the SoyFACE experiment were used to evaluate the newly
calibrated parameters. The result shows good performance for yield, with the
modelled yield being within the spread of the SoyFACE observations. Although
JULES-crop is able to reproduce observed LAI seasonality, its magnitude is
underestimated. The newly calibrated version of JULES will be applied
regionally and globally in future JULES simulations. This study helps to
build a state-of-the-art impact assessment model and contribute to a more
complete understanding of the impacts of climate change on food production.
.
Abstract.
Leung F, Williams K, Sitch S, Tai APK, Wiltshire A, Gornall J, Ainsworth EA, Arkebauer T, Scoby D (2020). Calibrating soybean parameters in JULES5.0 from the US-Ne2/3 FLUXNET sites and the SoyFACE-O&lt;sub&gt;3&lt;/sub&gt; experiment.
Abstract:
Calibrating soybean parameters in JULES5.0 from the US-Ne2/3 FLUXNET sites and the SoyFACE-O<sub>3</sub> experiment
Abstract. Tropospheric ozone (O3) is the third most important anthropogenic greenhouse gas. O3 is detrimental to plant productivity, and it has a significant impact on crop yield. Currently, the Joint UK Land Environment Simulator (JULES) land surface model includes a representation of global crops (JULES-crop), but does not have crop-specific O3 damage parameters, and applies default C3 grass O3 parameters for soybean that underestimates O3 damage. Physiological parameters for O3 damage in soybean in JULES-crop were calibrated against leaf gas-exchange measurements from the Soybean Free-Air-Concentration-Enrichment (SoyFACE) with O3 experiment in Illinois, USA. Other plant parameters were calibrated using an extensive array of soybean observations such as crop height, leaf carbon, etc. and meteorological data from FLUXNET sites near Mead, Nebraska, USA. The yield, aboveground carbon and leaf area index (LAI) of soybean from the SoyFACE experiment were used to evaluate the newly calibrated parameters. The result shows good performance for yield, with the modelled yield being within the spread of the SoyFACE observations. Although JULES-crop is able to reproduce observed LAI seasonality, its magnitude is underestimated. The newly calibrated version of JULES will be applied regionally and globally in future JULES simulations. This study helps to build a state-of-the-art impact assessment model and contribute to a more complete understanding of the impacts of climate change on food production.
.
Abstract.
Wang K, Wang Y, Wang X, He Y, Li X, Keeling RF, Ciais P, Heimann M, Peng S, Chevallier F, et al (2020). Causes of slowing-down seasonal CO2 amplitude at Mauna Loa.
Glob Chang Biol,
26(8), 4462-4477.
Abstract:
Causes of slowing-down seasonal CO2 amplitude at Mauna Loa.
Changing amplitude of the seasonal cycle of atmospheric CO2 (SCA) in the northern hemisphere is an emerging carbon cycle property. Mauna Loa (MLO) station (20°N, 156°W), which has the longest continuous northern hemisphere CO2 record, shows an increasing SCA before the 1980s (p
Abstract.
Author URL.
Yang H, Ciais P, Santoro M, Huang Y, Li W, Wang Y, Bastos A, Goll D, Arneth A, Anthoni P, et al (2020). Comparison of forest above‐ground biomass from dynamic global vegetation models with spatially explicit remotely sensed observation‐based estimates.
Global Change Biology,
26(7), 3997-4012.
Abstract:
Comparison of forest above‐ground biomass from dynamic global vegetation models with spatially explicit remotely sensed observation‐based estimates
AbstractGaps in our current understanding and quantification of biomass carbon stocks, particularly in tropics, lead to large uncertainty in future projections of the terrestrial carbon balance. We use the recently published GlobBiomass data set of forest above‐ground biomass (AGB) density for the year 2010, obtained from multiple remote sensing and in situ observations at 100 m spatial resolution to evaluate AGB estimated by nine dynamic global vegetation models (DGVMs). The global total forest AGB of the nine DGVMs is 365 ± 66 Pg C, the spread corresponding to the standard deviation between models, compared to 275 Pg C with an uncertainty of ~13.5% from GlobBiomass. Model‐data discrepancy in total forest AGB can be attributed to their discrepancies in the AGB density and/or forest area. While DGVMs represent the global spatial gradients of AGB density reasonably well, they only have modest ability to reproduce the regional spatial gradients of AGB density at scales below 1000 km. The 95th percentile of AGB density (AGB95) in tropics can be considered as the potential maximum of AGB density which can be reached for a given annual precipitation. GlobBiomass data show local deficits of AGB density compared to the AGB95, particularly in transitional and/or wet regions in tropics. We hypothesize that local human disturbances cause more AGB density deficits from GlobBiomass than from DGVMs, which rarely represent human disturbances. We then analyse empirical relationships between AGB density deficits and forest cover changes, population density, burned areas and livestock density. Regression analysis indicated that more than 40% of the spatial variance of AGB density deficits in South America and Africa can be explained; in Southeast Asia, these factors explain only ~25%. This result suggests TRENDY v6 DGVMs tend to underestimate biomass loss from diverse and widespread anthropogenic disturbances, and as a result overestimate turnover time in AGB.
Abstract.
Bastos A, Ciais P, Friedlingstein P, Sitch S, Pongratz J, Fan L, Wigneron JP, Weber U, Reichstein M, Fu Z, et al (2020). Direct and seasonal legacy effects of the 2018 heat wave and drought on European ecosystem productivity.
Science Advances,
6(24).
Abstract:
Direct and seasonal legacy effects of the 2018 heat wave and drought on European ecosystem productivity
Ecosystems responded asymmetrically to the 2018 European drought.
Abstract.
Cunliffe AM, Anderson K, Boschetti F, Brazier RE, Graham HA, Myers-Smith IH, Astor T, Boer MM, Calvo L, Clark PE, et al (2020). Drone-derived canopy height predicts biomass across non-forest ecosystems globally.
Abstract:
Drone-derived canopy height predicts biomass across non-forest ecosystems globally
AbstractNon-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, yet are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely-sensed biomass products and are undersampled by in-situ monitoring. Current global change threats emphasise the need for new tools to capture biomass change in non-forest ecosystems at appropriate scales. Here we assess whether canopy height inferred from drone photogrammetry allows the estimation of aboveground biomass (AGB) across low-stature plant species sampled through a global site network. We found mean canopy height is strongly predictive of AGB across species, demonstrating standardised photogrammetric approaches are generalisable across growth forms and environmental settings. Biomass per-unit-of-height was similar within, but different among, plant functional types. We find drone-based photogrammetry allows for monitoring of AGB across large spatial extents and can advance understanding of understudied and vulnerable non-forested ecosystems across the globe.
Abstract.
Yun J, Jeong S, Ho C-H, Park H, Liu J, Lee H, Sitch S, Friedlingstein P, Lienert S, Lombardozzi D, et al (2020). Enhanced regional terrestrial carbon uptake over Korea revealed by atmospheric CO2 measurements from 1999 to 2017.
Glob Chang Biol,
26(6), 3368-3383.
Abstract:
Enhanced regional terrestrial carbon uptake over Korea revealed by atmospheric CO2 measurements from 1999 to 2017.
Understanding changes in terrestrial carbon balance is important to improve our knowledge of the regional carbon cycle and climate change. However, evaluating regional changes in the terrestrial carbon balance is challenging due to the lack of surface flux measurements. This study reveals that the terrestrial carbon uptake over the Republic of Korea has been enhanced from 1999 to 2017 by analyzing long-term atmospheric CO2 concentration measurements at the Anmyeondo Station (36.53°N, 126.32°E) located in the western coast. The influence of terrestrial carbon flux on atmospheric CO2 concentrations (ΔCO2 ) is estimated from the difference of CO2 concentrations that were influenced by the land sector (through easterly winds) and the Yellow Sea sector (through westerly winds). We find a significant trend in ΔCO2 of -4.75 ppm per decade (p
Abstract.
Author URL.
Pan S, Pan N, Tian H, Friedlingstein P, Sitch S, Shi H, Arora VK, Haverd V, Jain AK, Kato E, et al (2020). Evaluation of global terrestrial evapotranspiration using state-of-the-art approaches in remote sensing, machine learning and land surface modeling.
HYDROLOGY AND EARTH SYSTEM SCIENCES,
24(3), 1485-1509.
Author URL.
Collalti A, Ibrom A, Stockmarr A, Cescatti A, Alkama R, Fernández-Martínez M, Matteucci G, Sitch S, Friedlingstein P, Ciais P, et al (2020). Forest production efficiency increases with growth temperature.
Abstract:
Forest production efficiency increases with growth temperature
Introductory paragraphWe present a global analysis of the relationship of forest production efficiency (FPE) to stand age and climate, based on a large compilation of data on gross primary production and either biomass production or net primary production. FPE is important for both forest production and atmospheric carbon dioxide uptake. Earlier findings – FPE declining with age – are supported by this analysis. However, FPE also increases with absolute latitude, precipitation and (all else equal) with temperature. The temperature effect is opposite to what would be expected based on the short-term physiological response of respiration rates to temperature. It implies top-down regulation of forest carbon loss, perhaps reflecting the higher carbon costs of nutrient acquisition in colder climates. Current ecosystem models do not reproduce this phenomenon. They consistently predict lower FPE in warmer climates, and are therefore likely to overestimate carbon losses in a warming climate.
Abstract.
Collalti A, Ibrom A, Stockmarr A, Cescatti A, Alkama R, Fernández-Martínez M, Matteucci G, Sitch S, Friedlingstein P, Ciais P, et al (2020). Forest production efficiency increases with growth temperature.
Nature Communications,
11(1).
Abstract:
Forest production efficiency increases with growth temperature
AbstractForest production efficiency (FPE) metric describes how efficiently the assimilated carbon is partitioned into plants organs (biomass production, BP) or—more generally—for the production of organic matter (net primary production, NPP). We present a global analysis of the relationship of FPE to stand-age and climate, based on a large compilation of data on gross primary production and either BP or NPP. FPE is important for both forest production and atmospheric carbon dioxide uptake. We find that FPE increases with absolute latitude, precipitation and (all else equal) with temperature. Earlier findings—FPE declining with age—are also supported by this analysis. However, the temperature effect is opposite to what would be expected based on the short-term physiological response of respiration rates to temperature, implying a top-down regulation of carbon loss, perhaps reflecting the higher carbon costs of nutrient acquisition in colder climates. Current ecosystem models do not reproduce this phenomenon. They consistently predict lower FPE in warmer climates, and are therefore likely to overestimate carbon losses in a warming climate.
Abstract.
Friedlingstein P, O'Sullivan M, Jones MW, Andrew RM, Hauck J, Olsen A, Peters GP, Peters W, Pongratz J, Sitch S, et al (2020). Global Carbon Budget 2020.
Friedlingstein P, O'Sullivan M, Jones MW, Andrew RM, Hauck J, Olsen A, Peters GP, Peters W, Pongratz J, Sitch S, et al (2020). Global Carbon Budget 2020.
Earth System Science Data,
12(4), 3269-3340.
Abstract:
Global Carbon Budget 2020
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and
their redistribution among the atmosphere, ocean, and terrestrial biosphere
in a changing climate – the “global carbon budget” – is important to
better understand the global carbon cycle, support the development of
climate policies, and project future climate change. Here we describe and
synthesize data sets and methodology to quantify the five major components
of the global carbon budget and their uncertainties. Fossil CO2
emissions (EFOS) are based on energy statistics and cement production
data, while emissions from land-use change (ELUC), mainly
deforestation, are based on land use and land-use change data and
bookkeeping models. Atmospheric CO2 concentration is measured directly
and its growth rate (GATM) is computed from the annual changes in
concentration. The ocean CO2 sink (SOCEAN) and terrestrial
CO2 sink (SLAND) are estimated with global process models
constrained by observations. The resulting carbon budget imbalance
(BIM), the difference between the estimated total emissions and the
estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a
measure of imperfect data and understanding of the contemporary carbon
cycle. All uncertainties are reported as ±1σ. For the last
decade available (2010–2019), EFOS was 9.6 ± 0.5 GtC yr−1 excluding the cement carbonation sink (9.4 ± 0.5 GtC yr−1 when the cement carbonation sink is included), and
ELUC was 1.6 ± 0.7 GtC yr−1. For the same decade, GATM was 5.1 ± 0.02 GtC yr−1 (2.4 ± 0.01 ppm yr−1), SOCEAN 2.5 ± 0.6 GtC yr−1, and SLAND 3.4 ± 0.9 GtC yr−1, with a budget
imbalance BIM of −0.1 GtC yr−1 indicating a near balance between
estimated sources and sinks over the last decade. For the year 2019 alone, the
growth in EFOS was only about 0.1 % with fossil emissions increasing
to 9.9 ± 0.5 GtC yr−1 excluding the cement carbonation sink (9.7 ± 0.5 GtC yr−1 when cement carbonation sink is included), and ELUC was 1.8 ± 0.7 GtC yr−1, for total anthropogenic CO2 emissions of 11.5 ± 0.9 GtC yr−1 (42.2 ± 3.3 GtCO2). Also for 2019, GATM was
5.4 ± 0.2 GtC yr−1 (2.5 ± 0.1 ppm yr−1), SOCEAN
was 2.6 ± 0.6 GtC yr−1, and SLAND was 3.1 ± 1.2 GtC yr−1, with a BIM of 0.3 GtC. The global atmospheric CO2
concentration reached 409.85 ± 0.1 ppm averaged over 2019. Preliminary
data for 2020, accounting for the COVID-19-induced changes in emissions,
suggest a decrease in EFOS relative to 2019 of about −7 % (median
estimate) based on individual estimates from four studies of −6 %, −7 %,
−7 % (−3 % to −11 %), and −13 %. Overall, the mean and trend in the
components of the global carbon budget are consistently estimated over the
period 1959–2019, but discrepancies of up to 1 GtC yr−1 persist for the
representation of semi-decadal variability in CO2 fluxes. Comparison of
estimates from diverse approaches and observations shows (1) no consensus
in the mean and trend in land-use change emissions over the last decade, (2)
a persistent low agreement between the different methods on the magnitude of
the land CO2 flux in the northern extra-tropics, and (3) an apparent
discrepancy between the different methods for the ocean sink outside the
tropics, particularly in the Southern Ocean. This living data update
documents changes in the methods and data sets used in this new global
carbon budget and the progress in understanding of the global carbon cycle
compared with previous publications of this data set (Friedlingstein et al.
2019; Le Quéré et al. 2018b, a, 2016, 2015b, a, 2014,
2013). The data presented in this work are available at https://doi.org/10.18160/gcp-2020 (Friedlingstein et al. 2020).
.
Abstract.
Lasslop G, Hantson S, Harrison SP, Bachelet D, Burton C, Forkel M, Forrest M, Li F, Melton JR, Yue C, et al (2020). Global ecosystems and fire: Multi-model assessment of fire-induced tree-cover and carbon storage reduction.
Glob Chang Biol,
26(9), 5027-5041.
Abstract:
Global ecosystems and fire: Multi-model assessment of fire-induced tree-cover and carbon storage reduction.
In this study, we use simulations from seven global vegetation models to provide the first multi-model estimate of fire impacts on global tree cover and the carbon cycle under current climate and anthropogenic land use conditions, averaged for the years 2001-2012. Fire globally reduces the tree covered area and vegetation carbon storage by 10%. Regionally, the effects are much stronger, up to 20% for certain latitudinal bands, and 17% in savanna regions. Global fire effects on total carbon storage and carbon turnover times are lower with the effect on gross primary productivity (GPP) close to 0. We find the strongest impacts of fire in savanna regions. Climatic conditions in regions with the highest burned area differ from regions with highest absolute fire impact, which are characterized by higher precipitation. Our estimates of fire-induced vegetation change are lower than previous studies. We attribute these differences to different definitions of vegetation change and effects of anthropogenic land use, which were not considered in previous studies and decreases the impact of fire on tree cover. Accounting for fires significantly improves the spatial patterns of simulated tree cover, which demonstrates the need to represent fire in dynamic vegetation models. Based upon comparisons between models and observations, process understanding and representation in models, we assess a higher confidence in the fire impact on tree cover and vegetation carbon compared to GPP, total carbon storage and turnover times. We have higher confidence in the spatial patterns compared to the global totals of the simulated fire impact. As we used an ensemble of state-of-the-art fire models, including effects of land use and the ensemble median or mean compares better to observational datasets than any individual model, we consider the here presented results to be the current best estimate of global fire effects on ecosystems.
Abstract.
Author URL.
Eller CB, Meireles LD, Sitch S, Burgess SSO, Oliveira RS (2020). How Climate Shapes the Functioning of Tropical Montane Cloud Forests.
CURRENT FORESTRY REPORTS,
6(2), 97-114.
Author URL.
Bastos A, Fu Z, Ciais P, Friedlingstein P, Sitch S, Pongratz J, Weber U, Reichstein M, Anthoni P, Arneth A, et al (2020). Impacts of extreme summers on European ecosystems: a comparative analysis of 2003, 2010 and 2018.
Philos Trans R Soc Lond B Biol Sci,
375(1810).
Abstract:
Impacts of extreme summers on European ecosystems: a comparative analysis of 2003, 2010 and 2018.
In Europe, three widespread extreme summer drought and heat (DH) events have occurred in 2003, 2010 and 2018. These events were comparable in magnitude but varied in their geographical distribution and biomes affected. In this study, we perform a comparative analysis of the impact of the DH events on ecosystem CO2 fluxes over Europe based on an ensemble of 11 dynamic global vegetation models (DGVMs), and the observation-based FLUXCOM product. We find that all DH events were associated with decreases in net ecosystem productivity (NEP), but the gross summer flux anomalies differ between DGVMs and FLUXCOM. At the annual scale, FLUXCOM and DGVMs indicate close to neutral or above-average land CO2 uptake in DH2003 and DH2018, due to increased productivity in spring and reduced respiration in autumn and winter compensating for less photosynthetic uptake in summer. Most DGVMs estimate lower gross primary production (GPP) sensitivity to soil moisture during extreme summers than FLUXCOM. Finally, we show that the different impacts of the DH events at continental-scale GPP are in part related to differences in vegetation composition of the regions affected and to regional compensating or offsetting effects from climate anomalies beyond the DH centres. This article is part of the theme issue 'Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.
Abstract.
Author URL.
Forzieri G, Miralles DG, Ciais P, Alkama R, Ryu Y, Duveiller G, Zhang K, Robertson E, Kautz M, Martens B, et al (2020). Increased control of vegetation on global terrestrial energy fluxes.
NATURE CLIMATE CHANGE,
10(4), 356-+.
Author URL.
Piao S, Wang X, Wang K, Li X, Bastos A, Canadell JG, Ciais P, Friedlingstein P, Sitch S (2020). Interannual variation of terrestrial carbon cycle: Issues and perspectives.
Glob Chang Biol,
26(1), 300-318.
Abstract:
Interannual variation of terrestrial carbon cycle: Issues and perspectives.
With accumulation of carbon cycle observations and model developments over the past decades, exploring interannual variation (IAV) of terrestrial carbon cycle offers the opportunity to better understand climate-carbon cycle relationships. However, despite growing research interest, uncertainties remain on some fundamental issues, such as the contributions of different regions, constituent fluxes and climatic factors to carbon cycle IAV. Here we overviewed the literature on carbon cycle IAV about current understanding of these issues. Observations and models of the carbon cycle unanimously show the dominance of tropical land ecosystems to the signal of global carbon cycle IAV, where tropical semiarid ecosystems contribute as much as the combination of all other tropical ecosystems. Vegetation photosynthesis contributes more than ecosystem respiration to IAV of the global net land carbon flux, but large uncertainties remain on the contribution of fires and other disturbance fluxes. Climatic variations are the major drivers to the IAV of net land carbon flux. Although debate remains on whether the dominant driver is temperature or moisture variability, their interaction,that is, the dependence of carbon cycle sensitivity to temperature on moisture conditions, is emerging as key regulators of the carbon cycle IAV. On timescales from the interannual to the centennial, global carbon cycle variability will be increasingly contributed by northern land ecosystems and oceans. Therefore, both improving Earth system models (ESMs) with the progressive understanding on the fast processes manifested at interannual timescale and expanding carbon cycle observations at broader spatial and longer temporal scales are critical to better prediction on evolution of the carbon-climate system.
Abstract.
Author URL.
Lawal S, Sitch S, Lombardozzi D, Nabel JEMS, Wey H-W, Friedlingstein P, Tian H, Hewitson B (2020). Investigating the response of LAI to droughts in southern African vegetation using observations and model-simulations.
Abstract:
Investigating the response of LAI to droughts in southern African vegetation using observations and model-simulations
Abstract. In many regions of the world, frequent and continual dry spells are exacerbating drought conditions, which have severe impacts on vegetation biomes. Vegetation in southern Africa is among the most affected by drought. Here, we assessed the spatiotemporal characteristics of meteorological drought in southern Africa using the Standardized Precipitation Evapotranspiration Index over a 30-year period (1982–2011). The severity and the effects of droughts on vegetation productiveness were examined at different drought time-scales (1- to 24-month time-scales). In this study, we characterized vegetation using the Leaf Area Index, after evaluating its relationship with the Normalized Difference Vegetation Index. We found that the LAI responds strongly (r = 0.6) to drought over the central and south eastern parts of the region, with weaker impacts (r
.
Abstract.
Wiltshire AJ, Burke EJ, Chadburn SE, Jones CD, Cox PM, Davies-Barnard T, Friedlingstein P, Harper AB, Liddicoat S, Sitch SA, et al (2020). JULES-CN: a coupled terrestrial Carbon-Nitrogen Scheme (JULES vn5.1).
Abstract:
JULES-CN: a coupled terrestrial Carbon-Nitrogen Scheme (JULES vn5.1)
Abstract. Understanding future changes in the terrestrial carbon cycle is important for reliable projections of climate change and impacts on ecosystems. It is known that nitrogen could limit plants' response to increased atmospheric carbon dioxide and is therefore important to include in Earth System Models. Here we present the implementation of the terrestrial nitrogen cycle in the JULES land surface model (JULES-CN). Two versions are discussed – the one implemented within the UK Earth System Model (UKESM1) which has a bulk soil biogeochemical model and a development version which resolves the soil biogeochemistry with depth. The nitrogen cycle is based on the existing carbon cycle in the model. It represents all the key terrestrial nitrogen processes in an efficient way. Biological fixation and nitrogen deposition are external inputs, and loss occurs via leaching and a bulk gas loss parameterisation. Nutrient limitation reduces carbon-use efficiency (CUE – ratio of net to gross primary productivity) and can slow soil decomposition. We show that ecosystem level limitation of net primary productivity by nitrogen is consistent with observational estimates and that simulated carbon and nitrogen pools and fluxes are comparable to the limited available observations. The impact of N limitation is most pronounced in northern mid-latitudes. The introduction of a nitrogen cycle improves the representation of interannual variability of global net ecosystem exchange which was much too pronounced in the carbon cycle only versions of JULES (JULES-C). It also reduces the CUE and alters its response over the twentieth century and limits the CO2-fertilisation effect, such that the simulated current day land carbon sink is reduced by about 0.5 Pg C yr−1. The inclusion of a prognostic land nitrogen scheme marks a step forward in functionality and realism for the JULES and UKESM models.
.
Abstract.
Yue X, Liao H, Wang H, Zhang T, Unger N, Sitch S, Feng Z, Yang J (2020). Pathway dependence of ecosystem responses. in China to 1.5 °C global warming.
Atmospheric Chemistry and Physics,
20(4), 2353-2366.
Abstract:
Pathway dependence of ecosystem responses. in China to 1.5 °C global warming
Abstract. China is currently the world's largest emitter of both CO2 and
short-lived air pollutants. Ecosystems in China help mitigate a part of
the country's carbon emissions, but they are subject to perturbations in CO2, climate, and air pollution. Here, we use a dynamic vegetation model and data from three model inter-comparison projects to examine ecosystem responses in China under different emission pathways towards the 1.5 ∘C warming target set by the Paris Agreement. At 1.5 ∘C warming, gross primary productivity (GPP) increases by 15.5±5.4 % in a stabilized pathway and 11.9±4.4 % in a transient pathway. CO2 fertilization is the dominant driver of GPP enhancement and climate change is the main source of uncertainties. However, differences in ozone and aerosols explain the GPP differences between pathways at 1.5 ∘C warming. Although the land carbon sink is weakened by 17.4±19.6 % in the stabilized pathway, the ecosystems mitigate 10.6±1.4 % of national emissions in the stabilized pathway, more efficient than the fraction of 6.3±0.8 % in the transient pathway. To achieve the 1.5 ∘C warming target, our analysis suggests a higher allowable carbon budget for China under a stabilized pathway with reduced emissions in both CO2 and air pollutants.
.
Abstract.
Hantson S, Kelley DI, Arneth A, Harrison SP, Archibald S, Bachelet D, Forrest M, Hickler T, Lasslop G, Li F, et al (2020). Quantitative assessment of fire and vegetation properties in simulations with fire-enabled vegetation models from the Fire Model Intercomparison Project.
GEOSCIENTIFIC MODEL DEVELOPMENT,
13(7), 3299-3318.
Author URL.
Wang S, Zhang Y, Ju W, Chen JM, Ciais P, Cescatti A, Sardans J, Janssens IA, Wu M, Berry JA, et al (2020). Recent global decline of CO2 fertilization effects on vegetation photosynthesis.
Science,
370(6522), 1295-1300.
Abstract:
Recent global decline of CO2 fertilization effects on vegetation photosynthesis.
The enhanced vegetation productivity driven by increased concentrations of carbon dioxide (CO2) [i.e. the CO2 fertilization effect (CFE)] sustains an important negative feedback on climate warming, but the temporal dynamics of CFE remain unclear. Using multiple long-term satellite- and ground-based datasets, we showed that global CFE has declined across most terrestrial regions of the globe from 1982 to 2015, correlating well with changing nutrient concentrations and availability of soil water. Current carbon cycle models also demonstrate a declining CFE trend, albeit one substantially weaker than that from the global observations. This declining trend in the forcing of terrestrial carbon sinks by increasing amounts of atmospheric CO2 implies a weakening negative feedback on the climatic system and increased societal dependence on future strategies to mitigate climate warming.
Abstract.
Author URL.
Hayman GD, Comyn-Platt E, Huntingford C, Harper AB, Powell T, Cox PM, Collins W, Webber C, Lowe J, Sitch S, et al (2020). Regional variation in the effectiveness of methane-based and land-based climate mitigation options.
Abstract:
Regional variation in the effectiveness of methane-based and land-based climate mitigation options
Abstract. Scenarios avoiding global warming greater than 1.5 or 2 °C, as stipulated in the Paris Agreement, may require the combined mitigation of anthropogenic greenhouse gas emissions alongside enhancing negative emissions through approaches such as afforestation/reforestation (AR) and biomass energy with carbon capture and storage (BECCS). We use the JULES land-surface model coupled to an inverted form of the IMOGEN climate emulator to investigate mitigation scenarios that achieve the 1.5 or 2 °C warming targets of the Paris Agreement. Specifically, we characterise the global and regional effectiveness of land-based (BECCS and/or AR) and anthropogenic methane (CH4) emission mitigation, separately and in combination, on the anthropogenic fossil fuel carbon dioxide emission budgets (AFFEBs) to 2100, using consistent data and socio-economic assumptions from the IMAGE integrated assessment model. The analysis includes the effects of the methane and carbon-climate feedbacks from wetlands and permafrost thaw, which we have shown previously to be significant constraints on the AFFEBs. Globally, mitigation of anthropogenic CH4 emissions has large impacts on the anthropogenic fossil fuel emission budgets, potentially offsetting (i.e. allowing extra) carbon dioxide emissions of 188–212 GtC. Methane mitigation is beneficial everywhere, particularly for the major CH4-emitting regions of India, USA and China. Land-based mitigation has the potential to offset 51–100 GtC globally, but both the effectiveness and the preferred land-management strategy (i.e. AR or BECCS) have strong regional dependencies. Additional analysis shows extensive BECCS could adversely affect water security for several regions. Our results highlight the extra potential CO2 emissions that can occur, while still keeping global warming below key warming thresholds, by investment in regionally appropriate mitigation strategies.
.
Abstract.
Jung M, Schwalm C, Migliavacca M, Walther S, Camps-Valls G, Koirala S, Anthoni P, Besnard S, Bodesheim P, Carvalhais N, et al (2020). Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach.
Biogeosciences,
17(5), 1343-1365.
Abstract:
Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach
Abstract. FLUXNET comprises globally distributed eddy-covariance-based estimates of carbon fluxes between the biosphere and the atmosphere. Since eddy covariance flux towers have a relatively small footprint and are distributed unevenly across the world, upscaling the observations is necessary to obtain global-scale estimates of biosphere–atmosphere exchange. Based on cross-consistency checks with atmospheric inversions, sun-induced fluorescence (SIF) and dynamic global vegetation models (DGVMs), here we provide a systematic assessment of the latest upscaling efforts for gross primary production (GPP) and net ecosystem exchange (NEE) of the FLUXCOM initiative, where different machine learning methods, forcing data sets and sets of predictor variables were employed. Spatial patterns of mean GPP are consistent across FLUXCOM and DGVM ensembles (R2>0.94 at 1∘ spatial resolution) while the majority of DGVMs show, for 70 % of the land surface, values outside the FLUXCOM range. Global mean GPP magnitudes for 2008–2010 from FLUXCOM members vary within 106 and 130 PgC yr−1 with the largest uncertainty in the tropics. Seasonal variations in independent SIF estimates agree better with FLUXCOM GPP (mean global pixel-wise R2∼0.75) than with GPP from DGVMs (mean global pixel-wise R2∼0.6). Seasonal variations in FLUXCOM NEE show good consistency with atmospheric inversion-based net land carbon fluxes, particularly for temperate and boreal regions (R2>0.92). Interannual variability of global NEE in FLUXCOM is underestimated compared to inversions and DGVMs. The FLUXCOM version which also uses meteorological inputs shows a strong co-variation in interannual patterns with inversions (R2=0.87 for 2001–2010). Mean regional NEE from FLUXCOM shows larger uptake than inversion and DGVM-based estimates, particularly in the tropics with discrepancies of up to several hundred grammes of carbon per square metre per year. These discrepancies can only partly be reconciled by carbon loss pathways that are implicit in inversions but not captured by the flux tower measurements such as carbon emissions from fires and water bodies. We hypothesize that a combination of systematic biases in the underlying eddy covariance data, in particular in tall tropical forests, and a lack of site history effects on NEE in FLUXCOM are likely responsible for the too strong tropical carbon sink estimated by FLUXCOM. Furthermore, as FLUXCOM does not account for CO2 fertilization effects, carbon flux trends are not realistic. Overall, current FLUXCOM estimates of mean annual and seasonal cycles of GPP as well as seasonal NEE variations provide useful constraints of global carbon cycling, while interannual variability patterns from FLUXCOM are valuable but require cautious interpretation. Exploring the diversity of Earth observation data and of machine learning concepts along with improved quality and quantity of flux tower measurements will facilitate further improvements of the FLUXCOM approach overall.
Abstract.
Ritchie P, Smith G, Davis K, Fezzi C, Halleck-Vega S, Harper A, Boulton C, Binner A, Day B, Gallego-Sala A, et al (2020). Shifts in national land use and food production in Great Britain after a climate tipping point. Nature Food, 1, 76-83.
Bastos A, O'Sullivan M, Ciais P, Makowski D, Sitch S, Friedlingstein P, Chevallier F, Rödenbeck C, Pongratz J, Luijkx IT, et al (2020). Sources of Uncertainty in Regional and Global Terrestrial CO<inf>2</inf> Exchange Estimates.
Global Biogeochemical Cycles,
34(2).
Abstract:
Sources of Uncertainty in Regional and Global Terrestrial CO2 Exchange Estimates
The Global Carbon Budget 2018 (GCB2018) estimated by the atmospheric CO2 growth rate, fossil fuel emissions, and modeled (bottom-up) land and ocean fluxes cannot be fully closed, leading to a “budget imbalance,” highlighting uncertainties in GCB components. However, no systematic analysis has been performed on which regions or processes contribute to this term. To obtain deeper insight on the sources of uncertainty in global and regional carbon budgets, we analyzed differences in Net Biome Productivity (NBP) for all possible combinations of bottom-up and top-down data sets in GCB2018: (i) 16 dynamic global vegetation models (DGVMs), and (ii) 5 atmospheric inversions that match the atmospheric CO2 growth rate. We find that the global mismatch between the two ensembles matches well the GCB2018 budget imbalance, with Brazil, Southeast Asia, and Oceania as the largest contributors. Differences between DGVMs dominate global mismatches, while at regional scale differences between inversions contribute the most to uncertainty. At both global and regional scales, disagreement on NBP interannual variability between the two approaches explains a large fraction of differences. We attribute this mismatch to distinct responses to El Niño–Southern Oscillation variability between DGVMs and inversions and to uncertainties in land use change emissions, especially in South America and Southeast Asia. We identify key needs to reduce uncertainty in carbon budgets: reducing uncertainty in atmospheric inversions (e.g. through more observations in the tropics) and in land use change fluxes, including more land use processes and evaluating land use transitions (e.g. using high-resolution remote-sensing), and, finally, improving tropical hydroecological processes and fire representation within DGVMs.
Abstract.
Kondo M, Patra PK, Sitch S, Friedlingstein P, Poulter B, Chevallier F, Ciais P, Canadell JG, Bastos A, Lauerwald R, et al (2020). State of the science in reconciling top-down and bottom-up approaches for terrestrial CO2 budget.
Glob Chang Biol,
26(3), 1068-1084.
Abstract:
State of the science in reconciling top-down and bottom-up approaches for terrestrial CO2 budget.
Robust estimates of CO2 budget, CO2 exchanged between the atmosphere and terrestrial biosphere, are necessary to better understand the role of the terrestrial biosphere in mitigating anthropogenic CO2 emissions. Over the past decade, this field of research has advanced through understanding of the differences and similarities of two fundamentally different approaches: "top-down" atmospheric inversions and "bottom-up" biosphere models. Since the first studies were undertaken, these approaches have shown an increasing level of agreement, but disagreements in some regions still persist, in part because they do not estimate the same quantity of atmosphere-biosphere CO2 exchange. Here, we conducted a thorough comparison of CO2 budgets at multiple scales and from multiple methods to assess the current state of the science in estimating CO2 budgets. Our set of atmospheric inversions and biosphere models, which were adjusted for a consistent flux definition, showed a high level of agreement for global and hemispheric CO2 budgets in the 2000s. Regionally, improved agreement in CO2 budgets was notable for North America and Southeast Asia. However, large gaps between the two methods remained in East Asia and South America. In other regions, Europe, boreal Asia, Africa, South Asia, and Oceania, it was difficult to determine whether those regions act as a net sink or source because of the large spread in estimates from atmospheric inversions. These results highlight two research directions to improve the robustness of CO2 budgets: (a) to increase representation of processes in biosphere models that could contribute to fill the budget gaps, such as forest regrowth and forest degradation; and (b) to reduce sink-source compensation between regions (dipoles) in atmospheric inversion so that their estimates become more comparable. Advancements on both research areas will increase the level of agreement between the top-down and bottom-up approaches and yield more robust knowledge of regional CO2 budgets.
Abstract.
Author URL.
Eller CB, Rowland L, Mencuccini M, Rosas T, Williams K, Harper A, Medlyn BE, Wagner Y, Klein T, Teodoro GS, et al (2020). Stomatal optimization based on xylem hydraulics (SOX) improves land surface model simulation of vegetation responses to climate.
New Phytol,
226(6), 1622-1637.
Abstract:
Stomatal optimization based on xylem hydraulics (SOX) improves land surface model simulation of vegetation responses to climate.
Land surface models (LSMs) typically use empirical functions to represent vegetation responses to soil drought. These functions largely neglect recent advances in plant ecophysiology that link xylem hydraulic functioning with stomatal responses to climate. We developed an analytical stomatal optimization model based on xylem hydraulics (SOX) to predict plant responses to drought. Coupling SOX to the Joint UK Land Environment Simulator (JULES) LSM, we conducted a global evaluation of SOX against leaf- and ecosystem-level observations. SOX simulates leaf stomatal conductance responses to climate for woody plants more accurately and parsimoniously than the existing JULES stomatal conductance model. An ecosystem-level evaluation at 70 eddy flux sites shows that SOX decreases the sensitivity of gross primary productivity (GPP) to soil moisture, which improves the model agreement with observations and increases the predicted annual GPP by 30% in relation to JULES. SOX decreases JULES root-mean-square error in GPP by up to 45% in evergreen tropical forests, and can simulate realistic patterns of canopy water potential and soil water dynamics at the studied sites. SOX provides a parsimonious way to incorporate recent advances in plant hydraulics and optimality theory into LSMs, and an alternative to empirical stress factors.
Abstract.
Author URL.
Song X, Li F, Harrison SP, Luo T, Arneth A, Forrest M, Hantson S, Lasslop G, Mangeon S, Ni J, et al (2020). Vegetation biomass change in China in the 20th century: an assessment based on a combination of multi-model simulations and field observations.
ENVIRONMENTAL RESEARCH LETTERS,
15(9).
Author URL.
Yang H, Huntingford C, Wiltshire A, Sitch S, Mercado L (2019). Compensatory climate effects link trends in global runoff to rising atmospheric CO<sub>2</sub> concentration.
ENVIRONMENTAL RESEARCH LETTERS,
14(12).
Author URL.
Bastos A, Ciais P, Chevallier F, Rödenbeck C, Ballantyne AP, Maignan F, Yin Y, Fernández-Martínez M, Friedlingstein P, Peñuelas J, et al (2019). Contrasting effects of CO&lt;sub&gt;2&lt;/sub&gt; fertilisation, land-use change and
warming on seasonal amplitude of northern hemisphere CO&lt;sub&gt;2&lt;/sub&gt;
exchange.
Abstract:
Contrasting effects of CO<sub>2</sub> fertilisation, land-use change and
warming on seasonal amplitude of northern hemisphere CO<sub>2</sub>
exchange
Abstract. Continuous atmospheric CO2 monitoring data indicate an increase in seasonal-cycle amplitude (SCA) of CO2 exchange in northern high latitudes. The major drivers of enhanced SCA remain unclear and intensely debated with land-use change, CO2 fertilization and warming identified as likely contributors. We integrated CO2-flux data from two atmospheric inversions (consistent with atmospheric records) and from and 11 state-of-the-art land-surface models (LSMs) to evaluate the relative importance of individual contributors to trends and drivers of the SCA of CO2-fluxes for 1980−2015. The LSMs generally reproduce the latitudinal increase in SCA trends within the inversions range. Inversions and LSMs attribute SCA increase to boreal Asia and Europe due to enhanced vegetation productivity (in LSMs) and point to contrasting effects of CO2 fertilisation (positive) and warming (negative) on SCA. Our results do not support land-use change as a key contributor to the increase in SCA. The sensitivity of simulated microbial respiration to temperature in LSMs explained biases in SCA trends, which suggests SCA could help to constrain model turnover times.
.
Abstract.
Bastos A, Ciais P, Chevallier F, Roedenbeck C, Ballantyne AP, Maignan F, Yin Y, Fernandez-Martinez M, Friedlingstein P, Penuelas J, et al (2019). Contrasting effects of CO<sub>2</sub> fertilization, land-use change and warming on seasonal amplitude of Northern Hemisphere CO<sub>2</sub> exchange.
ATMOSPHERIC CHEMISTRY AND PHYSICS,
19(19), 12361-12375.
Author URL.
Forkel M, Andela N, P Harrison S, Lasslop G, Van Marle M, Chuvieco E, Dorigo W, Forrest M, Hantson S, Heil A, et al (2019). Emergent relationships with respect to burned area in global satellite observations and fire-enabled vegetation models.
Biogeosciences,
16(1), 57-76.
Abstract:
Emergent relationships with respect to burned area in global satellite observations and fire-enabled vegetation models
Recent climate changes have increased fire-prone weather conditions in many regions and have likely affected fire occurrence, which might impact ecosystem functioning, biogeochemical cycles, and society. Prediction of how fire impacts may change in the future is difficult because of the complexity of the controls on fire occurrence and burned area. Here we aim to assess how process-based fire-enabled dynamic global vegetation models (DGVMs) represent relationships between controlling factors and burned area. We developed a pattern-oriented model evaluation approach using the random forest (RF) algorithm to identify emergent relationships between climate, vegetation, and socio-economic predictor variables and burned area. We applied this approach to monthly burned area time series for the period from 2005 to 2011 from satellite observations and from DGVMs from the "Fire Modeling Intercomparison Project" (FireMIP) that were run using a common protocol and forcing data sets. The satellite-derived relationships indicate strong sensitivity to climate variables (e.g. maximum temperature, number of wet days), vegetation properties (e.g. vegetation type, previous-season plant productivity and leaf area, woody litter), and to socio-economic variables (e.g. human population density). DGVMs broadly reproduce the relationships with climate variables and, for some models, with population density. Interestingly, satellite-derived responses show a strong increase in burned area with an increase in previous-season leaf area index and plant productivity in most fire-prone ecosystems, which was largely underestimated by most DGVMs. Hence, our pattern-oriented model evaluation approach allowed us to diagnose that vegetation effects on fire are a main deficiency regarding fire-enabled dynamic global vegetation models' ability to accurately simulate the role of fire under global environmental change.
Abstract.
Pan S, Pan N, Tian H, Friedlingstein P, Sitch S, Shi H, Arora VK, Haverd V, Jain AK, Kato E, et al (2019). Evaluation of global terrestrial evapotranspiration by state-of-the-art. approaches in remote sensing, machine learning, and land surface models.
Abstract:
Evaluation of global terrestrial evapotranspiration by state-of-the-art. approaches in remote sensing, machine learning, and land surface models
Abstract. Evapotranspiration (ET) is a critical component in global water cycle and links terrestrial water, carbon and energy cycles. Accurate estimate of terrestrial ET is important for hydrological, meteorological, and agricultural research and applications, such as quantifying surface energy and water budgets, weather forecasting, and scheduling of irrigation. However, direct measurement of global terrestrial ET is not feasible. Here, we first gave a retrospective introduction to the basic theory and recent developments of state-of-the-art approaches for estimating global terrestrial ET, including remote sensing-based physical models, machine learning algorithms and land surface models (LSMs). Then, we utilized six remote sensing-based models (including four physical models and two machine learning algorithms) and fourteen LSMs to analyze the spatial and temporal variations in global terrestrial ET. The results showed that the mean annual global terrestrial ET ranged from 50.7 × 103 km3 yr−1（454 mm yr−1）to 75.7 × 103 km3 yr−1 (6977 mm yr−1), with the average being 65.5 × 103 km3 yr−1 (588 mm yr−1), during 1982–2011. LSMs had significant uncertainty in the ET magnitude in tropical regions especially the Amazon Basin, while remote sensing-based ET products showed larger inter-model range in arid and semi-arid regions than LSMs. LSMs and remote sensing-based physical models presented much larger inter-annual variability (IAV) of ET than machine learning algorithms in southwestern U.S. and the Southern Hemisphere, particularly in Australia. LSMs suggested stronger control of precipitation on ET IAV than remote sensing-based models. The ensemble remote sensing-based physical models and machine-learning algorithm suggested significant increasing trends in global terrestrial ET at the rate of 0.62 mm yr−2 (p 0.05), even though most of the individual LSMs reproduced the increasing trend. Moreover, all models suggested a positive effect of vegetation greening on ET intensification. Spatially, all methods showed that ET significantly increased in western and southern Africa, western India and northeastern Australia, but decreased severely in southwestern U.S. southern South America and Mongolia. Discrepancies in ET trend mainly appeared in tropical regions like the Amazon Basin. The ensemble means of the three ET categories showed generally good consistency, however, considerable uncertainties still exist in both the temporal and spatial variations in global ET estimates. The uncertainties were induced by multiple factors, including parameterization of land processes, meteorological forcing, lack of in situ measurements, remote sensing acquisition and scaling effects. Improvements in the representation of water stress and canopy dynamics are essentially needed to reduce uncertainty in LSM-simulated ET. Utilization of latest satellite sensors and deep learning methods, theoretical advancements in nonequilibrium thermodynamics, and application of integrated methods that fuse different ET estimates or relevant key biophysical variables will improve the accuracy of remote sensing-based models.
.
Abstract.
Friedlingstein P, Jones MW, O'Sullivan M, Andrew RM, Hauck J, Peters GP, Peters W, Pongratz J, Sitch S, Le Quéré C, et al (2019). Global Carbon Budget 2019.
Abstract:
Global Carbon Budget 2019
Abstract. Not available.
.
Abstract.
Friedlingstein P, Jones MW, O'Sullivan M, Andrew RM, Hauck J, Peters GP, Peters W, Pongratz J, Sitch S, Le Quéré C, et al (2019). Global Carbon Budget 2019.
Earth System Science Data,
11(4), 1783-1838.
Abstract:
Global Carbon Budget 2019
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and
their redistribution among the atmosphere, ocean, and terrestrial biosphere
– the “global carbon budget” – is important to better understand the
global carbon cycle, support the development of climate policies, and
project future climate change. Here we describe data sets and methodology to
quantify the five major components of the global carbon budget and their
uncertainties. Fossil CO2 emissions (EFF) are based on energy
statistics and cement production data, while emissions from land use change
(ELUC), mainly deforestation, are based on land use and land use change
data and bookkeeping models. Atmospheric CO2 concentration is measured
directly and its growth rate (GATM) is computed from the annual changes
in concentration. The ocean CO2 sink (SOCEAN) and terrestrial
CO2 sink (SLAND) are estimated with global process models
constrained by observations. The resulting carbon budget imbalance
(BIM), the difference between the estimated total emissions and the
estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a
measure of imperfect data and understanding of the contemporary carbon
cycle. All uncertainties are reported as ±1σ. For the last
decade available (2009–2018), EFF was 9.5±0.5 GtC yr−1,
ELUC 1.5±0.7 GtC yr−1, GATM 4.9±0.02 GtC yr−1 (2.3±0.01 ppm yr−1), SOCEAN 2.5±0.6 GtC yr−1, and SLAND 3.2±0.6 GtC yr−1, with a budget
imbalance BIM of 0.4 GtC yr−1 indicating overestimated emissions
and/or underestimated sinks. For the year 2018 alone, the growth in EFF was
about 2.1 % and fossil emissions increased to 10.0±0.5 GtC yr−1, reaching 10 GtC yr−1 for the first time in history,
ELUC was 1.5±0.7 GtC yr−1, for total anthropogenic
CO2 emissions of 11.5±0.9 GtC yr−1 (42.5±3.3 GtCO2). Also for 2018, GATM was 5.1±0.2 GtC yr−1 (2.4±0.1 ppm yr−1), SOCEAN was 2.6±0.6 GtC yr−1, and SLAND was 3.5±0.7 GtC yr−1, with a BIM of 0.3 GtC. The global atmospheric CO2 concentration reached 407.38±0.1 ppm averaged over 2018. For 2019, preliminary data for the first 6–10 months indicate a reduced growth in EFF of +0.6 % (range of
−0.2 % to 1.5 %) based on national emissions projections for China, the
USA, the EU, and India and projections of gross domestic product corrected
for recent changes in the carbon intensity of the economy for the rest of
the world. Overall, the mean and trend in the five components of the global
carbon budget are consistently estimated over the period 1959–2018, but
discrepancies of up to 1 GtC yr−1 persist for the representation of
semi-decadal variability in CO2 fluxes. A detailed comparison among
individual estimates and the introduction of a broad range of observations
shows (1) no consensus in the mean and trend in land use change emissions
over the last decade, (2) a persistent low agreement between the different
methods on the magnitude of the land CO2 flux in the northern
extra-tropics, and (3) an apparent underestimation of the CO2
variability by ocean models outside the tropics. This living data update
documents changes in the methods and data sets used in this new global
carbon budget and the progress in understanding of the global carbon cycle
compared with previous publications of this data set (Le Quéré et
al. 2018a, b, 2016, 2015a, b, 2014, 2013). The data generated by
this work are available at https://doi.org/10.18160/gcp-2019 (Friedlingstein
et al. 2019).
.
Abstract.
Fernandez-Martinez M, Sardans J, Chevallier F, Ciais P, Obersteiner M, Vicca S, Canadell JG, Bastos A, Friedlingstein P, Sitch S, et al (2019). Global trends in carbon sinks and their relationships with CO<sub>2</sub> and temperature.
NATURE CLIMATE CHANGE,
9(1), 73-+.
Author URL.
Anav A, De Marco A, Friedlingstein P, Savi F, Sicard P, Sitch S, Vitale M, Paoletti E (2019). Growing season extension affects ozone uptake by European forests.
Science of the Total Environment,
669, 1043-1052.
Abstract:
Growing season extension affects ozone uptake by European forests
Climate change significantly modifies terrestrial ecosystems and vegetation activity, yet little is known about how climate change and ozone pollution interact to affect forest health. Here we compared the trends of two metrics widely used to protect forests against negative impacts of ozone pollution, the AOT40 (Accumulated Ozone over Threshold of 40 ppb) which only depends on surface air ozone concentrations, and the POD (Phytotoxic Ozone Dose) which relies on the amount of ozone uptaken by plants through stomata. Using a chemistry transport model, driven by anthropogenic emission inventories, we found that European-averaged ground-level ozone concentrations significantly declined (−1.6%) over the time period 2000–2014, following successful control strategies to reduce the ozone precursors emission; as a consequence, the AOT40 metric declined (−22%). In contrast, climate change increased both growing season length (~7 days/decade) and stomatal conductance and thus enhanced the stomatal ozone uptake by forests (5.9%), leading to an overall increase of potential ozone damage on plants, despite the reduction in ozone concentrations. Our results suggest that stomatal-flux based strategies of forest protection against ozone in a changing climate require a proper consideration of the duration of the growing season with a better estimation of start and end of the growing season.
Abstract.
Li F, Val Martin M, Andreae MO, Arneth A, Hantson S, Kaiser JW, Lasslop G, Yue C, Bachelet D, Forrest M, et al (2019). Historical (1700-2012) global multi-model estimates of the fire emissions from the Fire Modeling Intercomparison Project (FireMIP).
Atmospheric Chemistry and Physics,
19(19), 12545-12567.
Abstract:
Historical (1700-2012) global multi-model estimates of the fire emissions from the Fire Modeling Intercomparison Project (FireMIP)
Fire emissions are a critical component of carbon and nutrient cycles and strongly affect climate and air quality. Dynamic global vegetation models (DGVMs) with interactive fire modeling provide important estimates for long-term and large-scale changes in fire emissions. Here we present the first multi-model estimates of global gridded historical fire emissions for 1700-2012, including carbon and 33 species of trace gases and aerosols. The dataset is based on simulations of nine DGVMs with different state-of-the-art global fire models that participated in the Fire Modeling Intercomparison Project (FireMIP), using the same and standardized protocols and forcing data, and the most up-to-date fire emission factor table based on field and laboratory studies in various land cover types. We evaluate the simulations of present-day fire emissions by comparing them with satellite-based products. The evaluation results show that most DGVMs simulate present-day global fire emission totals within the range of satellite-based products. They can capture the high emissions over the tropical savannas and low emissions over the arid and sparsely vegetated regions, and the main features of seasonality. However, most models fail to simulate the interannual variability, partly due to a lack of modeling peat fires and tropical deforestation fires. Before the 1850s, all models show only a weak trend in global fire emissions, which is consistent with the multi-source merged historical reconstructions used as input data for CMIP6. On the other hand, the trends are quite different among DGVMs for the 20th century, with some models showing an increase and others a decrease in fire emissions, mainly as a result of the discrepancy in their simulated responses to human population density change and land use and land cover change (LULCC). Our study provides an important dataset for further development of regional and global multi-source merged historical reconstructions, analyses of the historical changes in fire emissions and their uncertainties, and quantification of the role of fire emissions in the Earth system. It also highlights the importance of accurately modeling the responses of fire emissions to LULCC and population density change in reducing uncertainties in historical reconstructions of fire emissions and providing more reliable future projections.
Abstract.
Yuan W, Zheng Y, Piao S, Ciais P, Lombardozzi D, Wang Y, Ryu Y, Chen G, Dong W, Hu Z, et al (2019). Increased atmospheric vapor pressure deficit reduces global vegetation growth.
Science Advances,
5(8).
Abstract:
Increased atmospheric vapor pressure deficit reduces global vegetation growth
Atmospheric vapor pressure deficit (VPD) is a critical variable in determining plant photosynthesis. Synthesis of four global climate datasets reveals a sharp increase of VPD after the late 1990s. In response, the vegetation greening trend indicated by a satellite-derived vegetation index (GIMMS3g), which was evident before the late 1990s, was subsequently stalled or reversed. Terrestrial gross primary production derived from two satellite-based models (revised EC-LUE and MODIS) exhibits persistent and widespread decreases after the late 1990s due to increased VPD, which offset the positive CO2 fertilization effect. Six Earth system models have consistently projected continuous increases of VPD throughout the current century. Our results highlight that the impacts of VPD on vegetation growth should be adequately considered to assess ecosystem responses to future climate conditions.
Abstract.
Chen W, Zhu D, Huang C, Ciais P, Yao Y, Friedlingstein P, Sitch S, Haverd V, Jain AK, Kato E, et al (2019). Negative extreme events in gross primary productivity and their drivers in China during the past three decades.
Agricultural and Forest Meteorology,
275, 47-58.
Abstract:
Negative extreme events in gross primary productivity and their drivers in China during the past three decades
Climate extremes have remarkable impacts on ecosystems and are expected to increase with future global warming. However, only few studies have focused on the ecological extreme events and their drivers in China. In this study, we carried out an analysis of negative extreme events in gross primary productivity (GPP)in China and the sub-regions during 1982–2015, using monthly GPP simulated by 12 process-based models (TRENDYv6)and an observation-based model (Yao-GPP). Extremes were defined as the negative 5th percentile of GPP anomalies, which were further merged into individual extreme events using a three-dimensional contiguous algorithm. Spatio-temporal patterns of negative GPP anomalies were analyzed by taking the 1000 largest extreme events into consideration. Results showed that the effects of extreme events decreased annual GPP by 2.8% (i.e. 208 TgC year−1)in TRENDY models and 2.3% (i.e. 151 TgC year−1)in Yao-GPP. Hotspots of extreme GPP deficits were mainly observed in North China (−53 gC m−2 year−1)in TRENDY models and Northeast China (−42 gC m−2 year−1)in Yao-GPP. For China as a whole, attribution analyses suggested that extreme low precipitation was associated with 40%–50% of extreme negative GPP events. Most events in northern and western China could be explained by meteorological droughts (i.e. low precipitation)while GPP extreme events in southern China were more associated with temperature extremes, in particular with cold spells. GPP was revealed to be much more sensitive to heat/drought than to cold/wet extreme events. Combined with projected changes in climate extremes in China, GPP negative anomalies caused by drought events in northern China and by temperature extremes in southern China might be more prominent in the future.
Abstract.
Yue X, Liao H, Wang H, Zhang T, Unger N, Sitch S, Feng Z, Yang J (2019). Pathway dependence of ecosystem responses in China to 1.5 °C global warming.
Abstract:
Pathway dependence of ecosystem responses in China to 1.5 °C global warming
Abstract. China is currently the world's largest emitter of both CO2 and short-lived air pollutants. The ecosystems in China help mitigate a part of its carbon emissions, but are subject to perturbations in CO2, climate, and air pollution. Here, we use a dynamic vegetation model and data from three model inter-comparison projects to examine ecosystem responses in China under different emission pathways towards the 1.5 °C warming target set by the Paris Agreement. At 1.5 °C warming, gross primary productivity (GPP) increases by 15.5 ± 5.4 % in a stabilized pathway and 11.9 ± 4.4 % in a transient pathway. CO2 fertilization is the dominant driver of GPP enhancement and climate change is the main source of uncertainties. However, differences in ozone and aerosols explain the GPP differences between pathways at 1.5 °C warming. Although the land carbon sink is weakened by 17.4 ± 19.6 % in the stabilized pathway, the ecosystems mitigate 10.6 ± 1.4 % of national emissions in the stabilized pathway, more efficient than the fraction of 6.3 ± 0.8 % in the transient pathway. To achieve the 1.5 °C warming target, our analysis suggests a higher allowable carbon budget for China under a stabilized pathway with reduced emissions in both CO2 and air pollution.
.
Abstract.
Teckentrup L, Harrison SP, Hantson S, Heil A, Melton JR, Forrest M, Li F, Yue C, Arneth A, Hickler T, et al (2019). Response of simulated burned area to historical changes in environmental and anthropogenic factors: a comparison of seven fire models.
Biogeosciences,
16(19), 3883-3910.
Abstract:
Response of simulated burned area to historical changes in environmental and anthropogenic factors: a comparison of seven fire models
Understanding how fire regimes change over time is of major importance for understanding their future impact on the Earth system, including society. Large differences in simulated burned area between fire models show that there is substantial uncertainty associated with modelling global change impacts on fire regimes. We draw here on sensitivity simulations made by seven global dynamic vegetation models participating in the Fire Model Intercomparison Project (FireMIP) to understand how differences in models translate into differences in fire regime projections. The sensitivity experiments isolate the impact of the individual drivers on simulated burned area, which are prescribed in the simulations. Specifically these drivers are atmospheric CO2 concentration, population density, land-use change, lightning and climate. The seven models capture spatial patterns in burned area. However, they show considerable differences in the burned area trends since 1921. We analyse the trajectories of differences between the sensitivity and reference simulation to improve our understanding of what drives the global trends in burned area. Where it is possible, we link the inter-model differences to model assumptions. Overall, these analyses reveal that the largest uncertainties in simulating global historical burned area are related to the representation of anthropogenic ignitions and suppression and effects of land use on vegetation and fire. In line with previous studies this highlights the need to improve our understanding and model representation of the relationship between human activities and fire to improve our abilities to model fire within Earth system model applications. Only two models show a strong response to atmospheric CO2 concentration. The effects of changes in atmospheric CO2 concentration on fire are complex and quantitative information of how fuel loads and how flammability changes due to this factor is missing. The response to lightning on global scale is low. The response of burned area to climate is spatially heterogeneous and has a strong inter-annual variation. Climate is therefore likely more important than the other factors for short-term variations and extremes in burned area. This study provides a basis to understand the uncertainties in global fire modelling. Both improvements in process understanding and observational constraints reduce uncertainties in modelling burned area trends.
Abstract.
Malavelle FF, Haywood JM, Mercado LM, Folberth GA, Bellouin N, Sitch S, Artaxo P (2019). Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth system model.
Atmospheric Chemistry and Physics,
19(2), 1301-1326.
Abstract:
Studying the impact of biomass burning aerosol radiative and climate effects on the Amazon rainforest productivity with an Earth system model
Diffuse light conditions can increase the efficiency of photosynthesis and carbon uptake by vegetation canopies. The diffuse fraction of photosynthetically active radiation (PAR) can be affected by either a change in the atmospheric aerosol burden and/or a change in cloudiness. During the dry season, a hotspot of biomass burning on the edges of the Amazon rainforest emits a complex mixture of aerosols and their precursors and climate-active trace gases (e.g. CO 2 , CH 4 , NO x ). This creates potential for significant interactions between chemistry, aerosol, cloud, radiation and the biosphere across the Amazon region. The combined effects of biomass burning on the terrestrial carbon cycle for the present day are potentially large, yet poorly quantified. Here, we quantify such effects using the Met Office Hadley Centre Earth system model HadGEM2-ES, which provides a fully coupled framework with interactive aerosol, radiative transfer, dynamic vegetation, atmospheric chemistry and biogenic volatile organic compound emission components. Results show that for present day, defined as year 2000 climate, the overall net impact of biomass burning aerosols is to increase net primary productivity (NPP) by +80 to +105 TgC yr -1 , or 1.9% to 2.7 %, over the central Amazon Basin on annual mean. For the first time we show that this enhancement is the net result of multiple competing effects: an increase in diffuse light which stimulates photosynthetic activity in the shaded part of the canopy (+65 to +110 TgC yr -1 ), a reduction in the total amount of radiation (-52 to -1 05 TgC yr -1 ) which reduces photosynthesis and feedback from climate adjustments in response to the aerosol forcing which increases the efficiency of biochemical processes (+67 to +100 TgC yr -1 ). These results illustrate that despite a modest direct aerosol effect (the sum of the first two counteracting mechanisms), the overall net impact of biomass burning aerosols on vegetation is sizeable when indirect climate feedbacks are considered. We demonstrate that capturing the net impact of aerosols on vegetation should be assessed considering the system-wide behaviour.
Abstract.
Pugh TAM, Jones CD, Huntingford C, Burton C, Arneth A, Brovkin V, Ciais P, Lomas M, Robertson E, Piao SL, et al (2018). A Large Committed Long-Term Sink of Carbon due to Vegetation Dynamics.
Earth's FutureAbstract:
A Large Committed Long-Term Sink of Carbon due to Vegetation Dynamics
©2018. The Authors. The terrestrial biosphere shows substantial inertia in its response to environmental change. Hence, assessments of transient changes in ecosystem properties to 2100 do not capture the full magnitude of the response realized once ecosystems reach an effective equilibrium with the changed environmental boundary conditions. This equilibrium state can be termed the committed state, in contrast to a transient state in which the ecosystem is in disequilibrium. The difference in ecosystem properties between the transient and committed states represents the committed change yet to be realized. Here an ensemble of dynamic global vegetation model simulations was used to assess the changes in tree cover and carbon storage for a variety of committed states, relative to a preindustrial baseline, and to attribute the drivers of uncertainty. Using a subset of simulations, the committed changes in these variables post-2100, assuming climate stabilization, were calculated. The results show large committed changes in tree cover and carbon storage, with model disparities driven by residence time in the tropics, and residence time and productivity in the boreal. Large changes remain ongoing well beyond the end of the 21st century. In boreal ecosystems, the simulated increase in vegetation carbon storage above preindustrial levels was 20–95 Pg C at 2 K of warming, and 45–201 Pg C at 5 K, of which 38–155 Pg C was due to expansion in tree cover. Reducing the large uncertainties in long-term commitment and rate-of-change of terrestrial carbon uptake will be crucial for assessments of emissions budgets consistent with limiting climate change.
Abstract.
Wu D, Ciais P, Viovy N, Knapp AK, Wilcox K, Bahn M, Smith MD, Vicca S, Fatichi S, Zscheischler J, et al (2018). Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites.
Biogeosciences,
15, 3421-3437.
Abstract:
Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites
© 2018 Author(s). Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry), whereas increases in ANPP are lower in magnitude in extreme wet years compared to reductions during extreme drought (negative asymmetry). Whether the current generation of ecosystem models with a coupled carbon-water system in grasslands are capable of simulating these asymmetric ANPP responses is an unresolved question. In this study, we evaluated the simulated responses of temperate grassland primary productivity to scenarios of altered precipitation with 14 ecosystem models at three sites: Shortgrass steppe (SGS), Konza Prairie (KNZ) and Stubai Valley meadow (STU), spanning a rainfall gradient from dry to moist. We found that (1) the spatial slopes derived from modeled primary productivity and precipitation across sites were steeper than the temporal slopes obtained from inter-annual variations, which was consistent with empirical data; (2) the asymmetry of the responses of modeled primary productivity under normal inter-annual precipitation variability differed among models, and the mean of the model ensemble suggested a negative asymmetry across the three sites, which was contrary to empirical evidence based on filed observations; (3) the mean sensitivity of modeled productivity to rainfall suggested greater negative response with reduced precipitation than positive response to an increased precipitation under extreme conditions at the three sites; and (4) gross primary productivity (GPP), net primary productivity (NPP), aboveground NPP (ANPP) and belowground NPP (BNPP) all showed concave-down nonlinear responses to altered precipitation in all the models, but with different curvatures and mean values. Our results indicated that most models overestimate the negative drought effects and/or underestimate the positive effects of increased precipitation on primary productivity under normal climate conditions, highlighting the need for improving eco-hydrological processes in those models in the future.
Abstract.
Duveiller G, Forzieri G, Robertson E, Li W, Georgievski G, Lawrence P, Wiltshire A, Ciais P, Pongratz J, Sitch S, et al (2018). Biophysics and vegetation cover change: a process-based evaluation framework for confronting land surface models with satellite observations.
Earth System Science Data,
10(3), 1265-1279.
Abstract:
Biophysics and vegetation cover change: a process-based evaluation framework for confronting land surface models with satellite observations
Land use and land cover change (LULCC) alter the biophysical properties of the Earth's surface. The associated changes in vegetation cover can perturb the local surface energy balance, which in turn can affect the local climate. The sign and magnitude of this change in climate depends on the specific vegetation transition, its timing and its location, as well as on the background climate. Land surface models (LSMs) can be used to simulate such land-climate interactions and study their impact in past and future climates, but their capacity to model biophysical effects accurately across the globe remain unclear due to the complexity of the phenomena. Here we present a framework to evaluate the performance of such models with respect to a dedicated dataset derived from satellite remote sensing observations. Idealized simulations from four LSMs (JULES, ORCHIDEE, JSBACH and CLM) are combined with satellite observations to analyse the changes in radiative and turbulent fluxes caused by 15 specific vegetation cover transitions across geographic, seasonal and climatic gradients. The seasonal variation in net radiation associated with land cover change is the process that models capture best, whereas LSMs perform poorly when simulating spatial and climatic gradients of variation in latent, sensible and ground heat fluxes induced by land cover transitions. We expect that this analysis will help identify model limitations and prioritize efforts in model development as well as inform where consensus between model and observations is already met, ultimately helping to improve the robustness and consistency of model simulations to better inform land-based mitigation and adaptation policies.
Abstract.
Comyn-Platt E, Hayman G, Huntingford C, Chadburn SE, Burke EJ, Harper AB, Collins WJ, Webber CP, Powell T, Cox PM, et al (2018). Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks.
Nature Geoscience, 1-6.
Abstract:
Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks
© 2018 the Author(s) Global methane emissions from natural wetlands and carbon release from permafrost thaw have a positive feedback on climate, yet are not represented in most state-of-the-art climate models. Furthermore, a fraction of the thawed permafrost carbon is released as methane, enhancing the combined feedback strength. We present simulations with an inverted intermediate complexity climate model, which follows prescribed global warming pathways to stabilization at 1.5 or 2.0 °C above pre-industrial levels by the year 2100, and which incorporates a state-of-the-art global land surface model with updated descriptions of wetland and permafrost carbon release. We demonstrate that the climate feedbacks from those two processes are substantial. Specifically, permissible anthropogenic fossil fuel CO2 emission budgets are reduced by 17–23% (47–56 GtC) for stabilization at 1.5 °C, and 9–13% (52–57 GtC) for 2.0 °C stabilization. In our simulations these feedback processes respond more quickly at temperatures below 1.5 °C, and the differences between the 1.5 and 2 °C targets are disproportionately small. This key finding holds for transient emission pathways to 2100 and does not account for longer-term implications of these feedback processes. We conclude that natural feedback processes from wetlands and permafrost must be considered in assessments of transient emission pathways to limit global warming.
Abstract.
Wang J, Zeng N, Wang M, Jiang F, Chen J, Friedlingstein P, Jain AK, Jiang Z, Ju W, Lienert S, et al (2018). Contrasting behaviors of the atmospheric CO&lt;sub&gt;2&lt;/sub&gt; interannual variability during two types of El Niños.
Abstract:
Contrasting behaviors of the atmospheric CO<sub>2</sub> interannual variability during two types of El Niños
Abstract. El Niño has two different flavors: eastern Pacific (EP) and central Pacific (CP) El Niños, with different global teleconnections. However, their different impacts on carbon cycle interannual variability remain unclear. We here compared the behaviors of the atmospheric CO2 interannual variability and analyzed their terrestrial mechanisms during these two types of El Niños, based on Mauna Loa (MLO) CO2 growth rate (CGR) and Dynamic Global Vegetation Models (DGVMs) historical simulations. Composite analysis shows that evolutions of MLO CGR anomaly have three clear differences in terms of (1) negative and neutral precursors in boreal spring of El Niño developing years (denoted as “yr0”), (2) strong and weak amplitudes, and (3) durations of peak from December (yr0) to April of El Niño decaying year (denoted as “yr1”) and from October (yr0) to January (yr1) during EP and CP El Niños, respectively. Models simulated global land–atmosphere carbon flux (FTA) is able to capture the essentials of these characteristics. We further find that the gross primary productivity (GPP) over the tropics and extratropical southern hemisphere (Trop+SH) generally dominates the global FTA variations during both El Niño types. Regionally, significant anomalous carbon uptake caused by more precipitation and colder temperature, corresponding to the negative precursor, occurs between 30° S and 20° N from January (yr0) to June (yr0), while the strongest anomalous carbon releases, due largely to the reduced GPP induced by low precipitation and warm temperature, happen between equator and 20° N from February (yr1) to August (yr1) during EP El Niño events. In contrast, during CP El Niño events, clear carbon releases exist between 10° N and 20° S from September (yr0) to September (yr1), resulted from the widespread dry and warm climate conditions. Different spatial patterns of land temperature and precipitation in different seasons associated with EP and CP El Niños account for the characteristics in evolutions of GPP, terrestrial ecosystem respiration (TER), and resultant FTA. Understanding these different behaviors of the atmospheric CO2 interannual variability along with their terrestrial mechanisms during EP and CP El Niños is important because CP El Niño occurrence rate might increase under global warming.
.
Abstract.
Wang J, Zeng N, Wang M, Jiang F, Chen J, Friedlingstein P, Jain AK, Jiang Z, Ju W, Lienert S, et al (2018). Contrasting interannual atmospheric CO2 variabilities and their terrestrial mechanisms for two types of El Ninos. Atmospheric Chemistry and Physics, 18(14), 10333-10345.
Comyn-Platt E, Hayman G, Huntingford C, Chadburn SE, Burke EJ, Harper AB, Collins WJ, Webber CP, Powell T, Cox PM, et al (2018). Erratum to: Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks (Nature Geoscience, (2018), 11, 8, (568-573), 10.1038/s41561-018-0174-9).
Nature Geoscience,
11(11), 882-886.
Abstract:
Erratum to: Carbon budgets for 1.5 and 2 °C targets lowered by natural wetland and permafrost feedbacks (Nature Geoscience, (2018), 11, 8, (568-573), 10.1038/s41561-018-0174-9)
In the version of this Article originally published, a parallelization coding problem, which meant that a subset of model grid cells were subjected to erroneous updating of atmospheric gas concentrations, resulted in incorrect calculation of atmospheric CO2 for these grid cells, and therefore underestimation of the carbon uptake by land through vegetation growth and eventual increases to soil carbon stocks. Having re-run the simulations using the corrected code, the authors found that the original estimates of the impact of the natural wetland methane feedback were overestimated. The permafrost and natural wetland methane feedback requires lower permissible emissions of 9–15% to achieve climate stabilization at 1.5 °C, compared with the original published estimate of 17–23%. The Article text, Table 1 and Fig. 3 have been updated online to reflect the revised numerical estimates. The Supplementary Information file has also been amended, with Supplementary Figs 6, 7, 8 and 9 replaced with revised versions produced using the corrected model output. As the strength of feedbacks remain significant, still require inclusion in climate policy and are nonlinear with global warming, the overall conclusions of the Article remain unchanged.
Abstract.
Forzieri G, Duveiller G, Georgievski G, Li W, Robertson E, Kautz M, Lawrence P, Garcia San Martin L, Anthoni P, Ciais P, et al (2018). Evaluating the Interplay Between Biophysical Processes and Leaf Area Changes in Land Surface Models.
Journal of Advances in Modeling Earth Systems,
10(5), 1102-1126.
Abstract:
Evaluating the Interplay Between Biophysical Processes and Leaf Area Changes in Land Surface Models
© 2018. The Authors. Land Surface Models (LSMs) are essential to reproduce biophysical processes modulated by vegetation and to predict the future evolution of the land-climate system. To assess the performance of an ensemble of LSMs (JSBACH, JULES, ORCHIDEE, CLM, and LPJ-GUESS) a consistent set of land surface energy fluxes and leaf area index (LAI) has been generated. Relationships of interannual variations of modeled surface fluxes and LAI changes have been analyzed at global scale across climatological gradients and compared with those obtained from satellite-based products. Model-specific strengths and deficiencies were diagnosed for tree and grass biomes. Results show that the responses of grasses are generally well represented in models with respect to the observed interplay between turbulent fluxes and LAI, increasing the confidence on how the LAI-dependent partition of net radiation into latent and sensible heat are simulated. On the contrary, modeled forest responses are characterized by systematic bias in the relation between the year-to-year variability in LAI and net radiation in cold and temperate climates, ultimately affecting the amount of absorbed radiation due to LAI-related effects on surface albedo. In addition, for tree biomes, the relationships between LAI and turbulent fluxes appear to contradict the experimental evidences. The dominance of the transpiration-driven over the observed albedo-driven effects might suggest that LSMs have the incorrect balance of these two processes. Such mismatches shed light on the limitations of our current understanding and process representation of the vegetation control on the surface energy balance and help to identify critical areas for model improvement.
Abstract.
Le Quéré C, Andrew RM, Friedlingstein P, Sitch S, Pongratz J, Manning AC, Ivar Korsbakken J, Peters GP, Canadell JG, Jackson RB, et al (2018). Global Carbon Budget 2017.
Earth System Science Data,
10(1), 405-448.
Abstract:
Global Carbon Budget 2017
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere-the "global carbon budget"-is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on land-cover change data and bookkeeping models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1δ. For the last decade available (2007-2016), EFF was 9.4±0.5 GtC yr-1, ELUC 1.3±0.7 GtC yr-1, GATM 4.7±0.1 GtC yr-1, SOCEAN 2.4±0.5 GtC yr-1, and SLAND 3.0±0.8 GtC yr-1, with a budget imbalance BIM of 0.6 GtC yr-1 indicating overestimated emissions and/or underestimated sinks. For year 2016 alone, the growth in EFF was approximately zero and emissions remained at 9.9±0.5 GtC yr-1. Also for 2016, ELUC was 1.3±0.7 GtC yr-1, GATM was 6.1±0.2 GtC yr-1, SOCEAN was 2.6±0.5 GtC yr-1, and SLAND was 2.7±1.0 GtC yr-1, with a small BIM of-0.3 GtC. GATM continued to be higher in 2016 compared to the past decade (2007-2016), reflecting in part the high fossil emissions and the small SLAND consistent with El Ninõ conditions. The global atmospheric CO2 concentration reached 402.8±0.1 ppm averaged over 2016. For 2017, preliminary data for the first 6-9 months indicate a renewed growth in EFF of C2.0% (range of 0.8 to 3.0 %) based on national emissions projections for China, USA, and India, and projections of gross domestic product (GDP) corrected for recent changes in the carbon intensity of the economy for the rest of the world. This living data update documents changes in the methods and data sets used in this new global carbon budget compared with previous publications of this data set (Le Quéré et al. 2016, 2015b, a, 2014, 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2017 (GCP, 2017).
Abstract.
Le Quéré C, Andrew RM, Friedlingstein P, Sitch S, Hauck J, Pongratz J, Pickers PA, Korsbakken JI, Peters GP, Canadell JG, et al (2018). Global Carbon Budget 2018. Earth System Science Data, 10, 2141-2194.
Le Quéré C, Andrew RM, Friedlingstein P, Sitch S, Hauck J, Pongratz J, Pickers P, Korsbakken JI, Peters GP, Canadell JG, et al (2018). Global Carbon Budget 2018.
Bastos A, Friedlingstein P, Sitch S, Chen C, Mialon A, Wigneron J-P, Arora VK, Briggs PR, Canadell JG, Ciais P, et al (2018). Impact of the 2015/2016 El Niño on the terrestrial carbon cycle constrained by bottom-up and top-down approaches.
Philos Trans R Soc Lond B Biol Sci,
373(1760).
Abstract:
Impact of the 2015/2016 El Niño on the terrestrial carbon cycle constrained by bottom-up and top-down approaches.
Evaluating the response of the land carbon sink to the anomalies in temperature and drought imposed by El Niño events provides insights into the present-day carbon cycle and its climate-driven variability. It is also a necessary step to build confidence in terrestrial ecosystems models' response to the warming and drying stresses expected in the future over many continents, and particularly in the tropics. Here we present an in-depth analysis of the response of the terrestrial carbon cycle to the 2015/2016 El Niño that imposed extreme warming and dry conditions in the tropics and other sensitive regions. First, we provide a synthesis of the spatio-temporal evolution of anomalies in net land-atmosphere CO2 fluxes estimated by two in situ measurements based on atmospheric inversions and 16 land-surface models (LSMs) from TRENDYv6. Simulated changes in ecosystem productivity, decomposition rates and fire emissions are also investigated. Inversions and LSMs generally agree on the decrease and subsequent recovery of the land sink in response to the onset, peak and demise of El Niño conditions and point to the decreased strength of the land carbon sink: by 0.4-0.7 PgC yr-1 (inversions) and by 1.0 PgC yr-1 (LSMs) during 2015/2016. LSM simulations indicate that a decrease in productivity, rather than increase in respiration, dominated the net biome productivity anomalies in response to ENSO throughout the tropics, mainly associated with prolonged drought conditions.This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.
Abstract.
Author URL.
Collins WJ, Webber CP, Cox PM, Huntingford C, Lowe J, Sitch S, Chadburn SE, Comyn-Platt E, Harper AB, Hayman G, et al (2018). Increased importance of methane reduction for a 1.5 degree target.
ENVIRONMENTAL RESEARCH LETTERS,
13(5).
Author URL.
Kondo M, Ichii K, Patra PK, Canadell JG, Poulter B, Sitch S, Calle L, Liu YY, van Dijk AIJM, Saeki T, et al (2018). Land use change and El Niño-Southern Oscillation drive decadal carbon balance shifts in Southeast Asia.
Nature Communications,
9Abstract:
Land use change and El Niño-Southern Oscillation drive decadal carbon balance shifts in Southeast Asia.
An integrated understanding of the biogeochemical consequences of climate extremes and land use changes is needed to constrain land-surface feedbacks to atmospheric CO2 from associated climate change. Past assessments of the global carbon balance have shown particularly high uncertainty in Southeast Asia. Here, we use a combination of model ensembles to show that intensified land use change made Southeast Asia a strong source of CO2 from the 1980s to 1990s, whereas the region was close to carbon neutral in the 2000s due to an enhanced CO2 fertilization effect and absence of moderate-to-strong El Niño events. Our findings suggest that despite ongoing deforestation, CO2 emissions were substantially decreased during the 2000s, largely owing to milder climate that restores photosynthetic capacity and suppresses peat and deforestation fire emissions. The occurrence of strong El Niño events after 2009 suggests that the region has returned to conditions of increased vulnerability of carbon stocks.
Abstract.
Harper AB, Powell T, Cox PM, House J, Huntingford C, Lenton TM, Sitch S, Burke E, Chadburn SE, Collins WJ, et al (2018). Land-use emissions play a critical role in land-based mitigation for Paris climate targets.
Nat Commun,
9(1).
Abstract:
Land-use emissions play a critical role in land-based mitigation for Paris climate targets.
Scenarios that limit global warming to below 2 °C by 2100 assume significant land-use change to support large-scale carbon dioxide (CO2) removal from the atmosphere by afforestation/reforestation, avoided deforestation, and Biomass Energy with Carbon Capture and Storage (BECCS). The more ambitious mitigation scenarios require even greater land area for mitigation and/or earlier adoption of CO2 removal strategies. Here we show that additional land-use change to meet a 1.5 °C climate change target could result in net losses of carbon from the land. The effectiveness of BECCS strongly depends on several assumptions related to the choice of biomass, the fate of initial above ground biomass, and the fossil-fuel emissions offset in the energy system. Depending on these factors, carbon removed from the atmosphere through BECCS could easily be offset by losses due to land-use change. If BECCS involves replacing high-carbon content ecosystems with crops, then forest-based mitigation could be more efficient for atmospheric CO2 removal than BECCS.
Abstract.
Author URL.
Oliver RJ, Mercado LM, Sitch S, Simpson D, Medlyn BE, Lin YS, Folberth GA (2018). Large but decreasing effect of ozone on the European carbon sink.
Biogeosciences,
15, 4245-4269.
Abstract:
Large but decreasing effect of ozone on the European carbon sink
The capacity of the terrestrial biosphere to sequester carbon and mitigate climate change is governed by the ability of vegetation to remove emissions of CO2 through photosynthesis. Tropospheric O3, a globally abundant and potent greenhouse gas, is, however, known to damage plants, causing reductions in primary productivity. Despite emission control policies across Europe, background concentrations of tropospheric O3 have risen significantly over the last decades due to hemispheric-scale increases in O3 and its precursors. Therefore, plants are exposed to increasing background concentrations, at levels currently causing chronic damage. Studying the impact of O3 on European vegetation at the regional scale is important for gaining greater understanding of the impact of O3 on the land carbon sink at large spatial scales. In this work we take a regional approach and update the JULES land surface model using new measurements specifically for European vegetation. Given the importance of stomatal conductance in determining the flux of O3 into plants, we implement an alternative stomatal closure parameterisation and account for diurnal variations in O3 concentration in our simulations. We conduct our analysis specifically for the European region to quantify the impact of the interactive effects of tropospheric O3 and CO2 on gross primary productivity (GPP) and land carbon storage across Europe. A factorial set of model experiments showed that tropospheric O3 can suppress terrestrial carbon uptake across Europe over the period 1901 to 2050. By 2050, simulated GPP was reduced by 4 to 9 % due to plant O3 damage and land carbon storage was reduced by 3 to 7 %. The combined physiological effects of elevated future CO2 (acting to reduce stomatal opening) and reductions in O3 concentrations resulted in reduced O3 damage in the future. This alleviation of O3 damage by CO2-induced stomatal closure was around 1 to 2 % for both land carbon and GPP, depending on plant sensitivity to O3. Reduced land carbon storage resulted from diminished soil carbon stocks consistent with the reduction in GPP. Regional variations are identified with larger impacts shown for temperate Europe (GPP reduced by 10 to 20 %) compared to boreal regions (GPP reduced by 2 to 8 %). These results highlight that O3 damage needs to be considered when predicting GPP and land carbon, and that the effects of O3 on plant physiology need to be considered in regional land carbon cycle assessments.
Abstract.
Krause A, Pugh TAM, Bayer AD, Li W, Leung F, Bondeau A, Doelman JC, Humpenöder F, Anthoni P, Bodirsky BL, et al (2018). Large uncertainty in carbon uptake potential of land-based climate-change mitigation efforts.
Glob Chang Biol,
24(7), 3025-3038.
Abstract:
Large uncertainty in carbon uptake potential of land-based climate-change mitigation efforts.
Most climate mitigation scenarios involve negative emissions, especially those that aim to limit global temperature increase to 2°C or less. However, the carbon uptake potential in land-based climate change mitigation efforts is highly uncertain. Here, we address this uncertainty by using two land-based mitigation scenarios from two land-use models (IMAGE and MAgPIE) as input to four dynamic global vegetation models (DGVMs; LPJ-GUESS, ORCHIDEE, JULES, LPJmL). Each of the four combinations of land-use models and mitigation scenarios aimed for a cumulative carbon uptake of ~130 GtC by the end of the century, achieved either via the cultivation of bioenergy crops combined with carbon capture and storage (BECCS) or avoided deforestation and afforestation (ADAFF). Results suggest large uncertainty in simulated future land demand and carbon uptake rates, depending on the assumptions related to land use and land management in the models. Total cumulative carbon uptake in the DGVMs is highly variable across mitigation scenarios, ranging between 19 and 130 GtC by year 2099. Only one out of the 16 combinations of mitigation scenarios and DGVMs achieves an equivalent or higher carbon uptake than achieved in the land-use models. The large differences in carbon uptake between the DGVMs and their discrepancy against the carbon uptake in IMAGE and MAgPIE are mainly due to different model assumptions regarding bioenergy crop yields and due to the simulation of soil carbon response to land-use change. Differences between land-use models and DGVMs regarding forest biomass and the rate of forest regrowth also have an impact, albeit smaller, on the results. Given the low confidence in simulated carbon uptake for a given land-based mitigation scenario, and that negative emissions simulated by the DGVMs are typically lower than assumed in scenarios consistent with the 2°C target, relying on negative emissions to mitigate climate change is a highly uncertain strategy.
Abstract.
Author URL.
He W, Ju W, Schwalm CR, Sippel S, Wu X, He Q, Song L, Zhang C, Li J, Sitch S, et al (2018). Large-Scale Droughts Responsible for Dramatic Reductions of Terrestrial Net Carbon Uptake over North America in 2011 and 2012.
Journal of Geophysical Research: Biogeosciences,
123(7), 2053-2071.
Abstract:
Large-Scale Droughts Responsible for Dramatic Reductions of Terrestrial Net Carbon Uptake over North America in 2011 and 2012
Recently, severe droughts that occurred in North America are likely to have impacted its terrestrial carbon sink. However, process-based understanding of how meteorological conditions prior to the onset of drought, for instance warm or cold springs, affect drought-induced carbon cycle effects remains scarce. Here we assess and compare the response of terrestrial carbon fluxes to summer droughts in 2011 and 2012 characterized by contrasting spring conditions. The analysis is based on a comprehensive ensemble of carbon cycle models, including FLUXCOM, TRENDY v5, SiBCASA, CarbonTracker Europe, and CarbonTracker, and emerging Earth observations. In 2011, large reductions of net ecosystem production (NEP; −0.24 ± 0.17 Pg C/year) are due to decreased gross primary production (−0.17 ± 0.18 Pg C/year) and slightly increased ecosystem respiration (+0.07 ± 0.17 Pg C/year). Conversely, in 2012, NEP reductions (−0.17 ± 0.25 Pg C/year) are attributed to a larger increase of ecosystem respiration (+0.48 ± 0.27 Pg C/year) than gross primary production (+0.31 ± 0.29 Pg C/year), induced predominantly by an extra warmer spring prior to summer drought. Two temperate ecoregions crops/agriculture and the grass/shrubs contribute largest to these reductions and also dominate the interannual variations of NEP during 2007–2014. Moreover, the warming spring compensated largely the negative carbon anomaly due to summer drought, consistent with earlier studies; however, the compensation occurred only in some specific ecoregions. Overall, our analysis offers a refined view on recent carbon cycle variability and extremes in North America. It corroborates earlier results but also highlights differences with respect to ecoregion-specific carbon cycle responses to drought and heat.
Abstract.
Piao S, Huang M, Liu Z, Wang X, Ciais P, Canadell JG, Wang K, Bastos A, Friedlingstein P, Houghton RA, et al (2018). Lower land-use emissions responsible for increased net land carbon sink during the slow warming period.
Nature Geoscience,
11(10), 739-743.
Abstract:
Lower land-use emissions responsible for increased net land carbon sink during the slow warming period
The terrestrial carbon sink accelerated during 1998–2012, concurrently with the slow warming period, but the mechanisms behind this acceleration are unclear. Here we analyse recent changes in the net land carbon sink (NLS) and its driving factors, using atmospheric inversions and terrestrial carbon models. We show that the linear trend of NLS during 1998–2012 is about 0.17 ± 0.05 Pg C yr−2 , which is three times larger than during 1980–1998 (0.05 ± 0.05 Pg C yr−2). According to terrestrial carbon model simulations, the intensification of the NLS cannot be explained by CO2 fertilization or climate change alone. We therefore use a bookkeeping model to explore the contribution of changes in land-use emissions and find that decreasing land-use emissions are the dominant cause of the intensification of the NLS during the slow warming period. This reduction of land-use emissions is due to both decreased tropical forest area loss and increased afforestation in northern temperate regions. The estimate based on atmospheric inversions shows consistently reduced land-use emissions, whereas another bookkeeping model did not reproduce such changes, probably owing to missing the signal of reduced tropical deforestation. These results highlight the importance of better constraining emissions from land-use change to understand recent trends in land carbon sinks.
Abstract.
Eller CB, Rowland L, Oliveira RS, Bittencourt PRL, Barros FV, da Costa ACL, Meir P, Friend AD, Mencuccini M, Sitch S, et al (2018). Modelling tropical forest responses to drought and El Niño with a stomatal optimization model based on xylem hydraulics.
Philos Trans R Soc Lond B Biol Sci,
373(1760).
Abstract:
Modelling tropical forest responses to drought and El Niño with a stomatal optimization model based on xylem hydraulics.
The current generation of dynamic global vegetation models (DGVMs) lacks a mechanistic representation of vegetation responses to soil drought, impairing their ability to accurately predict Earth system responses to future climate scenarios and climatic anomalies, such as El Niño events. We propose a simple numerical approach to model plant responses to drought coupling stomatal optimality theory and plant hydraulics that can be used in dynamic global vegetation models (DGVMs). The model is validated against stand-scale forest transpiration (E) observations from a long-term soil drought experiment and used to predict the response of three Amazonian forest sites to climatic anomalies during the twentieth century. We show that our stomatal optimization model produces realistic stomatal responses to environmental conditions and can accurately simulate how tropical forest E responds to seasonal, and even long-term soil drought. Our model predicts a stronger cumulative effect of climatic anomalies in Amazon forest sites exposed to soil drought during El Niño years than can be captured by alternative empirical drought representation schemes. The contrasting responses between our model and empirical drought factors highlight the utility of hydraulically-based stomatal optimization models to represent vegetation responses to drought and climatic anomalies in DGVMs.This article is part of a discussion meeting issue 'The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications'.
Abstract.
Author URL.
Piao S, Liu Z, Wang Y, Ciais P, Yao Y, Peng S, Chevallier F, Friedlingstein P, Janssens IA, Peñuelas J, et al (2018). On the causes of trends in the seasonal amplitude of atmospheric CO2.
Glob Chang Biol,
24(2), 608-616.
Abstract:
On the causes of trends in the seasonal amplitude of atmospheric CO2.
No consensus has yet been reached on the major factors driving the observed increase in the seasonal amplitude of atmospheric CO2 in the northern latitudes. In this study, we used atmospheric CO2 records from 26 northern hemisphere stations with a temporal coverage longer than 15 years, and an atmospheric transport model prescribed with net biome productivity (NBP) from an ensemble of nine terrestrial ecosystem models, to attribute change in the seasonal amplitude of atmospheric CO2. We found significant (p 50°N), consistent with previous observations that the amplitude increased faster at Barrow (Arctic) than at Mauna Loa (subtropics). The multi-model ensemble mean (MMEM) shows that the response of ecosystem carbon cycling to rising CO2 concentration (eCO2 ) and climate change are dominant drivers of the increase in AMPP-T and AMPT-P in the high latitudes. At the Barrow station, the observed increase of AMPP-T and AMPT-P over the last 33 years is explained by eCO2 (39% and 42%) almost equally than by climate change (32% and 35%). The increased carbon losses during the months with a net carbon release in response to eCO2 are associated with higher ecosystem respiration due to the increase in carbon storage caused by eCO2 during carbon uptake period. Air-sea CO2 fluxes (10% for AMPP-T and 11% for AMPT-P ) and the impacts of land-use change (marginally significant 3% for AMPP-T and 4% for AMPT-P ) also contributed to the CO2 measured at Barrow, highlighting the role of these factors in regulating seasonal changes in the global carbon cycle.
Abstract.
Author URL.
Grassi G, House J, Kurz WA, Cescatti A, Houghton RA, Peters GP, Sanz MJ, Viñas RA, Alkama R, Arneth A, et al (2018). Reconciling global-model estimates and country reporting of anthropogenic forest CO<inf>2</inf> sinks.
Nature Climate Change,
8(10), 914-920.
Abstract:
Reconciling global-model estimates and country reporting of anthropogenic forest CO2 sinks
Achieving the long-term temperature goal of the Paris Agreement requires forest-based mitigation. Collective progress towards this goal will be assessed by the Paris Agreement’s Global stocktake. At present, there is a discrepancy of about 4 GtCO2 yr−1 in global anthropogenic net land-use emissions between global models (reflected in IPCC assessment reports) and aggregated national GHG inventories (under the UNFCCC). We show that a substantial part of this discrepancy (about 3.2 GtCO2 yr−1) can be explained by conceptual differences in anthropogenic forest sink estimation, related to the representation of environmental change impacts and the areas considered as managed. For a more credible tracking of collective progress under the Global stocktake, these conceptual differences between models and inventories need to be reconciled. We implement a new method of disaggregation of global land model results that allows greater comparability with GHG inventories. This provides a deeper understanding of model–inventory differences, allowing more transparent analysis of forest-based mitigation and facilitating a more accurate Global stocktake.
Abstract.
Humphrey V, Zscheischler J, Ciais P, Gudmundsson L, Sitch S, Seneviratne SI (2018). Sensitivity of atmospheric CO2 growth rate to observed changes in terrestrial water storage.
Nature,
560(7720), 628-631.
Abstract:
Sensitivity of atmospheric CO2 growth rate to observed changes in terrestrial water storage.
Land ecosystems absorb on average 30 per cent of anthropogenic carbon dioxide (CO2) emissions, thereby slowing the increase of CO2 concentration in the atmosphere1. Year-to-year variations in the atmospheric CO2 growth rate are mostly due to fluctuating carbon uptake by land ecosystems1. The sensitivity of these fluctuations to changes in tropical temperature has been well documented2-6, but identifying the role of global water availability has proved to be elusive. So far, the only usable proxies for water availability have been time-lagged precipitation anomalies and drought indices3-5, owing to a lack of direct observations. Here, we use recent observations of terrestrial water storage changes derived from satellite gravimetry7 to investigate terrestrial water effects on carbon cycle variability at global to regional scales. We show that the CO2 growth rate is strongly sensitive to observed changes in terrestrial water storage, drier years being associated with faster atmospheric CO2 growth. We demonstrate that this global relationship is independent of known temperature effects and is underestimated in current carbon cycle models. Our results indicate that interannual fluctuations in terrestrial water storage strongly affect the terrestrial carbon sink and highlight the importance of the interactions between the water and carbon cycles.
Abstract.
Author URL.
Arnold SR, Lombardozzi D, Lamarque JF, Richardson T, Emmons LK, Tilmes S, Sitch SA, Folberth G, Hollaway MJ, Val Martin M, et al (2018). Simulated Global Climate Response to Tropospheric Ozone-Induced Changes in Plant Transpiration.
Geophysical Research Letters,
45(23), 13-079.
Abstract:
Simulated Global Climate Response to Tropospheric Ozone-Induced Changes in Plant Transpiration
Tropospheric ozone (O 3 ) pollution is known to damage vegetation, reducing photosynthesis and stomatal conductance, resulting in modified plant transpiration to the atmosphere. We use an Earth system model to show that global transpiration response to near-present-day surface tropospheric ozone results in large-scale global perturbations to net outgoing long-wave and incoming shortwave radiation. Our results suggest that the radiative effect is dominated by a reduction in shortwave cloud forcing in polluted regions, in response to ozone-induced reduction in land-atmosphere moisture flux and atmospheric humidity. We simulate a statistically significant response of annual surface air temperature of up to ~ +1.5 K due to this ozone effect in vegetated regions subjected to ozone pollution. This mechanism is expected to further increase the net warming resulting from historic and future increases in tropospheric ozone.
Abstract.
Zhou S, Liang J, Lu X, Li Q, Jiang L, Zhang Y, Schwalm CR, Fisher JB, Tjiputra J, Sitch S, et al (2018). Sources of Uncertainty in Modeled Land Carbon Storage within and across Three MIPs: Diagnosis with Three New Techniques.
JOURNAL OF CLIMATE,
31(7), 2833-2851.
Author URL.
Huntingford C, Oliver RJ, Mercado LM, Sitch S (2018). Technical Note: a simple theoretical model framework to describe plant stomatal sluggishness in response to elevated ozone concentrations.
Abstract:
Technical Note: a simple theoretical model framework to describe plant stomatal sluggishness in response to elevated ozone concentrations
Abstract. Elevated levels of tropospheric Ozone [O3] causes damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. Climatic impacts under future raised atmospheric Greenhouse Gas (GHG) concentrations will also impact on the Net Primary Productivity (NPP) of vegetation, which might for instance alter viability of some crops. Together, ozone damage and climate change may adjust the current ability of terrestrial vegetation to offset a significant fraction of carbon dioxide (CO2) emissions. Climate impacts on the land surface are well studied, but arguably large-scale modelling of raised surface level [O3] effects is less advanced. To date most models representing ozone damage use either [O3] concentration or, more recently, flux-uptake related reduction of stomatal opening, estimating suppressed land-atmosphere water and CO2 fluxes. However there is evidence that for some species, [O3] damage can also cause an inertial sluggishness of stomatal response to changing surface meteorological conditions. In some circumstances e.g. droughts, this loss of stomata control can cause them to be more open than without ozone interference. The extent of this effect may be dependent on magnitude and cumulated time of exposure to raised [O3], suggesting experiments to analyze this require operation over long timescales such as full growing seasons. To both aid model development and provide empiricists with a system on to which measurements can be mapped, we present a parameter-sparse framework specifically designed to capture sluggishness. This contains a single time-delay parameter τO3, characterising the timescale for stomata to catch up with the level of opening they would have with- out damage. The larger the value of this parameter, the more sluggish the modelled stomatal response. Through variation of τO3, we find it is possible to have qualitatively similar responses to factorial experiments with and without raised [O3], when comparing to measurement timeseries presented in the literature. This low-parameter approach lends itself to the inclusion of ozone-induced inertial effects being incorporated in the terrestrial vegetation component of Earth System Models (ESMs).
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Abstract.
Huntingford C, Oliver RJ, Mercado LM, Sitch S (2018). Technical note: a simple theoretical model framework to describe plant stomatal "sluggishness" in response to elevated ozone concentrations.
Biogeosciences,
15(17), 5415-5422.
Abstract:
Technical note: a simple theoretical model framework to describe plant stomatal "sluggishness" in response to elevated ozone concentrations
Elevated levels of tropospheric ozone, O3, cause damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. Climatic impacts under future raised atmospheric greenhouse gas (GHG) concentrations will also impact on the net primary productivity (NPP) of vegetation, which might for instance alter viability of some crops. Together, ozone damage and climate change may adjust the current ability of terrestrial vegetation to offset a significant fraction of carbon dioxide (CO2) emissions. Climate impacts on the land surface are well studied, but arguably large-scale modelling of raised surface level O3 effects is less advanced. To date most models representing ozone damage use either O3 concentration or, more recently, flux-uptake-related reduction of stomatal opening, estimating suppressed land-atmosphere water and CO2 fluxes. However there is evidence that, for some species, O3 damage can also cause an inertial sluggishness of stomatal response to changing surface meteorological conditions. In some circumstances (e.g. droughts), this loss of stomata control can cause them to be more open than without ozone interference. To both aid model development and provide empiricists with a system on to which measurements can be mapped, we present a parameter-sparse framework specifically designed to capture sluggishness. This contains a single time-delay parameter τO3, characterizing the timescale for stomata to catch up with the level of opening they would have without damage. The larger the value of this parameter, the more sluggish the modelled stomatal response. Through variation of τO3, we find it is possible to have qualitatively similar responses to factorial experiments with and without raised O3, when comparing to reported measurement time series presented in the literature. This low-parameter approach lends itself to the inclusion of ozone-induced inertial effects being incorporated in the terrestrial vegetation component of Earth system models (ESMs).
Abstract.
Salazar A, Sanchez A, Villegas JC, Salazar JF, Ruiz Carrascal D, Sitch S, Restrepo JD, Poveda G, Feeley KJ, Mercado LM, et al (2018). The ecology of peace: preparing Colombia for new political and planetary climates.
Frontiers in Ecology and the Environment,
16(9), 525-531.
Abstract:
The ecology of peace: preparing Colombia for new political and planetary climates
Colombia, one of the world's most species-rich nations, is currently undergoing a profound social transition: the end of a decades-long conflict with the Revolutionary Armed Forces of Colombia, known as FARC. The peace agreement process will likely transform the country's physical and socioeconomic landscapes at a time when humans are altering Earth's atmosphere and climate in unprecedented ways. We discuss ways in which these transformative events will act in combination to shape the ecological and environmental future of Colombia. We also highlight the risks of creating perverse development incentives in these critical times, along with the potential benefits – for the country and the world – if Colombia can navigate through the peace process in a way that protects its own environment and ecosystems.
Abstract.
Harper AB, Wiltshire AJ, Cox PM, Friedlingstein P, Jones CD, Mercado LM, Sitch S, Williams K, Duran-Rojas C (2018). Vegetation distribution and terrestrial carbon cycle in. a carbon-cycle configuration of JULES4.6 with new plant functional types.
Abstract:
Vegetation distribution and terrestrial carbon cycle in. a carbon-cycle configuration of JULES4.6 with new plant functional types
Abstract. Dynamic global vegetation models (DGVMs) are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES (the Joint UK Land Environment Simulator) represents the land surface in the Hadley Centre climate models and in the UK Earth System Model. Recently the number of plant functional types (PFTs) in JULES were expanded from 5 to 9 to better represent functional diversity in global ecosystems. Here we introduce a more mechanistic representation of vegetation dynamics in TRIFFID, the dynamic vegetation component of JULES, that allows for any number of PFTs to compete based solely on their height, removing the previous hardwired dominance hierarchy where dominant types are assumed to outcompete subdominant types. With the new set of 9 PFTs, JULES is able to more accurately reproduce global vegetation distribution compared to the former 5 PFT version. Improvements include the coverage of trees within tropical and boreal forests, and a reduction in shrubs, which dominated at high latitudes. We show that JULES is able to realistically represent several aspects of the global carbon cycle. The simulated gross primary productivity (GPP) is within the range of observations, but simulated net primary productivity (NPP) is slightly too high. GPP in JULES from 1982–2011 was 133 PgC yr−1, compared to observation-based estimates between 123±8 (over the same time period) and 150–175 PgC yr−1. NPP from 2000–2013 was 72 PgC yr−1, compared to satellite-derived NPP of 55 PgC yr−1 over the same period and independent estimates of 56.2±14.3 PgC yr−1. The simulated carbon stored in vegetation is 542 PgC, compared to an observation-based range of 400–600 PgC. Soil carbon is much lower (1422 PgC) than estimates from measurements (>2400 PgC), with large underestimations of soil carbon in the tropical and boreal forests. We also examined some aspects of the historical terrestrial carbon sink as simulated by JULES. Between the 1900s and 2000s, increased atmospheric carbon dioxide levels enhanced vegetation productivity and litter inputs into the soils, while land-use change removed vegetation and reduced soil carbon. The result was a simulated increase in soil carbon of 57 PgC but a decrease in vegetation carbon by of PgC. JULES simulated a loss of soil and vegetation carbon of 14 and 124 PgC, respectively, due to land-use change from 1900–2009. The simulated land carbon sink was 2.0±1.0 PgC yr−1 from 2000–2009, in close agreement to estimates from the IPCC and Global Carbon Project.
.
Abstract.
Harper AB, Wiltshire AJ, Cox PM, Friedlingstein P, Jones CD, Mercado LM, Sitch S, Williams K, Duran-Rojas C (2018). Vegetation distribution and terrestrial carbon cycle in a carbon cycle configuration of JULES4.6 with new plant functional types.
Geoscientific Model Development,
11(7), 2857-2873.
Abstract:
Vegetation distribution and terrestrial carbon cycle in a carbon cycle configuration of JULES4.6 with new plant functional types
Dynamic global vegetation models (DGVMs) are used for studying historical and future changes to vegetation and the terrestrial carbon cycle. JULES (the Joint UK Land Environment Simulator) represents the land surface in the Hadley Centre climate models and in the UK Earth System Model. Recently the number of plant functional types (PFTs) in JULES was expanded from five to nine to better represent functional diversity in global ecosystems. Here we introduce a more mechanistic representation of vegetation dynamics in TRIFFID, the dynamic vegetation component of JULES, which allows for any number of PFTs to compete based solely on their height; therefore, the previous hardwired dominance hierarchy is removed. With the new set of nine PFTs, JULES is able to more accurately reproduce global vegetation distribution compared to the former five PFT version. Improvements include the coverage of trees within tropical and boreal forests and a reduction in shrubs, the latter of which dominated at high latitudes. We show that JULES is able to realistically represent several aspects of the global carbon (C) cycle. The simulated gross primary productivity (GPP) is within the range of observations, but simulated net primary productivity (NPP) is slightly too high. GPP in JULES from 1982 to 2011 is 133PgCyrg'1, compared to observation-based estimates (over the same time period) between 1238 and 150-175PgCyrg'1. NPP from 2000 to 2013 is 72PgCyrg'1, compared to satellite-derived NPP of 55PgCyrg'1 over the same period and independent estimates of 56.214.3PgCyrg'1. The simulated carbon stored in vegetation is 542PgC, compared to an observation-based range of 400-600PgC. Soil carbon is much lower (1422PgC) than estimates from measurements ( > 2400PgC), with large underestimations of soil carbon in the tropical and boreal forests. We also examined some aspects of the historical terrestrial carbon sink as simulated by JULES. Between the 1900s and 2000s, increased atmospheric carbon dioxide levels enhanced vegetation productivity and litter inputs into the soils, while land use change removed vegetation and reduced soil carbon. The result is a simulated increase in soil carbon of 57PgC but a decrease in vegetation carbon of 98PgC. The total simulated loss of soil and vegetation carbon due to land use change is 138PgC from 1900 to 2009, compared to a recent observationally constrained estimate of 15550PgC from 1901 to 2012. The simulated land carbon sink is 2.01.0PgCyrg'1 from 2000 to 2009, in close agreement with estimates from the IPCC and Global Carbon Project.
Abstract.
Buermann W, Forkel M, O'Sullivan M, Sitch S, Friedlingstein P, Haverd V, Jain AK, Kato E, Kautz M, Lienert S, et al (2018). Widespread seasonal compensation effects of spring warming on northern plant productivity.
Nature,
562(7725), 110-114.
Abstract:
Widespread seasonal compensation effects of spring warming on northern plant productivity.
Climate change is shifting the phenological cycles of plants1, thereby altering the functioning of ecosystems, which in turn induces feedbacks to the climate system2. In northern (north of 30° N) ecosystems, warmer springs lead generally to an earlier onset of the growing season3,4 and increased ecosystem productivity early in the season5. In situ6 and regional7-9 studies also provide evidence for lagged effects of spring warmth on plant productivity during the subsequent summer and autumn. However, our current understanding of these lagged effects, including their direction (beneficial or adverse) and geographic distribution, is still very limited. Here we analyse satellite, field-based and modelled data for the period 1982-2011 and show that there are widespread and contrasting lagged productivity responses to spring warmth across northern ecosystems. On the basis of the observational data, we find that roughly 15 per cent of the total study area of about 41 million square kilometres exhibits adverse lagged effects and that roughly 5 per cent of the total study area exhibits beneficial lagged effects. By contrast, current-generation terrestrial carbon-cycle models predict much lower areal fractions of adverse lagged effects (ranging from 1 to 14 per cent) and much higher areal fractions of beneficial lagged effects (ranging from 9 to 54 per cent). We find that elevation and seasonal precipitation patterns largely dictate the geographic pattern and direction of the lagged effects. Inadequate consideration in current models of the effects of the seasonal build-up of water stress on seasonal vegetation growth may therefore be able to explain the differences that we found between our observation-constrained estimates and the model-constrained estimates of lagged effects associated with spring warming. Overall, our results suggest that for many northern ecosystems the benefits of warmer springs on growing-season ecosystem productivity are effectively compensated for by the accumulation of seasonal water deficits, despite the fact that northern ecosystems are thought to be largely temperature- and radiation-limited10.
Abstract.
Author URL.
Rogers A, Medlyn BE, Dukes JS, Bonan G, von Caemmerer S, Dietze MC, Kattge J, Leakey ADB, Mercado LM, Niinemets Ü, et al (2017). A roadmap for improving the representation of photosynthesis in Earth system models.
New Phytol,
213(1), 22-42.
Abstract:
A roadmap for improving the representation of photosynthesis in Earth system models.
Accurate representation of photosynthesis in terrestrial biosphere models (TBMs) is essential for robust projections of global change. However, current representations vary markedly between TBMs, contributing uncertainty to projections of global carbon fluxes. Here we compared the representation of photosynthesis in seven TBMs by examining leaf and canopy level responses of photosynthetic CO2 assimilation (A) to key environmental variables: light, temperature, CO2 concentration, vapor pressure deficit and soil water content. We identified research areas where limited process knowledge prevents inclusion of physiological phenomena in current TBMs and research areas where data are urgently needed for model parameterization or evaluation. We provide a roadmap for new science needed to improve the representation of photosynthesis in the next generation of terrestrial biosphere and Earth system models.
Abstract.
Author URL.
Campbell JE, Kesselmeier J, Yakir D, Berry JA, Peylin P, Belviso S, Vesala T, Maseyk K, Seibt U, Chen H, et al (2017). Assessing a new clue to how much carbon plants take up. Eos (United States), 98(10), 24-29.
Schwalm CR, Huntingford C, Sitch S, Ahlström A, Arneth A, Camps-Valls G, Ciais P, Friedlingstein P, Jung M, Reichstein M, et al (2017). Compensatory water effects link yearly global land CO2 sink changes to temperature.
Nature,
541(7638), 516-520.
Abstract:
Compensatory water effects link yearly global land CO2 sink changes to temperature.
Large interannual variations in the measured growth rate of atmospheric carbon dioxide (CO2) originate primarily from fluctuations in carbon uptake by land ecosystems. It remains uncertain, however, to what extent temperature and water availability control the carbon balance of land ecosystems across spatial and temporal scales. Here we use empirical models based on eddy covariance data and process-based models to investigate the effect of changes in temperature and water availability on gross primary productivity (GPP), terrestrial ecosystem respiration (TER) and net ecosystem exchange (NEE) at local and global scales. We find that water availability is the dominant driver of the local interannual variability in GPP and TER. To a lesser extent this is true also for NEE at the local scale, but when integrated globally, temporal NEE variability is mostly driven by temperature fluctuations. We suggest that this apparent paradox can be explained by two compensatory water effects. Temporal water-driven GPP and TER variations compensate locally, dampening water-driven NEE variability. Spatial water availability anomalies also compensate, leaving a dominant temperature signal in the year-to-year fluctuations of the land carbon sink. These findings help to reconcile seemingly contradictory reports regarding the importance of temperature and water in controlling the interannual variability of the terrestrial carbon balance. Our study indicates that spatial climate covariation drives the global carbon cycle response.
Abstract.
Author URL.
Schneider GF, Cheesman AW, Winter K, Turner BL, Sitch S, Kursar TA (2017). Current ambient concentrations of ozone in Panama modulate the leaf chemistry of the tropical tree Ficus insipida.
Chemosphere,
172, 363-372.
Abstract:
Current ambient concentrations of ozone in Panama modulate the leaf chemistry of the tropical tree Ficus insipida.
Tropospheric ozone (O3) is a major air pollutant and greenhouse gas, affecting carbon dynamics, ecological interactions, and agricultural productivity across continents and biomes. Elevated [O3] has been documented in tropical evergreen forests, the epicenters of terrestrial primary productivity and plant-consumer interactions. However, the effects of O3 on vegetation have not previously been studied in these forests. In this study, we quantified ambient O3 in a region shared by forests and urban/commercial zones in Panama and found levels two to three times greater than in remote tropical sites. We examined the effects of these ambient O3 levels on the growth and chemistry of seedlings of Ficus insipida, a regionally widespread tree with high stomatal conductance, using open-top chambers supplied with ozone-free or ambient air. We evaluated the differences across treatments in biomass and, using UPLC-MS-MS, leaf secondary metabolites and membrane lipids. Mean [O3] in ambient air was below the levels that induce chronic stress in temperate broadleaved trees, and biomass did not differ across treatments. However, leaf secondary metabolites - including phenolics and a terpenoid - were significantly downregulated in the ambient air treatment. Membrane lipids were present at lower concentrations in older leaves grown in ambient air, suggesting accelerated senescence. Thus, in a tree species with high O3 uptake via high stomatal conductance, current ambient [O3] in Panamanian forests are sufficient to induce chronic effects on leaf chemistry.
Abstract.
Author URL.
Prestele R, Arneth A, Bondeau A, de Noblet-Ducoudre N, Pugh TAM, Sitch S, Stehfest E, Verburg PH (2017). Current challenges of implementing anthropogenic land-use and land-cover change in models contributing to climate change assessments.
EARTH SYSTEM DYNAMICS,
8(2), 369-386.
Author URL.
Le Quéré C, Andrew RM, Friedlingstein P, Sitch S, Pongratz J, Manning AC, Korsbakken JI, Peters GP, Canadell JG, Jackson RB, et al (2017). Global Carbon Budget 2017.
Abstract:
Global Carbon Budget 2017
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere – the "global carbon budget" – is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify the five major components of the global carbon budget and their uncertainties. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on land-cover change data and bookkeeping models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The ocean CO2 sink (SOCEAN) and terrestrial CO2 sink (SLAND) are estimated with global process models constrained by observations. The resulting carbon budget imbalance (BIM), the difference between the estimated total emissions and the estimated changes in the atmosphere, ocean, and terrestrial biosphere, is a measure of our imperfect data and understanding of the contemporary carbon cycle. All uncertainties are reported as ±1σ. For the last decade available (2007–2016), EFF was 9.4 ± 0.5 GtC yr−1, ELUC 1.3 ± 0.7 GtC yr−1, GATM 4.7 ± 0.1 GtC yr−1, SOCEAN 2.4 ± 0.5 GtC yr−1, and SLAND 3.0 ± 0.8 GtC yr−1, with a budget imbalance BIM of 0.6 GtC yr−1 indicating overestimated emissions and/or underestimated sinks. For year 2016 alone, the growth in EFF was approximately zero and emissions remained at 9.9 ± 0.5 GtC yr−1. Also for 2016, ELUC was 1.3 ± 0.7 GtC yr−1, GATM was 6.1 ± 0.2 GtC yr−1, SOCEAN was 2.6 ± 0.5 GtC yr−1 and SLAND was 2.7 ± 1.0 GtC yr−1, with a small BIM of −0.3 GtC. GATM continued to be higher in 2016 compared to the past decade (2007–2016), reflecting in part the higher fossil emissions and smaller SLAND for that year consistent with El Niño conditions. The global atmospheric CO2 concentration reached 402.8 ± 0.1 ppm averaged over 2016. For 2017, preliminary data indicate a renewed growth in EFF of +2.0 % (range of 0.8 % to 3.0 %) based on national emissions projections for China, USA, and India, and projections of Gross Domestic Product corrected for recent changes in the carbon intensity of the economy for the rest of the world. For 2017, initial data indicate an increase in atmospheric CO2 concentration of around 5.3 GtC (2.5 ppm), attributed to a combination of increasing emissions and receding El Niño conditions. This living data update documents changes in the methods and data sets used in this new global carbon budget compared with previous publications of this data set (Le Quéré et al. 2016; 2015b; 2015a; 2014; 2013). All results presented here can be downloaded from https://doi.org/10.18160/GCP-2017.
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Abstract.
Arneth A, Sitch S, Pongratz J, Stocker BD, Ciais P, Poulter B, Bayer AD, Bondeau A, Calle L, Chini LP, et al (2017). Historical carbon dioxide emissions caused by land-use changes are possibly larger than assumed.
NATURE GEOSCIENCE,
10(2), 79-+.
Author URL.
Huntingford C, Atkin OK, Martinez-de la Torre A, Mercado LM, Heskel MA, Harper AB, Bloomfield KJ, O'Sullivan OS, Reich PB, Wythers KR, et al (2017). Implications of improved representations of plant respiration in a changing climate.
NATURE COMMUNICATIONS,
8 Author URL.
Li W, Ciais P, Peng S, Yue C, Wang Y, Thurner M, Saatchi SS, Arneth A, Avitabile V, Carvalhais N, et al (2017). Land-use and land-cover change carbon emissions between 1901 and 2012 constrained by biomass observations.
BIOGEOSCIENCES,
14(22), 5053-5067.
Author URL.
Oliver RJ, Mercado LM, Sitch S, Simpson D, Medlyn BE, Lin Y-S, Folberth GA (2017). Large but decreasing effect of ozone on the European carbon sink.
Abstract:
Large but decreasing effect of ozone on the European carbon sink
Abstract. The capacity of the terrestrial biosphere to sequester carbon and mitigate climate change is governed by the ability of vegetation to remove emissions of CO2 through photosynthesis. Tropospheric O3, a globally abundant and potent greenhouse gas, is, however, known to damage plants, causing reductions in primary productivity, yet the impact of this gas on European vegetation and the land carbon sink is largely unknown. Despite emission control policies across Europe, background concentrations of tropospheric O3 have risen significantly over the last decades due to hemispheric-scale increases in O3 and its precursors. Therefore, plants are exposed to increasing background concentrations, at levels currently causing chronic damage. We use the JULES land-surface model recalibrated for O3 impacts on European vegetation, with an improved stomatal conductance parameterization, to quantify the impact of tropospheric O3, and its interaction with CO2, on gross primary productivity (GPP) and land carbon storage across Europe. A factorial set of model experiments showed that tropospheric O3 can significantly suppress terrestrial carbon uptake across Europe over the period 1901 to 2050. By 2050, simulated GPP was reduced by 4 to 9 % due to plant ozone damage, however, the combined effects of elevated future CO2 (acting to reduce stomatal opening) and reductions in O3 concentrations resulted in reduced O3 damage in the future, contrary to predictions from earlier studies. Reduced land carbon storage resulted from diminished soil carbon stocks consistent with the reduction in GPP. Regional variations are identified with larger impacts shown for temperate Europe compared to boreal regions. These results highlight that the effects of O3 on plant physiology add to the uncertainty of future trends in the land carbon sink and, as such, this should be incorporated into carbon cycle assessments.
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Abstract.
Booth BBB, Harris GR, Murphy JM, House JI, Jones CD, Sexton D, Sitch S (2017). Narrowing the Range of Future Climate Projections Using Historical Observations of Atmospheric CO<sub>2</sub>.
JOURNAL OF CLIMATE,
30(8), 3039-3053.
Author URL.
Wu C, Venevsky S, Sitch S, Yang Y, Wang M, Wang L, Gao Y (2017). Present-day and future contribution of climate and fires to vegetation composition in the boreal forest of China.
Ecosphere,
8(8).
Abstract:
Present-day and future contribution of climate and fires to vegetation composition in the boreal forest of China
Climate is well known as an important determinant of biogeography. Although climate is directly important for vegetation composition in the boreal forests, these ecosystems are strongly sensitive to an indirect effect of climate via fire disturbance. However, the driving balance of fire disturbance and climate on composition is poorly understood. In this study, we quantitatively analyzed their individual contributions for the boreal forests of the Heilongjiang Province, China, and their response to climate change using four warming scenarios (+1.5°, 2°, 3°, and 4°C). This study employs the statistical methods of Redundancy Analysis (RDA) and variation partitioning combined with simulation results from a SErgey VERsion Dynamic Global Vegetation Model (SEVER-DGVM), and remote sensing datasets of global land cover (GLC2000) and the third version of Global Fire Emissions Database (GFED3). Results show that the vegetation distribution for the present day is mainly determined directly by climate (35%) rather than fire (1-10.9%). However, with a future global warming of 1.5°C, local vegetation composition will be determined by fires rather than climate (36.3% > 29.3%). Above 1.5°C warming, temperature will be more important than fires in regulating vegetation distribution although other factors such as precipitation can also contribute. The spatial pattern in vegetation composition over the region, as evaluated by Moran's Eigenvector Map (MEM), has a significant impact on local vegetation coverage; for example, composition at any individual location is highly related to that in its neighborhood. It represents the largest contribution to vegetation distribution in all scenarios, but will not change the driving balance between climate and fires. Our results are highly relevant for forest and wildfires' management.
Abstract.
Rabin SS, Melton JR, Lasslop G, Bachelet D, Forrest M, Hantson S, Kaplan JO, Li F, Mangeon S, Ward DS, et al (2017). The Fire Modeling Intercomparison Project (FireMIP), phase 1: Experimental and analytical protocols with detailed model descriptions.
Geoscientific Model Development,
10(3), 1175-1197.
Abstract:
The Fire Modeling Intercomparison Project (FireMIP), phase 1: Experimental and analytical protocols with detailed model descriptions
The important role of fire in regulating vegetation community composition and contributions to emissions of greenhouse gases and aerosols make it a critical component of dynamic global vegetation models and Earth system models. Over 2 decades of development, a wide variety of model structures and mechanisms have been designed and incorporated into global fire models, which have been linked to different vegetation models. However, there has not yet been a systematic examination of how these different strategies contribute to model performance. Here we describe the structure of the first phase of the Fire Model Intercomparison Project (FireMIP), which for the first time seeks to systematically compare a number of models. By combining a standardized set of input data and model experiments with a rigorous comparison of model outputs to each other and to observations, we will improve the understanding of what drives vegetation fire, how it can best be simulated, and what new or improved observational data could allow better constraints on model behavior. In this paper, we introduce the fire models used in the first phase of FireMIP, the simulation protocols applied, and the benchmarking system used to evaluate the models. We have also created supplementary tables that describe, in thorough mathematical detail, the structure of each model.
Abstract.
Murray-Tortarolo G, Jaramillo VJ, Maass M, Friedlingstein P, Sitch S (2017). The decreasing range between dry- and wet- season precipitation over land and its effect on vegetation primary productivity.
PLoS One,
12(12).
Abstract:
The decreasing range between dry- and wet- season precipitation over land and its effect on vegetation primary productivity.
One consequence of climate change is the alteration of global water fluxes, both in amount and seasonality. As a result, the seasonal difference between dry- (p < 100 mm/month) and wet-season (p > 100 mm/month) precipitation (p) has increased over land during recent decades (1980-2005). However, our analysis expanding to a 60-year period (1950-2009) showed the opposite trend. This is, dry-season precipitation increased steadily, while wet-season precipitation remained constant, leading to reduced seasonality at a global scale. The decrease in seasonality was not due to a change in dry-season length, but in precipitation rate; thus, the dry season is on average becoming wetter without changes in length. Regionally, wet- and dry-season precipitations are of opposite sign, causing a decrease in the seasonal variation of the precipitation over 62% of the terrestrial ecosystems. Furthermore, we found a high correlation (r = 0.62) between the change in dry-season precipitation and the trend in modelled net primary productivity (NPP), which is explained based on different ecological mechanisms. This trend is not found with wet-season precipitation (r = 0.04), These results build on the argument that seasonal water availability has changed over the course of the last six decades and that the dry-season precipitation is a key driver of vegetation productivity at the global scale.
Abstract.
Author URL.
Peters GP, Le Quéré C, Andrew RM, Canadell JG, Friedlingstein P, Ilyina T, Jackson RB, Joos F, Korsbakken JI, McKinley GA, et al (2017). Towards real-time verification of CO<inf>2</inf> emissions. Nature Climate Change, 7(12), 848-850.
Anav A, De Marco A, Proietti C, Alessandri A, Dell'Aquila A, Cionni I, Friedlingstein P, Khvorostyanov D, Menut L, Paoletti E, et al (2016). Comparing concentration-based (AOT40) and stomatal uptake (PODY) metrics for ozone risk assessment to European forests.
Glob Chang Biol,
22(4), 1608-1627.
Abstract:
Comparing concentration-based (AOT40) and stomatal uptake (PODY) metrics for ozone risk assessment to European forests.
Tropospheric ozone (O3) produces harmful effects to forests and crops, leading to a reduction of land carbon assimilation that, consequently, influences the land sink and the crop yield production. To assess the potential negative O3 impacts to vegetation, the European Union uses the Accumulated Ozone over Threshold of 40 ppb (AOT40). This index has been chosen for its simplicity and flexibility in handling different ecosystems as well as for its linear relationships with yield or biomass loss. However, AOT40 does not give any information on the physiological O3 uptake into the leaves since it does not include any environmental constraints to O3 uptake through stomata. Therefore, an index based on stomatal O3 uptake (i.e. PODY), which describes the amount of O3 entering into the leaves, would be more appropriate. Specifically, the PODY metric considers the effects of multiple climatic factors, vegetation characteristics and local and phenological inputs rather than the only atmospheric O3 concentration. For this reason, the use of PODY in the O3 risk assessment for vegetation is becoming recommended. We compare different potential O3 risk assessments based on two methodologies (i.e. AOT40 and stomatal O3 uptake) using a framework of mesoscale models that produces hourly meteorological and O3 data at high spatial resolution (12 km) over Europe for the time period 2000-2005. Results indicate a remarkable spatial and temporal inconsistency between the two indices, suggesting that a new definition of European legislative standard is needed in the near future. Besides, our risk assessment based on AOT40 shows a good consistency compared to both in-situ data and other model-based datasets. Conversely, risk assessment based on stomatal O3 uptake shows different spatial patterns compared to other model-based datasets. This strong inconsistency can be likely related to a different vegetation cover and its associated parameterizations.
Abstract.
Author URL.
Navarrete D, Sitch S, Aragão LEOC, Pedroni L (2016). Conversion from forests to pastures in the Colombian Amazon leads to contrasting soil carbon dynamics depending on land management practices.
Glob Chang Biol,
22(10), 3503-3517.
Abstract:
Conversion from forests to pastures in the Colombian Amazon leads to contrasting soil carbon dynamics depending on land management practices.
Strategies to mitigate climate change by reducing deforestation and forest degradation (e.g. REDD+) require country- or region-specific information on temporal changes in forest carbon (C) pools to develop accurate emission factors. The soil C pool is one of the most important C reservoirs, but is rarely included in national forest reference emission levels due to a lack of data. Here, we present the soil organic C (SOC) dynamics along 20 years of forest-to-pasture conversion in two subregions with different management practices during pasture establishment in the Colombian Amazon: high-grazing intensity (HG) and low-grazing intensity (LG) subregions. We determined the pattern of SOC change resulting from the conversion from forest (C3 plants) to pasture (C4 plants) by analysing total SOC stocks and the natural abundance of the stable isotopes (13) C along two 20-year chronosequences identified in each subregion. We also analysed soil N stocks and the natural abundance of (15) N during pasture establishment. In general, total SOC stocks at 30 cm depth in the forest were similar for both subregions, with an average of 47.1 ± 1.8 Mg C ha(-1) in HG and 48.7 ± 3.1 Mg C ha(-1) in LG. However, 20 years after forest-to-pasture conversion SOC in HG decreased by 20%, whereas in LG SOC increased by 41%. This net SOC decrease in HG was due to a larger reduction in C3-derived input and to a comparatively smaller increase in C4-derived C input. In LG both C3- and C4-derived C input increased along the chronosequence. N stocks were generally similar in both subregions and soil N stock changes during pasture establishment were correlated with SOC changes. These results emphasize the importance of management practices involving low-grazing intensity in cattle activities to preserve SOC stocks and to reduce C emissions after land-cover change from forest to pasture in the Colombian Amazon.
Abstract.
Author URL.
Navarrete D, Sitch S, Aragão LEOC, Pedroni L, Duque A (2016). Conversion from forests to pastures in the Colombian Amazon leads to differences in dead wood dynamics depending on land management practices.
J Environ Manage,
171, 42-51.
Abstract:
Conversion from forests to pastures in the Colombian Amazon leads to differences in dead wood dynamics depending on land management practices.
Dead wood, composed of coarse standing and fallen woody debris (CWD), is an important carbon (C) pool in tropical forests and its accounting is needed to reduce uncertainties within the strategies to mitigate climate change by reducing deforestation and forest degradation (REDD+). To date, information on CWD stocks in tropical forests is scarce and effects of land-cover conversion and land management practices on CWD dynamics remain largely unexplored. Here we present estimates on CWD stocks in primary forests in the Colombian Amazon and their dynamics along 20 years of forest-to-pasture conversion in two sub-regions with different management practices during pasture establishment: high-grazing intensity (HG) and low-grazing intensity (LG) sub-regions. Two 20-year-old chronosequences describing the forest-to-pasture conversion were identified in both sub-regions. The line-intersect and the plot-based methods were used to estimate fallen and standing CWD stocks, respectively. Total necromass in primary forests was similar between both sub-regions (35.6 ± 5.8 Mg ha(-1) in HG and 37.0 ± 7.4 Mg ha(-1) in LG). An increase of ∼124% in CWD stocks followed by a reduction to values close to those at the intact forests were registered after slash-and-burn practice was implemented in both sub-regions during the first two years of forest-to-pasture conversion. Implementation of machinery after using fire in HG pastures led to a reduction of 82% in CWD stocks during the second and fifth years of pasture establishment, compared to a decrease of 41% during the same period in LG where mechanization is not implemented. Finally, average necromass 20 years after forest-to-pasture conversion decreased to 3.5 ± 1.4 Mg ha(-1) in HG and 9.3 ± 3.5 Mg ha(-1) in LG, representing a total reduction of between 90% and 75% in each sub-region, respectively. These results highlight the importance of low-grazing intensity management practices during ranching activities in the Colombian Amazon to reduce C emissions associated with land-cover change from forest to pasture.
Abstract.
Author URL.
Le Quéré C, Andrew RM, Canadell JG, Sitch S, Ivar Korsbakken J, Peters GP, Manning AC, Boden TA, Tans PP, Houghton RA, et al (2016). Global Carbon Budget 2016.
Earth System Science Data,
8(2), 605-649.
Abstract:
Global Carbon Budget 2016
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere-the "global carbon budget"-is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates and consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models. We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ± reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2006-2015), EFF was 9.3±0.5 GtC yr-1, ELUC 1.0±0.5 GtC yr-1, GATM 4.5±0.1 GtC yr-1, SOCEAN 2.6±0.5 GtC yr-1, and SLAND 3.1±0.9 GtC yr-1. For year 2015 alone, the growth in EFF was approximately zero and emissions remained at 9.9±0.5 GtC yr-1, showing a slowdown in growth of these emissions compared to the average growth of 1.8%yr-1 that took place during 2006-2015. Also, for 2015, ELUC was 1.3±0.5 GtC yr-1, GATM was 6.3±0.2 GtC yr-1, SOCEAN was 3.0±0.5 GtC yr-1, and SLAND was 1.9±0.9 GtC yr-1. GATM was higher in 2015 compared to the past decade (2006-2015), reflecting a smaller SLAND for that year. The global atmospheric CO2 concentration reached 399.4±0.1 ppm averaged over 2015. For 2016, preliminary data indicate the continuation of low growth in EFF with C0.2% (range of-1.0 to C1.8 %) based on national emissions projections for China and USA, and projections of gross domestic product corrected for recent changes in the carbon intensity of the economy for the rest of the world. In spite of the low growth of EFF in 2016, the growth rate in atmospheric CO2 concentration is expected to be relatively high because of the persistence of the smaller residual terrestrial sink (SLAND) in response to El Ninõ conditions of 2015-2016. From this projection of EFF and assumed constant ELUC for 2016, cumulative emissions of CO2 will reach 565±55 GtC (2075±205 GtCO2) for 1870-2016, about 75% from EFF and 25% from ELUC. This living data update documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this data set (Le Quéré et al. 2015b, a, 2014, 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center.
Abstract.
Zhu Z, Piao S, Myneni RB, Huang M, Zeng Z, Canadell JG, Ciais P, Sitch S, Friedlingstein P, Arneth A, et al (2016). Greening of the Earth and its drivers. Nature Climate Change, 6(8), 791-795.
Mangeon S, Voulgarakis A, Gilham R, Harper A, Sitch S, Folberth G (2016). INFERNO: a fire and emissions scheme for the UK Met Office's Unified Model.
Geoscientific Model Development,
9(8), 2685-2700.
Abstract:
INFERNO: a fire and emissions scheme for the UK Met Office's Unified Model
Warm and dry climatological conditions favour the occurrence of forest fires. These fires then become a significant emission source to the atmosphere. Despite this global importance, fires are a local phenomenon and are difficult to represent in large-scale Earth system models (ESMs). To address this, the INteractive Fire and Emission algoRithm for Natural envirOnments (INFERNO) was developed. INFERNO follows a reduced complexity approach and is intended for decadal- to centennial-scale climate simulations and assessment models for policy making. Fuel flammability is simulated using temperature, relative humidity (RH) and fuel load as well as precipitation and soil moisture. Combining flammability with ignitions and vegetation, the burnt area is diagnosed. Emissions of carbon and key species are estimated using the carbon scheme in the Joint UK Land Environment Simulator (JULES) land surface model. JULES also possesses fire index diagnostics, which we document and compare with our fire scheme. We found INFERNO captured global burnt area variability better than individual indices, and these performed best for their native regions. Two meteorology data sets and three ignition modes are used to validate the model. INFERNO is shown to effectively diagnose global fire occurrence (R Combining double low line 0.66) and emissions (R Combining double low line 0.59) through an approach appropriate to the complexity of an ESM, although regional biases remain.
Abstract.
Sitch SA (2016). INFERNO: a fire and emissions scheme for the Met Office’s Unified Model. Geosci. Model Dev. Discuss.
Jiang Y, Zhuang Q, Sitch S, O'Donnell JA, Kicklighter D, Sokolov A, Melillo J (2016). Importance of soil thermal regime in terrestrial ecosystem carbon dynamics in the circumpolar north.
Global and Planetary Change,
142, 28-40.
Abstract:
Importance of soil thermal regime in terrestrial ecosystem carbon dynamics in the circumpolar north
In the circumpolar north (45-90°N), permafrost plays an important role in vegetation and carbon (C) dynamics. Permafrost thawing has been accelerated by the warming climate and exerts a positive feedback to climate through increasing soil C release to the atmosphere. To evaluate the influence of permafrost on C dynamics, changes in soil temperature profiles should be considered in global C models. This study incorporates a sophisticated soil thermal model (STM) into a dynamic global vegetation model (LPJ-DGVM) to improve simulations of changes in soil temperature profiles from the ground surface to 3 m depth, and its impacts on C pools and fluxes during the 20th and 21st centuries. With cooler simulated soil temperatures during the summer, LPJ-STM estimates ~0.4 Pg C yr-1 lower present-day heterotrophic respiration but ~0.5 Pg C yr-1 higher net primary production than the original LPJ model resulting in an additional 0.8 to 1.0 Pg C yr-1 being sequestered in circumpolar ecosystems. Under a suite of projected warming scenarios, we show that the increasing active layer thickness results in the mobilization of permafrost C, which contributes to a more rapid increase in heterotrophic respiration in LPJ-STM compared to the stand-alone LPJ model. Except under the extreme warming conditions, increases in plant production due to warming and rising CO2, overwhelm the e nhanced ecosystem respiration so that both boreal forest and arctic tundra ecosystems remain a net C sink over the 21st century. This study highlights the importance of considering changes in the soil thermal regime when quantifying the C budget in the circumpolar north.
Abstract.
Harper A, Cox P, Friedlingstein P, Wiltshire A, Jones C, Sitch S, Mercado LM, Groenendijk M, Robertson E, Kattge J, et al (2016). Improved representation of plant functional types and. physiology in the Joint UK Land Environment Simulator. (JULES v4.2) using plant trait information.
Abstract:
Improved representation of plant functional types and. physiology in the Joint UK Land Environment Simulator. (JULES v4.2) using plant trait information
Abstract. Dynamic global vegetation models are used to predict the response of vegetation to climate change. They are essential for planning ecosystem management, understanding carbon cycleclimate feedbacks, and evaluating the potential impacts of climate change on global ecosystems. JULES (the Joint UK Land Environment Simulator) represents terrestrial processes in the UK Hadley Centre family of models and in the first generation UK Earth System Model. Previously, JULES represented five plant functional types (PFTs): broadleaf trees, needle-leaf trees, C3 and C4 grasses, and shrubs. This study addresses three developments in JULES. First, trees and shrubs were split into deciduous and evergreen PFTs to better represent the range of leaf lifespans and metabolic capacities that exists in nature. Second, we distinguished between temperate and tropical broadleaf evergreen trees. These first two changes result in a new set of nine PFTs: tropical and temperate broadleaf evergreen trees, broadleaf deciduous trees, needle-leaf evergreen and deciduous trees, C3 and C4 grasses, and evergreen and deciduous shrubs. Third, using data from the TRY database, we updated the relationship between leaf nitrogen and the maximum rate of carboxylation of Rubisco (Vcmax), and updated the model phenology to include a trade-off between leaf lifespan and leaf mass per unit area.
.
Abstract.
Harper AB, Cox PM, Friedlingstein P, Wiltshire AJ, Jones CD, Sitch S, Mercado LM, Groenendijk M, Robertson E, Kattge J, et al (2016). Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information.
Geoscientific Model Development,
9(7), 2415-2440.
Abstract:
Improved representation of plant functional types and physiology in the Joint UK Land Environment Simulator (JULES v4.2) using plant trait information
Dynamic global vegetation models are used to predict the response of vegetation to climate change. They are essential for planning ecosystem management, understanding carbon cycle-climate feedbacks, and evaluating the potential impacts of climate change on global ecosystems. JULES (the Joint UK Land Environment Simulator) represents terrestrial processes in the UK Hadley Centre family of models and in the first generation UK Earth System Model. Previously, JULES represented five plant functional types (PFTs): broadleaf trees, needle-leaf trees, C3 and C4 grasses, and shrubs. This study addresses three developments in JULES. First, trees and shrubs were split into deciduous and evergreen PFTs to better represent the range of leaf life spans and metabolic capacities that exists in nature. Second, we distinguished between temperate and tropical broadleaf evergreen trees. These first two changes result in a new set of nine PFTs: tropical and temperate broadleaf evergreen trees, broadleaf deciduous trees, needle-leaf evergreen and deciduous trees, C3 and C4 grasses, and evergreen and deciduous shrubs. Third, using data from the TRY database, we updated the relationship between leaf nitrogen and the maximum rate of carboxylation of Rubisco (Vcmax), and updated the leaf turnover and growth rates to include a trade-off between leaf life span and leaf mass per unit area. Overall, the simulation of gross and net primary productivity (GPP and NPP, respectively) is improved with the nine PFTs when compared to FLUXNET sites, a global GPP data set based on FLUXNET, and MODIS NPP. Compared to the standard five PFTs, the new nine PFTs simulate a higher GPP and NPP, with the exception of C3 grasses in cold environments and C4 grasses that were previously over-productive. On a biome scale, GPP is improved for all eight biomes evaluated and NPP is improved for most biomes - the exceptions being the tropical forests, savannahs, and extratropical mixed forests where simulated NPP is too high. With the new PFTs, the global present-day GPP and NPP are 128 and 62 Pg C year-1, respectively. We conclude that the inclusion of trait-based data and the evergreen/deciduous distinction has substantially improved productivity fluxes in JULES, in particular the representation of GPP. These developments increase the realism of JULES, enabling higher confidence in simulations of vegetation dynamics and carbon storage.
Abstract.
Zhang Y, Xiao X, Guanter L, Zhou S, Ciais P, Joiner J, Sitch S, Wu X, Nabel J, Dong J, et al (2016). Precipitation and carbon-water coupling jointly control the interannual variability of global land gross primary production.
Sci Rep,
6Abstract:
Precipitation and carbon-water coupling jointly control the interannual variability of global land gross primary production.
Carbon uptake by terrestrial ecosystems is increasing along with the rising of atmospheric CO2 concentration. Embedded in this trend, recent studies suggested that the interannual variability (IAV) of global carbon fluxes may be dominated by semi-arid ecosystems, but the underlying mechanisms of this high variability in these specific regions are not well known. Here we derive an ensemble of gross primary production (GPP) estimates using the average of three data-driven models and eleven process-based models. These models are weighted by their spatial representativeness of the satellite-based solar-induced chlorophyll fluorescence (SIF). We then use this weighted GPP ensemble to investigate the GPP variability for different aridity regimes. We show that semi-arid regions contribute to 57% of the detrended IAV of global GPP. Moreover, in regions with higher GPP variability, GPP fluctuations are mostly controlled by precipitation and strongly coupled with evapotranspiration (ET). This higher GPP IAV in semi-arid regions is co-limited by supply (precipitation)-induced ET variability and GPP-ET coupling strength. Our results demonstrate the importance of semi-arid regions to the global terrestrial carbon cycle and posit that there will be larger GPP and ET variations in the future with changes in precipitation patterns and dryland expansion.
Abstract.
Author URL.
Calle L, Canadell JG, Patra P, Ciais P, Ichii K, Tian H, Kondo M, Piao S, Arneth A, Harper AB, et al (2016). Regional carbon fluxes from land use and land cover change in Asia, 1980–2009. Environmental Research Letters, 11(7), 074011-074011.
Zhao F, Zeng N, Akihiko I, Asrar G, Friedlingstein P, Jain A, Kalnay E, Kato E, Koven CD, Poulter B, et al (2016). Role of CO&lt;sub&gt;2&lt;/sub&gt;, climate and land use in regulating the seasonal amplitude. increase of carbon fluxes in terrestrial ecosystems: a multimodel. analysis.
Abstract:
Role of CO<sub>2</sub>, climate and land use in regulating the seasonal amplitude. increase of carbon fluxes in terrestrial ecosystems: a multimodel. analysis
Abstract. We examined the net terrestrial carbon flux to the atmosphere (FTA) simulated by nine models from the TRENDY dynamic global vegetation model project during 1961–2012 for its seasonal cycle and amplitude trend. While some models exhibit similar phase and amplitude compared to atmospheric inversions, with spring drawdown and autumn rebound, others tend to rebound early in summer. The model ensemble mean underestimates the magnitude of the seasonal cycle by 40 % compared to atmospheric inversions. Global FTA amplitude increase (19 ± 8 %) and its decadal variability from the model ensemble are generally consistent with constraints from surface atmosphere observations. However, models disagree on attribution of this long-term amplitude increase, with factorial experiments attributing 83 ± 56 %, −3 ± 74 % and 20 ± 30 % to rising CO2, climate change and land use/cover change, respectively. Seven out of the nine models suggest that CO2 fertilization is a stronger control — with the notable exception of VEGAS, which attributes approximately equally to the three factors. Generally, all models display an enhanced seasonality over the boreal region in response to high-latitude warming, but a negative climate contribution from part of the Northern Hemisphere temperate region, and the net result is a divergence over climate change effect. Six of the nine models show land use/cover change amplifies the seasonal cycle of global FTA: some are due to forest regrowth while others are caused by crop expansion or agricultural intensification, as revealed by their divergent spatial patterns. We also discovered a moderate cross-model correlation between FTA amplitude increase and increase in land carbon sink (R2 = 0.61). Our results suggest that models can show similar results in some benchmarks with different underlying mechanisms, therefore the spatial traits of CO2 fertilization, climate change, and land use/cover changes are crucial in determining the right mechanisms in seasonal carbon cycle change as well as mean sink change.
.
Abstract.
Zhao F, Zeng N, Asrar G, Friedlingstein P, Ito A, Jain A, Kalnay E, Kato E, Koven C, Poulter B, et al (2016). Role of CO2, climate and land use in regulating the seasonal amplitude increase of carbon fluxes in terrestrial ecosystems: a multimodel analysis.
Biogeosciences,
13(17), 5121-5137.
Abstract:
Role of CO2, climate and land use in regulating the seasonal amplitude increase of carbon fluxes in terrestrial ecosystems: a multimodel analysis
We examined the net terrestrial carbon flux to the atmosphere (FTA) simulated by nine models from the TRENDY dynamic global vegetation model project for its seasonal cycle and amplitude trend during 1961-2012. While some models exhibit similar phase and amplitude compared to atmospheric inversions, with spring drawdown and autumn rebound, others tend to rebound early in summer. The model ensemble mean underestimates the magnitude of the seasonal cycle by 40g% compared to atmospheric inversions. Global FTA amplitude increase (19g±g8g%) and its decadal variability from the model ensemble are generally consistent with constraints from surface atmosphere observations. However, models disagree on attribution of this long-term amplitude increase, with factorial experiments attributing 83g±g56g%, ĝ'3g±g74 and 20g±g30g% to rising CO2, climate change and land use/cover change, respectively. Seven out of the nine models suggest that CO2 fertilization is the strongest control - with the notable exception of VEGAS, which attributes approximately equally to the three factors. Generally, all models display an enhanced seasonality over the boreal region in response to high-latitude warming, but a negative climate contribution from part of the Northern Hemisphere temperate region, and the net result is a divergence over climate change effect. Six of the nine models show that land use/cover change amplifies the seasonal cycle of global FTA: some are due to forest regrowth, while others are caused by crop expansion or agricultural intensification, as revealed by their divergent spatial patterns. We also discovered a moderate cross-model correlation between FTA amplitude increase and increase in land carbon sink (R2 Combining double low line g0.61). Our results suggest that models can show similar results in some benchmarks with different underlying mechanisms; therefore, the spatial traits of CO2 fertilization, climate change and land use/cover changes are crucial in determining the right mechanisms in seasonal carbon cycle change as well as mean sink change.
Abstract.
Murray-Tortarolo G, Friedlingstein P, Sitch S, Jaramillo VJ, Murguia-Flores F, Anav A, Liu Y, Arneth A, Arvanitis A, Harper A, et al (2016). The carbon cycle in Mexico: past, present and future of C stocks and fluxes.
BIOGEOSCIENCES,
13(1), 223-238.
Author URL.
Murray-Tortarolo G, Friedlingstein P, Sitch S, Seneviratne SI, Fletcher I, Mueller B, Greve P, Anav A, Liu Y, Ahlström A, et al (2016). The dry season intensity as a key driver of NPP trends.
Geophysical Research Letters,
43(6), 2632-2639.
Abstract:
The dry season intensity as a key driver of NPP trends
©2016. American Geophysical Union. All Rights Reserved.We analyze the impacts of changing dry season length and intensity on vegetation productivity and biomass. Our results show a wetness asymmetry in dry ecosystems, with dry seasons becoming drier and wet seasons becoming wetter, likely caused by climate change. The increasingly intense dry seasons were consistently correlated with a decreasing trend in net primary productivity (NPP) and biomass from different products and could potentially mean a reduction of 10-13% in NPP by 2100. We found that annual NPP in dry ecosystems is particularly sensitive to the intensity of the dry season, whereas an increase in precipitation during the wet season has a smaller effect. We conclude that changes in water availability over the dry season affect vegetation throughout the whole year, driving changes in regional NPP. Moreover, these results suggest that usage of seasonal water fluxes is necessary to improve our understanding of the link between water availability and the land carbon cycle.
Abstract.
Hantson S, Arneth A, Harrison SP, Kelley DI, Colin Prentice I, Rabin SS, Archibald S, Mouillot F, Arnold SR, Artaxo P, et al (2016). The status and challenge of global fire modelling.
Biogeosciences,
13(11), 3359-3375.
Abstract:
The status and challenge of global fire modelling
Biomass burning impacts vegetation dynamics, biogeochemical cycling, atmospheric chemistry, and climate, with sometimes deleterious socio-economic impacts. Under future climate projections it is often expected that the risk of wildfires will increase. Our ability to predict the magnitude and geographic pattern of future fire impacts rests on our ability to model fire regimes, using either well-founded empirical relationships or process-based models with good predictive skill. While a large variety of models exist today, it is still unclear which type of model or degree of complexity is required to model fire adequately at regional to global scales. This is the central question underpinning the creation of the Fire Model Intercomparison Project (FireMIP), an international initiative to compare and evaluate existing global fire models against benchmark data sets for present-day and historical conditions. In this paper we review how fires have been represented in fire-enabled dynamic global vegetation models (DGVMs) and give an overview of the current state of the art in fire-regime modelling. We indicate which challenges still remain in global fire modelling and stress the need for a comprehensive model evaluation and outline what lessons may be learned from FireMIP.
Abstract.
Hantson S, Arneth A, Harrison SP, Kelley DI, Prentice IC, Rabin SS, Archibald S, Mouillot F, Arnold SR, Artaxo P, et al (2016). The status and challenge of global fire modelling.
Biogeosciences Discussions,
2016Abstract:
The status and challenge of global fire modelling
Biomass burning impacts vegetation dynamics, biogeochemical cycling, atmospheric chemistry, and climate, with sometimes deleterious socio-economic impacts. Under future climate projections it is often expected that the risk of wildfires will increase. Our ability to predict the magnitude and geographic pattern of future fire impacts rests on our ability to model fire regimes, either using well-founded empirical relationships or process-based models with good predictive skill. A large variety of models exist today and it is still unclear which type of model or degree of complexity is required to model fire adequately at regional to global scales. This is the central question underpinning the creation of the Fire Model Intercomparison Project - FireMIP, an international project to compare and evaluate existing global fire models against benchmark data sets for present-day and historical conditions. In this paper we summarise the current state-of-the-art in fire regime modelling and model evaluation, and outline what lessons may be learned from FireMIP.
Abstract.
Friedlingstein P, Hanqin T, Lu C, Sitch S, Ciais P, Michalak A, Canadell J, Saikawa E, Huntzinger D, Gurney K, et al (2016). The terrestrial biosphere as a net source of greenhouse gases to the atmosphere.
Nature,
531(0028-0836), 225-228.
Abstract:
The terrestrial biosphere as a net source of greenhouse gases to the atmosphere
The terrestrial biosphere can release or absorb the greenhouse gases
carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O),
and therefore has an important role in regulating atmospheric
composition and climate1. Anthropogenic activities such as landuse
change and agricultural and waste management have altered
terrestrial biogenic greenhouse gas fluxes, and the resulting
increases in methane and nitrous oxide emissions in particular can
contribute to climate warming2,3. The terrestrial biogenic fluxes of
individual greenhouse gases have been studied extensively4–6, but
the net biogenic greenhouse gas balance as a result of anthropogenic
activities and its effect on the climate system remains uncertain.
Here we use bottom-up (inventory, statistical extrapolation of local
flux measurements, and process-based modelling) and top-down
(atmospheric inversions) approaches to quantify the global net
biogenic greenhouse gas balance between 1981 and 2010 as a result
of anthropogenic activities and its effect on the climate system. We
find that the cumulative warming capacity of concurrent biogenic
methane and nitrous oxide emissions is a factor of about two larger
than the cooling effect resulting from the global land carbon dioxide
uptake from 2001 to 2010. This results in a net positive cumulative
impact of the three greenhouse gases on the planetary energy
budget, with a best estimate (in petagrams of CO2 equivalent per
year) of 3.9 ± 3.8 (top down) and 5.4 ± 4.8 (bottom up) based on
the GWP100 metric (global warming potential on a 100-year time
horizon). Our findings suggest that a reduction in agricultural
methane and nitrous oxide emissions in particular in Southern Asia
may help mitigate climate change.
Abstract.
Cervarich M, Shu S, Jain AK, Arneth A, Canadell J, Friedlingstein P, Houghton RA, Kato E, Koven C, Patra P, et al (2016). The terrestrial carbon budget of South and Southeast Asia.
Environmental Research Letters,
11(10).
Abstract:
The terrestrial carbon budget of South and Southeast Asia
Accomplishing the objective of the current climate policies will require establishing carbon budget and flux estimates in each region and county of the globe by comparing and reconciling multiple estimates including the observations and the results of top-down atmospheric carbon dioxide (CO2) inversions and bottom-up dynamic global vegetation models. With this in view, this study synthesizes the carbon source/sink due to net ecosystem productivity (NEP), land cover land use change (E LUC), fires and fossil burning (E FIRE) for the South Asia (SA), Southeast Asia (SEA) and South and Southeast Asia (SSEA = SA + SEA) and each country in these regions using the multiple top-down and bottom-up modeling results. The terrestrial net biome productivity (NBP = NEP - E LUC - E FIRE) calculated based on bottom-up models in combination with E FIRE based on GFED4s data show net carbon sinks of 217 ±147, 10 ±55, and 227 ±279 TgC yr-1 for SA, SEA, and SSEA. The top-down models estimated NBP net carbon sinks were 20 ±170, 4 ±90 and 24 ±180 TgC yr-1. In comparison, regional emissions from the combustion of fossil fuels were 495, 275, and 770 TgC yr-1, which are many times higher than the NBP sink estimates, suggesting that the contribution of the fossil fuel emissions to the carbon budget of SSEA results in a significant net carbon source during the 2000s. When considering both NBP and fossil fuel emissions for the individual countries within the regions, Bhutan and Laos were net carbon sinks and rest of the countries were net carbon source during the 2000s. The relative contributions of each of the fluxes (NBP, NEP, E LUC, and E FIRE, fossil fuel emissions) to a nation's net carbon flux varied greatly from country to country, suggesting a heterogeneous dominant carbon fluxes on the country-level throughout SSEA.
Abstract.
Peng S, Ciais P, Chevallier F, Peylin P, Cadule P, Sitch S, Piao S, Ahlström A, Huntingford C, Levy P, et al (2015). Benchmarking the seasonal cycle of CO<inf>2</inf> fluxes simulated by terrestrial ecosystem models.
Global Biogeochemical CyclesAbstract:
Benchmarking the seasonal cycle of CO2 fluxes simulated by terrestrial ecosystem models
©2014. American Geophysical Union. All Rights Reserved. We evaluated the seasonality of CO 2. fluxes simulated by nine terrestrial ecosystem models of the TRENDY project against (1) the seasonal cycle of gross primary production (GPP) and net ecosystem exchange (NEE) measured at flux tower sites over different biomes, (2) gridded monthly Model Tree Ensembles-estimated GPP (MTE-GPP) and MTE-NEE obtained by interpolating many flux tower measurements with a machine-learning algorithm, (3) atmospheric CO 2. mole fraction measurements at surface sites, and (4) CO 2. total columns (X CO2 ) measurements from the Total Carbon Column Observing Network (TCCON). For comparison with atmospheric CO 2. measurements, the LMDZ4 transport model was run with time-varying CO 2. fluxes of each model as surface boundary conditions. Seven out of the nine models overestimate the seasonal amplitude of GPP and produce a too early start in spring at most flux sites. Despite their positive bias for GPP, the nine models underestimate NEE at most flux sites and in the Northern Hemisphere compared with MTE-NEE. Comparison with surface atmospheric CO 2. measurements confirms that most models underestimate the seasonal amplitude of NEE in the Northern Hemisphere (except CLM4C and SDGVM). Comparison with TCCON data also shows that the seasonal amplitude of X CO2. is underestimated by more than 10% for seven out of the nine models (except for CLM4C and SDGVM) and that the MTE-NEE product is closer to the TCCON data using LMDZ4. From CO 2. columns measured routinely at 10 TCCON sites, the constrained amplitude of NEE over the Northern Hemisphere is of 1.6±0.4 gC m -2 d -1 , which translates into a net CO 2. uptake during the carbon uptake period in the Northern Hemisphere of 7.9±2.0 PgC yr -1. Key Points: Seasonality of CO 2. fluxes from terrestrial ecosystem models is evaluatedMost models overestimate the seasonal amplitude of GPPGrowing season net uptake is 7.9±2.0 Pg C yr -1. for the northern Hemisphere
Abstract.
Peng S, Ciais P, Chevallier F, Peylin P, Cadule P, Sitch S, Piao S, Ahlström A, Huntingford C, Levy P, et al (2015). Benchmarking the seasonal cycle of CO<inf>2</inf> fluxes simulated by terrestrial ecosystem models.
Global Biogeochemical Cycles,
29(1), 46-64.
Abstract:
Benchmarking the seasonal cycle of CO2 fluxes simulated by terrestrial ecosystem models
© 2014. American Geophysical Union. All Rights Reserved. We evaluated the seasonality of CO 2. fluxes simulated by nine terrestrial ecosystem models of the TRENDY project against (1) the seasonal cycle of gross primary production (GPP) and net ecosystem exchange (NEE) measured at flux tower sites over different biomes, (2) gridded monthly Model Tree Ensembles-estimated GPP (MTE-GPP) and MTE-NEE obtained by interpolating many flux tower measurements with a machine-learning algorithm, (3) atmospheric CO 2. mole fraction measurements at surface sites, and (4) CO 2. total columns (X CO2 ) measurements from the Total Carbon Column Observing Network (TCCON). For comparison with atmospheric CO 2. measurements, the LMDZ4 transport model was run with time-varying CO 2. fluxes of each model as surface boundary conditions. Seven out of the nine models overestimate the seasonal amplitude of GPP and produce a too early start in spring at most flux sites. Despite their positive bias for GPP, the nine models underestimate NEE at most flux sites and in the Northern Hemisphere compared with MTE-NEE. Comparison with surface atmospheric CO 2. measurements confirms that most models underestimate the seasonal amplitude of NEE in the Northern Hemisphere (except CLM4C and SDGVM). Comparison with TCCON data also shows that the seasonal amplitude of X CO2. is underestimated by more than 10% for seven out of the nine models (except for CLM4C and SDGVM) and that the MTE-NEE product is closer to the TCCON data using LMDZ4. From CO 2. columns measured routinely at 10 TCCON sites, the constrained amplitude of NEE over the Northern Hemisphere is of 1.6 ± 0.4 gC m -2. d -1 , which translates into a net CO 2. uptake during the carbon uptake period in the Northern Hemisphere of 7.9 ± 2.0 PgC yr -1.
Abstract.
Pacifico F, Folberth GA, Sitch S, Haywood JM, Rizzo LV, Malavelle FF, Artaxo P (2015). Biomass burning related ozone damage on vegetation over the Amazon forest: a model sensitivity study.
Atmospheric Chemistry and Physics,
15(5), 2791-2804.
Abstract:
Biomass burning related ozone damage on vegetation over the Amazon forest: a model sensitivity study
The HadGEM2 earth system climate model was used to assess the impact of biomass burning on surface ozone concentrations over the Amazon forest and its impact on vegetation, under present-day climate conditions. Here we consider biomass burning emissions from wildfires, deforestation fires, agricultural forest burning, and residential and commercial combustion. Simulated surface ozone concentration is evaluated against observations taken at two sites in the Brazilian Amazon forest for years 2010 to 2012. The model is able to reproduce the observed diurnal cycle of surface ozone mixing ratio at the two sites, but overestimates the magnitude of the monthly averaged hourly measurements by 5-15 ppb for each available month at one of the sites. We vary biomass burning emissions over South America by ±20, 40, 60, 80 and 100% to quantify the modelled impact of biomass burning on surface ozone concentrations and ozone damage on vegetation productivity over the Amazon forest. We used the ozone damage scheme in the "high" sensitivity mode to give an upper limit for this effect. Decreasing South American biomass burning emissions by 100% (i.e. to zero) reduces surface ozone concentrations (by about 15 ppb during the biomass burning season) and suggests a 15% increase in monthly mean net primary productivity averaged over the Amazon forest, with local increases up to 60%. The simulated impact of ozone damage from present-day biomass burning on vegetation productivity is about 230 TgC yr-1. Taking into account that uncertainty in these estimates is substantial, this ozone damage impact over the Amazon forest is of the same order of magnitude as the release of carbon dioxide due to fire in South America; in effect it potentially doubles the impact of biomass burning on the carbon cycle.
Abstract.
De Costa WAJM, Tortarolo GM, Harper A, Sitch S (2015). Capacity for Carbon Sequestration and Climate Change Mitigation in Different Ecologically-Distinct Zones of Sri Lanka. Proceedings of International Forestry and Environment Symposium, 20(0).
Ahlström A, Raupach MR, Schurgers G, Smith B, Arneth A, Jung M, Reichstein M, Canadell JG, Friedlingstein P, Jain AK, et al (2015). Carbon cycle. The dominant role of semi-arid ecosystems in the trend and variability of the land CO₂ sink.
Science,
348(6237), 895-899.
Abstract:
Carbon cycle. The dominant role of semi-arid ecosystems in the trend and variability of the land CO₂ sink.
The growth rate of atmospheric carbon dioxide (CO2) concentrations since industrialization is characterized by large interannual variability, mostly resulting from variability in CO2 uptake by terrestrial ecosystems (typically termed carbon sink). However, the contributions of regional ecosystems to that variability are not well known. Using an ensemble of ecosystem and land-surface models and an empirical observation-based product of global gross primary production, we show that the mean sink, trend, and interannual variability in CO2 uptake by terrestrial ecosystems are dominated by distinct biogeographic regions. Whereas the mean sink is dominated by highly productive lands (mainly tropical forests), the trend and interannual variability of the sink are dominated by semi-arid ecosystems whose carbon balance is strongly associated with circulation-driven variations in both precipitation and temperature.
Abstract.
Author URL.
Huntingford C, Smith DM, Davies WJ, Falk R, Sitch S, Mercado LM (2015). Combining the [ABA] and net photosynthesis-based model equations of stomatal conductance.
Ecological Modelling,
300, 81-88.
Abstract:
Combining the [ABA] and net photosynthesis-based model equations of stomatal conductance
Stomatal conductance gs is variously depicted as being dependent on environmental conditions (Jarvis, 976), transpiration (Monteith, 1995), net photosynthesis (Leuning, 1995) or chemical signalling arriving in the xylem (Tardieu and Davies, 1993). Accurate descriptions of gs are being increasingly demanded in the large-scale land surface model components of General Circulation Models (GCMs) to predict future land-atmospheric fluxes of water vapour, heat and carbon dioxide. The JULES model, for instance, uses the net photosynthesis description combined with a relatively simple semi-linear dependence on soil moisture content that modulates the photosynthesis dependence (Cox et al. 1998).Dewar (2002) combines the Leuning (1995) and Tardieu and Davies (1993) models. We revisit that combination, and discuss whether the Vapour Pressure Deficit (VPD) implicit in both components is different or in common. Further, we show a potential re-arrangement of the combined equations reveals that this model for gs can be considered as being dependent on only four variables: evaporative flux Jw, net photosynthesis an, soil moisture content θ and ambient CO2 concentration ca. Expressed this way, gs is influenced by two relatively slowly varying stores of the hydrological and carbon cycles (soil water content and atmospheric CO2) and two more rapidly fluctuating fluxes from both cycles (evaporation and net photosynthesis). We consider how the modelling structure and its response to both canopy-level and soil environmental controls may make it suitable for inclusion in GCMs, and what this entails in terms of parameterisation.
Abstract.
Le Quéré C, Moriarty R, Andrew RM, Canadell JG, Sitch S, Korsbakken JI, Friedlingstein P, Peters GP, Andres RJ, Boden TA, et al (2015). Global Carbon Budget 2015.
Earth System Science Data,
7(2), 349-396.
Abstract:
Global Carbon Budget 2015
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates as well as consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuels and industry (EFF) are based on energy statistics and cement production data, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2, and land-cover change (some including nitrogen-carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2005-2014), EFF was 9.0 ± 0.5 GtC yrg'1, ELUC was 0.9 ± 0.5 GtC yrg'1, GATM was 4.4 ± 0.1 GtC yrg'1, SOCEAN was 2.6 ± 0.5 GtC yrg'1, and SLAND was 3.0 ± 0.8 GtC yrg'1. For the year 2014 alone, EFF grew to 9.8 ± 0.5 GtC yrg'1, 0.6 % above 2013, continuing the growth trend in these emissions, albeit at a slower rate compared to the average growth of 2.2 % yrg'1 that took place during 2005-2014. Also, for 2014, ELUC was 1.1 ± 0.5 GtC yrg'1, GATM was 3.9 ± 0.2 GtC yrg'1, SOCEAN was 2.9 ± 0.5 GtC yrg'1, and SLAND was 4.1 ± 0.9 GtC yrg'1. GATM was lower in 2014 compared to the past decade (2005-2014), reflecting a larger SLAND for that year. The global atmospheric CO2 concentration reached 397.15 ± 0.10 ppm averaged over 2014. For 2015, preliminary data indicate that the growth in EFF will be near or slightly below zero, with a projection of g'0.6 [range of g'1.6 to +0.5] %, based on national emissions projections for China and the USA, and projections of gross domestic product corrected for recent changes in the carbon intensity of the global economy for the rest of the world. From this projection of EFF and assumed constant ELUC for 2015, cumulative emissions of CO2 will reach about 555 ± 55 GtC (2035 ± 205 GtCO2) for 1870-2015, about 75 % from EFF and 25 % from ELUC. This living data update documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this data set (Le Quéré et al. 2015, 2014, 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP-2015).
Abstract.
Le Quéré C, Moriarty R, Andrew RM, Peters GP, Ciais P, Friedlingstein P, Jones SD, Sitch S, Tans P, Arneth A, et al (2015). Global carbon budget 2014.
Earth System Science Data,
7(1), 47-85.
Abstract:
Global carbon budget 2014
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics, and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics and cement production data, respectively, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover-change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2, and land-cover-change (some including nitrogen-carbon interactions). We compare the mean land and ocean fluxes and their variability to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004-2013) EFF was 8.9 ± 0.4 GtC yr-1, ELUC 0.9 ± 0.5 GtC yr-1, GATM 4.3 ± 0.1 GtC yr-1, SOCEAN 2.6 ± 0.5 GtC yr-1, and SLAND 2.9 ± 0.8 GtC yr-1. For year 2013 alone, EFF grew to 9.9 ± 0.5 GtC yr-1, 2.3% above 2012, continuing the growth trend in these emissions, ELUC was 0.9 ± 0.5 GtC yr-1, GATM was 5.4 ± 0.2 GtC yr-1, SOCEAN was 2.9 ± 0.5 GtC yr-1, and SLAND was 2.5 ± 0.9 GtC yr-1. GATM was high in 2013, reflecting a steady increase in EFF and smaller and opposite changes between SOCEAN and SLAND compared to the past decade (2004-2013). The global atmospheric CO2 concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that EFF will increase by 2.5% (1.3-3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO2 yr-1), 65% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the global economy. From this projection of EFF and assumed constant ELUC for 2014, cumulative emissions of CO2 will reach about 545 ± 55 GtC (2000 ± 200 GtCO2) for 1870-2014, about 75% from EFF and 25% from ELUC. This paper documents changes in the methods and data sets used in this new carbon budget compared with previous publications of this living data set (Le Quéré et al. 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP-2014).
Abstract.
Atkin OK, Bloomfield KJ, Reich PB, Tjoelker MG, Asner GP, Bonal D, Bönisch G, Bradford MG, Cernusak LA, Cosio EG, et al (2015). Global variability in leaf respiration in relation to climate, plant functional types and leaf traits.
New Phytologist,
206(2), 614-636.
Abstract:
Global variability in leaf respiration in relation to climate, plant functional types and leaf traits
Summary: Leaf dark respiration (R dark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of R dark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in R dark. Area-based R dark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, R dark at a standard T (25°C, R dark25 ) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher R dark25 at a given photosynthetic capacity (V cmax25 ) or leaf nitrogen concentration ([N]) than species at warmer sites. R dark25 values at any given V cmax25 or [N] were higher in herbs than in woody plants. The results highlight variation in R dark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of R dark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).
Abstract.
Atkin OK, Bloomfield KJ, Reich PB, Tjoelker MG, Asner GP, Bonal D, Bönisch G, Bradford MG, Cernusak LA, Cosio EG, et al (2015). Global variability in leaf respiration in relation to climate, plant functional types and leaf traits.
New Phytol,
206(2), 614-636.
Abstract:
Global variability in leaf respiration in relation to climate, plant functional types and leaf traits.
Leaf dark respiration (Rdark ) is an important yet poorly quantified component of the global carbon cycle. Given this, we analyzed a new global database of Rdark and associated leaf traits. Data for 899 species were compiled from 100 sites (from the Arctic to the tropics). Several woody and nonwoody plant functional types (PFTs) were represented. Mixed-effects models were used to disentangle sources of variation in Rdark. Area-based Rdark at the prevailing average daily growth temperature (T) of each site increased only twofold from the Arctic to the tropics, despite a 20°C increase in growing T (8-28°C). By contrast, Rdark at a standard T (25°C, Rdark (25) ) was threefold higher in the Arctic than in the tropics, and twofold higher at arid than at mesic sites. Species and PFTs at cold sites exhibited higher Rdark (25) at a given photosynthetic capacity (Vcmax (25) ) or leaf nitrogen concentration ([N]) than species at warmer sites. Rdark (25) values at any given Vcmax (25) or [N] were higher in herbs than in woody plants. The results highlight variation in Rdark among species and across global gradients in T and aridity. In addition to their ecological significance, the results provide a framework for improving representation of Rdark in terrestrial biosphere models (TBMs) and associated land-surface components of Earth system models (ESMs).
Abstract.
Author URL.
Yang H, Piao S, Zeng Z, Ciais P, Yin Y, Friedlingstein P, Sitch S, Ahlström A, Guimberteau M, Huntingford C, et al (2015). Multicriteria evaluation of discharge simulation in Dynamic Global Vegetation Models.
Journal of Geophysical Research,
120(15), 7488-7505.
Abstract:
Multicriteria evaluation of discharge simulation in Dynamic Global Vegetation Models
In this study, we assessed the performance of discharge simulations by coupling the runoff from seven Dynamic Global Vegetation Models (DGVMs; LPJ, ORCHIDEE, Sheffield-DGVM, TRIFFID, LPJ-GUESS, CLM4CN, and OCN) to one river routing model for 16 large river basins. The results show that the seasonal cycle of river discharge is generally modeled well in the low and middle latitudes but not in the high latitudes, where the peak discharge (due to snow and ice melting) is underestimated. For the annual mean discharge, the DGVMs chained with the routing model show an underestimation. Furthermore, the 30 year trend of discharge is also underestimated. For the interannual variability of discharge, a skill score based on overlapping of probability density functions (PDFs) suggests that most models correctly reproduce the observed variability (correlation coefficient higher than 0.5; i.e. models account for 50% of observed interannual variability) except for the Lena, Yenisei, Yukon, and the Congo river basins. In addition, we compared the simulated runoff from different simulations where models were forced with either fixed or varying land use. This suggests that both seasonal and annual mean runoff has been little affected by land use change but that the trend itself of runoff is sensitive to land use change. None of the models when considered individually show significantly better performances than any other and in all basins. This suggests that based on current modeling capability, a regional-weighted average of multimodel ensemble projections might be appropriate to reduce the bias in future projection of global river discharge.
Abstract.
Sitch S, Friedlingstein P, Gruber N, Jones SD, Murray-Tortarolo G, Ahlström A, Doney SC, Graven H, Heinze C, Huntingford C, et al (2015). Recent trends and drivers of regional sources and sinks of carbon dioxide.
Biogeosciences,
12(3), 653-679.
Abstract:
Recent trends and drivers of regional sources and sinks of carbon dioxide
The land and ocean absorb on average just over half of the anthropogenic emissions of carbon dioxide (CO2) every year. These CO2 "sinks" are modulated by climate change and variability. Here we use a suite of nine dynamic global vegetation models (DGVMs) and four ocean biogeochemical general circulation models (OBGCMs) to estimate trends driven by global and regional climate and atmospheric CO2 in land and oceanic CO2 exchanges with the atmosphere over the period 1990-2009, to attribute these trends to underlying processes in the models, and to quantify the uncertainty and level of inter-model agreement. The models were forced with reconstructed climate fields and observed global atmospheric CO2; land use and land cover changes are not included for the DGVMs. Over the period 1990-2009, the DGVMs simulate a mean global land carbon sink of g'2.4 ± 0.7 Pg C yrg'1 with a small significant trend of g'0.06 ± 0.03 Pg C yrg'2 (increasing sink). Over the more limited period 1990-2004, the ocean models simulate a mean ocean sink of g'2.2 ± 0.2 Pg C yrg'1 with a trend in the net C uptake that is indistinguishable from zero (g'0.01 ± 0.02 Pg C yrg'2). The two ocean models that extended the simulations until 2009 suggest a slightly stronger, but still small, trend of g'0.02 ± 0.01 Pg C yrg'2. Trends from land and ocean models compare favourably to the land greenness trends from remote sensing, atmospheric inversion results, and the residual land sink required to close the global carbon budget. Trends in the land sink are driven by increasing net primary production (NPP), whose statistically significant trend of 0.22 ± 0.08 Pg C yrg'2 exceeds a significant trend in heterotrophic respiration of 0.16 ± 0.05 Pg C yrg'2 - primarily as a consequence of widespread CO2 fertilisation of plant production. Most of the land-based trend in simulated net carbon uptake originates from natural ecosystems in the tropics (g'0.04 ± 0.01 Pg C yrg'2), with almost no trend over the northern land region, where recent warming and reduced rainfall offsets the positive impact of elevated atmospheric CO2 and changes in growing season length on carbon storage. The small uptake trend in the ocean models emerges because climate variability and change, and in particular increasing sea surface temperatures, tend to counter\-act the trend in ocean uptake driven by the increase in atmospheric CO2. Large uncertainty remains in the magnitude and sign of modelled carbon trends in several regions, as well as regarding the influence of land use and land cover changes on regional trends.
Abstract.
Osborne JM, Lambert FH, Groenendijk M, Harper AB, Koven CD, Poulter B, Pugh TAM, Sitch S, Stocker BD, Wiltshire A, et al (2015). Reconciling Precipitation with Runoff: Observed Hydrological Change in the Midlatitudes.
Journal of Hydrometeorology,
16(6), 2403-2420.
Abstract:
Reconciling Precipitation with Runoff: Observed Hydrological Change in the Midlatitudes
Abstract
. Century-long observed gridded land precipitation datasets are a cornerstone of hydrometeorological research. But recent work has suggested that observed Northern Hemisphere midlatitude (NHML) land mean precipitation does not show evidence of an expected negative response to mid-twentieth-century aerosol forcing. Utilizing observed river discharges, the observed runoff is calculated and compared with observed land precipitation. The results show a near-zero twentieth-century trend in observed NHML land mean runoff, in contrast to the significant positive trend in observed NHML land mean precipitation. However, precipitation and runoff share common interannual and decadal variability. An obvious split, or breakpoint, is found in the NHML land mean runoff–precipitation relationship in the 1930s. Using runoff simulated by six land surface models (LSMs), which are driven by the observed precipitation dataset, such breakpoints are absent. These findings support previous hypotheses that inhomogeneities exist in the early-twentieth-century NHML land mean precipitation record. Adjusting the observed precipitation record according to the observed runoff record largely accounts for the departure of the observed precipitation response from that predicted given the real-world aerosol forcing estimate, more than halving the discrepancy from about 6 to around 2 W m−2. Consideration of complementary observed runoff adds support to the suggestion that NHML-wide early-twentieth-century precipitation observations are unsuitable for climate change studies. The agreement between precipitation and runoff over Europe, however, is excellent, supporting the use of whole-twentieth-century observed precipitation datasets here.
Abstract.
Anav A, Friedlingstein P, Beer C, Ciais P, Harper A, Jones C, Murray-Tortarolo G, Papale D, Parazoo NC, Peylin P, et al (2015). Spatiotemporal patterns of terrestrial gross primary production: a review.
Reviews of GeophysicsAbstract:
Spatiotemporal patterns of terrestrial gross primary production: a review
Great advances have been made in the last decade in quantifying and understanding the spatiotemporal patterns of terrestrial gross primary production (GPP) with ground, atmospheric, and space observations. However, although global GPP estimates exist, each data set relies upon assumptions and none of the available data are based only on measurements. Consequently, there is no consensus on the global total GPP and large uncertainties exist in its benchmarking. The objective of this review is to assess how the different available data sets predict the spatiotemporal patterns of GPP, identify the differences among data sets, and highlight the main advantages/disadvantages of each data set. We compare GPP estimates for the historical period (1990-2009) from two observation-based data sets (Model Tree Ensemble and Moderate Resolution Imaging Spectroradiometer) to coupled carbon-climate models and terrestrial carbon cycle models from the Fifth Climate Model Intercomparison Project and TRENDY projects and to a new hybrid data set (CARBONES). Results show a large range in the mean global GPP estimates. The different data sets broadly agree on GPP seasonal cycle in terms of phasing, while there is still discrepancy on the amplitude. For interannual variability (IAV) and trends, there is a clear separation between the observation-based data that show little IAV and trend, while the process-based models have large GPP variability and significant trends. These results suggest that there is an urgent need to improve observation-based data sets and develop carbon cycle modeling with processes that are currently treated either very simplistically to correctly estimate present GPP and better quantify the future uptake of carbon dioxide by the world's vegetation.
Abstract.
Murray-Tortarolo G, Friedlingstein P, Sitch S, Jaramillo VJ, Murguía-Flores F, Anav A, Liu Y, Arneth A, Arvanitis A, Harper A, et al (2015). The carbon cycle in Mexico: past, present and future of C. stocks and fluxes.
Abstract:
The carbon cycle in Mexico: past, present and future of C. stocks and fluxes
Abstract. We modelled the carbon (C) cycle in Mexico with a process-based approach. We used different available products (satellite data, field measurements, models and flux towers) to estimate C stocks and fluxes in the country at three different time frames: present (defined as the period 2000–2005), the past century (1901–2000) and the remainder of this century (2010–2100). Our estimate of the gross primary productivity (GPP) for the country was 2137 ± 1023 Tg C yr−1 and a total C stock of 34 506 ± 7483 Tg C, with 20 347 ± 4622 Pg C in vegetation and 14 159 ± 3861 in the soil. Contrary to other current estimates for recent decades, our results showed that Mexico was a C sink over the period 1990–2009 (+31 Tg C yr−1) and that C accumulation over the last century amounted to 1210 ± 1040 Tg C. We attributed this sink to the CO2 fertilization effect on GPP, which led to an increase of 3408 ± 1060 Tg C, while both climate and land use reduced the country C stocks by −458 ± 1001 and −1740 ± 878 Tg C, respectively. Under different future scenarios the C sink will likely continue over 21st century, with decreasing C uptake as the climate forcing becomes more extreme. Our work provides valuable insights on relevant driving processes of the C-cycle such as the role of drought in marginal lands (e.g. grasslands and shrublands) and the impact of climate change on the mean residence time of C in tropical ecosystems.
.
Abstract.
Frank DC, Poulter B, Saurer M, Esper J, Huntingford C, Helle G, Treydte K, Zimmermann NE, Schleser GH, Ahlström A, et al (2015). Water-use efficiency and transpiration across European forests during the Anthropocene.
Nature Climate Change,
5(6), 579-583.
Abstract:
Water-use efficiency and transpiration across European forests during the Anthropocene
The Earth's carbon and hydrologic cycles are intimately coupled by gas exchange through plant stomata. However, uncertainties in the magnitude and consequences of the physiological responses of plants to elevated CO 2 in natural environments hinders modelling of terrestrial water cycling and carbon storage. Here we use annually resolved long-term δ 13 C tree-ring measurements across a European forest network to reconstruct the physiologically driven response of intercellular CO 2 (C i) caused by atmospheric CO 2 (C a) trends. When removing meteorological signals from the δ 13 C measurements, we find that trees across Europe regulated gas exchange so that for one ppmv atmospheric CO 2 increase, C i increased by ∼0.76 ppmv, most consistent with moderate control towards a constant C i /C a ratio. This response corresponds to twentieth-century intrinsic water-use efficiency (iWUE) increases of 14 ± 10 and 22 ± 6% at broadleaf and coniferous sites, respectively. An ensemble of process-based global vegetation models shows similar CO 2 effects on iWUE trends. Yet, when operating these models with climate drivers reintroduced, despite decreased stomatal opening, 5% increases in European forest transpiration are calculated over the twentieth century. This counterintuitive result arises from lengthened growing seasons, enhanced evaporative demand in a warming climate, and increased leaf area, which together oppose effects of CO 2 -induced stomatal closure. Our study questions changes to the hydrological cycle, such as reductions in transpiration and air humidity, hypothesized to result from plant responses to anthropogenic emissions.
Abstract.
Valentini R, Arneth A, Bombelli A, Castaldi S, Cazzolla Gatti R, Chevallier F, Ciais P, Grieco E, Hartmann J, Henry M, et al (2014). A full greenhouse gases budget of africa: Synthesis, uncertainties, and vulnerabilities.
Biogeosciences,
11(2), 381-407.
Abstract:
A full greenhouse gases budget of africa: Synthesis, uncertainties, and vulnerabilities
This paper, developed under the framework of the RECCAP initiative, aims at providing improved estimates of the carbon and GHG (CO2, CH4 and N2O) balance of continental Africa. The various components and processes of the African carbon and GHG budget are considered, existing data reviewed, and new data from different methodologies (inventories, ecosystem flux measurements, models, and atmospheric inversions) presented. Uncertainties are quantified and current gaps and weaknesses in knowledge and monitoring systems described in order to guide future requirements. The majority of results agree that Africa is a small sink of carbon on an annual scale, with an average value of -0.61 ± 0.58 Pg C yr-1. Nevertheless, the emissions of CH4 and N2O may turn Africa into a net source of radiative forcing in CO2 equivalent terms. At sub-regional level, there is significant spatial variability in both sources and sinks, due to the diversity of biomes represented and differences in the degree of anthropic impacts. Southern Africa is the main source region; while central Africa, with its evergreen tropical forests, is the main sink. Emissions from land-use change in Africa are significant (around 0.32 ± 0.05 Pg C yr-1), even higher than the fossil fuel emissions: this is a unique feature among all the continents. There could be significant carbon losses from forest land even without deforestation, resulting from the impact of selective logging. Fires play a significant role in the African carbon cycle, with 1.03 ± 0.22 Pg C yr-1 of carbon emissions, and 90% originating in savannas and dry woodlands. A large portion of the wild fire emissions are compensated by CO2 uptake during the growing season, but an uncertain fraction of the emission from wood harvested for domestic use is not. Most of these fluxes have large interannual variability, on the order of ±0.5 Pg C yr-1 in standard deviation, accounting for around 25% of the year-to-year variation in the global carbon budget. Despite the high uncertainty, the estimates provided in this paper show the important role that Africa plays in the global carbon cycle, both in terms of absolute contribution, and as a key source of interannual variability. © Author(s) 2014. CC Attribution 3.0 License.
Abstract.
Fyllas NM, Gloor E, Mercado LM, Sitch S, Quesada CA, Domingues TF, Galbraith DR, Torre-Lezama A, Vilanova E, Ramírez-Angulo H, et al (2014). Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1).
Abstract:
Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)
Abstract. Repeated long-term censuses have revealed large-scale spatial patterns in Amazon Basin forest structure and dynamism, with some forests in the west of the Basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the Basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR) has been developed. The model incorporates variations in tree size distribution, functional traits and soil physical properties and runs at the stand level with four functional traits, leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) used to represent a continuum of plant strategies found in tropical forests. We first applied the model to validate canopy-level water fluxes at three Amazon eddy flux sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for large trees. At the stand-level, simulations at 40 plots were used to explore the influence of climate and soil fertility on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. However all three measures of stand level productivity were positively related to annual precipitation and soil fertility.
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Abstract.
Fyllas NM, Gloor E, Mercado LM, Sitch S, Quesada CA, Domingues TF, Galbraith DR, Torre-Lezama A, Vilanova E, Ramírez-Angulo H, et al (2014). Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1).
Geoscientific Model Development,
7(4), 1251-1269.
Abstract:
Analysing Amazonian forest productivity using a new individual and trait-based model (TFS v.1)
Repeated long-term censuses have revealed large-scale spatial patterns in Amazon basin forest structure and dynamism, with some forests in the west of the basin having up to a twice as high rate of aboveground biomass production and tree recruitment as forests in the east. Possible causes for this variation could be the climatic and edaphic gradients across the basin and/or the spatial distribution of tree species composition. To help understand causes of this variation a new individual-based model of tropical forest growth, designed to take full advantage of the forest census data available from the Amazonian Forest Inventory Network (RAINFOR), has been developed. The model allows for within-stand variations in tree size distribution and key functional traits and between-stand differences in climate and soil physical and chemical properties. It runs at the stand level with four functional traits - leaf dry mass per area (Ma), leaf nitrogen (NL) and phosphorus (PL) content and wood density (DW) varying from tree to tree - in a way that replicates the observed continua found within each stand. We first applied the model to validate canopy-level water fluxes at three eddy covariance flux measurement sites. For all three sites the canopy-level water fluxes were adequately simulated. We then applied the model at seven plots, where intensive measurements of carbon allocation are available. Tree-by-tree multi-annual growth rates generally agreed well with observations for small trees, but with deviations identified for larger trees. At the stand level, simulations at 40 plots were used to explore the influence of climate and soil nutrient availability on the gross (ΠG) and net (ΠN) primary production rates as well as the carbon use efficiency (CU). Simulated ΠG, ΠN and CU were not associated with temperature. On the other hand, all three measures of stand level productivity were positively related to both mean annual precipitation and soil nutrient status. Sensitivity studies showed a clear importance of an accurate parameterisation of within- and between-stand trait variability on the fidelity of model predictions. For example, when functional tree diversity was not included in the model (i.e. with just a single plant functional type with mean basin-wide trait values) the predictive ability of the model was reduced. This was also the case when basin-wide (as opposed to site-specific) trait distributions were applied within each stand. We conclude that models of tropical forest carbon, energy and water cycling should strive to accurately represent observed variations in functionally important traits across the range of relevant scales. © Author(s) 2014.
Abstract.
Poulter B, Frank D, Ciais P, Myneni RB, Andela N, Bi J, Broquet G, Canadell JG, Chevallier F, Liu YY, et al (2014). Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle.
Nature,
509(7502), 600-603.
Abstract:
Contribution of semi-arid ecosystems to interannual variability of the global carbon cycle.
The land and ocean act as a sink for fossil-fuel emissions, thereby slowing the rise of atmospheric carbon dioxide concentrations. Although the uptake of carbon by oceanic and terrestrial processes has kept pace with accelerating carbon dioxide emissions until now, atmospheric carbon dioxide concentrations exhibit a large variability on interannual timescales, considered to be driven primarily by terrestrial ecosystem processes dominated by tropical rainforests. We use a terrestrial biogeochemical model, atmospheric carbon dioxide inversion and global carbon budget accounting methods to investigate the evolution of the terrestrial carbon sink over the past 30 years, with a focus on the underlying mechanisms responsible for the exceptionally large land carbon sink reported in 2011 (ref. 2). Here we show that our three terrestrial carbon sink estimates are in good agreement and support the finding of a 2011 record land carbon sink. Surprisingly, we find that the global carbon sink anomaly was driven by growth of semi-arid vegetation in the Southern Hemisphere, with almost 60 per cent of carbon uptake attributed to Australian ecosystems, where prevalent La Niña conditions caused up to six consecutive seasons of increased precipitation. In addition, since 1981, a six per cent expansion of vegetation cover over Australia was associated with a fourfold increase in the sensitivity of continental net carbon uptake to precipitation. Our findings suggest that the higher turnover rates of carbon pools in semi-arid biomes are an increasingly important driver of global carbon cycle inter-annual variability and that tropical rainforests may become less relevant drivers in the future. More research is needed to identify to what extent the carbon stocks accumulated during wet years are vulnerable to rapid decomposition or loss through fire in subsequent years.
Abstract.
Author URL.
Piao S, Nan H, Huntingford C, Ciais P, Friedlingstein P, Sitch S, Peng S, Ahlström A, Canadell JG, Cong N, et al (2014). Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity.
Nat Commun,
5Abstract:
Evidence for a weakening relationship between interannual temperature variability and northern vegetation activity.
Satellite-derived Normalized Difference Vegetation Index (NDVI), a proxy of vegetation productivity, is known to be correlated with temperature in northern ecosystems. This relationship, however, may change over time following alternations in other environmental factors. Here we show that above 30°N, the strength of the relationship between the interannual variability of growing season NDVI and temperature (partial correlation coefficient RNDVI-GT) declined substantially between 1982 and 2011. This decrease in RNDVI-GT is mainly observed in temperate and arctic ecosystems, and is also partly reproduced by process-based ecosystem model results. In the temperate ecosystem, the decrease in RNDVI-GT coincides with an increase in drought. In the arctic ecosystem, it may be related to a nonlinear response of photosynthesis to temperature, increase of hot extreme days and shrub expansion over grass-dominated tundra. Our results caution the use of results from interannual time scales to constrain the decadal response of plants to ongoing warming.
Abstract.
Author URL.
Le Quéré C, Peters GP, Andres RJ, Andrew RM, Boden TA, Ciais P, Friedlingstein P, Houghton RA, Marland G, Moriarty R, et al (2014). Global carbon budget 2013.
Earth System Science Data,
6(1), 235-263.
Abstract:
Global carbon budget 2013
Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe data sets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil-fuel combustion and cement production (EFF) are based on energy statistics, while emissions from land-use change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (G ATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated for the first time in this budget with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent dynamic global vegetation models forced by observed climate, CO2 and land cover change (some including nitrogen-carbon interactions). All uncertainties are reported as ±1σ , reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2003-2012), EFF was 8.6±0.4 GtC yr-1, ELUC 0.9±0.5 GtC yr-1, GATM 4.3±0.1 GtC yr-1, SOCEAN 2.5±0.5 GtC yr -1, and SLAND 2.8±0.8 GtC yr-1. For year 2012 alone, EFF grew to 9.7±0.5 GtC yr-1, 2.2% above 2011, reflecting a continued growing trend in these emissions, G ATM was 5.1±0.2 GtC yr-1, SOCEAN was 2.9±0.5 GtC yr-1, and assuming an ELUC of 1.0±0.5 GtC yr-1 (based on the 2001-2010 average), S LAND was 2.7±0.9 GtC yr-1. GATM was high in 2012 compared to the 2003-2012 average, almost entirely reflecting the high EFF. The global atmospheric CO2 concentration reached 392.52±0.10 ppm averaged over 2012. We estimate that EFF will increase by 2.1% (1.1- 3.1 %) to 9.9±0.5 GtC in 2013, 61% above emissions in 1990, based on projections of world gross domestic product and recent changes in the carbon intensity of the economy.With this projection, cumulative emissions ofCO2 will reach about 535±55 GtC for 1870-2013, about 70% from EFF (390±20 GtC) and 30% from ELUC (145±50 GtC). This paper also documents any changes in the methods and data sets used in this new carbon budget from previous budgets (Le Quéré et al. 2013). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP-2013-V2.3). © 2014 Author(s) CC Attribution 3.0 License.
Abstract.
Le Quéré C, Moriarty R, Andrew RM, Peters GP, Ciais P, Friedlingstein P, Jones SD, Sitch S, Tans P, Arneth A, et al (2014). Global carbon budget 2014.
Abstract:
Global carbon budget 2014
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe datasets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates, consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics and cement production data, respectively, while emissions from Land-Use Change (ELUC), mainly deforestation, are based on combined evidence from land-cover change data, fire activity associated with deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of independent Dynamic Global Vegetation Models forced by observed climate, CO2 and land cover change (some including nitrogen-carbon interactions). We compare the variability and mean land and ocean fluxes to estimates from three atmospheric inverse methods for three broad latitude bands. All uncertainties are reported as ±1σ, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2004–2013), EFF was 8.9 ± 0.4 GtC yr−1, ELUC 0.9 ± 0.5 GtC yr−1, GATM 4.3 ± 0.1 GtC yr−1, SOCEAN 2.6 ± 0.5 GtC yr−1, and SLAND 2.9 ± 0.8 GtC yr−1. For year 2013 alone, EFF grew to 9.9 ± 0.5 GtC yr−1, 2.3% above 2012, contining the growth trend in these emissions. ELUC was 0.9 ± 0.5 GtC yr−1, GATM was 5.4 ± 0.2 GtC yr−1, SOCEAN was 2.9 ± 0.5 GtC yr−1 and SLAND was 2.5 ± 0.9 GtC yr−1. GATM was high in 2013 reflecting a steady increase in EFF and smaller and opposite changes between SOCEAN and SLAND compared to the past decade (2004–2013). The global atmospheric CO2 concentration reached 395.31 ± 0.10 ppm averaged over 2013. We estimate that EFF will increase by 2.5% (1.3–3.5%) to 10.1 ± 0.6 GtC in 2014 (37.0 ± 2.2 GtCO2 yr−1), 65% above emissions in 1990, based on projections of World Gross Domestic Product and recent changes in the carbon intensity of the economy. From this projection of EFF and assumed constant ELUC for 2014, cumulative emissions of CO2 will reach about 545 ± 55 GtC (2000 ± 200 GtCO2) for 1870–2014, about 75% from EFF and 25% from ELUC. This paper documents changes in the methods and datasets used in this new carbon budget compared with previous publications of this living dataset (Le Quéré et al. 2013, 2014). All observations presented here can be downloaded from the Carbon Dioxide Information Analysis Center (doi:10.3334/CDIAC/GCP_2014). Italic font highlights significant methodological changes and results compared to the Le Quéré et al. (2014) manuscript that accompanies the previous version of this living data.
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Abstract.
Fisher JB, Huntzinger DN, Schwalm CR, Sitch S (2014). Modeling the terrestrial biosphere.
Annual Review of Environment and Resources,
39, 91-123.
Abstract:
Modeling the terrestrial biosphere
The land surface comprises the smallest areal fraction of the Earth system's major components (e.g. versus atmosphere or ocean with cryosphere). As such, how is it that some of the largest sources of uncertainty in future climate projections are found in the terrestrial biosphere? This uncertainty stems from how the terrestrial biosphere is modeled with respect to the myriad of biogeochemical, physical, and dynamic processes represented (or not) in numerous models that contribute to projections of Earth's future. Here, we provide an overview of the processes included in terrestrial biosphere models (TBMs), including various approaches to representing any one given process, as well as the processes that are missing and/or uncertain. We complement this with a comprehensive review of individual TBMs, marking the differences, uniqueness, and recent and planned developments. To conclude, we summarize the latest results in benchmarking activities, particularly as linked to recent model intercomparison projects, and outline a path forward to reducing uncertainty in the contribution of the terrestrial biosphere to global atmospheric change.
Abstract.
Fisher JB, Sikka M, Sitch S, Ciais P, Poulter B, Galbraith D, Lee JE, Huntingford C, Viovy N, Zeng N, et al (2013). African tropical rainforest net carbon dioxide fluxes in the twentieth century.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences,
368(1625).
Abstract:
African tropical rainforest net carbon dioxide fluxes in the twentieth century
The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO₂ fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (-0.02 kg C m⁻² yr⁻¹ or -0.04 Pg C yr⁻¹, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO₂ flux at the beginning of the century (σ1901 = 0.02 kg C m⁻² yr⁻¹), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m⁻² yr⁻¹). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO₂, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO₂ fluxes with increasing atmospheric CO₂ concentrations and extreme climatic events, as the uncertainties will only amplify in the next century.
Abstract.
Fisher JB, Sikka M, Sitch S, Ciais P, Poulter B, Galbraith D, Lee J-E, Huntingford C, Viovy N, Zeng N, et al (2013). African tropical rainforest net carbon dioxide fluxes in the twentieth century.
Philos Trans R Soc Lond B Biol Sci,
368(1625).
Abstract:
African tropical rainforest net carbon dioxide fluxes in the twentieth century.
The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO₂ fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (-0.02 kg C m⁻² yr⁻¹ or -0.04 Pg C yr⁻¹, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO₂ flux at the beginning of the century (σ1901 = 0.02 kg C m⁻² yr⁻¹), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m⁻² yr⁻¹). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO₂, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO₂ fluxes with increasing atmospheric CO₂ concentrations and extreme climatic events, as the uncertainties will only amplify in the next century.
Abstract.
Author URL.
Moriarty R, Buitenhuis ET, Le Quere C, Gosselin M-P (2013). Distribution of known macrozooplankton abundance and biomass in the global ocean.
EARTH SYSTEM SCIENCE DATA,
5(2), 241-257.
Author URL.
Wang W, Ciais P, Nemani RR, Canadell JG, Piao S, Sitch S, White MA, Hashimoto H, Milesi C, Myneni RB, et al (2013). Erratum: Variations in atmospheric CO2 growth rates coupled with tropical temperature (Proceedings of the National Academy of Sciences of the United States of America (2013) 110, 32 (13061-13066) DOI:10.1073/pnas.1219683110). Proceedings of the National Academy of Sciences of the United States of America, 110(37).
Anav A, Murray-Tortarolo G, Friedlingstein P, Sitch S, Piao S, Zhu Z (2013). Evaluation of land surface models in reproducing satellite derived leaf area index over the high-latitude northern hemisphere. Part II: Earth system models.
Remote Sensing,
5(8), 3637-3661.
Abstract:
Evaluation of land surface models in reproducing satellite derived leaf area index over the high-latitude northern hemisphere. Part II: Earth system models
Leaf Area Index (LAI) is a key parameter in the Earth System Models (ESMs) since it strongly affects land-surface boundary conditions and the exchange of matter and energy with the atmosphere. Observations and data products derived from satellite remote sensing are important for the validation and evaluation of ESMs from regional to global scales. Several decades' worth of satellite data products are now available at global scale which represents a unique opportunity to contrast observations against model results. The objective of this study is to assess whether ESMs correctly reproduce the spatial variability of LAI when compared with satellite data and to compare the length of the growing season in the different models with the satellite data. To achieve this goal we analyse outputs from 11 coupled carbon-climate models that are based on the set of new global model simulations planned in support of the IPCC Fifth Assessment Report. We focus on the average LAI and the length of the growing season on Northern Hemisphere over the period 1986-2005. Additionally we compare the results with previous analyses (Part I) of uncoupled land surface models (LSMs) to assess the relative contribution of vegetation and climatic drivers on the correct representation of LAI. Our results show that models tend to overestimate the average values of LAI and have a longer growing season due to the later dormancy. The similarities with the uncoupled models suggest that representing the correct vegetation fraction with the associated parameterizations; is more important in controlling the distribution and value of LAI than the climatic variables. © 2013 by the authors.
Abstract.
Murray-Tortarolo G, Anav A, Friedlingstein P, Sitch S, Piao S, Zhu Z, Poulter B, Zaehle S, Ahlström A, Lomas M, et al (2013). Evaluation of land surface models in reproducing satellite-derived LAI over the high-latitude northern hemisphere. Part I: Uncoupled DGVMs.
Remote Sensing,
5(10), 4819-4838.
Abstract:
Evaluation of land surface models in reproducing satellite-derived LAI over the high-latitude northern hemisphere. Part I: Uncoupled DGVMs
Leaf Area Index (LAI) represents the total surface area of leaves above a unit area of ground and is a key variable in any vegetation model, as well as in climate models. New high resolution LAI satellite data is now available covering a period of several decades. This provides a unique opportunity to validate LAI estimates from multiple vegetation models. The objective of this paper is to compare new, satellite-derived LAI measurements with modeled output for the Northern Hemisphere. We compare monthly LAI output from eight land surface models from the TRENDY compendium with satellite data from an Artificial Neural Network (ANN) from the latest version (third generation) of GIMMS AVHRR NDVI data over the period 1986-2005. Our results show that all the models overestimate the mean LAI, particularly over the boreal forest. We also find that seven out of the eight models overestimate the length of the active vegetation-growing season, mostly due to a late dormancy as a result of a late summer phenology. Finally, we find that the models report a much larger positive trend in LAI over this period than the satellite observations suggest, which translates into a higher trend in the growing season length. These results highlight the need to incorporate a larger number of more accurate plant functional types in all models and, in particular, to improve the phenology of deciduous trees. © 2013 by the authors.
Abstract.
Piao S, Sitch S, Ciais P, Friedlingstein P, Peylin P, Wang X, Ahlström A, Anav A, Canadell JG, Cong N, et al (2013). Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends.
Glob Chang Biol,
19(7), 2117-2132.
Abstract:
Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends.
The purpose of this study was to evaluate 10 process-based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux-tower-based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free-Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 ± 15 Pg C yr(-1) ) than JU11 (118 ± 6 Pg C yr(-1) ). In response to rising atmospheric CO2 concentration, modeled NPP increases on average by 16% (5-20%) per 100 ppm, a slightly larger apparent sensitivity of NPP to CO2 than that measured at the FACE experiment locations (13% per 100 ppm). Global NBP differs markedly among individual models, although the mean value of 2.0 ± 0.8 Pg C yr(-1) is remarkably close to the mean value of RLS (2.1 ± 1.2 Pg C yr(-1) ). The interannual variability in modeled NBP is significantly correlated with that of RLS for the period 1980-2009. Both model-to-model and interannual variation in model GPP is larger than that in model NBP due to the strong coupling causing a positive correlation between ecosystem respiration and GPP in the model. The average linear regression slope of global NBP vs. temperature across the 10 models is -3.0 ± 1.5 Pg C yr(-1) °C(-1) , within the uncertainty of what derived from RLS (-3.9 ± 1.1 Pg C yr(-1) °C(-1) ). However, 9 of 10 models overestimate the regression slope of NBP vs. precipitation, compared with the slope of the observed RLS vs. precipitation. With most models lacking processes that control GPP and NBP in addition to CO2 and climate, the agreement between modeled and observation-based GPP and NBP can be fortuitous. Carbon-nitrogen interactions (only separable in one model) significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models.
Abstract.
Author URL.
Piao S, Sitch S, Ciais P, Friedlingstein P, Peylin P, Wang X, Ahlström A, Anav A, Canadell JG, Cong N, et al (2013). Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO<inf>2</inf> trends.
Global Change Biology,
19(7), 2117-2132.
Abstract:
Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends
The purpose of this study was to evaluate 10 process-based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux-tower-based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free-Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 ± 15 Pg C yr-1) than JU11 (118 ± 6 Pg C yr-1). In response to rising atmospheric CO2 concentration, modeled NPP increases on average by 16% (5-20%) per 100 ppm, a slightly larger apparent sensitivity of NPP to CO2 than that measured at the FACE experiment locations (13% per 100 ppm). Global NBP differs markedly among individual models, although the mean value of 2.0 ± 0.8 Pg C yr-1 is remarkably close to the mean value of RLS (2.1 ± 1.2 Pg C yr-1). The interannual variability in modeled NBP is significantly correlated with that of RLS for the period 1980-2009. Both model-to-model and interannual variation in model GPP is larger than that in model NBP due to the strong coupling causing a positive correlation between ecosystem respiration and GPP in the model. The average linear regression slope of global NBP vs. temperature across the 10 models is -3.0 ± 1.5 Pg C yr-1 °C-1, within the uncertainty of what derived from RLS (-3.9 ± 1.1 Pg C yr-1 °C-1). However, 9 of 10 models overestimate the regression slope of NBP vs. precipitation, compared with the slope of the observed RLS vs. precipitation. With most models lacking processes that control GPP and NBP in addition to CO2 and climate, the agreement between modeled and observation-based GPP and NBP can be fortuitous. Carbon-nitrogen interactions (only separable in one model) significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models. © 2013 Blackwell Publishing Ltd.
Abstract.
Le Quéré C, Peters GP, Andres RJ, Andrew RM, Boden T, Ciais P, Friedlingstein P, Houghton RA, Marland G, Moriarty R, et al (2013). Global carbon budget 2013.
Abstract:
Global carbon budget 2013
Abstract. Accurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe datasets and a methodology to quantify all major components of the global carbon budget, including their uncertainties, based on the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. We discuss changes compared to previous estimates consistency within and among components, alongside methodology and data limitations. CO2 emissions from fossil-fuel combustion and cement production (EFF) are based on energy statistics, while emissions from Land-Use Change (ELUC), including deforestation, are based on combined evidence from land-cover change data, fire activity in regions undergoing deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the annual changes in concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. The variability in SOCEAN is evaluated for the first time in this budget with data products based on surveys of ocean CO2 measurements. The global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms of the global carbon budget and compared to results of Dynamic Global Vegetation Models. All uncertainties are reported as ± 1 sigma, reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. For the last decade available (2003–2012), EFF was 8.6 ± 0.4 GtC yr−1, ELUC 0.8 ± 0.5 GtC yr−1, GATM 4.3 ± 0.1 GtC yr−1, SOCEAN 2.6 ± 0.5 GtC yr−1, and SLAND 2.6 ± 0.8 GtC yr−1. For year 2012 alone, EFF grew to 9.7 ± 0.5 GtC yr−1, 2.2% above 2011, reflecting a continued trend in these emissions; GATM was 5.2 ± 0.2 GtC yr−1, SOCEAN was 2.9 ± 0.5 GtC yr−1, and assuming and ELUC of 0.9 ± 0.5 GtC yr−1 (based on 2001–2010 average), SLAND was 2.5 ± 0.9 GtC yr−1. GATM was high in 2012 compared to the 2003–2012 average, almost entirely reflecting the high EFF. The global atmospheric CO2 concentration reached 392.52 ± 0.10 ppm on average over 2012. We estimate that EFF will increase by 2.1% (1.1–3.1%) to 9.9 ± 0.5 GtC in 2013, 61% above emissions in 1990, based on projections of World Gross Domestic Product and recent changes in the carbon intensity of the economy. With this projection, cumulative emissions of CO2 will reach about 550 ± 60 GtC for 1870–2013, 70% from EFF (390 ± 20 GtC) and 30% from ELUC (160 ± 55 GtC). This paper is intended to provide a baseline to keep track of annual carbon budgets in the future. All data presented here can be downloaded from the Carbon Dioxide Information Analysis Center (10.3334/CDIAC/GCP_2013_v1.1).
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Abstract.
Huntingford C, Zelazowski P, Galbraith D, Mercado LM, Sitch S, Fisher R, Lomas M, Walker AP, Jones CD, Booth BBB, et al (2013). Simulated resilience of tropical rainforests to CO<inf>2</inf> -induced climate change.
Nature Geoscience,
6(4), 268-273.
Abstract:
Simulated resilience of tropical rainforests to CO2 -induced climate change
How tropical forest carbon stocks might alter in response to changes in climate and atmospheric composition is uncertain. However, assessing potential future carbon loss from tropical forests is important for evaluating the efficacy of programmes for reducing emissions from deforestation and degradation. Uncertainties are associated with different carbon stock responses in models with different representations of vegetation processes on the one hand, and differences in projected changes in temperature and precipitation patterns on the other hand. Here we present a systematic exploration of these sources of uncertainty, along with uncertainty arising from different emissions scenarios for all three main tropical forest regions: the Americas (that is, Amazonia and Central America), Africa and Asia. Using simulations with 22 climate models and the MOSES-TRIFFID land surface scheme, we find that only in one of the simulations are tropical forests projected to lose biomass by the end of the twenty-first century - and then only for the Americas. When comparing with alternative models of plant physiological processes, we find that the largest uncertainties are associated with plant physiological responses, and then with future emissions scenarios. Uncertainties from differences in the climate projections are significantly smaller. Despite the considerable uncertainties, we conclude that there is evidence of forest resilience for all three regions. © 2013 Macmillan Publishers Limited. All rights reserved.
Abstract.
Le Quéré C, Andres RJ, Boden T, Conway T, Houghton RA, House JI, Marland G, Peters GP, Van Der Werf GR, Ahlström A, et al (2013). The global carbon budget 1959-2011.
Earth System Science Data,
5(1), 165-185.
Abstract:
The global carbon budget 1959-2011
Accurate assessments of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere is important to better understand the global carbon cycle, support the climate policy process, and project future climate change. Present-day analysis requires the combination of a range of data, algorithms, statistics and model estimates and their interpretation by a broad scientific community. Here we describe datasets and a methodology developed by the global carbon cycle science community to quantify all major components of the global carbon budget, including their uncertainties. We discuss changes compared to previous estimates, consistency within and among components, and methodology and data limitations. CO2 emissions from fossil fuel combustion and cement production (EFF) are based on energy statistics, while emissions from Land-Use Change (ELUC), including deforestation, are based on combined evidence from land cover change data, fire activity in regions undergoing deforestation, and models. The global atmospheric CO2 concentration is measured directly and its rate of growth (GATM) is computed from the concentration. The mean ocean CO2 sink (SOCEAN) is based on observations from the 1990s, while the annual anomalies and trends are estimated with ocean models. Finally, the global residual terrestrial CO2 sink (SLAND) is estimated by the difference of the other terms. For the last decade available (2002-2011), EFF was 8.3 ± 0.4 PgC yr-1, ELUC 1.0 ± 0.5 PgC yr-1, GATM 4.3 ± 0.1PgC yr-1, SOCEAN 2.5 ± 0.5 PgC yr-1, and SLAND 2.6 ± 0.8 PgC yr-1. For year 2011 alone, EFF was 9.5 ± 0.5 PgC yr -1, 3.0 percent above 2010, reflecting a continued trend in these emissions; ELUC was 0.9 ± 0.5 PgC yr-1, approximately constant throughout the decade; GATM was 3.6 ± 0.2 PgC yr-1, SOCEAN was 2.7 ± 0.5 PgC yr-1, and SLAND was 4.1 ± 0.9 PgC yr-1. GATM was low in 2011 compared to the 2002-2011 average because of a high uptake by the land probably in response to natural climate variability associated to La Niña conditions in the Pacific Ocean. The global atmospheric CO2 concentration reached 391.31 ± 0.13 ppm at the end of year 2011. We estimate that EFF will have increased by 2.6% (1.9-3.5%) in 2012 based on projections of gross world product and recent changes in the carbon intensity of the economy. All uncertainties are reported as ±1 sigma (68% confidence assuming Gaussian error distributions that the real value lies within the given interval), reflecting the current capacity to characterise the annual estimates of each component of the global carbon budget. This paper is intended to provide a baseline to keep track of annual carbon budgets in the future. © 2013 Author(s).
Abstract.
Sitch S, Friedlingstein P, Gruber N, Jones SD, Murray-Tortarolo G, Ahlström A, Doney SC, Graven H, Heinze C, Huntingford C, et al (2013). Trends and drivers of regional sources and sinks of carbon dioxide over the past two decades.
Abstract:
Trends and drivers of regional sources and sinks of carbon dioxide over the past two decades
Abstract. The land and ocean absorb on average over half of the anthropogenic emissions of carbon dioxide (CO2) every year. These CO2 "sinks" are modulated by climate change and variability. Here we use a suite of nine Dynamic Global Vegetation Models (DGVMs) and four Ocean Biogeochemical General Circulation Models (OBGCMs) to quantify the global and regional climate and atmospheric CO2 – driven trends in land and oceanic CO2 exchanges with the atmosphere over the period 1990–2009, attribute these trends to underlying processes, and quantify the uncertainty and level of model agreement. The models were forced with reconstructed climate fields and observed global atmospheric CO2; Land Use and Land Cover Changes are not included for the DGVMs. Over the period 1990–2009, the DGVMs simulate a mean global land carbon sink of −2.4 ± 0.7 Pg C yr−1 with a small significant trend of −0.06 ± 0.03 Pg C yr−2 (increasing sink). Over the more limited period 1990–2004, the ocean models simulate a mean ocean sink of –2.2 ± 0.2 Pg C yr–1 with a trend in the net C uptake that is indistinguishable from zero (−0.01 ± 0.02 Pg C yr−2). The two ocean models that extended the simulations until 2009 suggest a slightly stronger, but still small trend of −0.02 ± 0.01 Pg C yr−2. Trends from land and ocean models compare favourably to the land greenness trends from remote sensing, atmospheric inversion results, and the residual land sink required to close the global carbon budget. Trends in the land sink are driven by increasing net primary production (NPP) whose statistically significant trend of 0.22 ± 0.08 Pg C yr−2 exceeds a significant trend in heterotrophic respiration of 0.16 ± 0.05 Pg C yr−2 – primarily as a consequence of wide-spread CO2 fertilisation of plant production. Most of the land-based trend in simulated net carbon uptake originates from natural ecosystems in the tropics (−0.04 ± 0.01 Pg C yr−2), with almost no trend over the northern land region, where recent warming and reduced rainfall offsets the positive impact of elevated atmospheric CO2 on carbon storage. The small uptake trend in the ocean models emerges because climate variability and change, and in particular increasing sea surface temperatures, tend to counteract the trend in ocean uptake driven by the increase in atmospheric CO2. Large uncertainty remains in the magnitude and sign of modelled carbon trends in several regions, and on the influence of land use and land cover changes on regional trends.
Abstract.
Wang W, Ciais P, Nemani RR, Canadell JG, Piao S, Sitch S, White MA, Hashimoto H, Milesi C, Myneni RB, et al (2013). Variations in atmospheric CO2 growth rates coupled with tropical temperature.
Proc Natl Acad Sci U S A,
110(32), 13061-13066.
Abstract:
Variations in atmospheric CO2 growth rates coupled with tropical temperature.
Previous studies have highlighted the occurrence and intensity of El Niño-Southern Oscillation as important drivers of the interannual variability of the atmospheric CO2 growth rate, but the underlying biogeophysical mechanisms governing such connections remain unclear. Here we show a strong and persistent coupling (r(2) ≈ 0.50) between interannual variations of the CO2 growth rate and tropical land-surface air temperature during 1959 to 2011, with a 1 °C tropical temperature anomaly leading to a 3.5 ± 0.6 Petagrams of carbon per year (PgC/y) CO2 growth-rate anomaly on average. Analysis of simulation results from Dynamic Global Vegetation Models suggests that this temperature-CO2 coupling is contributed mainly by the additive responses of heterotrophic respiration (Rh) and net primary production (NPP) to temperature variations in tropical ecosystems. However, we find a weaker and less consistent (r(2) ≈ 0.25) interannual coupling between CO2 growth rate and tropical land precipitation than diagnosed from the Dynamic Global Vegetation Models, likely resulting from the subtractive responses of tropical Rh and NPP to precipitation anomalies that partly offset each other in the net ecosystem exchange (i.e. net ecosystem exchange ≈ Rh - NPP). Variations in other climate variables (e.g. large-scale cloudiness) and natural disturbances (e.g. volcanic eruptions) may induce transient reductions in the temperature-CO2 coupling, but the relationship is robust during the past 50 y and shows full recovery within a few years after any such major variability event. Therefore, it provides an important diagnostic tool for improved understanding of the contemporary and future global carbon cycle.
Abstract.
Author URL.
Booth BBB, Jones CD, Collins M, Totterdell IJ, Cox PM, Sitch S, Huntingford C, Betts RA, Harris GR, Lloyd J, et al (2012). High sensitivity of future global warming to land carbon cycle processes.
Environmental Research Letters,
7(2).
Abstract:
High sensitivity of future global warming to land carbon cycle processes
Unknowns in future global warming are usually assumed to arise from uncertainties either in the amount of anthropogenic greenhouse gas emissions or in the sensitivity of the climate to changes in greenhouse gas concentrations. Characterizing the additional uncertainty in relating CO2 emissions to atmospheric concentrations has relied on either a small number of complex models with diversity in process representations, or simple models. To date, these models indicate that the relevant carbon cycle uncertainties are smaller than the uncertainties in physical climate feedbacks and emissions. Here, for a single emissions scenario, we use a full coupled climatecarbon cycle model and a systematic method to explore uncertainties in the land carbon cycle feedback. We find a plausible range of climatecarbon cycle feedbacks significantly larger than previously estimated. Indeed the range of CO2 concentrations arising from our single emissions scenario is greater than that previously estimated across the full range of IPCC SRES emissions scenarios with carbon cycle uncertainties ignored. The sensitivity of photosynthetic metabolism to temperature emerges as the most important uncertainty. This highlights an aspect of current land carbon modelling where there are open questions about the potential role of plant acclimation to increasing temperatures. There is an urgent need for better understanding of plant photosynthetic responses to high temperature, as these responses are shown here to be key contributors to the magnitude of future change. © 2012 IOP Publishing Ltd.
Abstract.
Gloor M, Gatti L, Brienen R, Feldpausch TR, Phillips OL, Miller J, Ometto JP, Rocha H, Baker T, De Jong B, et al (2012). The carbon balance of South America: a review of the status, decadal trends and main determinants.
Biogeosciences,
9(12), 5407-5430.
Abstract:
The carbon balance of South America: a review of the status, decadal trends and main determinants
We summarise the contemporary carbon budget of South America and relate it to its dominant controls: population and economic growth, changes in land use practices and a changing atmospheric environment and climate. Component flux estimate methods we consider sufficiently reliable for this purpose encompass fossil fuel emission inventories, biometric analysis of old-growth rainforests, estimation of carbon release associated with deforestation based on remote sensing and inventories, and agricultural export data. Alternative methods for the estimation of the continental-scale net land to atmosphere CO2 flux, such as atmospheric transport inverse modelling and terrestrial biosphere model predictions, are, we find, hampered by the data paucity, and improved parameterisation and validation exercises are required before reliable estimates can be obtained. From our analysis of available data, we suggest that South America was a net source to the atmosphere during the 1980s (∼ 0.3-0.4 Pg C a−1) and close to neutral (∼ 0.1 Pg C a−1) in the 1990s. During the latter period, carbon uptake in old-growth forests nearly compensated for the carbon release associated with fossil fuel burning and deforestation. Annual mean precipitation over tropical South America as inferred from Amazon River discharge shows a long-term upward trend. Although, over the last decade dry seasons have tended to be drier, with the years 2005 and 2010 in particular experiencing strong droughts. On the other hand, precipitation during the wet seasons also shows an increasing trend. Air temperatures have also increased slightly. Also with increases in atmospheric CO2 concentrations, it is currently unclear what effect these climate changes are having on the forest carbon balance of the region. Current indications are that the forests of the Amazon Basin have acted as a substantial long-term carbon sink, but with the most recent measurements suggesting that this sink may be weakening. Economic development of the tropical regions of the continent is advancing steadily, with exports of agricultural products being an important driver and witnessing a strong upturn over the last decade. © Author(s) 2012.
Abstract.
Gloor M, Gatti L, Brienen RJW, Feldpausch T, Phillips O, Miller J, Ometto J-P, Ribeiro da Rocha H, Baker T, Houghton R, et al (2012). The carbon balance of South America: status, decadal trends and main determinants.
Abstract:
The carbon balance of South America: status, decadal trends and main determinants
Abstract. We attempt to summarize the carbon budget of South America and relate it to its dominant controls: population and economic growth, changes in land use practices and a changing atmospheric environment and climate. Flux estimation methods which we consider sufficiently reliable are fossil fuel emission inventories, biometric analysis of old-growth rainforests, estimation of carbon release associated with deforestation based on remote sensing and inventories, and finally inventories of agricultural exports. Other routes to estimating land-atmosphere CO2 fluxes include atmospheric transport inverse modelling and vegetation model predictions but are hampered by the data paucity and the need for improved parameterisation. The available data we analyze suggest that South America was a net source to the atmosphere during the 1980s (∼0.3–0.4 Pg C yr−1) and close to neutral (∼0.1 Pg C yr−1) in the 1990s with carbon uptake in old-growth forests nearly compensating carbon losses due to fossil fuel burning and deforestation. Annual mean precipitation over tropical South America measured by Amazon River discharge has a long-term upward trend, although over the last decade, dry seasons have tended to be drier and longer (and thus wet seasons wetter), with the years 2005 and 2010 experiencing strong droughts. It is currently unclear what the effect of these climate changes on the old-growth forest carbon sink will be but first measurements suggest it may be weakened. Based on scaling of forest census data the net carbon balance of South America seems to have been an increased source roughly over the 2005–2010 period (a total of ∼1 Pg C of dead tree biomass released over several years) due to forest drought response. Finally, economic development of the tropical forest regions of the continent is advancing steadily with exports of agricultural products being an important driver and witnessing a strong upturn over the last decade.
Abstract.
Piao SL, Ito A, Li SG, Huang Y, Ciais P, Wang XH, Peng SS, Nan HJ, Zhao C, Ahlström A, et al (2012). The carbon budget of terrestrial ecosystems in East Asia over the last two decades.
Biogeosciences,
9(9), 3571-3586.
Abstract:
The carbon budget of terrestrial ecosystems in East Asia over the last two decades
This REgional Carbon Cycle Assessment and Processes regional study provides a synthesis of the carbon balance of terrestrial ecosystems in East Asia, a region comprised of China, Japan, North and South Korea, and Mongolia. We estimate the current terrestrial carbon balance of East Asia and its driving mechanisms during 1990-2009 using three different approaches: inventories combined with satellite greenness measurements, terrestrial ecosystem carbon cycle models and atmospheric inversion models. The magnitudes of East Asia's terrestrial carbon sink from these three approaches are comparable:-0. 293±0.033 PgC yr-1 from inventory-remote sensing model-data fusion approach,-0.413±0.141 PgC yr-1 (not considering biofuel emissions) or-0.224±0.141 PgC yr-1 (considering biofuel emissions) for carbon cycle models, and-0.270±0.507 PgC yr-1 for atmospheric inverse models. Here and in the following, the numbers behind ± signs are standard deviations. The ensemble of ecosystem modeling based analyses further suggests that at the regional scale, climate change and rising atmospheric CO2 together resulted in a carbon sink of-0.289±0.135 PgC yr-1, while land-use change and nitrogen deposition had a contribution of-0.013±0.029 PgC yr-1 and-0.107±0.025 PgC yr-1, respectively. Although the magnitude of climate change effects on the carbon balance varies among different models, all models agree that in response to climate change alone, southern China experienced an increase in carbon storage from 1990 to 2009, while northern East Asia including Mongolia and north China showed a decrease in carbon storage. Overall, our results suggest that about 13-27% of East Asia's CO2 emissions from fossil fuel burning have been offset by carbon accumulation in its terrestrial territory over the period from 1990 to 2009. The underlying mechanisms of carbon sink over East Asia still remain largely uncertain, given the diversity and intensity of land management processes, and the regional conjunction of many drivers such as nutrient deposition, climate, atmospheric pollution and CO2 changes, which cannot be considered as independent for their effects on carbon storage. © 2012 Author(s).
Abstract.
Ainsworth EA, Yendrek CR, Sitch S, Collins WJ, Emberson LD (2012). The effects of tropospheric ozone on net primary productivity and implications for climate change.
Annu Rev Plant Biol,
63, 637-661.
Abstract:
The effects of tropospheric ozone on net primary productivity and implications for climate change.
Tropospheric ozone (O(3)) is a global air pollutant that causes billions of dollars in lost plant productivity annually. It is an important anthropogenic greenhouse gas, and as a secondary air pollutant, it is present at high concentrations in rural areas far from industrial sources. It also reduces plant productivity by entering leaves through the stomata, generating other reactive oxygen species and causing oxidative stress, which in turn decreases photosynthesis, plant growth, and biomass accumulation. The deposition of O(3) into vegetation through stomata is an important sink for tropospheric O(3), but this sink is modified by other aspects of environmental change, including rising atmospheric carbon dioxide concentrations, rising temperature, altered precipitation, and nitrogen availability. We review the atmospheric chemistry governing tropospheric O(3) mass balance, the effects of O(3) on stomatal conductance and net primary productivity, and implications for agriculture, carbon sequestration, and climate change.
Abstract.
Author URL.
Jiang Y, Zhuang Q, Schaphoff S, Sitch S, Sokolov A, Kicklighter D, Melillo J (2012). Uncertainty analysis of vegetation distribution in the northern high latitudes during the 21st century with a dynamic vegetation model.
Ecol Evol,
2(3), 593-614.
Abstract:
Uncertainty analysis of vegetation distribution in the northern high latitudes during the 21st century with a dynamic vegetation model.
This study aims to assess how high-latitude vegetation may respond under various climate scenarios during the 21st century with a focus on analyzing model parameters induced uncertainty and how this uncertainty compares to the uncertainty induced by various climates. The analysis was based on a set of 10,000 Monte Carlo ensemble Lund-Potsdam-Jena (LPJ) simulations for the northern high latitudes (45(o)N and polewards) for the period 1900-2100. The LPJ Dynamic Global Vegetation Model (LPJ-DGVM) was run under contemporary and future climates from four Special Report Emission Scenarios (SRES), A1FI, A2, B1, and B2, based on the Hadley Centre General Circulation Model (GCM), and six climate scenarios, X901M, X902L, X903H, X904M, X905L, and X906H from the Integrated Global System Model (IGSM) at the Massachusetts Institute of Technology (MIT). In the current dynamic vegetation model, some parameters are more important than others in determining the vegetation distribution. Parameters that control plant carbon uptake and light-use efficiency have the predominant influence on the vegetation distribution of both woody and herbaceous plant functional types. The relative importance of different parameters varies temporally and spatially and is influenced by climate inputs. In addition to climate, these parameters play an important role in determining the vegetation distribution in the region. The parameter-based uncertainties contribute most to the total uncertainty. The current warming conditions lead to a complexity of vegetation responses in the region. Temperate trees will be more sensitive to climate variability, compared with boreal forest trees and C3 perennial grasses. This sensitivity would result in a unanimous northward greenness migration due to anomalous warming in the northern high latitudes. Temporally, boreal needleleaved evergreen plants are projected to decline considerably, and a large portion of C3 perennial grass is projected to disappear by the end of the 21st century. In contrast, the area of temperate trees would increase, especially under the most extreme A1FI scenario. As the warming continues, the northward greenness expansion in the Arctic region could continue.
Abstract.
Author URL.
Blyth E, Clark DB, Ellis R, Huntingford C, Los S, Pryor M, Best M, Sitch S (2011). A comprehensive set of benchmark tests for a land surface model of simultaneous fluxes of water and carbon at both the global and seasonal scale.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(2), 255-269.
Author URL.
Pan Y, Birdsey RA, Fang J, Houghton R, Kauppi PE, Kurz WA, Phillips OL, Shvidenko A, Lewis SL, Canadell JG, et al (2011). A large and persistent carbon sink in the world's forests.
Science,
333(6045), 988-993.
Abstract:
A large and persistent carbon sink in the world's forests.
The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year(-1)) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year(-1) from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year(-1) partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year(-1). Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year(-1), with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.
Abstract.
Author URL.
Good P, Caesar J, Bernie D, Lowe JA, van der Linden P, Gosling SN, Warren R, Arnell NW, Smith S, Bamber J, et al (2011). A review of recent developments in climate change science. Part I: Understanding of future change in the large-scale climate system.
Progress in Physical Geography,
35(3), 281-296.
Abstract:
A review of recent developments in climate change science. Part I: Understanding of future change in the large-scale climate system
This article reviews some of the major lines of recent scientific progress relevant to the choice of global climate policy targets, focusing on changes in understanding since publication of the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). Developments are highlighted in the following major climate system components: ice sheets; sea ice; the Atlantic Meridional Overturning Circulation; tropical forests; and accelerated carbon release from permafrost and ocean hydrates. The most significant developments in each component are identified by synthesizing input from multiple experts from each field. Overall, while large uncertainties remain in all fields, some substantial progress in understanding is revealed. © the Author(s) 2011.
Abstract.
Zelazowski P, Malhi Y, Huntingford C, Sitch S, Fisher JB (2011). Changes in the potential distribution of humid tropical forests on a warmer planet.
Philos Trans a Math Phys Eng Sci,
369(1934), 137-160.
Abstract:
Changes in the potential distribution of humid tropical forests on a warmer planet.
The future of tropical forests has become one of the iconic issues in climate-change science. A number of studies that have explored this subject have tended to focus on the output from one or a few climate models, which work at low spatial resolution, whereas society and conservation-relevant assessment of potential impacts requires a finer scale. This study focuses on the role of climate on the current and future distribution of humid tropical forests (HTFs). We first characterize their contemporary climatological niche using annual rainfall and maximum climatological water stress, which also adequately describe the current distribution of other biomes within the tropics. As a first-order approximation of the potential extent of HTFs in future climate regimes defined by global warming of 2°C and 4°C, we investigate changes in the niche through a combination of climate-change anomaly patterns and higher resolution (5 km) maps of current climatology. The climate anomalies are derived using data from 17 coupled Atmosphere-Ocean General Circulation Models (AOGCMs) used in the Fourth Assessment of the Intergovernmental Panel for Climate Change. Our results confirm some risk of forest retreat, especially in eastern Amazonia, Central America and parts of Africa, but also indicate a potential for expansion in other regions, for example around the Congo Basin. The finer spatial scale enabled the depiction of potential resilient and vulnerable zones with practically useful detail. We further refine these estimates by considering the impact of new environmental regimes on plant water demand using the UK Met Office land-surface scheme (of the HadCM3 AOGCM). The CO(2)-related reduction in plant water demand lowers the risk of die-back and can lead to possible niche expansion in many regions. The analysis presented here focuses primarily on hydrological determinants of HTF extent. We conclude by discussing the role of other factors, notably the physiological effects of higher temperature.
Abstract.
Author URL.
Collins WJ, Bellouin N, Doutriaux-Boucher M, Gedney N, Halloran P, Hinton T, Hughes J, Jones CD, Joshi M, Liddicoat S, et al (2011). Development and evaluation of an Earth-System model-HadGEM2.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(4), 1051-1075.
Author URL.
Van der Molen MK, Dolman AJ, Ciais P, Eglin T, Gobron N, Law BE, Meir P, Peters W, Phillips OL, Reichstein M, et al (2011). Drought and ecosystem carbon cycling.
Agricultural and Forest Meteorology,
151(7), 765-773.
Abstract:
Drought and ecosystem carbon cycling
Drought as an intermittent disturbance of the water cycle interacts with the carbon cycle differently than the 'gradual' climate change. During drought plants respond physiologically and structurally to prevent excessive water loss according to species-specific water use strategies. This has consequences for carbon uptake by photosynthesis and release by total ecosystem respiration. After a drought the disturbances in the reservoirs of moisture, organic matter and nutrients in the soil and carbohydrates in plants lead to longer-term effects in plant carbon cycling, and potentially mortality. Direct and carry-over effects, mortality and consequently species competition in response to drought are strongly related to the survival strategies of species. Here we review the state of the art of the understanding of the relation between soil moisture drought and the interactions with the carbon cycle of the terrestrial ecosystems. We argue that plant strategies must be given an adequate role in global vegetation models if the effects of drought on the carbon cycle are to be described in a way that justifies the interacting processes. © 2011 Elsevier B.V.
Abstract.
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patiño S (2011). Erratum: Modelling basin-wide variations in Amazon forest productivity &ndash; Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis" published in Biogeosciences, 6, 1247&ndash;1272, 2009 (Biogeosciences). Biogeosciences, 8(3), 653-656.
Pacifico F, Harrison SP, Jones CD, Arneth A, Sitch S, Weedon GP, Barkley MP, Palmer PI, Serça D, Potosnak M, et al (2011). Evaluation of a photosynthesis-based biogenic isoprene emission scheme in JULES and simulation of isoprene emissions under present-day climate conditions.
Atmospheric Chemistry and Physics,
11(9), 4371-4389.
Abstract:
Evaluation of a photosynthesis-based biogenic isoprene emission scheme in JULES and simulation of isoprene emissions under present-day climate conditions
We have incorporated a semi-mechanistic isoprene emission module into the JULES land-surface scheme, as a first step towards a modelling tool that can be applied for studies of vegetation-atmospheric chemistry interactions, including chemistry-climate feedbacks. Here, we evaluate the coupled model against local above-canopy isoprene emission flux measurements from six flux tower sites as well as satellite-derived estimates of isoprene emission over tropical South America and east and south Asia. The model simulates diurnal variability well: correlation coefficients are significant (at the 95 % level) for all flux tower sites. The model reproduces day-to-day variability with significant correlations (at the 95 % confidence level) at four of the six flux tower sites. At the UMBS site, a complete set of seasonal observations is available for two years (2000 and 2002). The model reproduces the seasonal pattern of emission during 2002, but does less well in the year 2000. The model overestimates observed emissions at all sites, which is partially because it does not include isoprene loss through the canopy. Comparison with the satellite-derived isoprene-emission estimates suggests that the model simulates the main spatial patterns, seasonal and inter-annual variability over tropical regions. The model yields a global annual isoprene emission of 535 ± 9 TgC yr-1 during the 1990s, 78 % of which from forested areas. © 2011 Author(s).
Abstract.
Huntingford C, Cox PM, Mercado LM, Sitch S, Bellouin N, Boucher O, Gedney N (2011). Highly contrasting effects of different climate forcing agents on terrestrial ecosystem services.
Philos Trans a Math Phys Eng Sci,
369(1943), 2026-2037.
Abstract:
Highly contrasting effects of different climate forcing agents on terrestrial ecosystem services.
Many atmospheric constituents besides carbon dioxide (CO(2)) contribute to global warming, and it is common to compare their influence on climate in terms of radiative forcing, which measures their impact on the planetary energy budget. A number of recent studies have shown that many radiatively active constituents also have important impacts on the physiological functioning of ecosystems, and thus the 'ecosystem services' that humankind relies upon. CO(2) increases have most probably increased river runoff and had generally positive impacts on plant growth where nutrients are non-limiting, whereas increases in near-surface ozone (O(3)) are very detrimental to plant productivity. Atmospheric aerosols increase the fraction of surface diffuse light, which is beneficial for plant growth. To illustrate these differences, we present the impact on net primary productivity and runoff of higher CO(2), higher near-surface O(3), and lower sulphate aerosols, and for equivalent changes in radiative forcing. We compare this with the impact of climate change alone, arising, for example, from a physiologically inactive gas such as methane (CH(4)). For equivalent levels of change in radiative forcing, we show that the combined climate and physiological impacts of these individual agents vary markedly and in some cases actually differ in sign. This study highlights the need to develop more informative metrics of the impact of changing atmospheric constituents that go beyond simple radiative forcing.
Abstract.
Author URL.
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patino S (2011). Modelling basin-wide variations in Amazon forest productivity - Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis (vol 6, pg 1247, 2009).
BIOGEOSCIENCES,
8(3), 653-656.
Author URL.
Best MJ, Pryor M, Clark DB, Rooney GG, Essery RLH, Menard CB, Edwards JM, Hendry MA, Porson A, Gedney N, et al (2011). The Joint UK Land Environment Simulator (JULES), model description - Part 1: Energy and water fluxes.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(3), 677-699.
Author URL.
Clark DB, Mercado LM, Sitch S, Jones CD, Gedney N, Best MJ, Pryor M, Rooney GG, Essery RLH, Blyth E, et al (2011). The Joint UK Land Environment Simulator (JULES), model description - Part 2: Carbon fluxes and vegetation dynamics.
GEOSCIENTIFIC MODEL DEVELOPMENT,
4(3), 701-722.
Author URL.
Mercado LM, Patiño S, Domingues TF, Fyllas NM, Weedon GP, Sitch S, Quesada CA, Phillips OL, Aragão LEOC, Malhi Y, et al (2011). Variations in Amazon forest productivity correlated with foliar nutrients and modelled rates of photosynthetic carbon supply.
Philos Trans R Soc Lond B Biol Sci,
366(1582), 3316-3329.
Abstract:
Variations in Amazon forest productivity correlated with foliar nutrients and modelled rates of photosynthetic carbon supply.
The rate of above-ground woody biomass production, W(P), in some western Amazon forests exceeds those in the east by a factor of 2 or more. Underlying causes may include climate, soil nutrient limitations and species composition. In this modelling paper, we explore the implications of allowing key nutrients such as N and P to constrain the photosynthesis of Amazon forests, and also we examine the relationship between modelled rates of photosynthesis and the observed gradients in W(P). We use a model with current understanding of the underpinning biochemical processes as affected by nutrient availability to assess: (i) the degree to which observed spatial variations in foliar [N] and [P] across Amazonia affect stand-level photosynthesis; and (ii) how these variations in forest photosynthetic carbon acquisition relate to the observed geographical patterns of stem growth across the Amazon Basin. We find nutrient availability to exert a strong effect on photosynthetic carbon gain across the Basin and to be a likely important contributor to the observed gradient in W(P). Phosphorus emerges as more important than nitrogen in accounting for the observed variations in productivity. Implications of these findings are discussed in the context of future tropical forests under a changing climate.
Abstract.
Author URL.
Fisher R, McDowell N, Purves D, Moorcroft P, Sitch S, Cox P, Huntingford C, Meir P, Woodward FI (2010). Assessing uncertainties in a second-generation dynamic vegetation model caused by ecological scale limitations.
New Phytol,
187(3), 666-681.
Abstract:
Assessing uncertainties in a second-generation dynamic vegetation model caused by ecological scale limitations.
*Second-generation Dynamic Global Vegetation Models (DGVMs) have recently been developed that explicitly represent the ecological dynamics of disturbance, vertical competition for light, and succession. Here, we introduce a modified second-generation DGVM and examine how the representation of demographic processes operating at two-dimensional spatial scales not represented by these models can influence predicted community structure, and responses of ecosystems to climate change. The key demographic processes we investigated were seed advection, seed mixing, sapling survival, competitive exclusion and plant mortality. We varied these parameters in the context of a simulated Amazon rainforest ecosystem containing seven plant functional types (PFTs) that varied along a trade-off surface between growth and the risk of starvation induced mortality. Varying the five unconstrained parameters generated community structures ranging from monocultures to equal co-dominance of the seven PFTs. When exposed to a climate change scenario, the competing impacts of CO(2) fertilization and increasing plant mortality caused ecosystem biomass to diverge substantially between simulations, with mid-21st century biomass predictions ranging from 1.5 to 27.0 kg C m(-2). Filtering the results using contemporary observation ranges of biomass, leaf area index (LAI), gross primary productivity (GPP) and net primary productivity (NPP) did not substantially constrain the potential outcomes. We conclude that demographic processes represent a large source of uncertainty in DGVM predictions.
Abstract.
Author URL.
Cadule P, Friedlingstein P, Bopp L, Sitch S, Jones CD, Ciais P, Piao SL, Peylin P (2010). Benchmarking coupled climate-carbon models against long-term atmospheric CO<inf>2</inf> measurements.
Global Biogeochemical Cycles,
24(2).
Abstract:
Benchmarking coupled climate-carbon models against long-term atmospheric CO2 measurements
We evaluated three global models of the coupled carbon.climate system against atmospheric CO2 concentration measured at a network of stations. These three models, HadCM3LC, IPSL.CM2.C, and IPSL.CM4.LOOP, participated in the C4MIP experiment and in various other simulations of the future climate impacts on the land and ocean carbon cycle. A new set of performance metrics is defined and applied to quantify each model's ability to reproduce the global growth rate, the seasonal cycle, the El Niño. Southern Oscillation (ENSO)-forced interannual variability of atmospheric CO2, and the sensitivity to climatic variations. Knowing that the uncertainty on the amplitude, in 2100, of the climate.carbon feedback is mainly due to the uncertainty of the response of the terrestrial biosphere to the climate change, our new metrics primarily target the evaluation of the land parameterization of the carbon cycle. The modeled fluxes are prescribed to the same global atmospheric transport model LMDZ4, and the simulated concentrations are compared to available observations. We found that the IPSL.CM4. LOOP model is best able to reproduce the phase and amplitude of the atmospheric CO 2 seasonal cycle in the Northern Hemisphere, while the other two models generally underestimate the seasonal amplitude. This points to some shortcomings in describing the vegetation phenology and heterotropic respiration response to climate. We also found that IPSL.CM2.C produces a climate.driven abnormal source of CO2 to the atmosphere in response to El Nino anomalies. Here a good model performance rests upon a realistic simulation of ENSO.type climate variability and the subsequent tropical carbon cycle response. The three climate models underestimate the sea surface temperature warm anomaly during an El Nino, but HadCM3LC does best in reproducing the interannual CO2 variability. More efforts are needed to further develop metrics for assessing the sensitivity of the carbon cycle to climate change, and this work should now be extended to assess ocean carbon models against observations. Copyright 2010 by the American Geophysical Union.
Abstract.
Fisher JB, Sitch S, Malhi Y, Fisher RA, Huntingford C, Tan S-Y (2010). Carbon cost of plant nitrogen acquisition: a mechanistic, globally applicable model of plant nitrogen uptake, retranslocation, and fixation.
GLOBAL BIOGEOCHEMICAL CYCLES,
24 Author URL.
Pacifico F, Harrison SP, Jones CD, Arneth A, Sitch S, Weedon GP, Barkley MP, Palmer PI, Serça D, Potosnak M, et al (2010). Evaluation of a photosynthesis-based biogenic isoprene emission scheme in JULES and simulation of isoprene emissions under modern climate conditions. Atmospheric Chemistry and Physics Discussions, 10(11), 28311-28354.
Arneth A, Sitch S, Bondeau A, Butterbach-Bahl K, Foster P, Gedney N, De Noblet-Ducoudré N, Prentice IC, Sanderson M, Thonicke K, et al (2010). From biota to chemistry and climate: Towards a comprehensive description of trace gas exchange between the biosphere and atmosphere.
Biogeosciences,
7(1), 121-149.
Abstract:
From biota to chemistry and climate: Towards a comprehensive description of trace gas exchange between the biosphere and atmosphere
Exchange of non-CO2 trace gases between the land surface and the atmosphere plays an important role in atmospheric chemistry and climate. Recent studies have highlighted its importance for interpretation of glacial-interglacial ice-core records, the simulation of the pre-industrial and present atmosphere, and the potential for large climate-chemistry and climate-aerosol feedbacks in the coming century. However, spatial and temporal variations in trace gas emissions and the magnitude of future feedbacks are a major source of uncertainty in atmospheric chemistry, air quality and climate science. To reduce such uncertainties Dynamic Global Vegetation Models (DGVMs) are currently being expanded to mechanistically represent processes relevant to non-CO2 trace gas exchange between land biota and the atmosphere. In this paper we present a review of important non-CO2 trace gas emissions, the state-of-the-art in DGVM modelling of processes regulating these emissions, identify key uncertainties for global scale model applications, and discuss a methodology for model integration and evaluation.
Abstract.
Collins WJ, Sitch S, Boucher O (2010). How vegetation impacts affect climate metrics for ozone precursors.
Journal of Geophysical Research Atmospheres,
115(23).
Abstract:
How vegetation impacts affect climate metrics for ozone precursors
We examine the effect of ozone damage to vegetation as caused by anthropogenic emissions of ozone precursor species and quantify it in terms of its impact on terrestrial carbon stores. A simple climate model is then used to assess the expected changes in global surface temperature from the resulting perturbations to atmospheric concentrations of carbon dioxide, methane, and ozone. The concept of global temperature change potential (GTP) metric, which relates the global average surface temperature change induced by the pulse emission of a species to that induced by a unit mass of carbon dioxide, is used to characterize the impact of changes in emissions of ozone precursors on surface temperature as a function of time. For NOx emissions, the longer-timescale methane perturbation is of the opposite sign to the perturbations in ozone and carbon dioxide, so NOx emissions are warming in the short term, but cooling in the long term. For volatile organic compound (VOC), CO, and methane emissions, all the terms are warming for an increase in emissions. The GTPs for the 20 year time horizon are strong functions of emission location, with a large component of the variability owing to the different vegetation responses on different continents. At this time horizon, the induced change in the carbon cycle is the largest single contributor to the GTP metric for NOx and VOC emissions. For NO x emissions, we estimate a GTP20 of -9 (cooling) to +24 (warming) depending on assumptions of the sensitivity of vegetation types to ozone damage.
Abstract.
Huntingford C, Booth BBB, Sitch S, Gedney N, Lowe JA, Liddicoat SK, Mercado LM, Best MJ, Weedon GP, Fisher RA, et al (2010). IMOGEN: an intermediate complexity model to evaluate terrestrial impacts of a changing climate.
GEOSCIENTIFIC MODEL DEVELOPMENT,
3(2), 679-687.
Author URL.
Doherty RM, Sitch S, Smith B, Lewis SL, Thornton PK (2010). Implications of future climate and atmospheric CO<inf>2</inf> content for regional biogeochemistry, biogeography and ecosystem services across East Africa.
Global Change Biology,
16(2), 617-640.
Abstract:
Implications of future climate and atmospheric CO2 content for regional biogeochemistry, biogeography and ecosystem services across East Africa
We model future changes in land biogeochemistry and biogeography across East Africa. East Africa is one of few tropical regions where general circulation model (GCM) future climate projections exhibit a robust response of strong future warming and general annual-mean rainfall increases. Eighteen future climate projections from nine GCMs participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment were used as input to the LPJ dynamic global vegetation model (DGVM), which predicted vegetation patterns and carbon storage in agreement with satellite observations and forest inventory data under the present-day climate. All simulations showed future increases in tropical woody vegetation over the region at the expense of grasslands. Regional increases in net primary productivity (NPP) (18-36%) and total carbon storage (3-13%) by 2080-2099 compared with the present-day were common to all simulations. Despite decreases in soil carbon after 2050, seven out of nine simulations continued to show an annual net land carbon sink in the final decades of the 21st century because vegetation biomass continued to increase. The seasonal cycles of rainfall and soil moisture show future increases in wet season rainfall across the GCMs with generally little change in dry season rainfall. Based on the simulated present-day climate and its future trends, the GCMs can be grouped into four broad categories. Overall, our model results suggest that East Africa, a populous and economically poor region, is likely to experience some ecosystem service benefits through increased precipitation, river runoff and fresh water availability. Resulting enhancements in NPP may lead to improved crop yields in some areas. Our results stand in partial contradiction to other studies that suggest possible negative consequences for agriculture, biodiversity and other ecosystem services caused by temperature increases. © 2009 Blackwell Publishing Ltd.
Abstract.
Galbraith D, Levy PE, Sitch S, Huntingford C, Cox P, Williams M, Meir P (2010). Multiple mechanisms of Amazonian forest biomass losses in three dynamic global vegetation models under climate change.
New Phytol,
187(3), 647-665.
Abstract:
Multiple mechanisms of Amazonian forest biomass losses in three dynamic global vegetation models under climate change.
*The large-scale loss of Amazonian rainforest under some future climate scenarios has generally been considered to be driven by increased drying over Amazonia predicted by some general circulation models (GCMs). However, the importance of rainfall relative to other drivers has never been formally examined. Here, we conducted factorial simulations to ascertain the contributions of four environmental drivers (precipitation, temperature, humidity and CO(2)) to simulated changes in Amazonian vegetation carbon (C(veg)), in three dynamic global vegetation models (DGVMs) forced with climate data based on HadCM3 for four SRES scenarios. Increased temperature was found to be more important than precipitation reduction in causing losses of Amazonian C(veg) in two DGVMs (Hyland and TRIFFID), and as important as precipitation reduction in a third DGVM (LPJ). Increases in plant respiration, direct declines in photosynthesis and increases in vapour pressure deficit (VPD) all contributed to reduce C(veg) under high temperature, but the contribution of each mechanism varied greatly across models. Rising CO(2) mitigated much of the climate-driven biomass losses in the models. Additional work is required to constrain model behaviour with experimental data under conditions of high temperature and drought. Current models may be overly sensitive to long-term elevated temperatures as they do not account for physiological acclimation.
Abstract.
Author URL.
Poulter B, Hattermann F, Hawkins E, Zaehle S, Sitch S, Restrepo-Coupe N, Heyder U, Cramer W (2010). Robust dynamics of Amazon dieback to climate change with perturbed ecosystem model parameters.
Global Change Biology,
16(9), 2476-2495.
Abstract:
Robust dynamics of Amazon dieback to climate change with perturbed ecosystem model parameters
Climate change science is increasingly concerned with methods for managing and integrating sources of uncertainty from emission storylines, climate model projections, and ecosystem model parameterizations. In tropical ecosystems, regional climate projections and modeled ecosystem responses vary greatly, leading to a significant source of uncertainty in global biogeochemical accounting and possible future climate feedbacks. Here, we combine an ensemble of IPCC-AR4 climate change projections for the Amazon Basin (eight general circulation models) with alternative ecosystem parameter sets for the dynamic global vegetation model, LPJmL. We evaluate LPJmL simulations of carbon stocks and fluxes against flux tower and aboveground biomass datasets for individual sites and the entire basin. Variability in LPJmL model sensitivity to future climate change is primarily related to light and water limitations through biochemical and water-balance-related parameters. Temperature-dependent parameters related to plant respiration and photosynthesis appear to be less important than vegetation dynamics (and their parameters) for determining the magnitude of ecosystem response to climate change. Variance partitioning approaches reveal that relationships between uncertainty from ecosystem dynamics and climate projections are dependent on geographic location and the targeted ecosystem process. Parameter uncertainty from the LPJmL model does not affect the trajectory of ecosystem response for a given climate change scenario and the primary source of uncertainty for Amazon 'dieback' results from the uncertainty among climate projections. Our approach for describing uncertainty is applicable for informing and prioritizing policy options related to mitigation and adaptation where long-term investments are required. © 2010 Blackwell Publishing Ltd.
Abstract.
Friedlingstein P, Cadule P, Piao SL, Ciais P, Sitch S (2010). The African contribution to the global climate-carbon cycle feedback of the 21st century.
Biogeosciences,
7(2), 513-519.
Abstract:
The African contribution to the global climate-carbon cycle feedback of the 21st century
Future climate change will have impact on global and regional terrestrial carbon balances. The fate of African tropical forests over the 21st century has been investigated through global coupled climate carbon cycle model simulations. Under the SRES-A2 socio-economic CO2 emission scenario of the IPCC, and using the Institut Pierre Simon Laplace coupled ocean-terrestrial carbon cycle and climate model, IPSL-CM4-LOOP, we found that the warming over African ecosystems induces a reduction of net ecosystem productivity, making a 38% contribution to the global climate-carbon cycle positive feedback. Most of this contribution comes from African grasslands, followed by African savannahs, African tropical forest contributing little to the global climate-carbon feedback. However, the vulnerability of the African rainforest ecosystem is quite large. In contrast, the Amazon forest, despite its lower vulnerability, has a much larger overall contribution due to its 6 times larger extent.
Abstract.
Lewis SL, Lloyd J, Sitch S, Mitchard ETA, Laurance WF (2009). Changing ecology of tropical forests: Evidence and drivers.
Annual Review of Ecology, Evolution, and Systematics,
40, 529-549.
Abstract:
Changing ecology of tropical forests: Evidence and drivers
Global environmental changes may be altering the ecology of tropical forests. Long-term monitoring plots have provided much of the evidence for large-scale, directional changes in tropical forests, but the results have been controversial. Here we review evidence from six complementary approaches to understanding possible changes: plant physiology experiments, long-term monitoring plots, ecosystem flux techniques, atmospheric measurements, Earth observations, and global-scale vegetation models. Evidence from four of these approaches suggests that large-scale, directional changes are occurring in the ecology of tropical forests, with the other two approaches providing inconclusive results. Collectively, the evidence indicates that both gross and net primary productivity has likely increased over recent decades, as have tree growth, recruitment, and mortality rates, and forest biomass. These results suggest a profound reorganization of tropical forest ecosystems. We evaluate the most likely drivers of the suite of changes, and suggest increasing resource availability, potentially from rising atmospheric CO2 concentrations, is the most likely cause. Copyright © 2009 by Annual Reviews. All rights reserved.
Abstract.
Malhi Y, Aragão LEOC, Galbraith D, Huntingford C, Fisher R, Zelazowski P, Sitch S, McSweeney C, Meir P (2009). Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest.
Proc Natl Acad Sci U S A,
106(49), 20610-20615.
Abstract:
Exploring the likelihood and mechanism of a climate-change-induced dieback of the Amazon rainforest.
We examine the evidence for the possibility that 21st-century climate change may cause a large-scale "dieback" or degradation of Amazonian rainforest. We employ a new framework for evaluating the rainfall regime of tropical forests and from this deduce precipitation-based boundaries for current forest viability. We then examine climate simulations by 19 global climate models (GCMs) in this context and find that most tend to underestimate current rainfall. GCMs also vary greatly in their projections of future climate change in Amazonia. We attempt to take into account the differences between GCM-simulated and observed rainfall regimes in the 20th century. Our analysis suggests that dry-season water stress is likely to increase in E. Amazonia over the 21st century, but the region tends toward a climate more appropriate to seasonal forest than to savanna. These seasonal forests may be resilient to seasonal drought but are likely to face intensified water stress caused by higher temperatures and to be vulnerable to fires, which are at present naturally rare in much of Amazonia. The spread of fire ignition associated with advancing deforestation, logging, and fragmentation may act as nucleation points that trigger the transition of these seasonal forests into fire-dominated, low biomass forests. Conversely, deliberate limitation of deforestation and fire may be an effective intervention to maintain Amazonian forest resilience in the face of imposed 21st-century climate change. Such intervention may be enough to navigate E. Amazonia away from a possible "tipping point," beyond which extensive rainforest would become unsustainable.
Abstract.
Author URL.
Mercado LM, Bellouin N, Sitch S, Boucher O, Huntingford C, Wild M, Cox PM (2009). Impact of changes in diffuse radiation on the global land carbon sink.
Nature,
458(7241), 1014-1017.
Abstract:
Impact of changes in diffuse radiation on the global land carbon sink.
Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions. Changes in cloud cover or atmospheric aerosol loadings, arising from either volcanic or anthropogenic emissions, alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse, with uncertain overall effects on global plant productivity and the land carbon sink. Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. We estimate that variations in diffuse fraction, associated largely with the 'global dimming' period, enhanced the land carbon sink by approximately one-quarter between 1960 and 1999. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO(2) is stabilized, this 'diffuse-radiation' fertilization effect declines rapidly to near zero by the end of the twenty-first century.
Abstract.
Author URL.
Pacifico F, Harrison SP, Jones CD, Sitch S (2009). Isoprene emissions and climate.
Atmospheric Environment,
43(39), 6121-6135.
Abstract:
Isoprene emissions and climate
Biogenic volatile organic compounds (BVOCs) play an important role in atmospheric chemistry and the carbon cycle. Isoprene is quantitatively the most important of the non-methane BVOCs (NMBVOCs), with an annual emission of about 400-600 TgC; about 90% of this is emitted by terrestrial plants. Incorporating a mechanistic treatment of isoprene emissions within land-surface schemes has recently become a focus for the modelling community, the aim being to quantify the potential magnitude of associated climate feedbacks. However, these efforts are hampered by major uncertainties about why plants emit isoprene and the relative importance of different environmental controls on isoprene emission. The availability and reliability of observations of isoprene fluxes from different types of vegetation is limited, and this also imposes constraints on model development. Nevertheless, progress is being made towards the development of mechanistic models of isoprene emission which, in conjunction with atmospheric chemistry models, will ultimately allow improved quantification of the feedbacks between the terrestrial biosphere and climate under past and future climate states. © 2009.
Abstract.
Mercado LM, Lloyd J, Dolman AJ, Sitch S, Patiño S (2009). Modelling basin-wide variations in Amazon forest productivity - Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis.
Biogeosciences,
6(7), 1247-1272.
Abstract:
Modelling basin-wide variations in Amazon forest productivity - Part 1: Model calibration, evaluation and upscaling functions for canopy photosynthesis
Given the importance of Amazon rainforest in the global carbon and hydrological cycles, there is a need to parameterize and validate ecosystem gas exchange and vegetation models for this region in order to adequately simulate present and future carbon and water balances. In this study, a sun and shade canopy gas exchange model is calibrated and evaluated at five rainforest sites using eddy correlation measurements of carbon and energy fluxes. Results from the model-data evaluation suggest that with adequate parameterisation, photosynthesis models taking into account the separation of diffuse and direct irradiance and the dynamics of sunlit and shaded leaves can accurately represent photosynthesis in these forests. Also, stomatal conductance formulations that only take into account atmospheric demand fail to correctly simulate moisture and CO2 fluxes in forests with a pronounced dry season, particularly during afternoon conditions. Nevertheless, it is also the case that large uncertainties are associated not only with the eddy correlation data, but also with the estimates of ecosystem respiration required for model validation. To accurately simulate Gross Primary Productivity (GPP) and energy partitioning the most critical parameters and model processes are the quantum yield of photosynthetic uptake, the maximum carboxylation capacity of Rubisco, and simulation of stomatal conductance. © Author(s) 2009.
Abstract.
Piao S, Fang J, Ciais P, Peylin P, Huang Y, Sitch S, Wang T (2009). The carbon balance of terrestrial ecosystems in China.
Nature,
458(7241), 1009-1013.
Abstract:
The carbon balance of terrestrial ecosystems in China.
Global terrestrial ecosystems absorbed carbon at a rate of 1-4 Pg yr(-1) during the 1980s and 1990s, offsetting 10-60 per cent of the fossil-fuel emissions. The regional patterns and causes of terrestrial carbon sources and sinks, however, remain uncertain. With increasing scientific and political interest in regional aspects of the global carbon cycle, there is a strong impetus to better understand the carbon balance of China. This is not only because China is the world's most populous country and the largest emitter of fossil-fuel CO(2) into the atmosphere, but also because it has experienced regionally distinct land-use histories and climate trends, which together control the carbon budget of its ecosystems. Here we analyse the current terrestrial carbon balance of China and its driving mechanisms during the 1980s and 1990s using three different methods: biomass and soil carbon inventories extrapolated by satellite greenness measurements, ecosystem models and atmospheric inversions. The three methods produce similar estimates of a net carbon sink in the range of 0.19-0.26 Pg carbon (PgC) per year, which is smaller than that in the conterminous United States but comparable to that in geographic Europe. We find that northeast China is a net source of CO(2) to the atmosphere owing to overharvesting and degradation of forests. By contrast, southern China accounts for more than 65 per cent of the carbon sink, which can be attributed to regional climate change, large-scale plantation programmes active since the 1980s and shrub recovery. Shrub recovery is identified as the most uncertain factor contributing to the carbon sink. Our data and model results together indicate that China's terrestrial ecosystems absorbed 28-37 per cent of its cumulated fossil carbon emissions during the 1980s and 1990s.
Abstract.
Author URL.
Le Quéré C, Raupach MR, Canadell JG, Marland G, Bopp L, Ciais P, Conway TJ, Doney SC, Feely RA, Foster P, et al (2009). Trends in the sources and sinks of carbon dioxide.
Nature Geoscience,
2(12), 831-836.
Abstract:
Trends in the sources and sinks of carbon dioxide
Efforts to control climate change require the stabilization of atmospheric CO 2 concentrations. This can only be achieved through a drastic reduction of global CO 2 emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO 2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO 2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO 2 by the carbon sinks in response to climate change and variability. Changes in the CO 2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO 2 levels. It is therefore crucial to reduce the uncertainties. © 2009 Macmillan Publishers Limited. All rights reserved.
Abstract.
O'ishi R, Abe-Ouchi A, Prentice IC, Sitch S (2009). Vegetation dynamics and plant CO<inf>2</inf> responses as positive feedbacks in a greenhouse world.
Geophysical Research Letters,
36(11).
Abstract:
Vegetation dynamics and plant CO2 responses as positive feedbacks in a greenhouse world
An atmosphere-ocean-vegetation coupled model is used to quantify the biogeophysical feedback that emerges as vegetation adjusts dynamically to a quadrupling of atmospheric CO2. This feedback amplifies global warming by 13%. About half of it is due to climatically induced expansion of boreal forest into tundra, reinforced by reductions in snow and sea ice cover. The other half represents a global climatic effect of increased vegetative cover (an indirect consequence of plant physiological responses to CO2) in the semi-arid subtropics. Enhanced absorption of shortwave radiation in these regions produces a net surface warming, which the atmosphere communicates poleward. The greatest vegetation-induced wanning is co-located with large, vulnerable carbon stores in the north. These lose carbon, so that in the long term, the biospheric response to CO2 and climate change becomes dominated by positive feedbacks that overwhelm the effect of CO2 fertilization on terrestrial carbon stocks. Copyright 2009 by the American Geophysical Union.
Abstract.
Huntingford C, Fisher RA, Mercado L, Booth BBB, Sitch S, Harris PP, Cox PM, Jones CD, Betts RA, Malhi Y, et al (2008). "Towards quantifying uncertainty in predictions of Amazon """"dieback""""".
Phil. Trans. Roy. Soc. B. Author URL.
Sitch S, Huntingford C, Gedney N, Levy PE, Lomas M, Piao SL, Betts R, Ciais P, Cox P, Friedlingstein P, et al (2008). Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs).
GLOBAL CHANGE BIOL,
14(9), 2015-2039.
Abstract:
Evaluation of the terrestrial carbon cycle, future plant geography and climate-carbon cycle feedbacks using five Dynamic Global Vegetation Models (DGVMs)
This study tests the ability of five Dynamic Global Vegetation Models (DGVMs), forced with observed climatology and atmospheric CO2, to model the contemporary global carbon cycle. The DGVMs are also coupled to a fast 'climate analogue model', based on the Hadley Centre General Circulation Model (GCM), and run into the future for four Special Report Emission Scenarios (SRES): A1FI, A2, B1, B2. Results show that all DGVMs are consistent with the contemporary global land carbon budget. Under the more extreme projections of future environmental change, the responses of the DGVMs diverge markedly. In particular, large uncertainties are associated with the response of tropical vegetation to drought and boreal ecosystems to elevated temperatures and changing soil moisture status. The DGVMs show more divergence in their response to regional changes in climate than to increases in atmospheric CO2 content. All models simulate a release of land carbon in response to climate, when physiological effects of elevated atmospheric CO2 on plant production are not considered, implying a positive terrestrial climate-carbon cycle feedback. All DGVMs simulate a reduction in global net primary production (NPP) and a decrease in soil residence time in the tropics and extra-tropics in response to future climate. When both counteracting effects of climate and atmospheric CO2 on ecosystem function are considered, all the DGVMs simulate cumulative net land carbon uptake over the 21st century for the four SRES emission scenarios. However, for the most extreme A1FI emissions scenario, three out of five DGVMs simulate an annual net source of CO2 from the land to the atmosphere in the final decades of the 21st century. For this scenario, cumulative land uptake differs by 494 Pg C among DGVMs over the 21st century. This uncertainty is equivalent to over 50 years of anthropogenic emissions at current levels.
Abstract.
Friedlingstein P, Cadule P, Piao SL, Ciais P, Sitch S (2008). The African contribution to the global climate-carbon cycle feedback of the 21st century. Biogeosciences Discussions, 5(6), 4847-4866.
Sitch S, McGuire AD, Kimball J, Gedney N, Gamon J, Engstrom R, Wolf A, Zhuang Q, Clein J, McDonald KC, et al (2007). Assessing the carbon balance of circumpolar Arctic tundra using remote sensing and process modeling.
Ecol Appl,
17(1), 213-234.
Abstract:
Assessing the carbon balance of circumpolar Arctic tundra using remote sensing and process modeling.
This paper reviews the current status of using remote sensing and process-based modeling approaches to assess the contemporary and future circumpolar carbon balance of Arctic tundra, including the exchange of both carbon dioxide and methane with the atmosphere. Analyses based on remote sensing approaches that use a 20-year data record of satellite data indicate that tundra is greening in the Arctic, suggesting an increase in photosynthetic activity and net primary production. Modeling studies generally simulate a small net carbon sink for the distribution of Arctic tundra, a result that is within the uncertainty range of field-based estimates of net carbon exchange. Applications of process-based approaches for scenarios of future climate change generally indicate net carbon sequestration in Arctic tundra as enhanced vegetation production exceeds simulated increases in decomposition. However, methane emissions are likely to increase dramatically, in response to rising soil temperatures, over the next century. Key uncertainties in the response of Arctic ecosystems to climate change include uncertainties in future fire regimes and uncertainties relating to changes in the soil environment. These include the response of soil decomposition and respiration to warming and deepening of the soil active layer, uncertainties in precipitation and potential soil drying, and distribution of wetlands. While there are numerous uncertainties in the projections of process-based models, they generally indicate that Arctic tundra will be a small sink for carbon over the next century and that methane emissions will increase considerably, which implies that exchange of greenhouse gases between the atmosphere and Arctic tundra ecosystems is likely to contribute to climate warming.
Abstract.
Author URL.
Friend AD, Arneth A, Kiang NY, Lomas M, Ogée J, Rödenbeck C, Running SW, Santaren JD, Sitch S, Viovy N, et al (2007). FLUXNET and modelling the global carbon cycle.
Global Change Biology,
13(3), 610-633.
Abstract:
FLUXNET and modelling the global carbon cycle
Measurements of the net CO2 flux between terrestrial ecosystems and the atmosphere using the eddy covariance technique have the potential to underpin our interpretation of regional CO2 source-sink patterns, CO2 flux responses to forcings, and predictions of the future terrestrial C balance. Information contained in FLUXNET eddy covariance data has multiple uses for the development and application of global carbon models, including evaluation/ validation, calibration, process parameterization, and data assimilation. This paper reviews examples of these uses, compares global estimates of the dynamics of the global carbon cycle, and suggests ways of improving the utility of such data for global carbon modelling. Net ecosystem exchange of CO2 (NEE) predicted by different terrestrial biosphere models compares favourably with FLUXNET observations at diurnal and seasonal timescales. However, complete model validation, particularly over the full annual cycle, requires information on the balance between assimilation and decomposition processes, information not readily available for most FLUXNET sites. Site history, when known, can greatly help constrain the model-data comparison. Flux measurements made over four vegetation types were used to calibrate the land-surface scheme of the Goddard Institute for Space Studies global climate model, significantly improving simulated climate and demonstrating the utility of diurnal FLUXNET data for climate modelling. Land-surface temperatures in many regions cool due to higher canopy conductances and latent heat fluxes, and the spatial distribution of CO2 uptake provides a significant additional constraint on the realism of simulated surface fluxes. FLUXNET data are used to calibrate a global production efficiency model (PEM). This model is forced by satellite-measured absorbed radiation and suggests that global net primary production (NPP) increased 6.2% over 1982-1999. Good agreement is found between global trends in NPP estimated by the PEM and a dynamic global vegetation model (DGVM), and between the DGVM and estimates of global NEE derived from a global inversion of atmospheric CO2 measurements. Combining the PEM, DGVM, and inversion results suggests that CO2 fertilization is playing a major role in current increases in NPP, with lesser impacts from increasing N deposition and growing season length. Both the PEM and the inversion identify the Amazon basin as a key region for the current net terrestrial CO2 uptake (i.e. 33% of global NEE), as well as its interannual variability. The inversion's global NEE estimate of -1.2 Pg [C] yr-1 for 1982-1995 is compatible with the PEM- and DGVM-predicted trends in NPP. There is, thus, a convergence in understanding derived from process-based models, remote-sensing-based observations, and inversion of atmospheric data. Future advances in field measurement techniques, including eddy covariance (particularly concerning the problem of night-time fluxes in dense canopies and of advection or flow distortion over complex terrain), will result in improved constraints on land-atmosphere CO2 fluxes and the rigorous attribution of mechanisms to the current terrestrial net CO2 uptake and its spatial and temporal heterogeneity. Global ecosystem models play a fundamental role in linking information derived from FLUXNET measurements to atmospheric CO2 variability. A number of recommendations concerning FLUXNET data are made, including a request for more comprehensive site data (particularly historical information), more measurements in undisturbed ecosystems, and the systematic provision of error estimates. The greatest value of current FLUXNET data for global carbon cycle modelling is in evaluating process representations, rather than in providing an unbiased estimate of net CO2 exchange. © 2007 Blackwell Publishing Ltd.
Abstract.
Sitch S, Cox PM, Collins W, Huntingford C (2007). Indirect radiative forcing of climate change through ozone effects on the land-carbon sink. Nature, 448(7155), 791-794.
Zaehle S, Bondeau A, Carter TR, Cramer W, Erhard M, Prentice IC, Reginster I, Rounsevell MDA, Sitch S, Smith B, et al (2007). Projected changes in terrestrial carbon storage in Europe under climate and land-use change, 1990-2100.
Ecosystems,
10(3), 380-401.
Abstract:
Projected changes in terrestrial carbon storage in Europe under climate and land-use change, 1990-2100
Changes in climate and land use, caused by socio-economic changes, greenhouse gas emissions, agricultural policies and other factors, are known to affect both natural and managed ecosystems, and will likely impact on the European terrestrial carbon balance during the coming decades. This study presents a comprehensive European Union wide (EU15 plus Norway and Switzerland, EU*) assessment of potential future changes in terrestrial carbon storage considering these effects based on four illustrative IPCC-SRES storylines (A1FI, A2, B1, B2). A process-based land vegetation model (LPJ-DGVM), adapted to include a generic representation of managed ecosystems, is forced with changing fields of land-use patterns from 1901 to 2100 to assess the effect of land-use and cover changes on the terrestrial carbon balance of Europe. The uncertainty in the future carbon balance associated with the choice of a climate change scenario is assessed by forcing LPJ-DGVM with output from four different climate models (GCMs: CGCM2, CSIRO2, HadCM3, PCM2) for the same SRES storyline. Decrease in agricultural areas and afforestation leads to simulated carbon sequestration for all land-use change scenarios with an average net uptake of 17-38 Tg C/year between 1990 and 2100, corresponding to 1.9-2.9% of the EU*s CO2 emissions over the same period. Soil carbon losses resulting from climate warming reduce or even offset carbon sequestration resulting from growth enhancement induced by climate change and increasing atmospheric CO2 concentrations in the second half of the twenty-first century. Differences in future climate change projections among GCMs are the main cause for uncertainty in the cumulative European terrestrial carbon uptake of 4.4-10.1 Pg C between 1990 and 2100. © 2007 Springer Science+Business Media, LLC.
Abstract.
Pope V, Brown S, Clark R, Collins M, Collins W, Dearden C, Gunson J, Harris G, Jones C, Keen A, et al (2007). The Met Office Hadley Centre climate modelling capability: the competing requirements for improved resolution, complexity and dealing with uncertainty.
Philos Trans a Math Phys Eng Sci,
365(1860), 2635-2657.
Abstract:
The Met Office Hadley Centre climate modelling capability: the competing requirements for improved resolution, complexity and dealing with uncertainty.
Predictions of future climate change require complex computer models of the climate system to represent the full range of processes and interactions that influence climate. The Met Office Hadley Centre uses 'families' of models as part of the Met Office Unified Model Framework to address different classes of problems. The HadGEM family is a suite of state-of-the-art global environment models that are used to reduce uncertainty and represent and predict complex feedbacks. The HadCM3 family is a suite of well established but cheaper models that are used for multiple simulations, for example, to quantify uncertainty or to test the impact of multiple emissions scenarios.
Abstract.
Author URL.
Ni J, Harrison SP, Colin Prentice I, Kutzbach JE, Sitch S (2006). Impact of climate variability on present and Holocene vegetation: a model-based study.
Ecological Modelling,
191(3-4), 469-486.
Abstract:
Impact of climate variability on present and Holocene vegetation: a model-based study
A series of nine simulations has been made with the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM) in order to explore the impacts of climate variability and Holocene changes in variability (as simulated by the Fast Ocean-Atmosphere Model, FOAM) on vegetation in three forest-dominated regions of China and in the semi-arid Sahelian region of northern Africa. The simulations illustrate that changes both in the magnitude of climate variability and in the persistence of above/below average conditions have the potential to modify the vegetation response to changes in mean climate. Simulated changes in moisture availability affect vegetation through drought stress or through changing the fuel availability in semi-arid regions where lack of fuel often limits the incidence of fire. Increasing moisture availability causes trees to replace grasses in China by reducing drought stress; increasing moisture availability in the Sahel increases the available fuel and hence reduces fire return times, favouring grasses. The modelling results imply that climate variability is important to vegetation dynamics; that not only the magnitude, but also the temporal structure of variability is important; and that correctly simulating vegetation changes in response to climate variability requires a realistic "baseline" simulation of plant community composition. They further indicate that the impacts of climate change on ecosystems can sometimes derive as much from changes in variability as from changes in mean climate. © 2005 Elsevier B.V. All rights reserved.
Abstract.
Schaphoff S, Lucht W, Gerten D, Sitch S, Cramer W, Prentice IC (2006). Terrestrial biosphere carbon storage under alternative climate projections.
Climatic Change,
74(1-3), 97-122.
Abstract:
Terrestrial biosphere carbon storage under alternative climate projections
This study investigates commonalities and differences in projected land biosphere carbon storage among climate change projections derived from one emission scenario by five different general circulation models (GCMs). Carbon storage is studied using a global biogeochemical process model of vegetation and soil that includes dynamic treatment of changes in vegetation composition, a recently enhanced version of the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM). Uncertainty in future terrestrial carbon storage due to differences in the climate projections is large. Changes by the end of the century range from -106 to +201 PgC, thus, even the sign of the response whether source or sink, is uncertain. Three out of five climate projections produce a land carbon source by the year 2100, one is approximately neutral and one a sink. A regional breakdown shows some robust qualitative features. Large areas of the boreal forest are shown as a future CO2 source, while a sink appears in the arctic. The sign of the response in tropical and sub-tropical ecosystems differs among models, due to the large variations in simulated precipitation patterns. The largest uncertainty is in the response of tropical rainforests of South America and Central Africa. © Springer 2006.
Abstract.
Zaehle S, Sitch S, Prentice IC, Liski J, Cramer W, Erhard M, Hickler T, Smith B (2006). The importance of age-related decline in forest NPP for modeling regional carbon balances.
Ecol Appl,
16(4), 1555-1574.
Abstract:
The importance of age-related decline in forest NPP for modeling regional carbon balances.
We show the implications of the commonly observed age-related decline in aboveground productivity of forests, and hence forest age structure, on the carbon dynamics of European forests in response to historical changes in environmental conditions. Size-dependent carbon allocation in trees to counteract increasing hydraulic resistance with tree height has been hypothesized to be responsible for this decline. Incorporated into a global terrestrial biosphere model (the Lund-Potsdam-Jena model, LPJ), this hypothesis improves the simulated increase in biomass with stand age. Application of the advanced model, including a generic representation of forest management in even-aged stands, for 77 European provinces shows that model-based estimates of biomass development with age compare favorably with inventory-based estimates for different tree species. Model estimates of biomass densities on province and country levels, and trends in growth increment along an annual mean temperature gradient are in broad agreement with inventory data. However, the level of agreement between modeled and inventory-based estimates varies markedly between countries and provinces. The model is able to reproduce the present-day age structure of forests and the ratio of biomass removals to increment on a European scale based on observed changes in climate, atmospheric CO2 concentration, forest area, and wood demand between 1948 and 2000. Vegetation in European forests is modeled to sequester carbon at a rate of 100 Tg C/yr, which corresponds well to forest inventory-based estimates.
Abstract.
Author URL.
Krinner G, Viovy N, de Noblet-Ducoudré N, Ogée J, Polcher J, Friedlingstein P, Ciais P, Sitch S, Prentice IC (2005). A dynamic global vegetation model for studies of the coupled atmosphere-biosphere system.
Global Biogeochemical Cycles,
19(1), 1-33.
Abstract:
A dynamic global vegetation model for studies of the coupled atmosphere-biosphere system
This work presents a new dynamic global vegetation model designed as an extension of an existing surface-vegetation-atmosphere transfer scheme which is included in a coupled ocean-atmosphere general circulation model. The new dynamic global vegetation model simulates the principal processes of the continental biosphere influencing the global carbon cycle (photosynthesis, autotrophic and heterotrophic respiration of plants and in soils, fire, etc.) as well as latent, sensible, and kinetic energy exchanges at the surface of soils and plants. As a dynamic vegetation model, it explicitly represents competitive processes such as light competition, sapling establishment, etc. It can thus be used in simulations for the study of feedbacks between transient climate and vegetation cover changes, but it can also be used with a prescribed vegetation distribution. The whole seasonal phenological cycle is prognostically calculated without any prescribed dates or use of satellite data. The model is coupled to the IPSL-CM4 coupled atmosphere-ocean-vegetation model. Carbon and surface energy fluxes from the coupled hydrology-vegetation model compare well with observations at FluxNet sites. Simulated vegetation distribution and leaf density in a global simulation are evaluated against observations, and carbon stocks and fluxes are compared to available estimates, with satisfying results. Copyright 2005 by the American Geophysical Union.
Abstract.
Morales P, Sykes MT, Prentice IC, Smith P, Smith B, Bugmann H, Zierl B, Friedlingstein P, Viovy N, Sabaté S, et al (2005). Comparing and evaluating process-based ecosystem model predictions of carbon and water fluxes in major European forest biomes.
Global Change Biology,
11(12), 2211-2233.
Abstract:
Comparing and evaluating process-based ecosystem model predictions of carbon and water fluxes in major European forest biomes
Process-based models can be classified into: (a) terrestrial biogeochemical models (TBMs), which simulate fluxes of carbon, water and nitrogen coupled within terrestrial ecosystems, and (b) dynamic global vegetation models (DGVMs), which further couple these processes interactively with changes in slow ecosystem processes depending on resource competition, establishment, growth and mortality of different vegetation types. In this study, four models - RHESSys, GOTILWA +, LPJ-GUESS and ORCHIDEE - representing both modelling approaches were compared and evaluated against benchmarks provided by eddy-covariance measurements of carbon and water fluxes at 15 forest sites within the EUROFLUX project. Overall, model-measurement agreement varied greatly among sites. Both modelling approaches have somewhat different strengths, but there was no model among those tested that universally performed well on the two variables evaluated. Small biases and errors suggest that ORCHIDEE and GOTILWA + performed better in simulating carbon fluxes while LPJ-GUESS and RHESSys did a better job in simulating water fluxes. In general, the models can be considered as useful tools for studies of climate change impacts on carbon and water cycling in forests. However, the various sources of variation among models simulations and between models simulations and observed data described in this study place some constraints on the results and to some extent reduce their reliability. For example, at most sites in the Mediterranean region all models generally performed poorly most likely because of problems in the representation of water stress effects on both carbon uptake by photosynthesis and carbon release by heterotrophic respiration (Rh). The use of flux data as a means of assessing key processes in models of this type is an important approach to improving model performance. Our results show that the models have value but that further model development is necessary with regard to the representation of the some of the key ecosystem processes. © 2005 Blackwell Publishing Ltd.
Abstract.
Schröter D, Cramer W, Leemans R, Prentice IC, Araújo MB, Arnell NW, Bondeau A, Bugmann H, Carter TR, Gracia CA, et al (2005). Ecology: Ecosystem service supply and vulnerability to global change in Europe.
Science,
310(5752), 1333-1337.
Abstract:
Ecology: Ecosystem service supply and vulnerability to global change in Europe
Global change will alter the supply of ecosystem services that are vital for human well-being. To investigate ecosystem service supply during the 21st century, we used a range of ecosystem models and scenarios of climate and land-use change to conduct a Europe-wide assessment. Large changes in climate and land use typically resulted in large changes in ecosystem service supply. Some of these trends may be positive (for example, increases in forest area and productivity) or offer opportunities (for example, "surplus land" for agricultural extensification and bioenergy production). However, many changes increase vulnerability as a result of a decreasing supply of ecosystem services (for example, declining soil fertility, declining water availability, increasing risk of forest fires), especially in the Mediterranean and mountain regions.
Abstract.
Schröter D, Cramer W, Leemans R, Prentice IC, Araújo MB, Arnell NW, Bondeau A, Bugmann H, Carter TR, Gracia CA, et al (2005). Ecosystem service supply and vulnerability to global change in Europe.
Science,
310(5752), 1333-1337.
Abstract:
Ecosystem service supply and vulnerability to global change in Europe.
Global change will alter the supply of ecosystem services that are vital for human well-being. To investigate ecosystem service supply during the 21st century, we used a range of ecosystem models and scenarios of climate and land-use change to conduct a Europe-wide assessment. Large changes in climate and land use typically resulted in large changes in ecosystem service supply. Some of these trends may be positive (for example, increases in forest area and productivity) or offer opportunities (for example, "surplus land" for agricultural extensification and bioenergy production). However, many changes increase vulnerability as a result of a decreasing supply of ecosystem services (for example, declining soil fertility, declining water availability, increasing risk of forest fires), especially in the Mediterranean and mountain regions.
Abstract.
Author URL.
Zaehle S, Sitch S, Smith B, Hatterman F (2005). Effects of parameter uncertainties on the modeling of terrestrial biosphere dynamics.
Global Biogeochemical Cycles,
19(3), 1-16.
Abstract:
Effects of parameter uncertainties on the modeling of terrestrial biosphere dynamics
Dynamic global vegetation models (DGVMs) have been shown to broadly reproduce seasonal and interannual patterns of carbon exchange, as well as realistic vegetation dynamics. To assess the uncertainties in these results associated with model parameterization, the Lund-Potsdam-Jena-DGVM (LPJ-DGVM) is analyzed in terms of model robustness and key sensitive parameters. Present-day global land-atmosphere carbon fluxes are relatively well constrained, despite considerable uncertainty in global net primary production mainly propagating from uncertainty in parameters controlling assimilation rate, plant respiration and plant water balance. In response to climate change, water-use efficiency driven increases in net carbon assimilation by plants, transient changes in vegetation composition and global warming effects on soil organic matter dynamics are robust model results. As a consequence, long-term trends in land-atmosphere fluxes are consistently modeled despite an uncertainty range of -3.35 ± 1.45 PgC yr-1 at the end of the twenty-first century for the specific scenario used. Copyright 2005 by the American Geophysical Union.
Abstract.
Sitch S, Brovkin V, von Bloh W, van Vuuren D, Eickhout B, Ganopolski A (2005). Impacts of future land cover changes on atmospheric CO<inf>2</inf> and climate.
Global Biogeochemical Cycles,
19(2), 1-15.
Abstract:
Impacts of future land cover changes on atmospheric CO2 and climate
Climate-carbon cycle model CLIMBER2-LPJ is run with consistent fields of future fossil fuel CO2 emissions and geographically explicit land cover changes for four Special Report on Emissions Scenarios (SRES) scenarios, A1B, A2, B1, and B2. By 2100, increases in global mean temperatures range between 1.7°C (B1) and 2.7°C (A2) relative to the present day. Biogeochemical warming associated with future tropical land conversion is larger than its corresponding biogeophysical cooling effect in A2, and amplifies biogeophysical warming associated with Northern Hemisphere land abandonment in B1. In 2100, simulated atmospheric CO2 ranged from 592 ppm (B1) to 957 ppm (A2). Future CO2 concentrations simulaued with the model are higher than previously reported for the same SRES emission scenarios, indicating the effect of future CO2 emission scenarios and land cover changes may hitherto be underestimated. The maximum contribution of land cover changes to future atmospheric CO2 among the four SRES scenarios represents a modest 127 ppm, or 22% in relative terms, with the remainder attributed to fossil fuel CO2 emissions. Copyright 2005 by the American Geophysical Union.
Abstract.
Peylin P, Bousquet P, Le Quéré C, Sitch S, Friedlingstein P, McKinley G, Gruber N, Rayner P, Ciais P (2005). Multiple constraints on regional CO<inf>2</inf> flux variations over land and oceans.
Global Biogeochemical Cycles,
19(1), 1-21.
Abstract:
Multiple constraints on regional CO2 flux variations over land and oceans
To increase our understanding of the carbon cycle, we compare regional estimates of CO2 flux variability for 1980-1998 from atmospheric CO2 inversions and from process-based models of the land (SLAVE and LPJ) and ocean (OPA and MIT). Over the land, the phase and amplitude of the different estimates agree well, especially at continental scale. Flux variations are predominantly controlled by El Niño events, with the exception of the post-Pinatubo period of the early 1990s. Differences between the two land models result mainly from the response of heterotrophic respiration to precipitation and temperature. The "Lloyd and Taylor" formulation of LPJ [Lloyd and Taylor, 1994] agrees better with the inverse estimates. Over the ocean, inversion and model results agree only in the equatorial Pacific and partly in the austral ocean. In the austral ocean, an increased CO2 sink is present in the inversion and OPA model, and results from increased stratification of the ocean. In the northern oceans, the inversions estimate large flux variations in line with time-series observations of the subtropical Atlantic, but not supported by the two model estimates, thus suggesting that the CO2 variability from high-latitude oceans needs further investigation. Copyright 2005 by the American Geophysical Union.
Abstract.
Callaghan TV, Björn LO, Chernov Y, Chapin T, Christensen TR, Huntley B, Ims RA, Johansson M, Jolly D, Jonasson S, et al (2004). Effects of changes in climate on landscape and regional processes, and feedbacks to the climate system.
Ambio,
33(7), 459-468.
Abstract:
Effects of changes in climate on landscape and regional processes, and feedbacks to the climate system.
Biological and physical processes in the Arctic system operate at various temporal and spatial scales to impact large-scale feedbacks and interactions with the earth system. There are four main potential feedback mechanisms between the impacts of climate change on the Arctic and the global climate system: albedo, greenhouse gas emissions or uptake by ecosystems, greenhouse gas emissions from methane hydrates, and increased freshwater fluxes that could affect the thermohaline circulation. All these feedbacks are controlled to some extent by changes in ecosystem distribution and character and particularly by large-scale movement of vegetation zones. Indications from a few, full annual measurements of CO2 fluxes are that currently the source areas exceed sink areas in geographical distribution. The little available information on CH4 sources indicates that emissions at the landscape level are of great importance for the total greenhouse balance of the circumpolar North. Energy and water balances of Arctic landscapes are also important feedback mechanisms in a changing climate. Increasing density and spatial expansion of vegetation will cause a lowering of the albedo and more energy to be absorbed on the ground. This effect is likely to exceed the negative feedback of increased C sequestration in greater primary productivity resulting from the displacements of areas of polar desert by tundra, and areas of tundra by forest. The degradation of permafrost has complex consequences for trace gas dynamics. In areas of discontinuous permafrost, warming, will lead to a complete loss of the permafrost. Depending on local hydrological conditions this may in turn lead to a wetting or drying of the environment with subsequent implications for greenhouse gas fluxes. Overall, the complex interactions between processes contributing to feedbacks, variability over time and space in these processes, and insufficient data have generated considerable uncertainties in estimating the net effects of climate change on terrestrial feedbacks to the climate system. This uncertainty applies to magnitude, and even direction of some of the feedbacks.
Abstract.
Author URL.
Callaghan TV, Björn LO, Chernov Y, Chapin T, Christensen TR, Huntley B, Ims RA, Johansson M, Jolly D, Jonasson S, et al (2004). Key findings and extended summaries.
Ambio,
33(7), 386-392.
Author URL.
Badeck FW, Bondeau A, Böttcher K, Doktor D, Lucht W, Schaber J, Sitch S (2004). Responses of spring phenology to climate change.
New Phytologist,
162(2), 295-309.
Abstract:
Responses of spring phenology to climate change
Climate change effects on seasonal activity in terrestrial ecosystems are significant and well documented, especially in the middle and higher latitudes. Temperature is a main driver of many plant developmental processes, and in many cases higher temperatures have been shown to speed up plant development and lead to earlier switching to the next ontogenetic stage. Qualitatively consistent advancement of vegetation activity in spring has been documented using three independent methods, based on ground observations, remote sensing, and analysis of the atmospheric CO2 signal. However, estimates of the trends for advancement obtained using the same method differ substantially. We propose that a high fraction of this uncertainty is related to the time frame analysed and changes in trends at decadal time scales. Furthermore, the correlation between estimates of the initiation of spring activity derived from ground observations and remote sensing at interannual time scales is often weak. We propose that this is caused by qualitative differences in the traits observed using the two methods, as well as the mixture of different ecosystems and species within the satellite scenes. © New Phytologist (2004).
Abstract.
Brovkin V, Sitch S, von Bloh W, Claussen M, Bauer E, Cramer W (2004). Role of land cover changes for atmospheric CO<inf>2</inf> increase and climate change during the last 150 years.
Global Change Biology,
10(8), 1253-1266.
Abstract:
Role of land cover changes for atmospheric CO2 increase and climate change during the last 150 years
We assess the role of changing natural (volcanic, aerosol, insolation) and anthropogenic (CO2 emissions, land cover) forcings on the global climate system over the last 150 years using an earth system model of intermediate complexity, CLIMBER-2. We apply several datasets of historical land-use reconstructions: the cropland dataset by Ramankutty & Foley (1999) (R&F), the HYDE land cover dataset of Klein Goldewijk (2001), and the land-use emissions data from Houghton & Hackler (2002). Comparison between the simulated and observed temporal evolution of atmospheric CO2 and δ13 CO2 are used to evaluate these datasets. To check model uncertainty, CLIMBER-2 was coupled to the more complex Lund-Potsdam-jena (LPJ) dynamic global vegetation model. In simulation with R&F dataset, biogeophysical mechanisms due to land cover changes tend to decrease global air temperature by 0.26 °C, while biogeochemical mechanisms act to warm the climate by 0.18 °C. The net effect on climate is negligible on a global scale, but pronounced over the land in the temperate and high northern latitudes where a cooling due to an increase in land surface albedo offsets the warming due to land-use CO2 emissions. Land cover changes led to estimated increases in atmospheric CO2 of between 22 and 43 ppmv. Over the entire period 1800-2000, simulated δ13 CO2 with HYDE compares most favourably with ice core during 1850-1950 and Cape Grim data, indicating preference of earlier land clearance in HYDE over R&F. In relative terms, land cover forcing corresponds to 25-49% of the observed growth in atmospheric CO2. This contribution declined from 36-60% during 1850-1960 to 4-35% during 1960-2000. CLIMBER-2-LPJ simulates the land cover contribution to atmospheric CO2 growth to decrease from 68% during 1900-1960 to 12% in the 1980s. Overall, our simulations show a decline in the relative role of land cover changes for atmospheric CO2 increase during the last 150 years. © 2004 Blackwell Publishing Ltd.
Abstract.
Callaghan TV, Björn LO, Chernov Y, Chapin T, Christensen TR, Huntley B, Ims RA, Johansson M, Jolly D, Jonasson S, et al (2004). Synthesis of effects in four Arctic subregions.
Ambio,
33(7), 469-473.
Abstract:
Synthesis of effects in four Arctic subregions.
An assessment of impacts on Arctic terrestrial ecosystems has emphasized geographical variability in responses of species and ecosystems to environmental change. This variability is usually associated with north-south gradients in climate, biodiversity, vegetation zones, and ecosystem structure and function. It is clear, however, that significant east-west variability in environment, ecosystem structure and function, environmental history, and recent climate variability is also important. Some areas have cooled while others have become warmer. Also, east-west differences between geographical barriers of oceans, archipelagos and mountains have contributed significantly in the past to the ability of species and vegetation zones to relocate in response to climate changes, and they have created the isolation necessary for genetic differentiation of populations and biodiversity hot-spots to occur. These barriers will also affect the ability of species to relocate during projected future warming. To include this east-west variability and also to strike a balance between overgeneralization and overspecialization, the ACIA identified four major sub regions based on large-scale differences in weather and climate-shaping factors. Drawing on information, mostly model output that can be related to the four ACIA subregions, it is evident that geographical barriers to species re-location, particularly the distribution of landmasses and separation by seas, will affect the northwards shift in vegetation zones. The geographical constraints--or facilitation--of northward movement of vegetation zones will affect the future storage and release of carbon, and the exchange of energy and water between biosphere and atmosphere. In addition, differences in the ability of vegetation zones to re-locate will affect the biodiversity associated with each zone while the number of species threatened by climate change varies greatly between subregions with a significant hot-spot in Beringia. Overall, the subregional synthesis demonstrates the difficulty of generalizing projections of responses of ecosystem structure and function, species loss, and biospheric feedbacks to the climate system for the whole Arctic region and implies a need for a far greater understanding of the spatial variability in the responses of terrestrial arctic ecosystems to climate change.
Abstract.
Author URL.
Gerten D, Schaphoff S, Haberlandt U, Lucht W, Sitch S (2004). Terrestrial vegetation and water balance - Hydrological evaluation of a dynamic global vegetation model.
Journal of Hydrology,
286(1-4), 249-270.
Abstract:
Terrestrial vegetation and water balance - Hydrological evaluation of a dynamic global vegetation model
Earth's vegetation plays a pivotal role in the global water balance. Hence, there is a need to model dynamic interactions and feedbacks between the terrestrial biosphere and the water cycle. Here, the hydrological performance of the Lund-Potsdam-Jena model (LPJ), a prominent dynamic global vegetation model, is evaluated. Models of this type simulate the coupled terrestrial carbon and water cycle, thus they are well suited for investigating biosphere-hydrosphere interactions over large domains. We demonstrate that runoff and evapotranspiration computed by LPJ agree well with respective results from state-of-the-art global hydrological models, while in some regions, runoff is significantly over- or underestimated compared to observations. The direction and magnitude of these biases is largely similar to those from other macro-scale models, rather than specific to LPJ. They are attributable primarily to uncertainties in the climate input data, and to human interventions not considered by the model (e.g. water withdrawal, land cover conversions). Additional model development is required to perform integrated assessments of water exchanges among the biosphere, the hydrosphere, and the anthroposphere. Yet, the LPJ model can now be used to study inter-relations between the world's major vegetation types and the terrestrial water balance. As an example, it is shown that a doubling of atmospheric CO2 content alone would result in pronounced changes in evapotranspiration and runoff for many parts of the world. Although significant, these changes would remain unseen by stand-alone hydrological models, thereby emphasizing the importance of simulating the coupled carbon and water cycle. © 2003 Elsevier B.V. All rights reserved.
Abstract.
Cramer W, Bondeau A, Schaphoff S, Lucht W, Smith B, Sitch S (2004). Tropical forests and the global carbon cycle: impacts of atmospheric carbon dioxide, climate change and rate of deforestation.
Philos Trans R Soc Lond B Biol Sci,
359(1443), 331-343.
Abstract:
Tropical forests and the global carbon cycle: impacts of atmospheric carbon dioxide, climate change and rate of deforestation.
The remaining carbon stocks in wet tropical forests are currently at risk because of anthropogenic deforestation, but also because of the possibility of release driven by climate change. To identify the relative roles of CO2 increase, changing temperature and rainfall, and deforestation in the future, and the magnitude of their impact on atmospheric CO2 concentrations, we have applied a dynamic global vegetation model, using multiple scenarios of tropical deforestation (extrapolated from two estimates of current rates) and multiple scenarios of changing climate (derived from four independent offline general circulation model simulations). Results show that deforestation will probably produce large losses of carbon, despite the uncertainty about the deforestation rates. Some climate models produce additional large fluxes due to increased drought stress caused by rising temperature and decreasing rainfall. One climate model, however, produces an additional carbon sink. Taken together, our estimates of additional carbon emissions during the twenty-first century, for all climate and deforestation scenarios, range from 101 to 367 Gt C, resulting in CO2 concentration increases above background values between 29 and 129 p.p.m. An evaluation of the method indicates that better estimates of tropical carbon sources and sinks require improved assessments of current and future deforestation, and more consistent precipitation scenarios from climate models. Notwithstanding the uncertainties, continued tropical deforestation will most certainly play a very large role in the build-up of future greenhouse gas concentrations.
Abstract.
Author URL.
Bonan GB, Levis S, Sitch S, Vertenstein M, Oleson KW (2003). A dynamic global vegetation model for use with climate models: Concepts and description of simulated vegetation dynamics.
Global Change Biology,
9(11), 1543-1566.
Abstract:
A dynamic global vegetation model for use with climate models: Concepts and description of simulated vegetation dynamics
Changes in vegetation structure and biogeography due to climate change feedback to alter climate by changing fluxes of energy, moisture, and momentum between land and atmosphere. While the current class of land process models used with climate models parameterizes these fluxes in detail, these models prescribe surface vegetation and leaf area from data sets. In this paper, we describe an approach in which ecological concepts from a global vegetation dynamics model are added to the land component of a climate model to grow plants interactively. The vegetation dynamics model is the LundPotsdam-Jena (LPJ) dynamic global vegetation model. The land model is the National Center for Atmospheric Research (NCAR) Land Surface Model (LSM). Vegetation is defined in terms of plant functional types. Each plant functional type is represented by an individual plant with the average biomass, crown area, height, and stem diameter (trees only) of its population, by the number of individuals in the population, and by the fractional cover in the grid cell. Three time-scales (minutes, days, and years) govern the processes. Energy fluxes, the hydrologic cycle, and carbon assimilation, core processes in LSM, occur at a 20 min time step. Instantaneous net assimilated carbon is accumulated annually to update vegetation once a year. This is carried out with the addition of establishment, resource competition, growth, mortality, and fire parameterizations from LPJ. The leaf area index is updated daily based on prevailing environmental conditions, but the maximum value depends on the annual vegetation dynamics. The coupling approach is successful. The model simulates global biogeography, net primary production, and dynamics of tundra, boreal forest, northern hardwood forest, tropical rainforest, and savanna ecosystems, which are consistent with observations. This suggests that the model can be used with a climate model to study biogeophysical feedbacks in the climate system related to vegetation dynamics.
Abstract.
Gerber S, Joos F, Brügger P, Stocker TF, Mann ME, Sitch S, Scholze M (2003). Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO<inf>2</inf>.
Climate Dynamics,
20(2-3), 281-299.
Abstract:
Constraining temperature variations over the last millennium by comparing simulated and observed atmospheric CO2
The response of atmospheric CO2 and climate to the reconstructed variability in solar irradiance and radiative forcing by volcanoes over the last millennium is examined by applying a coupled physical-biogeochemical climate model that includes the Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM) and a simplified analogue of a coupled atmosphere-ocean general circulation model. The modeled variations of atmospheric CO2 and Northern Hemisphere (NH) mean surface temperature are compatible with reconstructions from different Antarctic ice cores and temperature proxy data. Simulations where the magnitude of solar irradiance changes is increased yield a mismatch between model results and CO2 data, providing evidence for modest changes in solar irradiance and global mean temperatures over the past millennium and arguing against a significant amplification of the response of global or hemispheric annual mean temperature to solar forcing. Linear regression (r = 0.97) between modeled changes in atmospheric CO2 and NH mean surface temperature yields a CO2 increase of about 12 ppm for a temperature increase of 1 °C and associated precipitation and cloud cover changes. Then, the CO2 data range of 12 ppm implies that multi-decadal NH temperature changes between 1100 and 1700 AD had to be within 1 °C. Modeled preindustrial variations in atmospheric δ13C are small compared to the uncertainties in ice core δ13C data. Simulations with natural forcings only suggest that atmospheric CO2 would have remained around the preindustrial concentration of 280 ppm without anthropogenic emissions. Sensitivity experiments show that atmospheric CO2 closely follows decadal-mean temperature changes when changes in ocean circulation and ocean-sediment interactions are not important. The response in terrestrial carbon storage to factorial changes in temperature, the seasonality of temperature, precipitation, and atmospheric CO2 has been determined.
Abstract.
Sitch S, Smith B, Prentice IC, Arneth A, Bondeau A, Cramer W, Kaplan JO, Levis S, Lucht W, Sykes MT, et al (2003). Evaluation of ecosystem dynamics, plant geography and terrestrial carbon cycling in the LPJ dynamic global vegetation model.
Global Change Biology,
9(2), 161-185.
Abstract:
Evaluation of ecosystem dynamics, plant geography and terrestrial carbon cycling in the LPJ dynamic global vegetation model
The Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ) combines process-based, large-scale representations of terrestrial vegetation dynamics and land-atmosphere carbon and water exchanges in a modular framework. Features include feedback through canopy conductance between photosynthesis and transpiration and interactive coupling between these 'fast' processes and other ecosystem processes including resource competition, tissue turnover, population dynamics, soil organic matter and litter dynamics and fire disturbance. Ten plants functional types (PFTs) are differentiated by physiological, morphological, phenological, bioclimatic and fire-response attributes. Resource competition and differential responses to fire between PFTs influence their relative fractional cover from year to year. Photosynthesis, evapotranspiration and soil water dynamics are modelled on a daily time step, while vegetation structure and PFT population densities are updated annually. Simulations have been made over the industrial period both for specific sites where field measurements were available for model evaluation, and globally on a 0.5° × 0.5° grid. Modelled vegetation patterns are consistent with observations, including remotely sensed vegetation structure and phenology. Seasonal cycles of net ecosystem exchange and soil moisture compare well with local measurements. Global carbon exchange fields used as input to an atmospheric tracer transport model (TM2) provided a good fit to observed seasonal cycles of CO2 concentration at all latitudes. Simulated inter-annual variability of the global terrestrial carbon balance is in phase with and comparable in amplitude to observed variability in the growth rate of atmospheric CO2. Global terrestrial carbon and water cycle parameters (pool sizes and fluxes) lie within their accepted ranges. The model is being used to study past, present and future terrestrial ecosystem dynamics, biochemical and biophysical interactions between ecosystems and the atmosphere, and as a component of coupled Earth system models.
Abstract.
Bachelet D, Neilson RP, Hickler T, Drapek RJ, Lenihan JM, Sykes MT, Smith B, Sitch S, Thonicke K (2003). Simulating past and future dynamics of natural ecosystems in the United States.
Global Biogeochemical Cycles,
17(2).
Abstract:
Simulating past and future dynamics of natural ecosystems in the United States
Simulations of potential vegetation distribution, natural fire frequency, carbon pools, and fluxes are presented for two DGVMs (Dynamic Global Vegetation Models) from the second phase of the Vegetation/Ecosystem Modeling and Analysis Project. Results link vegetation dynamics to biogeochemical cycling for the conterminous United States. Two climate change scenarios were used: a moderately warm scenario from the Hadley Climate Centre and a warmer scenario from the Canadian Climate Center. Both include sulfate aerosols and assume a gradual CO2 increase. Both DGVMs simulate a reduction of southwestern desert areas, a westward expansion of eastern deciduous forests, and the expansion of forests in the western part of the Pacific Northwest and in north-central California. Both DGVMs predict an increase in total biomass burnt in the next century, with a more pronounced increase under the Canadian scenario. Under the Hadley scenario, both DGVMs simulate increases in total carbon stocks. Under the Canadian scenario, both DGVMs simulate a decrease in live vegetation carbon. We identify similarities in model behavior due to the climate forcing and explain differences by the different structure of the models and their different sensitivity to CO2. We compare model output with data to enhance our confidence in their ability to simulate potential vegetation distribution and ecosystem processes. We compare changes in the area of drought-induced decreases in vegetation density with a spatial index derived from the Palmer Drought Severity Index to illustrate the ability of the vegetation to cope with water limitations in the future and the role of the CO2 fertilization effect.
Abstract.
Pan Y, McGuire AD, Melillo JM, Kicklighter DW, Sitch S, Prentice IC (2002). A biogeochemistry-based dynamic vegetation model and its application along a moisture gradient in the continental United States. Journal of Vegetation Science, 13(3), 369-382.
Lucht W, Prentice IC, Myneni RB, Sitch S, Friedlingstein P, Cramer W, Bousquet P, Buermann W, Smith B (2002). Climatic control of the high-latitude vegetation greening trend and Pinatubo effect.
Science,
296(5573), 1687-1689.
Abstract:
Climatic control of the high-latitude vegetation greening trend and Pinatubo effect.
A biogeochemical model of vegetation using observed climate data predicts the high northern latitude greening trend over the past two decades observed by satellites and a marked setback in this trend after the Mount Pinatubo volcano eruption in 1991. The observed trend toward earlier spring budburst and increased maximum leaf area is produced by the model as a consequence of biogeochemical vegetation responses mainly to changes in temperature. The post-Pinatubo decline in vegetation in 1992-1993 is apparent as the effect of temporary cooling caused by the eruption. High-latitude CO(2) uptake during these years is predicted as a consequence of the differential response of heterotrophic respiration and net primary production.
Abstract.
Author URL.
Dargaville RJ, Heimann M, McGuire AD, Prentice IC, Kicklighter DW, Joos F, Clein JS, Esser G, Foley J, Kaplan J, et al (2002). Evaluation of terrestrial carbon cycle models with atmospheric CO<inf>2</inf> measurements: Results from transient simulations considering increasing CO<inf>2</inf>, climate, and land-use effects.
Global Biogeochemical Cycles,
16(4).
Abstract:
Evaluation of terrestrial carbon cycle models with atmospheric CO2 measurements: Results from transient simulations considering increasing CO2, climate, and land-use effects
An atmospheric transport model and observations of atmospheric CO2 are used to evaluate the performance of four Terrestrial Carbon Models (TCMs) in simulating the seasonal dynamics and interannual variability of atmospheric CO2 between 1980 and 1991. The TCMs were forced with time varying atmospheric CO2 concentrations, climate, and land use to simulate the net exchange of carbon between the terrestrial biosphere and the atmosphere. The monthly surface CO2 fluxes from the TCMs were used to drive the Model of Atmospheric Transport and Chemistry and the simulated seasonal cycles and concentration anomalies are compared with observations from several stations in the CMDL network. The TCMs underestimate the amplitude of the seasonal cycle and tend to simulate too early an uptake of CO2 during the spring by approximately one to two months. The model fluxes show an increase in amplitude as a result of land-use change, but that pattern is not so evident in the simulated atmospheric amplitudes, and the different models suggest different causes for the amplitude increase (i.e. CO2 fertilization, climate variability or land use change). The comparison of the modeled concentration anomalies with the observed anomalies indicates that either the TCMs underestimate interannual variability in the exchange of CO2 between the terrestrial biosphere and the atmosphere, or that either the variability in the ocean fluxes or the atmospheric transport may be key factors in the atmospheric interannual variability.
Abstract.
Venevsky S, Thonicke K, Sitch S, Cramer W (2002). Simulating fire regimes in human-dominated ecosystems: Iberian Peninsula case study.
Global Change Biology,
8(10), 984-998.
Abstract:
Simulating fire regimes in human-dominated ecosystems: Iberian Peninsula case study
A new fire model is proposed which estimates areas burnt on a macro-scale (10-100 km). It consists of three parts: evaluation of fire danger due to climatic conditions, estimation of the number of fires and the extent of the area burnt. The model can operate on three time steps, daily, monthly and yearly, and interacts with a Dynamic Global Vegetation Model (DGVM), thereby providing an important forcing for natural competition. Fire danger is related to number of dry days and amplitude of daily temperature during these days. The number of fires during fire days varies with human population density. Areas burnt are calculated based on average wind speed, available fuel and fire duration. The model has been incorporated into the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM) and has been tested for peninsular Spain. LPJ-DGVM was modified to allow bi-directional feedback between fire disturbance and vegetation dynamics. The number of fires and areas burnt were simulated for the period 1974-94 and compared against observations. The model produced realistic results, which are well correlated, both spatially and temporally, with the fire statistics. Therefore, a relatively simple mechanistic fire model can be used to reproduce fire regime patterns in human-dominated ecosystems over a large region and a long time period.
Abstract.
McGuire AD, Sitch S, Clein JS, Dargaville R, Esser G, Foley J, Heimann M, Joos F, Kaplan J, Kicklighter DW, et al (2001). Carbon balance of the terrestrial biosphere in the twentieth century: Analyses of CO<inf>2</inf>, climate and land use effects with four process-based ecosytem models.
Global Biogeochemical Cycles,
15(1), 183-206.
Abstract:
Carbon balance of the terrestrial biosphere in the twentieth century: Analyses of CO2, climate and land use effects with four process-based ecosytem models
The concurrent effects of increasing atmospheric CO2 concentration, climate variability, and cropland establishment and abandonment on terrestrial carbon storage between 1920 and 1992 were assessed using a standard simulation protocol with four process-based terrestrial biosphere models. Over the long-term (1920-1992), the simulations yielded a time history of terrestrial uptake that is consistent (within the uncertainty with a long-term analysis based on ice core and atmospheric CO2 data. Up to 1958, three of four analyses indicated a net release of carbon from terrestrial ecosystems to the atmosphere caused by cropland establishment. After 1958, all analyses indicate a net uptake of carbon by terrestrial ecosystems, primarily because of the physiological effects of rapidly rising atmospheric CO2. During the 1980s the simulations indicate that terrestrial ecosystems stored between 0.3 and 1.5 Pg C yr-1, which is within the uncertainty of analysis based on CO2 and O2 budgets. Three of the four models indicated (in accordance with O2 evidence) that the tropics were approximately neutral while a net sink existed in ecosystems north of the tropics. Although all of the models agree that the long-term effect of climate on carbon storage has been small relative to the effects of increasing atmospheric CO2 and land use, the models disagree as to whether climate variability and change in the twentieth century has promoted carbon storage or release. Simulated interannual variability from 1958 generally reproduced the El Niño/Southern Oscillation (ENSO)-scale variability in the atmospheric CO2 increase, but there were substantial differences in the magnitude of interannual variability simulated by the models. The analysis of the ability of the models to simulate the changing amplitude of the seasonal cycle of atmospheric CO2 suggested that the observed trend may be a consequence of CO2 effects, climate variability, land use changes, or a combination of these effects. The next steps for improving the process-based simulation of historical terrestrial carbon include (1) the transfer of insight gained from stand-level process studies to improve the sensitivity of simulated carbon storage responses to changes in CO2 and climate, (2) improvements in the data sets used to drive the models so that they incorporate the timing, extent, and types of major disturbances, (3) the enhancement of the models so that they consider major crop types and management schemes, (4) development of data sets that identify the spatial extent of major crop types and management schemes through time, and (5) the consideration of the effects of anthropogenic nitrogen deposition. The evaluation of the performance of the models in the context of a more complete consideration of the factors influencing historical terrestrial carbon dynamics is important for reducing uncertainties in representing the role of terrestrial ecosystems in future projections of the Earth system.
Abstract.
Cramer W, Bondeau A, Woodward FI, Prentice IC, Betts RA, Brovkin V, Cox PM, Fisher V, Foley JA, Friend AD, et al (2001). Global response of terrestrial ecosystem structure and function to CO<inf>2</inf> and climate change: Results from six dynamic global vegetation models.
Global Change Biology,
7(4), 357-373.
Abstract:
Global response of terrestrial ecosystem structure and function to CO2 and climate change: Results from six dynamic global vegetation models
The possible responses of ecosystem processes to rising atmospheric CO2 concentration and climate change are illustrated using six dynamic global vegetation models that explicitly represent the interactions of ecosystem carbon and water exchanges with vegetation dynamics. The models are driven by the IPCC IS92a scenario of rising CO2 (Wigley et al. 1991), and by climate changes resulting from effective CO2 concentrations corresponding to IS92a, simulated by the coupled ocean atmosphere model HadCM2-SUL. Simulations with changing CO2 alone show a widely distributed terrestrial carbon sink of 1.4-3.8 Pg Cy-1 during the 1990s, rising to 3.7-8.6 Pg Cy-1 a century later. Simulations including climate change show a reduced sink both today (0.6-3.0PgCy-1) and a century later (0.3-6.6PgCy-1) as a result of the impacts of climate change on NEP of tropical and southern hemisphere ecosystems. In all models, the rate of increase of NEP begins to level off around 2030 as a consequence of the 'diminishing return' of physiological CO2 effects at high CO2 concentrations. Four out of the six models show a further, climate-induced decline in NEP resulting from increased heterotrophic respiration and declining tropical NPP after 2050. Changes in vegetation structure influence the magnitude and spatial pattern of the carbon sink and, in combination with changing climate, also freshwater availability (runoff). It is shown that these changes, once set in motion, would continue to evolve for at least a century even if atmospheric CO2 concentration and climate could be instantaneously stabilized. The results should be considered illustrative in the sense that the choice of CO2 concentration scenario was arbitrary and only one climate model scenario was used. However, the results serve to indicate a range of possible biospheric responses to CO2 and climate change. They reveal major uncertainties about the response of NEP to climate change resulting, primarily, from differences in the way that modelled global NPP responds to a changing climate. The simulations illustrate, however, that the magnitude of possible biospheric influences on the carbon balance requires that this factor is taken into account for future scenarios of atmospheric CO2 and climate change.
Abstract.
Joos F, Colin Prentice I, Sitch S, Meyer R, Hooss G, Plattner GK, Gerber S, Hasselmann K (2001). Global warming feedbacks on terrestrial carbon uptake under the intergovernmental Panel on Climate Change (IPCC) emission scenarios.
Global Biogeochemical Cycles,
15(4), 891-907.
Abstract:
Global warming feedbacks on terrestrial carbon uptake under the intergovernmental Panel on Climate Change (IPCC) emission scenarios
A coupled physical-biogeochemical climate model that includes a dynamic global vegetation model and a representation of a coupled atmosphere-ocean general circulation model is driven by the nonintervention emission scenarios recently developed by the Intergovernmental Panel on Climate Change (IPCC). Atmospheric CO2, carbon sinks, radiative forcing by greenhouse gases (GHGs) and aerosols, changes in the fields of surface-air temperature, precipitation, cloud cover, ocean thermal expansion, and vegetation structure are projected. Up to 2100, atmospheric CO2 increases to 540 ppm for the lowest and to 960 ppm for the highest emission scenario analyzed. Sensitivity analyses suggest an uncertainty in these projections of - 10 to +30% for a given emission scenario. Radiative forcing is estimated to increase between 3 and 8 W m-2 between now and 2100. Simulated warmer conditions in North America and Eurasia affect ecosystem structure: boreal trees expand poleward in high latitudes and are partly replaced by temperate trees and grasses at lower latitudes. The consequences for terrestrial carbon storage depend on the assumed sensitivity of climate to radiative forcing, the sensitivity of soil respiration to temperature, and the rate of increase in radiative forcing by both CO2 and other GHGs. In the most extreme cases, the terrestrial biosphere becomes a source of carbon during the second half of the century. High GHG emissions and high contributions of non-CO2 agents to radiative forcing favor a transient terrestrial carbon source by enhancing warming and the associated release of soil carbon.
Abstract.
Thonicke K, Venevsky S, Sitch S, Cramer W (2001). The role of fire disturbance for global vegetation dynamics: Coupling fire into a dynamic global vegetation model.
Global Ecology and Biogeography,
10(6), 661-677.
Abstract:
The role of fire disturbance for global vegetation dynamics: Coupling fire into a dynamic global vegetation model
1 Disturbances from fire, wind-throw, insects and other herbivores are, besides climate, CO2 and soils, critical factors for composition, structure and dynamics of most vegetation. To simulate the influence of fire on the dynamic equilibrium, as well as on potential change, of vegetation at the global scale, we have developed a fire model, running inside the modular framework of the Lund-Postdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM). 2 Estimated litter moisture is the main driver of day-to-day fire probability. The length of the fire season is used to estimate the fractional area of a grid cell which is burnt in a given year. This affected area is converted into an average fire return interval which can be compared to observations. 3 When driven by observed climate for the 20th century (at a 0.5° longitude/latitude resolution), the model yielded fire return intervals in good agreement with observations for many regions (except parts of semiarid Africa and boreal Siberia). We suggest that further improvement for these regions must involve additional process descriptions such as permafrost and fuel/fire dynamics.
Abstract.
Prentice IC, Heimann M, Sitch S (2000). The carbon balance of the terrestrial biosphere: Ecosystem models and atmospheric observations.
Ecological Applications,
10(6), 1553-1573.
Abstract:
The carbon balance of the terrestrial biosphere: Ecosystem models and atmospheric observations
Precise measurements in air are helping to clarify the fate of CO2 released by human activities. Oxygen-to-nitrogen ratios in firn (the transition state from snow to ice) and archived air samples indicate that the terrestrial biosphere was approximately carbon-neutral on average during the 1980s. CO2 release by forest clearance during this period must have been compensated for by CO2 sinks elsewhere on land. Direct atmospheric O2:N2 measurements became available during the 1990s. These measurements indicate net terrestrial CO2 uptake of ~2 Pg C/yr. From the north-south O2:N2 gradient, it has been inferred that about this amount was taken up by terrestrial ecosystems in the northern nontropics while additional CO2 released by tropical-forest clearance must have been compensated for by additional, tropical, terrestrial CO2 sinks. These and other atmospheric observations provide independent tests of carbon-cycle reconstructions made with process-based terrestrial ecosystem models. Such models can account for major features of the atmospheric-CO2 record, including the amplitude and phase of the seasonal cycle of atmospheric-CO2 concentration at different latitudes, and much of the interannual variability in the rate of increase of atmospheric CO2. Models also predict direct effects of rising atmospheric-CO2 concentration on primary production, modified by feedbacks at the plant and ecosystem levels. These effects translate into a global carbon sink the right order of magnitude to compensate for forest clearance during the 1980s. The modeled sink depends on continuously increasing CO2 to maintain disequilibrium between primary production and carbon storage. There are still substantial differences among the carbon-balance estimates made by different models, reflecting limitations in current understanding of ecosystem-level responses to atmospheric-CO2 concentration, especially with regard to the interactions of C and N cycling and interactions with land-use change. Scenario calculations nevertheless agree that if atmospheric CO2 continues its rise unchecked then the terrestrial sink will start to decline by the middle of the next century, for reasons including saturation of the direct CO2 effect on photosynthesis.
Abstract.
Fosberg MA, Cramer W, Brovkin V, Fleming R, Gardner R, Gill AM, Goldammer JG, Keane R, Koehler P, Lenihan J, et al (1999). Strategy for a Fire Module in Dynamic Global Vegetation Models. International Journal of Wildland Fire, 9(1), 79-84.
Heimann M, Esser G, Haxeltine A, Kaduk J, Kicklighter DW, Knorr W, Kohlmaier GH, McGuire AD, Melillo J, Moore B, et al (1998). Evaluation of terrestrial carbon cycle models through simulations of the seasonal cycle of atmospheric CO<inf>2</inf>: First results of a model intercomparison study.
Global Biogeochemical Cycles,
12(1), 1-24.
Abstract:
Evaluation of terrestrial carbon cycle models through simulations of the seasonal cycle of atmospheric CO2: First results of a model intercomparison study
Results of an intercomparison among terrestrial biogeochemical models (TBMs) are reported, in which one diagnostic and five prognostic models have been run with the same long-term climate forcing. Monthly fields of net ecosystem production (NEP), which is the difference between net primary production (NPP) and heterotrophic respiration RH, at 0.5° resolution have been generated for the terrestrial biosphere. The monthly estimates of NEP in conjunction with seasonal CO2 flux fields generated by the seasonal Hamburg Model of the Oceanic Carbon Cycle (HAMOCC3) and fossil fuel source fields were subsequently coupled to the three-dimensional atmospheric tracer transport model TM2 forced by observed winds. The resulting simulated seasonal signal of the atmospheric CO2 concentration extracted at the grid cells corresponding to the locations of 27 background monitoring stations of the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory network is compared with measurements from these sites. The Simple Diagnostic Biosphere Model (SDBM1), which is tuned to the atmospheric CO2 concentration at five monitoring stations in the northern hemisphere, successfully reproduced the seasonal signal of CO2 at the other monitoring stations. The SDBM1 simulations confirm that the north-south gradient in the amplitude of the atmospheric CO2 signal results from the greater northern hemisphere land area and the more pronounced seasonality of radiation and temperature in higher latitudes. In southern latitudes, ocean-atmosphere gas exchange plays an important role in determining the seasonal signal of CO2. Most of the five prognostic models (i.e. models driven by climatic inputs) included in the intercomparison predict in the northern hemisphere a reasonably accurate seasonal cycle in terms of amplitude and, to some extent, also with respect to phase. In the tropics, however, the prognostic models generally tend to overpredict the net seasonal exchanges and stronger seasonal cycles than indicated by the diagnostic model and by observations. The differences from the observed seasonal signal of CO2 may be caused by shortcomings in the phenology algorithms of the prognostic models or by not properly considering the effects of land use and vegetation fires on CO2 fluxes between the atmosphere and terrestrial biosphere.
Abstract.
Pan Y, Melillo JM, McGuire AD, Kicklighter DW, Pitelka LF, Hibbard K, Pierce LL, Running SW, Ojima DS, Parton WJ, et al (1998). Modeled responses of terrestrial ecosystems to elevated atmospheric CO<inf>2</inf>: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP).
Oecologia,
114(3), 389-404.
Abstract:
Modeled responses of terrestrial ecosystems to elevated atmospheric CO2: a comparison of simulations by the biogeochemistry models of the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)
Although there is a great deal of information concerning responses to increases in atmospheric CO2 at the tissue and plant levels, there are substantially fewer studies that have investigated ecosystem-level responses in the context of integrated carbon, water, and nutrient cycles. Because our understanding of ecosystem responses to elevated CO2 is incomplete, modeling is a tool that can be used to investigate the role of plant and soil interactions in the response of terrestrial ecosystems to elevated CO2. In this study, we analyze the responses of net primary production (NPP) to doubled CO2 from 355 to 710 ppmv among three biogeochemistry models in the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP): BIOME-BGC (BioGeochemical Cycles), Century, and the Terrestrial Ecosystem Model (TEM). For the conterminous United States, doubled atmospheric CO2 causes NPP to increase by 5% in Century, 8% in TEM, and 11% in BIOME-BGC. Multiple regression analyses between the NPP response to doubled CO2 and the mean annual temperature and annual precipitation of biomes or grid cells indicate that there are negative relationships between precipitation and the response of NPP to doubled CO2 for all three models. In contrast, there are different relationships between temperature and the response of NPP to doubled CO2 for the three models: there is a negative relationship in the responses of BIOME-BGC, no relationship in the responses of Century, and a positive relationship in the responses of TEM. In BIOME-BGC, the NPP response to doubled CO2 is controlled by the change in transpiration associated with reduced leaf conductance to water vapor. This change affects soil water, then leaf area development and, finally, NPP. In Century, the response of NPP to doubled CO2 is controlled by changes in decomposition rates associated with increased soil moisture that results from reduced evapotranspiration. This change affects nitrogen availability for plants, which influences NPP. In TEM, the NPP response to doubled CO2 is controlled by increased carboxylation which is modified by canopy conductance and the degree to which nitrogen constraints cause down-regulation of photosynthesis. The implementation of these different mechanisms has consequences for the spatial pattern of NPP responses, and represents, in part, conceptual uncertainty about controls over NPP responses. Progress in reducing these uncertainties requires research focused at the ecosystem level to understand how interactions between the carbon, nitrogen, and water cycles influence the response of NPP to elevated atmospheric CO2.
Abstract.
Schimel DS, Braswell BH, Emanuel W, Rizzo B, Smith T, Woodward FI, Fisher H, Kittel TGF, McKeown R, Painter T, et al (1997). Continental scale variability in ecosystem processes: Models, data, and the role of disturbance.
Ecological Monographs,
67(2), 251-271.
Abstract:
Continental scale variability in ecosystem processes: Models, data, and the role of disturbance
Management of ecosystems at large regional or continental scales and determination of the vulnerability of ecosystems to large-scale changes in climate or atmospheric chemistry require understanding how ecosystem processes are governed at large spatial scales. A collaborative project, the Vegetation and Ecosystem Modeling and Analysis Project (VEMAP), addressed modeling of multiple resource limitation at the scale of the conterminous United States, and the responses of ecosystems to environmental change. In this paper, we evaluate the model-generated patterns of spatial variability within and between ecosystems using Century, TEM, and Biome-BGC, and the relationships between modeled water balance, nutrients, and carbon dynamics. We present evaluations of models against mapped and site-specific data. In this analysis, we compare model-generated patterns of variability in net primary productivity (NPP) and soil organic carbon (SOC) to, respectively, a satellite proxy and mapped SOC from the VEMAP soils database (derived from USDA-NRCS [Natural Resources Conservation Service] information) and also compare modeled results to site-specific data from forests and grasslands. The VEMAP models simulated spatial variability in ecosystem processes in substantially different ways, reflecting the models' differing implementations of multiple resource limitation of NPP. The models had substantially higher COrrelations across vegetation types compared to within vegetation types. All three models showed correlation among water use, nitrogen availability, and primary production, indicating that water and nutrient limitations of NPP were equilibrated with each other at steady state. This model result may explain a number of seemingly contradictory observations and provides a series of testable predictions. The VEMAP ecosystem models were implicitly or explicitly sensitive to disturbance in their simulation of NPP and carbon storage. Knowledge of the effects of disturbance (human and natural) and spatial data describing disturbance regimes are needed for spatial modeling of ecosystems. Improved consideration of disturbance is a key 'next step' for spatial ecosystem models.
Abstract.
Foley JA, Prentice IC, Ramankutty N, Levis S, Pollard D, Sitch S, Haxeltine A (1996). An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics.
Global Biogeochemical Cycles,
10(4), 603-628.
Abstract:
An integrated biosphere model of land surface processes, terrestrial carbon balance, and vegetation dynamics
Here we present a new terrestrial biosphere model (the Integrated Biosphere Simulator - IBIS) which demonstrates how land surface biophysics, terrestrial carbon fluxes, and global vegetation dynamics can be represented in a single, physically consistent modeling framework. In order to integrate a wide range of biophysical, physiological, and ecological processes, the model is designed around a hierarchical, modular structure and uses a common state description throughout. First, a coupled simulation of the surface water, energy, and carbon fluxes is performed on hourly timesteps and is integrated over the year to estimate the annual water and carbon balance. Next, the annual carbon balance is used to predict changes in the leaf area index and biomass for each of nine plant functional types, which compete for light and water using different ecological strategies. The resulting patterns of annual evapotranspiration, runoff, and net primary productivity are in good agreement with observations. In addition, the model simulates patterns of vegetation dynamics that qualitatively agree with features of the natural process of secondary succession. Comparison of the model's inferred near-equilibrium vegetation categories with a potential natural vegetation map shows a fair degree of agreement. This integrated modeling framework provides a means of simulating both rapid biophysical processes and long-term ecosystem dynamics that can be directly incorporated within atmospheric models.
Abstract.
Christensen TR, Prentice IC, Kaplan J, Haxeltine A, Sitch S (1996). Methane flux from northern wetlands and tundra: an ecosystem source modelling approach.
Tellus, Series B: Chemical and Physical Meteorology,
48(5), 652-661.
Abstract:
Methane flux from northern wetlands and tundra: an ecosystem source modelling approach
The magnitude and geographical distribution of natural sources and sinks of atmospheric CH4 in the biosphere are still poorly known. Estimates of the net contribution from northern wetlands have been lowered during recent years. According to current consensus, about 35 Tg CH4/yr originates from northern wetlands and tundra. A process-oriented ecosystem source model for CH4 is used here to obtain an independent estimate for this flux. The model estimates steady-state seasonal cycles of NPP and heterotrophic respiration (HR). It accounts for peatland carbon storage and then obtains CH4 emission as a proportion of HR with the constant of proportionality (as a range) estimated from observations. The model was shown consistent with seasonal data (including winter) on NPP, soil respiration and CH4 emission at sites spanning a range of latitudes and climates. Applied on a 1° grid basis using standard climatological and wetland distribution data sets, this approach yields a total non-forested wetland and tundra emission (>50°N) of 8.7±5.8 Tg CH4/yr. After inclusion of forested wetlands, we estimate a total emission from northern wetlands and tundra of 20±13 Tg CH4/yr. This is somewhat lower than current atmospherically based estimates. The difference may be due to localized high emissions, which have been reported, e.g. for West Siberian wetlands but which are not well understood and not included in current models.
Abstract.
MELILLO JM, BORCHERS J, CHANEY J, FISHER H, FOX S, HAXELTINE A, JANETOS A, KICKLIGHTER DW, KITTEL TGF, MCGUIRE AD, et al (1995). VEGETATION ECOSYSTEM MODELING AND ANALYSIS PROJECT - COMPARING BIOGEOGRAPHY AND BIOGEOCHEMISTRY MODELS IN a CONTINENTAL-SCALE STUDY OF TERRESTRIAL ECOSYSTEM RESPONSES TO CLIMATE-CHANGE AND CO2 DOUBLING.
GLOBAL BIOGEOCHEMICAL CYCLES,
9(4), 407-437.
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