Publications by year
In Press
Eager-Nash J, Mayne N, Nicholson A, Prins J, Young O, Daines S, Sergeev D, Lambert F, Manners J, Boutle I, et al (In Press). 3D climate simulations of the Archean find that Methane has a strong cooling effect at high concentrations. Journal of Geophysical Research: Atmospheres
Lenton T, Buxton J, Abrams J, Boulton C, Powell T, Cunliffe A (In Press). A resilience sensing system for the biosphere.
Philosophical Transactions of the Royal Society B: Biological SciencesAbstract:
A resilience sensing system for the biosphere
We are in a climate and ecological emergency, where climate change and direct anthropogenic interference with the biosphere are risking abrupt and/or irreversible changes that threaten our life-support systems. Efforts are underway to increase the resilience of some ecosystems that are under threat, yet collective awareness and action are modest at best. Here we highlight the potential for a biosphere resilience sensing system to make it easier to see where things are going wrong, and to see whether deliberate efforts to make things better are working. We focus on global resilience sensing of the terrestrial biosphere at high spatial and temporal resolution through satellite remote sensing, utilising the generic mathematical behaviour of complex systems – loss of resilience corresponds to slower recovery from perturbations, gain of resilience equates to faster recovery. We consider what subset of biosphere resilience remote sensing can monitor, critically reviewing existing studies. Then we present illustrative, global results for vegetation resilience and trends in resilience over the last 20 years, from both satellite data and model simulations. We close by discussing how resilience sensing nested across global, biome-ecoregion, and local ecosystem scales, could aid management and governance at these different scales, and identify priorities for further work.
Abstract.
Buxton J, Powell T, Ambler J, Boulton C, Nicholson A, Arthur R, Lees K, Williams H, Lenton T (In Press). Community-driven tree planting greens the neighbouring landscape.
Abstract:
Community-driven tree planting greens the neighbouring landscape
Abstract
. Nature-based solutions to climate change are growing policy priorities yet remain hard to quantify. Here we use remote sensing to quantify direct and indirect benefits from community-led agroforestry by the International Small group and Tree planting program (TIST) in Kenya. Since 2005, TIST-Kenya has incentivised smallholder farmers to plant trees for agricultural benefit and to sequester CO2. We use Landsat-7 satellite imagery to examine the effect on the historically deforested landscape around Mount Kenya. We identify positive greening trends in TIST groves during 2000-2019 relative to the wider landscape. These groves cover 27,198 hectares, and a further 27,750 hectares of neighbouring agricultural land is also positively influenced by TIST. This positive ‘spill-over’ impact of TIST activity occurs at up to 360m distance. TIST also benefits local forests, e.g. through reducing fuelwood and fodder extraction. Our results show that community-led initiatives can lead to successful landscape-scale regreening on decadal timescales.
Abstract.
Williamson MS, Bathiany S, Lenton TM (In Press). Early warning signals of tipping points in periodically forced systems.
Abstract:
Early warning signals of tipping points in periodically forced systems
Abstract. The prospect of finding generic early warning signals of an approaching tipping point in a complex system has generated much recent interest. Existing methods are predicated on a separation of timescales between the system studied and its forcing. However, many systems, including several candidate tipping elements in the climate system, are forced periodically at a timescale comparable to their internal dynamics. Here we find alternative early warning signals of tipping points due to local bifurcations in systems subjected to periodic forcing whose time scale is similar to the period of the forcing. These systems are not in, or close to, a fixed point. Instead their steady state is described by a periodic attractor. We show that the phase lag and amplification of the system response provide early warning signals, based on a linear dynamics approximation. Furthermore, the power spectrum of the system's time series reveals the generation of harmonics of the forcing period, the size of which are proportional to how nonlinear the system's response is becoming with nonlinear effects becoming more prominent closer to a bifurcation. We apply these indicators to a simple conceptual system and satellite observations of Arctic sea ice area, the latter conjectured to have a bifurcation type tipping point. We find no detectable signal of the Arctic sea ice approaching a local bifurcation.
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Abstract.
Thomas ZA, Kwasniok F, Boulton CA, Cox PM, Jones RT, Lenton TM, Turney CSM (In Press). Early warnings and missed alarms for abrupt monsoon transitions.
Abstract:
Early warnings and missed alarms for abrupt monsoon transitions
Abstract. Palaeo-records from China (Cheng et al. 2009; Wang et al. 2008, 2001) demonstrate the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesised that over these timescales, the EASM exhibits two stable states with bifurcation-type tipping points between them (Schewe et al. 2012). Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem records from Sanbao Cave and Hulu Cave, China (Wang et al. 2008, 2001), spanning the penultimate glacial cycle, and in multiple model simulations derived from the data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. We detect critical slowing down prior to an abrupt monsoon shift during the penultimate deglaciation consistent with long-term orbital forcing. However, such signals are only detectable when the change in system stability is sufficiently slow to be detected by the sampling resolution of the dataset, raising the possibility that the alarm was missed and a similar forcing drove earlier EASM shifts.
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Abstract.
Lenton T (In Press). Earth system boundaries and Earth system justice: Sharing the ecospace. Environmental Politics
Lenton T, Krause AJ, Mills BJW, Merdith AS, Poulton SW (In Press). Extreme variability in atmospheric oxygen levels in the late Precambrian.
Science AdvancesAbstract:
Extreme variability in atmospheric oxygen levels in the late Precambrian
Mapping the history of atmospheric O2 during the late Precambrian is vital for evaluating potential links to the animal evolution. Ancient O2 levels are often inferred from geochemical analyses of marine sediments, leading to the assumption that the Earth experienced a stepwise increase in atmospheric O2 during the Neoproterozoic. However, the nature of this hypothesized oxygenation event remains unknown, with suggestions of a more dynamic O2 history in the oceans, and major uncertainty over any direct connection between the marine realm and atmospheric O2. Here we present a continuous quantitative reconstruction of atmospheric O2 over the last 1.5 billion years, using an isotope mass balance approach that combines bulk geochemistry and tectonic recycling rate calculations. We predict that atmospheric O2 levels during the Neoproterozoic oscillated between ~1% and ~50% PAL (Present Atmospheric Level). We conclude that there was no simple unidirectional rise in atmospheric O2 during the Neoproterozoic, and the first animals evolved against a backdrop of extreme O2 variability.
Abstract.
Rammelt CF, Gupta J, Liverman D, Scholtens J, Ciobanu D, Abrams JF, Bai X, Gifford L, Gordon C, Hurlbert M, et al (In Press). Impacts of Meeting Minimum Access on Critical Earth Systems amidst the Great Inequality.
Abstract:
Impacts of Meeting Minimum Access on Critical Earth Systems amidst the Great Inequality
The UN 2030 Agenda includes 17 Sustainable Development Goals towards improving access to resources and services, reducing environmental degradation and bringing down inequality. However, there is debate on the magnitude of the environmental burden that would arise from meeting the needs of the poorest, especially compared to much larger burdens from the rich. We first show that the ‘Great Acceleration’ of human impacts is characterized by a ‘Great Inequality’ in utilising and damaging the environment. We then operationalize ‘just access’ to minimum energy, water, food and infrastructure. Third, in an unequal world, we show that hypothetically meeting ‘just access’ would add 2-26% to current impacts on the Earth’s natural systems of climate, water, land and nutrients. These additional impacts, hypothetically caused by about a third of humanity, equal those currently caused by the wealthiest 1-4%. Nevertheless, achieving ‘just access’ calls for redistribution within stable Earth System Boundaries.
Abstract.
Littleton EW, Harper AB, Vaughan NE, Oliver RJ, Duran-Rojas MC, Lenton TM (In Press). JULES-BE: representation of bioenergy crops and harvesting in the Joint UK Land Environment Simulator vn5.1.
Abstract:
JULES-BE: representation of bioenergy crops and harvesting in the Joint UK Land Environment Simulator vn5.1
Abstract. We describe developments to a land surface model, allowing for flexible user-prescribed harvest regimes of various perennial bioenergy crops or natural vegetation types. Our aim is to integrate the most useful aspects of dedicated bioenergy models into dynamic global vegetation models, in order that assessment of bioenergy options can benefit from state-of-the-art Earth system modelling. A new plant functional type (PFT) representing Miscanthus is also presented. The Miscanthus PFT fits well with growth parameters observed at a site in Lincolnshire, UK; however, global observed yields of Miscanthus are far more variable than is captured by the model, suggesting missing model components that influence growth and yields. Global expansion of bioenergy crop areas under a 2 °C emissions scenario and balanced greenhouse gas mitigation strategy from the IMAGE integrated assessment model (RCP2.6-SSP2) achieves a mean yield of 4.3 billion tonnes dry matter per year over 2040–2099, around 30 % higher than the biomass availability projected by IMAGE. In addition to perennial grasses, JULES-BE can also be used to represent short-rotation coppicing; residue harvesting from cropland or forestry; and rotation forestry.
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Abstract.
Nicholson A, Daines S, Mayne N, Eager J, Lenton T, Kohary K (In Press). Predicting biosignatures for nutrient limited biospheres. Monthly Notices of the Royal Astronomical Society
Boulton C, Lenton T, Boers N (In Press). Pronounced loss of Amazon rainforest resilience since the early 2000s.
Abstract:
Pronounced loss of Amazon rainforest resilience since the early 2000s
Abstract
. The resilience of the Amazon rainforest to climate and land-use change is of critical importance for biodiversity, regional climate, and the global carbon cycle. Some models project future climate-driven Amazon rainforest dieback and transition to savanna1. Deforestation and climate change, via increasing dry-season length2,3 and drought frequency – with three 1-in-100-year droughts since 20054-6 – may already have pushed the Amazon close to a critical threshold of rainforest dieback7,8. However, others argue that CO2 fertilization should make the forest more resilient9,10. Here we quantify Amazon resilience by applying established indicators11 to remotely-sensed vegetation data with focus on vegetation optical depth (1991-2016), which correlates well with broadleaf tree coverage. We find that the Amazon rainforest has been losing resilience since 2003, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall, and in parts of the rainforest that are closer to human activity. Given observed increases in dry-season length2,3 and drought frequency4-6, and expanding areas of land use change, loss of resilience is likely to continue. We provide direct empirical evidence that the Amazon rainforest is losing stability, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.
Abstract.
von der Heydt AS, Ashwin P, Camp CD, Crucifix M, Dijstra HA, Ditlevsen P, Lenton TM (In Press). Quantification and Interpretation of the Climate Variability Record. Global and Planetary Change
Lenton T, Abrams J (In Press). Quantifying the Human Cost of Global Warming. Nature Sustainability
Smith T, Zotta R-M, Boulton CA, Lenton TM, Dorigo W, Boers N (In Press). Reliability of Resilience Estimation based on Multi-Instrument Time Series.
Abstract:
Reliability of Resilience Estimation based on Multi-Instrument Time Series
Abstract. Many widely-used observational data sets are comprised of several overlapping instrument records. While data inter-calibration techniques often yield continuous and reliable data for trend analysis, less attention is generally paid to maintaining higher-order statistics such as variance and autocorrelation. A growing body of work uses these metrics to quantify the stability or resilience of a system under study, and potentially to anticipate an approaching critical transition in the system. Exploring the degree to which changes in resilience indicators such as the variance or autocorrelation can be attributed to non-stationary characteristics of the measurement process, rather than actual changes in the dynamical properties of the system, is important in this context. In this work we use both synthetic and empirical data to explore how changes in the noise structure of a data set are propagated into the commonly used resilience metrics lag-one autocorrelation and variance. We focus on examples from remotely sensed vegetation indicators such as the Vegetation Optical Depth and the Normalized Difference Vegetation Index from different satellite sources. We find that varying satellite noise levels and data aggregation schemes can lead to biases in inferred resilience changes. These biases are typically more pronounced when resilience metrics are aggregated (for example, by land-cover type or region), whereas estimates for individual time series remain reliable at reasonable sensor noise levels. Our work provides guidelines for the treatment and aggregation of multi-instrument data in studies of critical transitions and resilience.
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Abstract.
Lenton T (In Press). Spread of the cycles: a feedback perspective on the Anthropocene. Philosophical Transactions of the Royal Society B: Biological Sciences
Lenton T, Kohler TA, Marquet PA, Boyle RA, Crucifix M, Wilkinson DM, Scheffer M (In Press). Survival of the Systems. Trends in Ecology and Evolution
Watson T, Lenton T, Safra De Campos R (In Press). The Climate Change, Conflict and Migration Nexus: a Holistic View. Climate Resilience and Sustainability
Lenton T (In Press). Tipping Positive Change. Philosophical Transactions of the Royal Society B: Biological Sciences
Lenton T, Lees K (In Press). Using remote sensing to assess peatland resilience by estimating oil
surface moisture and drought recovery. Science of the Total Environment
Lenton T, Ripple WJ, wolf C, Gregg MG, Levin K, Rockström J, Kalmus P, Betts MG, Huq S, Law BE, et al (In Press). World Scientists’ Warning of a. Climate Emergency 2022.
BioscienceAbstract:
World Scientists’ Warning of a. Climate Emergency 2022
2022 marks the 30th anniversary of
the “World Scientists’ Warning to
Humanity,” signed by more than 1700
scientists in 1992. Since this original
warning, there has been a roughly 40%
increase in global greenhouse gas emis sions. This is despite numerous written
warnings from the Intergovernmental
Panel on Climate Change and a recent
scientists’ warning of a climate emer gency with nearly 15,000 signatories
from 158 countries (Ripple et al. 2020).
Current policies are taking the planet
to around 3 degrees Celsius warming
by 2100, a temperature level that Earth
has not experienced over the past 3
million years (Liu and Raftery 2021).
The consequences are becoming
increasingly extreme, and outcomes
such as global societal collapse are
plausible and dangerously underex plored (Kemp et. al. 2022). Motivated
by the moral urgency of this global
crisis, in the present article, we track
recent climate-related disasters, assess
planetary vital signs, and provide
sweeping policy recommendations
Abstract.
2023
Eager-Nash JK, Mayne NJ, Nicholson AE, Prins JE, Young OCF, Daines SJ, Sergeev DE, Lambert FH, Manners J, Boutle IA, et al (2023). 3D climate simulations of the Archean find that methane has a strong. cooling effect at high concentrations.
Abstract:
3D climate simulations of the Archean find that methane has a strong. cooling effect at high concentrations
Methane is thought to have been an important greenhouse gas during the
Archean, although its potential warming has been found to be limited at high
concentrations due to its high shortwave absorption. We use the Met Office
Unified Model, a general circulation model, to further explore the climatic
effect of different Archean methane concentrations. Surface warming peaks at a
pressure ratio CH$_4$:CO$_2$ of approximately 0.1, reaching a maximum of up to
7 K before significant cooling above this ratio. Equator-to-pole temperature
differences also tend to increase up to pCH$_4$ $\leq$300 Pa, which is driven
by a difference in radiative forcing at the equator and poles by methane and a
reduction in the latitudinal extend of the Hadley circulation. 3D models are
important to fully capture the cooling effect of methane, due to these impacts
of the circulation.
Abstract.
Author URL.
Wood RA, Crucifix M, Lenton TM, Mach KJ, Moore C, New M, Sharpe S, Stocker TF, Sutton RT (2023). A Climate Science Toolkit for High Impact-Low Likelihood Climate Risks.
Earth's Future,
11(4).
Abstract:
A Climate Science Toolkit for High Impact-Low Likelihood Climate Risks
An important component of the risks from climate change arises from outcomes that are very unlikely, but whose impacts if they were to occur would be extremely severe. Examples include levels of surface warming, or changes in the water cycle, that are at the extreme of plausible ranges, or crossing of a climate system “tipping point” such as ice sheet or ocean circulation instability. If such changes were to occur their impacts on infrastructure or ecosystems may exceed existing plans for adaptation. The traditional approach of ensemble climate change projections is not well suited to managing these High Impact-Low Likelihood (HILL) risks, where the objective is to “prepare for the worst” rather than to “plan for what's likely.” in this paper we draw together a number of ideas from recent literature, to classify four types of HILL climate outcome and to propose the development of a practical “toolkit” of physical climate information that can be used in future to inform HILL risk management. The toolkit consists of several elements that would need to be developed for each plausible HILL climate outcome, then deployed individually to develop targeted HILL risk management approaches for individual sectors. We argue that development of the HILL toolkit should be an important focus for physical climate research over the coming decade, and that the time is right for a focused assessment of HILL risks by the Intergovernmental Panel on Climate Change in its 7th Assessment Cycle.
Abstract.
Obura DO, DeClerck F, Verburg PH, Gupta J, Abrams JF, Bai X, Bunn S, Ebi KL, Gifford L, Gordon C, et al (2023). Achieving a nature- and people-positive future. One Earth, 6(2), 105-117.
Warszawski L, Kriegler E, Lenton TM, Gaffney O, Jacob D, Klingenfeld D, Koide R, Costa MM, Messner D, Nakicenovic N, et al (2023). Corrigendum: all options, not silver bullets, needed to limit global warming to 1.5 °C: a scenario appraisal (2021 Environ. Res. Lett. 16 064037). Environmental Research Letters, 18(4).
Gupta J, Liverman D, Prodani K, Aldunce P, Bai X, Broadgate W, Ciobanu D, Gifford L, Gordon C, Hurlbert M, et al (2023). Earth system justice needed to identify and live within Earth system boundaries. Nature Sustainability, 6(6), 630-638.
Krause AJ, Sluijs A, van der Ploeg R, Lenton TM, Pogge von Strandmann PAE (2023). Enhanced clay formation key in sustaining the Middle Eocene Climatic Optimum.
Nature Geoscience,
16(8), 730-738.
Abstract:
Enhanced clay formation key in sustaining the Middle Eocene Climatic Optimum
The Middle Eocene Climatic Optimum (around 40 million years ago) was a roughly 400,000-year-long global warming phase associated with an increase in atmospheric CO2 concentrations and deep-ocean acidification that interrupted the Eocene’s long-term cooling trend. The unusually long duration, compared with early Eocene global warming phases, is puzzling as temperature-dependent silicate weathering should have provided a negative feedback, drawing down CO2 over this timescale. Here we investigate silicate weathering during this climate warming event by measuring lithium isotope ratios (reported as δ7Li), which are a tracer for silicate weathering processes, from a suite of open-ocean carbonate-rich sediments. We find a positive δ7Li excursion—the only one identified for a warming event so far —of ~3‰. Box model simulations support this signal to reflect a global shift from congruent weathering, with secondary mineral dissolution, to incongruent weathering, with secondary mineral formation. We surmise that, before the climatic optimum, there was considerable soil shielding of the continents. An increase in continental volcanism initiated the warming event, but it was sustained by an increase in clay formation, which sequestered carbonate-forming cations, short-circuiting the carbonate–silicate cycle. Clay mineral dynamics may play an important role in the carbon cycle for climatic events occurring over intermediate (i.e. 100,000 year) timeframes.
Abstract.
Li Y, Svenning J-C, Zhou W, Zhu K, Abrams JF, Lenton TM, Teng SN, Dunn RR, Xu C (2023). Global Inequality in Cooling from Urban Green Spaces and its Climate. Change Adaptation Potential.
Abstract:
Global Inequality in Cooling from Urban Green Spaces and its Climate. Change Adaptation Potential
Heat extremes are projected to severely impact humanity and with increasing
geographic disparities. Global South countries are more exposed to heat
extremes and have reduced adaptation capacity. One documented source of such
adaptation inequality is a lack of resources to cool down indoor temperatures.
Less is known about the capacity to ameliorate outdoor heat stress. Here, we
assess global inequality in green infrastructure, on which urban residents
critically rely to ameliorate lethal heat stress outdoors. We use
satellite-derived indicators of land surface temperature and urban green space
area to quantify the daytime cooling capacity of urban green spaces in the
hottest months across ~500 cities with population size over 1 million per city
globally. Our results show a striking contrast with an about two-fold lower
cooling capacity in Global South cities compared to the Global North (2.1
degrees Celsius vs. 3.8 degrees Celsius). A similar gap occurs for the cooling
adaptation benefits received by an average urban resident (Global South 1.9
degrees Celsius vs. North 3.6 degrees Celsius), i.e. accounting for relative
spatial distributions of people and urban green spaces. This cooling adaptation
inequality is attributed to the discrepancies in urban green space quantity and
quality between Global North and South cities, jointly shaped by natural and
socioeconomic factors. Our analyses suggest vast potential for enhancing
outdoor cooling adaptation while reducing its global inequality through
expanding and optimizing urban green infrastructure.
Abstract.
Author URL.
Ripple WJ, Wolf C, Lenton TM, Gregg JW, Natali SM, Duffy PB, Rockström J, Schellnhuber HJ (2023). Many risky feedback loops amplify the need for climate action.
One Earth,
6(2), 86-91.
Abstract:
Many risky feedback loops amplify the need for climate action
Many feedback loops significantly increase warming due to greenhouse gas emissions. However, not all of these feedbacks are fully accounted for in climate models. Thus, associated mitigation pathways could fail to sufficiently limit temperatures. A targeted expansion of research and an accelerated reduction of emissions are needed to minimize risks.
Abstract.
Lees KJ, Carmenta R, Condliffe I, Gray A, Marquis L, Lenton TM (2023). Protecting peatlands requires understanding stakeholder perceptions and relational values: a case study of peatlands in the Yorkshire Dales.
Ambio,
52(7), 1282-1296.
Abstract:
Protecting peatlands requires understanding stakeholder perceptions and relational values: a case study of peatlands in the Yorkshire Dales.
Sustainable peatland management is a global environmental governance challenge given peat's carbon storage. Peatlands worldwide are sites of contested demands between stakeholders with distinct management priorities. In the United Kingdom, peatland management is a focus of political interest for nature-based solutions (NBS), causing tensions with land managers who feel their traditional knowledge is undervalued. Using Q-method (a semi-quantitative method for clarifying distinct viewpoints) with estate managers, gamekeepers, farmers, and employees of land-owning organisations, we explored perceptions around changing upland management in the Yorkshire Dales. Land managers hold strong values of ownership, aesthetics, and stewardship. The prospect of changing management causes fears of losing these relational values alongside instrumental values. Yorkshire Dales stakeholders agreed on NBS aims (reducing flooding, limiting wildfires, protecting wild birds), but disagreed on methods to achieve these. Our research supports engaging local stakeholders at all stages of peatland protection schemes to minimise resentment towards top-down management.
Abstract.
Author URL.
Krause AJ, Sluijs A, van der Ploeg R, Lenton TM, Pogge von Strandmann PAE (2023). Publisher Correction: Enhanced clay formation key in sustaining the Middle Eocene Climatic Optimum (Nature Geoscience, (2023), 16, 8, (730-738), 10.1038/s41561-023-01234-y).
Nature GeoscienceAbstract:
Publisher Correction: Enhanced clay formation key in sustaining the Middle Eocene Climatic Optimum (Nature Geoscience, (2023), 16, 8, (730-738), 10.1038/s41561-023-01234-y)
Correction to: Nature Geoscience, published online 31 July 2023. In the version of the article originally published, a reference was missing from the seventh paragraph of the “A global shift towards enhanced clay formation” section and the first paragraph of the “Further information on the successful model Scenario 8” section (in the latter instance, the reference is cited in the added text “although a global reorganisation of the silicon cycle may have also played a part”). The reference—Dunlea, A. G. et al. Cenozoic global cooling and increased seawater Mg/Ca via reduced reverse weathering. Nat. Commun. 8, 844 (2017)—has now been inserted as new ref. 54. In the “Data treatment and availability section”, the isotopic data, which can be found in the Figshare data repository at , were incorrectly said to be found in the PANGAEA data repository. These corrections have been made in the HTML and PDF versions of the article.
Abstract.
Smith T, Zotta R-M, Boulton CA, Lenton TM, Dorigo W, Boers N (2023). Reliability of resilience estimation based on multi-instrument time series.
Earth System Dynamics,
14(1), 173-183.
Abstract:
Reliability of resilience estimation based on multi-instrument time series
Abstract. Many widely used observational data sets are comprised of several overlapping instrument records. While data inter-calibration techniques often yield continuous and reliable data for trend analysis, less attention is generally paid to maintaining higher-order statistics such as variance and autocorrelation. A growing body of work uses these metrics to quantify the stability or resilience of a system under study and potentially to anticipate an approaching critical transition in the system. Exploring the degree to which changes in resilience indicators such as the variance or autocorrelation can be attributed to non-stationary characteristics of the measurement process – rather than actual changes in the dynamical properties of the system – is important in this context. In this work we use both synthetic and empirical data to explore how changes in the noise structure of a data set are propagated into the commonly used resilience metrics lag-one autocorrelation and variance. We focus on examples from remotely sensed vegetation indicators such as vegetation optical depth and the normalized difference vegetation index from different satellite sources. We find that time series resulting from mixing signals from sensors with varied uncertainties and covering overlapping time spans can lead to biases in inferred resilience changes. These biases are typically more pronounced when resilience metrics are aggregated (for example, by land-cover type or region), whereas estimates for individual time series remain reliable at reasonable sensor signal-to-noise ratios. Our work provides guidelines for the treatment and aggregation of multi-instrument data in studies of critical transitions and resilience.
.
Abstract.
Rockström J, Gupta J, Qin D, Lade SJ, Abrams JF, Andersen LS, Armstrong McKay DI, Bai X, Bala G, Bunn SE, et al (2023). Safe and just Earth system boundaries.
Nature,
619(7968), 102-111.
Abstract:
Safe and just Earth system boundaries.
The stability and resilience of the Earth system and human well-being are inseparably linked1-3, yet their interdependencies are generally under-recognized; consequently, they are often treated independently4,5. Here, we use modelling and literature assessment to quantify safe and just Earth system boundaries (ESBs) for climate, the biosphere, water and nutrient cycles, and aerosols at global and subglobal scales. We propose ESBs for maintaining the resilience and stability of the Earth system (safe ESBs) and minimizing exposure to significant harm to humans from Earth system change (a necessary but not sufficient condition for justice)4. The stricter of the safe or just boundaries sets the integrated safe and just ESB. Our findings show that justice considerations constrain the integrated ESBs more than safety considerations for climate and atmospheric aerosol loading. Seven of eight globally quantified safe and just ESBs and at least two regional safe and just ESBs in over half of global land area are already exceeded. We propose that our assessment provides a quantitative foundation for safeguarding the global commons for all people now and into the future.
Abstract.
Author URL.
Bowles AMC, Williamson CJ, Williams TA, Lenton TM, Donoghue PCJ (2023). The origin and early evolution of plants.
Trends in Plant Science,
28(3), 312-329.
Abstract:
The origin and early evolution of plants
Plant (archaeplastid) evolution has transformed the biosphere, but we are only now beginning to learn how this took place through comparative genomics, phylogenetics, and the fossil record. This has illuminated the phylogeny of Archaeplastida, Viridiplantae, and Streptophyta, and has resolved the evolution of key characters, genes, and genomes – revealing that many key innovations evolved long before the clades with which they have been casually associated. Molecular clock analyses estimate that Streptophyta and Viridiplantae emerged in the late Mesoproterozoic to late Neoproterozoic, whereas Archaeplastida emerged in the late-mid Palaeoproterozoic. Together, these insights inform on the coevolution of plants and the Earth system that transformed ecology and global biogeochemical cycles, increased weathering, and precipitated snowball Earth events, during which they would have been key to oxygen production and net primary productivity (NPP).
Abstract.
Littleton EW, Shepherd A, Harper AB, Hastings AFS, Vaughan NE, Doelman J, van Vuuren DP, Lenton TM (2023). Uncertain effectiveness of <i>Miscanthus</i> bioenergy expansion for climate change mitigation explored using land surface, agronomic and integrated assessment models.
GCB Bioenergy,
15(3), 303-318.
Abstract:
Uncertain effectiveness of Miscanthus bioenergy expansion for climate change mitigation explored using land surface, agronomic and integrated assessment models
AbstractLarge‐scale bioenergy plays a key role in climate change mitigation scenarios, but its efficacy is uncertain. This study aims to quantify that uncertainty by contrasting the results of three different types of models under the same mitigation scenario (RCP2.6‐SSP2), consistent with a 2°C temperature target. This analysis focuses on a single bioenergy feedstock, Miscanthus × giganteus, and contrasts projections for its yields and environmental effects from an integrated assessment model (IMAGE), a land surface and dynamic global vegetation model tailored to Miscanthus bioenergy (JULES) and a bioenergy crop model (MiscanFor). Under the present climate, JULES, IMAGE and MiscanFor capture the observed magnitude and variability in Miscanthus yields across Europe; yet in the tropics JULES and IMAGE predict high yields, whereas MiscanFor predicts widespread drought‐related diebacks. 2040–2049 projections show there is a rapid scale up of over 200 Mha bioenergy cropping area in the tropics. Resulting biomass yield ranges from 12 (MiscanFor) to 39 (JULES) Gt dry matter over that decade. Change in soil carbon ranges from +0.7 Pg C (MiscanFor) to −2.8 Pg C (JULES), depending on preceding land cover and soil carbon.2090–99 projections show large‐scale biomass energy with carbon capture and storage (BECCS) is projected in Europe. The models agree that <2°C global warming will increase yields in the higher latitudes, but drought stress in the Mediterranean region could produce low yields (MiscanFor), and significant losses of soil carbon (JULES and IMAGE). These results highlight the uncertainty in rapidly scaling‐up biomass energy supply, especially in dry tropical climates and in regions where future climate change could result in drier conditions. This has important policy implications—because prominently used scenarios to limit warming to ‘well below 2°C’ (including the one explored here) depend upon its effectiveness.
Abstract.
Dylewsky D, Lenton TM, Scheffer M, Bury TM, Fletcher CG, Anand M, Bauch CT (2023). Universal early warning signals of phase transitions in climate systems.
Journal of the Royal Society, Interface,
20(201).
Abstract:
Universal early warning signals of phase transitions in climate systems.
The potential for complex systems to exhibit tipping points in which an equilibrium state undergoes a sudden and often irreversible shift is well established, but prediction of these events using standard forecast modelling techniques is quite difficult. This has led to the development of an alternative suite of methods that seek to identify signatures of critical phenomena in data, which are expected to occur in advance of many classes of dynamical bifurcation. Crucially, the manifestations of these critical phenomena are generic across a variety of systems, meaning that data-intensive deep learning methods can be trained on (abundant) synthetic data and plausibly prove effective when transferred to (more limited) empirical datasets. This paper provides a proof of concept for this approach as applied to lattice phase transitions: a deep neural network trained exclusively on two-dimensional Ising model phase transitions is tested on a number of real and simulated climate systems with considerable success. Its accuracy frequently surpasses that of conventional statistical indicators, with performance shown to be consistently improved by the inclusion of spatial indicators. Tools such as this may offer valuable insight into climate tipping events, as remote sensing measurements provide increasingly abundant data on complex geospatially resolved Earth systems.
Abstract.
2022
Gontero B, Lenton TM, Maberly SC (2022). An introduction to productivityand carbon cyclingin aquatic ecosystems. In (Ed) Blue Planet, Red and Green Photosynthesis: Productivity and Carbon Cycling in Aquatic Ecosystems, 1-25.
Nicholson A, Daines S, Mayne N, Eager-Nash J, Lenton T (2022). Biosignatures independent of population dynamics. Goldschmidt2022 abstracts.
Ball TS, Vaughan NE, Powell TW, Lovett A, Lenton TM (2022). C-LLAMA 1.0: a traceable model for food, agriculture, and land use.
GEOSCIENTIFIC MODEL DEVELOPMENT,
15(2), 929-949.
Author URL.
Kemp L, Xu C, Depledge J, Ebi KL, Gibbins G, Kohler TA, Rockström J, Scheffer M, Schellnhuber HJ, Steffen W, et al (2022). Climate Endgame: Exploring catastrophic climate change scenarios.
Proc Natl Acad Sci U S A,
119(34).
Abstract:
Climate Endgame: Exploring catastrophic climate change scenarios.
Prudent risk management requires consideration of bad-to-worst-case scenarios. Yet, for climate change, such potential futures are poorly understood. Could anthropogenic climate change result in worldwide societal collapse or even eventual human extinction? at present, this is a dangerously underexplored topic. Yet there are ample reasons to suspect that climate change could result in a global catastrophe. Analyzing the mechanisms for these extreme consequences could help galvanize action, improve resilience, and inform policy, including emergency responses. We outline current knowledge about the likelihood of extreme climate change, discuss why understanding bad-to-worst cases is vital, articulate reasons for concern about catastrophic outcomes, define key terms, and put forward a research agenda. The proposed agenda covers four main questions: 1) What is the potential for climate change to drive mass extinction events? 2) What are the mechanisms that could result in human mass mortality and morbidity? 3) What are human societies' vulnerabilities to climate-triggered risk cascades, such as from conflict, political instability, and systemic financial risk? 4) How can these multiple strands of evidence-together with other global dangers-be usefully synthesized into an "integrated catastrophe assessment"? it is time for the scientific community to grapple with the challenge of better understanding catastrophic climate change.
Abstract.
Author URL.
Arellano-Nava B, Halloran PR, Boulton CA, Scourse J, Butler PG, Reynolds DJ, Lenton TM (2022). Destabilisation of the Subpolar North Atlantic prior to the Little Ice Age.
Nature Communications,
13(1).
Abstract:
Destabilisation of the Subpolar North Atlantic prior to the Little Ice Age
AbstractThe cooling transition into the Little Ice Age was the last notable shift in the climate system prior to anthropogenic global warming. It is hypothesised that sea-ice to ocean feedbacks sustained an initial cooling into the Little Ice Age by weakening the subpolar gyre circulation; a system that has been proposed to exhibit bistability. Empirical evidence for bistability within this transition has however been lacking. Using statistical indicators of resilience in three annually-resolved bivalve proxy records from the North Icelandic shelf, we show that the subpolar North Atlantic climate system destabilised during two episodes prior to the Little Ice Age. This loss of resilience indicates reduced attraction to one stable state, and a system vulnerable to an abrupt transition. The two episodes preceded wider subpolar North Atlantic change, consistent with subpolar gyre destabilisation and the approach of a tipping point, potentially heralding the transition to Little Ice Age conditions.
Abstract.
Snellen IAG, Snik F, Kenworthy M, Albrecht S, Anglada-Escude G, Baraffe I, Baudoz P, Benz W, Beuzit J-L, Biller B, et al (2022). Detecting life outside our solar system with a large high-contrast-imaging mission.
EXPERIMENTAL ASTRONOMY,
54(2-3), 1237-1274.
Author URL.
Keen S, Lenton TM, Garrett TJ, Rae JWB, Hanley BP, Grasselli M (2022). Estimates of economic and environmental damages from tipping points cannot be reconciled with the scientific literature.
Proc Natl Acad Sci U S A,
119(21).
Author URL.
Mills DB, Boyle RA, Daines SJ, Sperling EA, Pisani D, Donoghue PCJ, Lenton TM (2022). Eukaryogenesis and oxygen in Earth history.
Nat Ecol Evol,
6(5), 520-532.
Abstract:
Eukaryogenesis and oxygen in Earth history.
The endosymbiotic origin of mitochondria during eukaryogenesis has long been viewed as an adaptive response to the oxygenation of Earth's surface environment, presuming a fundamentally aerobic lifestyle for the free-living bacterial ancestors of mitochondria. This oxygen-centric view has been robustly challenged by recent advances in the Earth and life sciences. While the permanent oxygenation of the atmosphere above trace concentrations is now thought to have occurred 2.2 billion years ago, large parts of the deep ocean remained anoxic until less than 0.5 billion years ago. Neither fossils nor molecular clocks correlate the origin of mitochondria, or eukaryogenesis more broadly, to either of these planetary redox transitions. Instead, mitochondria-bearing eukaryotes are consistently dated to between these two oxygenation events, during an interval of pervasive deep-sea anoxia and variable surface-water oxygenation. The discovery and cultivation of the Asgard archaea has reinforced metabolic evidence that eukaryogenesis was initially mediated by syntrophic H2 exchange between an archaeal host and an α-proteobacterial symbiont living under anoxia. Together, these results temporally, spatially and metabolically decouple the earliest stages of eukaryogenesis from the oxygen content of the surface ocean and atmosphere. Rather than reflecting the ancestral metabolic state, obligate aerobiosis in eukaryotes is most probably derived, having only become globally widespread over the past 1 billion years as atmospheric oxygen approached modern levels.
Abstract.
Author URL.
Armstrong McKay DI, Staal A, Abrams JF, Winkelmann R, Sakschewski B, Loriani S, Fetzer I, Cornell SE, Rockström J, Lenton TM, et al (2022). Exceeding 1.5°C global warming could trigger multiple climate tipping points.
Science,
377(6611).
Abstract:
Exceeding 1.5°C global warming could trigger multiple climate tipping points.
Climate tipping points occur when change in a part of the climate system becomes self-perpetuating beyond a warming threshold, leading to substantial Earth system impacts. Synthesizing paleoclimate, observational, and model-based studies, we provide a revised shortlist of global "core" tipping elements and regional "impact" tipping elements and their temperature thresholds. Current global warming of ~1.1°C above preindustrial temperatures already lies within the lower end of some tipping point uncertainty ranges. Several tipping points may be triggered in the Paris Agreement range of 1.5 to
Abstract.
Author URL.
Rammelt CF, Gupta J, Liverman D, Scholtens J, Ciobanu D, Abrams JF, Bai X, Gifford L, Gordon C, Hurlbert M, et al (2022). Impacts of meeting minimum access on critical earth systems amidst the Great Inequality.
Nature Sustainability,
6(2), 212-221.
Abstract:
Impacts of meeting minimum access on critical earth systems amidst the Great Inequality
AbstractThe Sustainable Development Goals aim to improve access to resources and services, reduce environmental degradation, eradicate poverty and reduce inequality. However, the magnitude of the environmental burden that would arise from meeting the needs of the poorest is under debate—especially when compared to much larger burdens from the rich. We show that the ‘Great Acceleration’ of human impacts was characterized by a ‘Great Inequality’ in using and damaging the environment. We then operationalize ‘just access’ to minimum energy, water, food and infrastructure. We show that achieving just access in 2018, with existing inequalities, technologies and behaviours, would have produced 2–26% additional impacts on the Earth’s natural systems of climate, water, land and nutrients—thus further crossing planetary boundaries. These hypothetical impacts, caused by about a third of humanity, equalled those caused by the wealthiest 1–4%. Technological and behavioural changes thus far, while important, did not deliver just access within a stable Earth system. Achieving these goals therefore calls for a radical redistribution of resources.
Abstract.
Lenton TM (2022). James Lovelock (1919-2022).
Science,
377(6609).
Abstract:
James Lovelock (1919-2022).
Father of Earth system science.
Abstract.
Author URL.
Lenton TM, Benson S, Smith T, Ewer T, Lanel V, Petykowski E, Powell TWR, Abrams JF, Blomsma F, Sharpe S, et al (2022). Operationalising positive tipping points towards global sustainability.
Global Sustainability,
5Abstract:
Operationalising positive tipping points towards global sustainability
Non-technical summary Transforming towards global sustainability requires a dramatic acceleration of social change. Hence, there is growing interest in finding ‘positive tipping points’ at which small interventions can trigger self-reinforcing feedbacks that accelerate systemic change. Examples have recently been seen in power generation and personal transport, but how can we identify positive tipping points that have yet to occur? We synthesise theory and examples to provide initial guidelines for creating enabling conditions, sensing when a system can be positively tipped, who can trigger it, and how they can trigger it. All of us can play a part in triggering positive tipping points. Technical summary Recent work on positive tipping points towards sustainability has focused on social-technological systems and the agency of policymakers to tip change, whilst earlier work identified social-ecological positive feedbacks triggered by diverse actors. We bring these together to consider positive tipping points across social-technological-ecological systems and the potential for multiple actors and interventions to trigger them. Established theory and examples provide several generic mechanisms for triggering tipping points. From these we identify specific enabling conditions, reinforcing feedbacks, actors and interventions that can contribute to triggering positive tipping points in the adoption of sustainable behaviours and technologies. Actions that can create enabling conditions for positive tipping include targeting smaller populations, altering social network structure, providing relevant information, reducing price, improving performance, desirability and accessibility, and coordinating complementary technologies. Actions that can trigger positive tipping include social, technological and ecological innovations, policy interventions, public investment, private investment, broadcasting public information, and behavioural nudges. Positive tipping points can help counter widespread feelings of disempowerment in the face of global challenges and help unlock ‘paralysis by complexity’. A key research agenda is to consider how different agents and interventions can most effectively work together to create system-wide positive tipping points whilst ensuring a just transformation. Social media summary We identify key actors and actions that can enable and trigger positive tipping points towards global sustainability.
Abstract.
Sproson AD, Pogge von Strandmann PAE, Selby D, Jarochowska E, Frýda J, Hladil J, Loydell DK, Slavík L, Calner M, Maier G, et al (2022). Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations.
Earth and Planetary Science Letters,
577Abstract:
Osmium and lithium isotope evidence for weathering feedbacks linked to orbitally paced organic carbon burial and Silurian glaciations
The Ordovician (∼487 to 443 Ma) ended with the formation of extensive Southern Hemisphere ice sheets, known as the Hirnantian glaciation, and the second largest mass extinction in Earth History. It was followed by the Silurian (∼443 to 419 Ma), one of the most climatically unstable periods of the Phanerozoic as evidenced by several large scale (>5‰) carbon isotope (δ13C) perturbations associated with further extinction events. Despite several decades of research, the cause of these environmental instabilities remains enigmatic. Here, we provide osmium (187Os/188Os) and lithium (δ7Li) isotope measurements of marine sedimentary rocks that cover four Silurian δ13C excursions. Osmium and Li isotope records resemble those previously recorded for the Hirnantian glaciation suggesting a similar causal mechanism. When combined with a new dynamic carbon-osmium-lithium biogeochemical model we suggest that astronomical forcing of the marine organic carbon cycle, as opposed to a decline in volcanic arc degassing or the rise of early land plants, resulted in drawdown of atmospheric CO2, triggering continental scale glaciation, intense global cooling and eustatic sea-level lows recognised in the geological record. Lower atmospheric pCO2 and temperatures during the Hirnantian and Silurian glaciations suppressed CO2 removal by silicate weathering, driving 187Os/188Os and δ7Li variability, supporting the existence of climate-regulating feedbacks.
Abstract.
Nicholson AE, Daines SJ, Mayne NJ, Eager-Nash JK, Lenton TM, Kohary K (2022). Predicting biosignatures for nutrient limited biospheres.
Abstract:
Predicting biosignatures for nutrient limited biospheres
With the characterisations of potentially habitable planetary atmospheres on
the horizon, the search for biosignatures is set to become a major area of
research in the coming decades. To understand the atmospheric characteristics
that might indicate alien life we must understand the abiotic characteristics
of a planet and how life interacts with its environment. In the field of
biogeochemistry, sophisticated models of life-environment coupled systems
demonstrate that many assumptions specific to Earth-based life, e.g. specific
ATP maintenance costs, are unnecessary to accurately model a biosphere. We
explore a simple model of a single-species microbial biosphere that produces
CH4 as a byproduct of the microbes' energy extraction - known as a type I
biosignature. We demonstrate that although significantly changing the
biological parameters has a large impact on the biosphere's total population,
such changes have only a minimal impact on the strength of the resulting
biosignature, while the biosphere is limited by H2 availability. We extend the
model to include more accurate microbial energy harvesting and show that
adjusting microbe parameters can lead to a regime change where the biosphere
becomes limited by energy availability and no longer fully exploits the
available H2, impacting the strength of the resulting biosignature. We
demonstrate that, for a nutrient limited biosphere, identifying the limiting
nutrient, understanding the abiotic processes that control its abundance, and
determining the biosphere's ability to exploit it, are more fundamental for
making type I biosignature predictions than the details of the population
dynamics of the biosphere.
Abstract.
Author URL.
Boulton CA, Lenton TM, Boers N (2022). Pronounced loss of Amazon rainforest resilience since the early 2000s.
Nature Climate Change,
12(3), 271-278.
Abstract:
Pronounced loss of Amazon rainforest resilience since the early 2000s
AbstractThe resilience of the Amazon rainforest to climate and land-use change is crucial for biodiversity, regional climate and the global carbon cycle. Deforestation and climate change, via increasing dry-season length and drought frequency, may already have pushed the Amazon close to a critical threshold of rainforest dieback. Here, we quantify changes of Amazon resilience by applying established indicators (for example, measuring lag-1 autocorrelation) to remotely sensed vegetation data with a focus on vegetation optical depth (1991–2016). We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.
Abstract.
Lenton TM, Xu C, Abrams JF, Ghadiali A, Loriani S, Sakschewski B, Zimm C, Ebi KL, Dunn RR, Svenning J-C, et al (2022). Quantifying the Human Cost of Global Warming.
Buxton JE, Abrams JF, Boulton CA, Barlow N, Rangel Smith C, Van Stroud S, Lees KJ, Lenton TM (2022). Quantitatively monitoring the resilience of patterned vegetation in the Sahel.
Glob Chang Biol,
28(2), 571-587.
Abstract:
Quantitatively monitoring the resilience of patterned vegetation in the Sahel.
Patterning of vegetation in drylands is a consequence of localized feedback mechanisms. Such feedbacks also determine ecosystem resilience-i.e. the ability to recover from perturbation. Hence, the patterning of vegetation has been hypothesized to be an indicator of resilience, that is, spots are less resilient than labyrinths. Previous studies have made this qualitative link and used models to quantitatively explore it, but few have quantitatively analysed available data to test the hypothesis. Here we provide methods for quantitatively monitoring the resilience of patterned vegetation, applied to 40 sites in the Sahel (a mix of previously identified and new ones). We show that an existing quantification of vegetation patterns in terms of a feature vector metric can effectively distinguish gaps, labyrinths, spots, and a novel category of spot-labyrinths at their maximum extent, whereas NDVI does not. The feature vector pattern metric correlates with mean precipitation. We then explored two approaches to measuring resilience. First we treated the rainy season as a perturbation and examined the subsequent rate of decay of patterns and NDVI as possible measures of resilience. This showed faster decay rates-conventionally interpreted as greater resilience-associated with wetter, more vegetated sites. Second we detrended the seasonal cycle and examined temporal autocorrelation and variance of the residuals as possible measures of resilience. Autocorrelation and variance of our pattern metric increase with declining mean precipitation, consistent with loss of resilience. Thus, drier sites appear less resilient, but we find no significant correlation between the mean or maximum value of the pattern metric (and associated morphological pattern types) and either of our measures of resilience.
Abstract.
Author URL.
Kemp L, Xu C, Depledge J, Ebi KL, Gibbins G, Kohler TA, Rockström J, Scheffer M, Schellnhuber HJ, Steffen W, et al (2022). Reply to Bhowmik et al.: Democratic climate action and studying extreme climate risks are not in tension.
Proc Natl Acad Sci U S A,
119(45).
Author URL.
Kemp L, Xu C, Depledge J, Ebi KL, Gibbins G, Kohler TA, Rockström J, Scheffer M, Schellnhuber HJ, Steffen W, et al (2022). Reply to Burgess et al: Catastrophic climate risks are neglected, plausible, and safe to study. Proceedings of the National Academy of Sciences of the United States of America, 119(42).
Kemp L, Xu C, Depledge J, Ebi KL, Gibbins G, Kohler TA, Rockström J, Scheffer M, Schellnhuber HJ, Steffen W, et al (2022). Reply to Kelman: the foundations for studying catastrophic climate risks. Proceedings of the National Academy of Sciences of the United States of America, 119(42).
Kemp L, Xu C, Depledge J, Ebi KL, Gibbins G, Kohler TA, Rockström J, Scheffer M, Schellnhuber HJ, Steffen W, et al (2022). Reply to Ruhl and Craig: Assessing and governing extreme climate risks needs to be legitimate and democratic. Proceedings of the National Academy of Sciences, 119(49).
Lenton TM, Boulton CA, Scheffer M (2022). Resilience of countries to COVID-19 correlated with trust.
Sci Rep,
12(1).
Abstract:
Resilience of countries to COVID-19 correlated with trust.
We characterized > 150 countries' resilience to COVID-19 as the nationwide decay rate of daily cases or deaths from peak levels. Resilience to COVID-19 varies by a factor of ~ 40 between countries for cases/capita and ~ 25 for deaths/capita. Trust within society is positively correlated with country-level resilience to COVID-19, as is the adaptive increase in stringency of government interventions when epidemic waves occur. By contrast, countries where governments maintain greater background stringency tend to have lower trust within society and tend to be less resilient. All countries where > 40% agree "most people can be trusted" achieve a near complete reduction of new cases and deaths, but so do several less-trusting societies. As the pandemic progressed, resilience tended to decline, as adaptive increases in stringency also declined. These results add to evidence that trust can improve resilience to epidemics and other unexpected disruptions, of which COVID-19 is unlikely to be the last.
Abstract.
Author URL.
Winkelmann R, Donges JF, Smith EK, Milkoreit M, Eder C, Heitzig J, Katsanidou A, Wiedermann M, Wunderling N, Lenton TM, et al (2022). Social tipping processes towards climate action: a conceptual framework.
Ecological Economics,
192Abstract:
Social tipping processes towards climate action: a conceptual framework
Societal transformations are necessary to address critical global challenges, such as mitigation of anthropogenic climate change and reaching UN sustainable development goals. Recently, social tipping processes have received increased attention, as they present a form of social change whereby a small change can shift a sensitive social system into a qualitatively different state due to strongly self-amplifying (mathematically positive) feedback mechanisms. Social tipping processes with respect to technological and energy systems, political mobilization, financial markets and sociocultural norms and behaviors have been suggested as potential key drivers towards climate action. Drawing from expert insights and comprehensive literature review, we develop a framework to identify and characterize social tipping processes critical to facilitating rapid social transformations. We find that social tipping processes are distinguishable from those of already more widely studied climate and ecological tipping dynamics. In particular, we identify human agency, social-institutional network structures, different spatial and temporal scales and increased complexity as key distinctive features underlying social tipping processes. Building on these characteristics, we propose a formal definition for social tipping processes and filtering criteria for those processes that could be decisive for future trajectories towards climate action. We illustrate this definition with the European political system as an example of potential social tipping processes, highlighting the prospective role of the FridaysForFuture movement. Accordingly, this conceptual framework for social tipping processes can be utilized to illuminate mechanisms for necessary transformative climate change mitigation policies and actions.
Abstract.
Boyle RA, Lenton TM (2022). The evolution of biogeochemical recycling by persistence-based selection.
COMMUNICATIONS EARTH & ENVIRONMENT,
3(1).
Author URL.
Eager-Nash J, Mayne N, Lenton T, Daines S (2022). Towards Coupled Modelling of the Biosphere and Atmosphere for the Archean Climate: the Importance of Methane. Goldschmidt2022 abstracts.
Dylewsky D, Lenton TM, Scheffer M, Bury TM, Fletcher CG, Anand M, Bauch CT (2022). Universal Early Warning Signals of Phase Transitions in Climate Systems.
Abstract:
Universal Early Warning Signals of Phase Transitions in Climate Systems
The potential for complex systems to exhibit tipping points in which an
equilibrium state undergoes a sudden and often irreversible shift is well
established, but prediction of these events using standard forecast modeling
techniques is quite difficult. This has led to the development of an
alternative suite of methods that seek to identify signatures of critical
phenomena in data, which are expected to occur in advance of many classes of
dynamical bifurcation. Crucially, the manifestations of these critical
phenomena are generic across a variety of systems, meaning that data-intensive
deep learning methods can be trained on (abundant) synthetic data and plausibly
prove effective when transferred to (more limited) empirical data sets. This
paper provides a proof of concept for this approach as applied to lattice phase
transitions: a deep neural network trained exclusively on 2D Ising model phase
transitions is tested on a number of real and simulated climate systems with
considerable success. Its accuracy frequently surpasses that of conventional
statistical indicators, with performance shown to be consistently improved by
the inclusion of spatial indicators. Tools such as this may offer valuable
insight into climate tipping events, as remote sensing measurements provide
increasingly abundant data on complex geospatially-resolved Earth systems.
Abstract.
Author URL.
Buxton J (2022). Using remote sensing to assess ecosystem resilience.
Abstract:
Using remote sensing to assess ecosystem resilience
Vegetation ecosystems are increasingly under pressure from both direct human influence and indirect anthropogenically-driven climate change. Increasing amounts of data are made available from satellite systems which can image these ecosystems from afar. The work in this thesis provides several examples of the utility of remotely sensed data from satellites to assess the resilience of ecosystems. This notion of resilience is measured by considering the return rate following a perturbation, with statistical metrics such as AR(1) and variance providing an indication of system resilience and the proximity to a potential tipping point. The first focus of this work is on direct human environmental intervention through community-based agroforestry groups in Kenya. These results show that the efforts of these groups can be detected with satellite data as a greening trend which occurs both within designated tree planting groves and in the surrounding landscape. These groups provide a case study for the power of positive social tipping points to achieve environmental improvement. Following this, the potential of high-resolution satellite data from Sentinel-2 to quantify patterned vegetation in the Sahel is explored. These striking patterns have often been associated with vegetation resilience in drylands. No correlation is found between pattern morphology and resilience, contrary to a previously held hypothesis from the literature. Precipitation is also identified as a key driver of these patterns. Moving beyond drylands, satellite data is utilised at a global scale to assess the link between vegetation resilience and climatic variables across the world. There is a clear relationship between average resilience, as measured by AR(1), and precipitation, which is evident at three spatial scales; the local (pixel), ecoregion and biome. There is also a temperature component, with hotter, drier locations displaying lower levels of resilience. This thesis finishes with a discussion of the potential for a resilience sensing framework constructed by combining remote sensing data with new cloud computing technologies. This will enable the monitoring of resilience change across the world and the identification of regions which require further investigation and intervention.
Abstract.
2021
Myers BJE, Weiskopf SR, Shiklomanov AN, Ferrier S, Weng E, Casey KA, Harfoot M, Jackson ST, Leidner AK, Lenton TM, et al (2021). A New Approach to Evaluate and Reduce Uncertainty of Model-Based Biodiversity Projections for Conservation Policy Formulation.
BioScience,
71(12), 1261-1273.
Abstract:
A New Approach to Evaluate and Reduce Uncertainty of Model-Based Biodiversity Projections for Conservation Policy Formulation
Biodiversity projections with uncertainty estimates under different climate, land-use, and policy scenarios are essential to setting and achieving international targets to mitigate biodiversity loss. Evaluating and improving biodiversity predictions to better inform policy decisions remains a central conservation goal and challenge. A comprehensive strategy to evaluate and reduce uncertainty of model outputs against observed measurements and multiple models would help to produce more robust biodiversity predictions. We propose an approach that integrates biodiversity models and emerging remote sensing and in-situ data streams to evaluate and reduce uncertainty with the goal of improving policy-relevant biodiversity predictions. In this article, we describe a multivariate approach to directly and indirectly evaluate and constrain model uncertainty, demonstrate a proof of concept of this approach, embed the concept within the broader context of model evaluation and scenario analysis for conservation policy, and highlight lessons from other modeling communities.
Abstract.
Warszawski L, Kriegler E, Lenton TM, Gaffney O, Jacob D, Klingenfeld D, Koide R, Costa MM, Messner D, Nakicenovic N, et al (2021). All options, not silver bullets, needed to limit global warming to 1.5 degrees C: a scenario appraisal.
ENVIRONMENTAL RESEARCH LETTERS,
16(6).
Author URL.
Huang G, Eager JK, Mayne NJ, Cui D, Manners J, Hebrard E, Liu Z, Lenton TM (2021). CO2 and O2 oxidized 2.7 Ga micrometeorites in two stages suggesting a >32% CO2 atmosphere. Precambrian Research, 366, 106423-106423.
Buxton J, Powell T, Ambler J, Boulton C, Nicholson A, Arthur R, Lees K, Williams H, Lenton T (2021). Community-driven tree planting greens the neighbouring landscape.
Buxton J, Powell T, Ambler J, Boulton C, Nicholson A, Arthur R, Lees K, Williams H, Lenton TM (2021). Community-driven tree planting greens the neighbouring landscape.
Sci Rep,
11(1).
Abstract:
Community-driven tree planting greens the neighbouring landscape.
Nature-based solutions to climate change are growing policy priorities yet remain hard to quantify. Here we use remote sensing to quantify direct and indirect benefits from community-led agroforestry by the International Small group and Tree planting program (TIST) in Kenya. Since 2005, TIST-Kenya has incentivised smallholder farmers to plant trees for agricultural benefit and to sequester CO2. We use Landsat-7 satellite imagery to examine the effect on the historically deforested landscape around Mount Kenya. We identify positive greening trends in TIST groves during 2000-2019 relative to the wider landscape. These groves cover 27,198 ha, and a further 27,750 ha of neighbouring agricultural land is also positively influenced by TIST. This positive 'spill-over' impact of TIST activity occurs at up to 360 m distance. TIST also benefits local forests, e.g. through reducing fuelwood and fodder extraction. Our results show that community-led initiatives can lead to successful landscape-scale regreening on decadal timescales.
Abstract.
Author URL.
Bury TM, Sujith RI, Pavithran I, Scheffer M, Lenton TM, Anand M, Bauch CT (2021). Deep learning for early warning signals of tipping points.
Proc Natl Acad Sci U S A,
118(39).
Abstract:
Deep learning for early warning signals of tipping points.
Many natural systems exhibit tipping points where slowly changing environmental conditions spark a sudden shift to a new and sometimes very different state. As the tipping point is approached, the dynamics of complex and varied systems simplify down to a limited number of possible "normal forms" that determine qualitative aspects of the new state that lies beyond the tipping point, such as whether it will oscillate or be stable. In several of those forms, indicators like increasing lag-1 autocorrelation and variance provide generic early warning signals (EWS) of the tipping point by detecting how dynamics slow down near the transition. But they do not predict the nature of the new state. Here we develop a deep learning algorithm that provides EWS in systems it was not explicitly trained on, by exploiting information about normal forms and scaling behavior of dynamics near tipping points that are common to many dynamical systems. The algorithm provides EWS in 268 empirical and model time series from ecology, thermoacoustics, climatology, and epidemiology with much greater sensitivity and specificity than generic EWS. It can also predict the normal form that characterizes the oncoming tipping point, thus providing qualitative information on certain aspects of the new state. Such approaches can help humans better prepare for, or avoid, undesirable state transitions. The algorithm also illustrates how a universe of possible models can be mined to recognize naturally occurring tipping points.
Abstract.
Author URL.
Littleton EW, Dooley K, Webb G, Harper AB, Powell T, Nicholls Z, Meinshausen M, Lenton T (2021). Dynamic modelling shows substantial contribution of ecosystem restoration to climate change mitigation.
Keen S, Lenton TM, Godin A, Yilmaz D, Grasselli M, Garrett TJ (2021). Economists' erroneous estimates of damages from climate change.
Abstract:
Economists' erroneous estimates of damages from climate change
Economists have predicted that damages from global warming will be as low as
2.1% of global economic production for a 3$^\circ$C rise in global average
surface temperature, and 7.9% for a 6$^\circ$C rise. Such relatively trivial
estimates of economic damages -- when these economists otherwise assume that
human economic productivity will be an order of magnitude higher than today --
contrast strongly with predictions made by scientists of significantly reduced
human habitability from climate change. Nonetheless, the coupled economic and
climate models used to make such predictions have been influential in the
international climate change debate and policy prescriptions. Here we review
the empirical work done by economists and show that it severely underestimates
damages from climate change by committing several methodological errors,
including neglecting tipping points, and assuming that economic sectors not
exposed to the weather are insulated from climate change. Most fundamentally,
the influential Integrated Assessment Model DICE is shown to be incapable of
generating an economic collapse, regardless of the level of damages. Given
these flaws, economists' empirical estimates of economic damages from global
warming should be rejected as unscientific, and models that have been
calibrated to them, such as DICE, should not be used to evaluate economic risks
from climate change, or in the development of policy to attenuate damages.
Abstract.
Author URL.
Rockström J, Gupta J, Lenton TM, Qin D, Lade SJ, Abrams JF, Jacobson L, Rocha JC, Zimm C, Bai X, et al (2021). Identifying a Safe and Just Corridor for People and the Planet.
Earth's Future,
9(4).
Abstract:
Identifying a Safe and Just Corridor for People and the Planet
Keeping the Earth system in a stable and resilient state, to safeguard Earth's life support systems while ensuring that Earth's benefits, risks, and related responsibilities are equitably shared, constitutes the grand challenge for human development in the Anthropocene. Here, we describe a framework that the recently formed Earth Commission will use to define and quantify target ranges for a “safe and just corridor” that meets these goals. Although “safe” and “just” Earth system targets are interrelated, we see safe as primarily referring to a stable Earth system and just targets as being associated with meeting human needs and reducing exposure to risks. To align safe and just dimensions, we propose to address the equity dimensions of each safe target for Earth system regulating systems and processes. The more stringent of the safe or just target ranges then defines the corridor. Identifying levers of social transformation aimed at meeting the safe and just targets and challenges associated with translating the corridor to actors at multiple scales present scope for future work.
Abstract.
Fabbri S, Hauschild MZ, Lenton TM, Owsianiak M (2021). Multiple Climate Tipping Points Metrics for Improved Sustainability Assessment of Products and Services.
Environ Sci Technol,
55(5), 2800-2810.
Abstract:
Multiple Climate Tipping Points Metrics for Improved Sustainability Assessment of Products and Services.
Mounting evidence indicates that climate tipping points can have large, potentially irreversible, impacts on the earth system and human societies. Yet, climate change metrics applied in current sustainability assessment methods generally do not consider these tipping points, with the use of arbitrarily determined time horizons and assumptions that the climate impact of a product or service is independent of emission timing. Here, we propose a new method for calculating climate tipping characterization factors for greenhouse gases (carbon dioxide, methane, and nitrous oxide) at midpoint. It covers 13 projected tipping points, incorporates the effect that the crossing of a given tipping point has on accelerating the crossing of other tipping points, and addresses uncertainties in the temperature thresholds that trigger the tipping points. To demonstrate the added value of the new metric, we apply it to emissions stemming from end-of-life of plastic polymers and compare them with commonly used metrics. This highlights the need to consider climate tipping in sustainability assessment of products and services.
Abstract.
Author URL.
Lenton T, Benson S, Smith T, Ewer T, Lanel V, Petykowski E, Powell TWR, Abrams JF, Blomsma F, Sharpe S, et al (2021). Operationalising Positive Tipping Points towards Global Sustainability.
Author URL.
Brovkin V, Brook E, Williams JW, Bathiany S, Lenton TM, Barton M, DeConto RM, Donges JF, Ganopolski A, McManus J, et al (2021). Past abrupt changes, tipping points and cascading impacts in the Earth system.
NATURE GEOSCIENCE,
14(8), 550-558.
Author URL.
Gupta J, Liverman D, Bai X, Gordon C, Hurlbert M, Inoue CYA, Jacobson L, Kanie N, Lenton TM, Obura D, et al (2021). Reconciling safe planetary targets and planetary justice: Why should social scientists engage with planetary targets?.
Earth System Governance,
10Abstract:
Reconciling safe planetary targets and planetary justice: Why should social scientists engage with planetary targets?
As human activity threatens to make the planet unsafe for humanity and other life forms, scholars are identifying planetary targets set at a safe distance from biophysical thresholds beyond which critical Earth systems may collapse. Yet despite the profound implications that both meeting and transgressing such targets may have for human wellbeing, including the potential for negative trade-offs, there is limited social science analysis that systematically considers the justice dimensions of such targets. Here we assess a range of views on planetary justice and present three arguments associated with why social scientists should engage with the scholarship on safe targets. We argue that complementing safe targets with just targets offers a fruitful approach for considering synergies and trade-offs between environmental and social aspirations and can inform inclusive deliberation on these important issues.
Abstract.
Yang Y, Zhang C, Lenton TM, Yan X, Zhu M, Zhou M, Tao J, Phelps TJ, Cao Z (2021). The Evolution Pathway of Ammonia-Oxidizing Archaea Shaped by Major Geological Events.
Mol Biol Evol,
38(9), 3637-3648.
Abstract:
The Evolution Pathway of Ammonia-Oxidizing Archaea Shaped by Major Geological Events.
Primordial nitrification processes have been studied extensively using geochemical approaches, but the biological origination of nitrification remains unclear. Ammonia-oxidizing archaea (AOA) are widely distributed nitrifiers and implement the rate-limiting step in nitrification. They are hypothesized to have been important players in the global nitrogen cycle in Earth's early history. We performed systematic phylogenomic and marker gene analyses to elucidate the diversification timeline of AOA evolution. Our results suggested that the AOA ancestor experienced terrestrial geothermal environments at ∼1,165 Ma (1,928-880 Ma), and gradually evolved into mesophilic soil at ∼652 Ma (767-554 Ma) before diversifying into marine settings at ∼509 Ma (629-412 Ma) and later into shallow and deep oceans, respectively. Corroborated by geochemical evidence and modeling, the timing of key diversification nodes can be linked to the global magmatism and glaciation associated with the assembly and breakup of the supercontinent Rodinia, and the later oxygenation of the deep ocean. Results of this integrated study shed light on the geological forces that may have shaped the evolutionary pathways of the AOA, which played an important role in the ancient global nitrogen cycle.
Abstract.
Author URL.
Martin K, Schmidt K, Toseland A, Boulton CA, Barry K, Beszteri B, Brussaard CPD, Clum A, Daum CG, Eloe-Fadrosh E, et al (2021). The biogeographic differentiation of algal microbiomes in the upper ocean from pole to pole.
Nature Communications,
12(1).
Abstract:
The biogeographic differentiation of algal microbiomes in the upper ocean from pole to pole
AbstractEukaryotic phytoplankton are responsible for at least 20% of annual global carbon fixation. Their diversity and activity are shaped by interactions with prokaryotes as part of complex microbiomes. Although differences in their local species diversity have been estimated, we still have a limited understanding of environmental conditions responsible for compositional differences between local species communities on a large scale from pole to pole. Here, we show, based on pole-to-pole phytoplankton metatranscriptomes and microbial rDNA sequencing, that environmental differences between polar and non-polar upper oceans most strongly impact the large-scale spatial pattern of biodiversity and gene activity in algal microbiomes. The geographic differentiation of co-occurring microbes in algal microbiomes can be well explained by the latitudinal temperature gradient and associated break points in their beta diversity, with an average breakpoint at 14 °C ± 4.3, separating cold and warm upper oceans. As global warming impacts upper ocean temperatures, we project that break points of beta diversity move markedly pole-wards. Hence, abrupt regime shifts in algal microbiomes could be caused by anthropogenic climate change.
Abstract.
Owen R (2021). The maintenance of habitability across multiple scales:. A meta ecosystem view of Gaia.
Abstract:
The maintenance of habitability across multiple scales:. A meta ecosystem view of Gaia.
The Gaia hypothesis postulates that life and the abiotic environment of planet Earth form a self-regulating system, capable of maintaining planetary habitability. Previous studies have highlighted mechanisms by which environmental regulation can emerge. The majority of prior work has modelled life-environment interactions at the level of organisms interacting with their local environment. The model presented in this thesis uses a meta ecosystems approach to look at not just how organisms interact with their environment but how ecosystems interact with each other and a shared global environment. It is hypothesised that interaction through a shared environment decreases the probability of ecosystem collapse within a world consisting of numerous ecosystems. To test this hypothesis a version of the flask model is used where numerous ecosystem flasks exist within a global flask and interact with a shared environment. It is found that when ecosystems are able to interact with, and through, a shared global environment the probability of ecosystem collapse is reduced. It is postulated that this is caused through a novel form of meta-ecosystem dynamics where, through interaction with a shared environment, ecosystems are able to affect one another's population and therefore likelihood of extinction. This appears to be another way, apart from regulation of abiotic factors and nutrient recycling, in which life environment feedbacks can affect the habitability of a global system.
Abstract.
Eager J, Lenton TM, Mayne N (2021). The non-linear effect of methane on climate in a three-dimensional Archean atmosphere. Goldschmidt2021 abstracts.
Belcher CM, Mills BJW, Vitali R, Baker SJ, Lenton TM, Watson AJ (2021). The rise of angiosperms strengthened fire feedbacks and improved the regulation of atmospheric oxygen.
Nature Communications,
12(1).
Abstract:
The rise of angiosperms strengthened fire feedbacks and improved the regulation of atmospheric oxygen
The source of oxygen to Earth’s atmosphere is organic carbon burial, whilst the main sink is oxidative weathering of fossil carbon. However, this sink is to insensitive to counteract oxygen rising above its current level of about 21%. Biogeochemical models suggest that wildfires provide an additional regulatory feedback mechanism. However, none have considered how the evolution of different plant groups through time have interacted with this feedback. The Cretaceous Period saw not only super-ambient levels of atmospheric oxygen but also the evolution of the angiosperms, that then rose to dominate Earth’s ecosystems. Here we show, using the COPSE biogeochemical model, that angiosperm-driven alteration of fire feedbacks likely lowered atmospheric oxygen levels from ~30% to 25% by the end of the Cretaceous. This likely set the stage for the emergence of closed-canopy angiosperm tropical rainforests that we suggest would not have been possible without angiosperm enhancement of fire feedbacks.
Abstract.
Lenton TM (2021). Tipping points in the climate system.
WEATHER,
76(10), 325-326.
Author URL.
Armstrong McKay D, Staal A, Abrams JF, Winkelmann R, Sakschewski B, Loriani S, Fetzer I, Cornell SE, Rockström J, Lenton TM, et al (2021). Updated assessment suggests >1.5°C global warming could trigger multiple climate tipping points.
Clarkson MO, Lenton TM, Andersen MB, Bagard M-L, Dickson AJ, Vance D (2021). Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes.
Nat Commun,
12(1).
Abstract:
Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes.
The Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering
Abstract.
Author URL.
Sharpe S, Lenton TM (2021). Upward-scaling tipping cascades to meet climate goals: plausible grounds for hope.
Climate Policy,
21(4), 421-433.
Abstract:
Upward-scaling tipping cascades to meet climate goals: plausible grounds for hope
Limiting global warming to well below 2°C requires a dramatic acceleration of decarbonization to reduce net anthropogenic greenhouse gas emissions to zero around mid-century. In complex systems–including human societies–tipping points can occur, in which a small perturbation transforms a system. Crucially, activating one tipping point can increase the likelihood of triggering another at a larger scale, and so on. Here, we show how such upward-scaling tipping cascades could accelerate progress in tackling climate change. We focus on two sectors–light road transport and power–where tipping points have already been triggered by policy interventions at individual nation scales. We show how positive-sum cooperation, between small coalitions of jurisdictions and their policymakers, could lead to global changes in the economy and emissions. The aim of activating tipping points and tipping cascades is a particular application of systems thinking. It represents a different starting point for policy to the theory of welfare economics, one that can be useful when the priority is to achieve dynamic rather than allocative efficiency. Key policy insights Pricing policies and targeted investments that bring clean technologies below the threshold of cost-parity with fossil fuel technologies can trigger reinforcing feedbacks that cascade up scales to propel disproportionately rapid decarbonization. Traditional approaches to climate policy based on welfare economics principles of minimizing marginal abatement costs, and pricing externalities, are likely to miss these opportunities. Systems thinking can help identify ways for policy to drive effective change. Positive-sum cooperation between small groups of countries can accelerate the activation of tipping points in the global economy, facilitating decarbonization in all countries. Early opportunities for this are in the power and light road transport sectors, where clean technologies are increasingly competitive with fossil fuels. The value of decarbonization policies should be judged not just on their immediate effects on emissions within the implementing jurisdiction, but also for their potential to contribute to upward-scaling tipping cascades in the global economy.
Abstract.
Lees KJ, Buxton J, Boulton CA, Abrams JF, Lenton TM (2021). Using satellite data to assess management frequency and rate of regeneration on heather moorlands in England as a resilience indicator.
ENVIRONMENTAL RESEARCH COMMUNICATIONS,
3(8).
Author URL.
Ripple WJ, Wolf C, Newsome TM, Gregg JW, Lenton TM, Palomo I, Eikelboom JAJ, Law BE, Huq S, Duffy PB, et al (2021). World Scientists’ Warning of a Climate Emergency 2021. BioScience, 71(9), 894-898.
2020
Boulton CA, Ritchie PDL, Lenton TM (2020). Abrupt changes in Great Britain vegetation carbon projected under climate change.
Global Change Biology,
26(8), 4436-4448.
Abstract:
Abrupt changes in Great Britain vegetation carbon projected under climate change
AbstractPast abrupt ‘regime shifts’ have been observed in a range of ecosystems due to various forcing factors. Large‐scale abrupt shifts are projected for some terrestrial ecosystems under climate change, particularly in tropical and high‐latitude regions. However, there is very little high‐resolution modelling of smaller‐scale future projected abrupt shifts in ecosystems, and relatively less focus on the potential for abrupt shifts in temperate terrestrial ecosystems. Here, we show that numerous climate‐driven abrupt shifts in vegetation carbon are projected in a high‐resolution model of Great Britain's land surface driven by two different climate change scenarios. In each scenario, the effects of climate and CO2 combined are isolated from the effects of climate change alone. We use a new algorithm to detect and classify abrupt shifts in model time series, assessing the sign and strength of the non‐linear responses. The abrupt ecosystem changes projected are non‐linear responses to climate change, not simply driven by abrupt shifts in climate. Depending on the scenario, 374–1,144 grid cells of 1.5 km × 1.5 km each, comprising 0.5%–1.5% of Great Britain's land area show abrupt shifts in vegetation carbon. We find that abrupt ecosystem shifts associated with increases (rather than decreases) in vegetation carbon, show the greatest potential for early warning signals (rising autocorrelation and variance beforehand). In one scenario, 89% of abrupt increases in vegetation carbon show increasing autocorrelation and variance beforehand. Across the scenarios, 81% of abrupt increases in vegetation carbon have increasing autocorrelation and 74% increasing variance beforehand, whereas for decreases in vegetation carbon these figures are 56% and 47% respectively. Our results should not be taken as specific spatial or temporal predictions of abrupt ecosystem change. However, they serve to illustrate that numerous abrupt shifts in temperate terrestrial ecosystems could occur in a changing climate, with some early warning signals detectable beforehand.
Abstract.
Lovecchio E, Lenton TM (2020). BPOP-v1 model: exploring the impact of changes in the biological pump on the shelf sea and ocean nutrient and redox state.
GEOSCIENTIFIC MODEL DEVELOPMENT,
13(4), 1865-1883.
Author URL.
Turner MG, Calder WJ, Cumming GS, Hughes TP, Jentsch A, LaDeau SL, Lenton TM, Shuman BN, Turetsky MR, Ratajczak Z, et al (2020). Climate change, ecosystems and abrupt change: Science priorities.
Philosophical Transactions of the Royal Society B: Biological Sciences,
375(1794).
Abstract:
Climate change, ecosystems and abrupt change: Science priorities
Ecologists have long studied patterns, directions and tempos of change, but there is a pressing need to extend current understanding to empirical observations of abrupt changes as climate warming accelerates. Abrupt changes in ecological systems (ACES)-changes that are fast in time or fast relative to their drivers-are ubiquitous and increasing in frequency. Powerful theoretical frameworks exist, yet applications in real-world landscapes to detect, explain and anticipate ACES have lagged.We highlight five insights emerging from empirical studies of ACES across diverse ecosystems: (i) ecological systems show ACES in some dimensions but not others; (ii) climate extremes may be more important than mean climate in generating ACES; (iii) interactions among multiple drivers often produce ACES; (iv) contingencies, such as ecological memory, frequency and sequence of disturbances, and spatial context are important; and (v) tipping points are often (but not always) associated with ACES. We suggest research priorities to advance understanding of ACES in the face of climate change. Progress in understanding ACES requires strong integration of scientific approaches (theory, observations, experiments and process-based models) and high-quality empirical data drawn from a diverse array of ecosystems.
Abstract.
Cao M, Daines SJ, Lenton TM, Cui H, Algeo TJ, Dahl TW, Shi W, Chen ZQ, Anbar A, Zhou YQ, et al (2020). Comparison of Ediacaran platform and slope δ<sup>238</sup>U records in South China: Implications for global-ocean oxygenation and the origin of the Shuram Excursion.
Geochimica et Cosmochimica Acta,
287, 111-124.
Abstract:
Comparison of Ediacaran platform and slope δ238U records in South China: Implications for global-ocean oxygenation and the origin of the Shuram Excursion
The Ediacaran Shuram negative carbon isotope excursion (SE) records major paleoceanographic changes during the late Neoproterozoic, possibly linked to a global oceanic oxygenation event, yet its cause(s) remain uncertain. Earlier studies of the upper Ediacaran Doushantuo Formation in South China based on local redox proxies have documented strong spatial redox heterogeneity along shelf-to-basin transects, but variations of δ238U (a global redox proxy) have not yet been examined in deep-water SE carbonates. In this study, we examined δ238U variations through the SE in the upper slope Siduping section. Similar to platform SE sections, Siduping exhibits a shift toward higher δ238U values correlative with the peak of the SE (i.e. maximum negative δ13Ccarb), confirming inferences of global ocean oxygenation during the SE. This raises an apparent paradox, because a global negative carbon isotope excursion implies net oxidant consumption, requiring an ocean-based oxygenation mechanism. We hypothesize that an increase in the efficiency of phosphorus burial due to a plankton-driven shift from dominantly dissolved organic matter (DOM) cycling to greater particulate organic matter (POM) export depleted the ocean of nutrient phosphorus. By producing a steep redox gradient close to the sediment-water interface, we suggest that ocean oxygenation also triggered a globally simultaneous diagenetic event in which isotopically light δ13Ccarb was precipitated in authigenic carbonate minerals. This scenario can account for δ238U differences between shallow-water and deep-water carbonates, which reflect precipitation of relatively larger amounts of authigenic carbonate minerals in shallow-water settings, generating both a larger negative δ13Ccarb shift and a larger early diagenetic δ238U offset.
Abstract.
Zhang F, Dahl TW, Lenton TM, Luo G, Shen SZ, Algeo TJ, Planavsky N, Liu J, Cui Y, Qie W, et al (2020). Extensive marine anoxia associated with the Late Devonian Hangenberg Crisis.
Earth and Planetary Science Letters,
533Abstract:
Extensive marine anoxia associated with the Late Devonian Hangenberg Crisis
The global Hangenberg Crisis near the Devonian-Carboniferous boundary (DCB) represents one of the major Phanerozoic mass extinction events, which shaped the roots of modern vertebrate biodiversity. Marine anoxia has been cited as the proximate kill mechanism for this event. However, the detailed timing, duration, and extent of global marine redox chemistry changes across this critical interval remain controversial because most of the studies to date only constrain changes in local or regional redox chemistry. Thus, opinions on the significance of anoxia as a kill mechanism are variable—from anoxia being a primary driver to being relatively unimportant. In this study, we explore the evolution of global marine redox chemistry using U isotopes of marine limestones. The δ238U trends at Long'an section in South China document systematic oscillations with three negative shifts punctuated by two positive events in between. The magnitude of the δ238U oscillations implies that the sediments do not record contemporaneous seawater with a constant offset at all times. The lack of covariation between δ238U data and diagenetic indicators (e.g. Mn and Sr contents, Mn/Sr ratio, δ18O) suggests that the δ238U trends are not produced by the same post-depositional diagenetic processes. Instead, trace-metal enrichments suggest that more reducing conditions prevailed during the deposition of the two positive events. We present plausible model scenarios that fit the observed δ238U trends in the context of redox-sensitive trace metal data suggesting marine anoxia expanded in the latest Devonian oceans to cover >5% of the continental shelf seafloor area. The rapid expansion of marine anoxia coincident with the onset of the Hangenberg Crisis supports marine anoxia as an important kill mechanism. Biogeochemical modeling of the coupled C-P-U cycles suggests that intensified continental weathering, for example, assisted by the spread of seed plants with deeper root systems at this time, could have triggered expansion of marine anoxia and other global changes (e.g. positive excursion in δ13Ccarb and decrease in sea surface temperature) in the latest Devonian. The anoxic event is inferred to have been transient as climatic cooling would have reduced weathering fluxes.
Abstract.
Xu C, Kohler TA, Lenton TM, Svenning J-C, Scheffer M (2020). Future of the human climate niche.
Proc Natl Acad Sci U S A,
117(21), 11350-11355.
Abstract:
Future of the human climate niche.
All species have an environmental niche, and despite technological advances, humans are unlikely to be an exception. Here, we demonstrate that for millennia, human populations have resided in the same narrow part of the climatic envelope available on the globe, characterized by a major mode around ∼11 °C to 15 °C mean annual temperature (MAT). Supporting the fundamental nature of this temperature niche, current production of crops and livestock is largely limited to the same conditions, and the same optimum has been found for agricultural and nonagricultural economic output of countries through analyses of year-to-year variation. We show that in a business-as-usual climate change scenario, the geographical position of this temperature niche is projected to shift more over the coming 50 y than it has moved since 6000 BP. Populations will not simply track the shifting climate, as adaptation in situ may address some of the challenges, and many other factors affect decisions to migrate. Nevertheless, in the absence of migration, one third of the global population is projected to experience a MAT >29 °C currently found in only 0.8% of the Earth's land surface, mostly concentrated in the Sahara. As the potentially most affected regions are among the poorest in the world, where adaptive capacity is low, enhancing human development in those areas should be a priority alongside climate mitigation.
Abstract.
Author URL.
Eager JK, Reichelt DJ, Mayne NJ, Lambert FH, Sergeev DE, Ridgway RJ, Manners J, Boutle IA, Lenton TM, Kohary K, et al (2020). Implications of different stellar spectra for the climate of. tidally-locked Earth-like exoplanets.
Eager J, Reichelt D, Mayne N, Lambert F, Sergeev D, Ridgway R, Manners J, Boutle I, Lenton T, Kohary K, et al (2020). Implications of different stellar spectra for the climate of tidally--locked Earth-like exoplanets. Astronomy and Astrophysics
Lenton TM, Dutreuil S, Latour B (2020). Life on Earth is hard to spot.
The Anthropocene Review,
7(3), 248-272.
Abstract:
Life on Earth is hard to spot
The triumph of the Gaia hypothesis was to spot the extraordinary influence of Life on the Earth. ‘Life’ is the clade including all extant living beings, as distinct from ‘life’ the class of properties common to all living beings. ‘Gaia’ is Life plus its effects on habitability. Life’s influence on the Earth was hard to spot for several reasons: biologists missed it because they focused on life not Life; climatologists missed it because Life is hard to see in the Earth’s energy balance; Earth system scientists opted instead for abiotic or human-centred approaches to the Earth system; Scientists in general were repelled by teleological arguments that Life acts to maintain habitable conditions. Instead, we reason from organisms’ metabolisms outwards, showing how Life’s coupling to its environment has led to profound effects on Earth’s habitability. Recognising Life’s impact on Earth and learning from it could be critical to understanding and successfully navigating the Anthropocene.
Abstract.
Cowling D (2020). Modelling the effect of different carbonate weathering rates on Earth system resilience.
Abstract:
Modelling the effect of different carbonate weathering rates on Earth system resilience
Carbonate weathering is an important feedback to regulate the carbon cycle and climate of the Earth system. Focus of the behaviour of this feedback has been on geological scales. Little attention has been given to the responses of this feedback to shorter-scale Earth system perturbations, especially how different uplifted masses of carbonate have influenced this strength. Hence, using the Earth system model cGENIE, this study will explore the carbon and climate responses to different carbonate weathering rates, and how these rates produce different resilience to a range past and future carbon perturbations. These experiments have shown a considerable carbon and climate influence from higher carbonate weathering rates. This is especially evident in response to perturbations, where higher carbonate weathering rates show considerable resilience contribution to the system, notably in the longer-term recovery period. This has therefore exposed an important role of carbonate weathering on a previously underappreciated temporal scale. Further, this study has also demonstrated carbonate weathering does have an important control on resilience and recovery direction, hence is an important variable to refine for future impacts and rate of recovery.
Abstract.
Lenton TM (2020). On the use of models in understanding the rise of complex life.
Interface Focus,
10(4), 20200018-20200018.
Abstract:
On the use of models in understanding the rise of complex life
. Recently, several seemingly irreconcilably different models have been proposed for relationships between Earth system processes and the rise of complex life. These models provide very different scenarios of Proterozoic atmospheric oxygen and ocean nutrient levels, whether they constrained complex life, and of how the rise of complex life affected biogeochemical conditions. For non-modellers, it can be hard to evaluate which—if any—of the models and their results have more credence—hence this article. I briefly review relevant hypotheses, how models are being used to incarnate and sometimes test those hypotheses, and key principles of biogeochemical cycling models should embody. Then I critically review the use of biogeochemical models in: inferring key variables from proxies; reconstructing ancient biogeochemical cycling; and examining how complex life affected biogeochemical cycling. Problems are found in published model results purporting to demonstrate long-term stable states of very low Proterozoic atmospheric
. p
. O
. 2
. and ocean P levels. I explain what they stem from and highlight key empirical uncertainties that need to be resolved. Then I suggest how models and data can be better combined to advance our scientific understanding of the relationship between Earth system processes and the rise of complex life.
.
Abstract.
Lenton TM (2020). On the use of models in understanding the rise of complex life.
Interface Focus,
10(4).
Abstract:
On the use of models in understanding the rise of complex life
Recently, several seemingly irreconcilably different models have been proposed for relationships between Earth system processes and the rise of complex life. These models provide very different scenarios of Proterozoic atmospheric oxygen and ocean nutrient levels, whether they constrained complex life, and of how the rise of complex life affected biogeochemical conditions. For non-modellers, it can be hard to evaluate which - if any - of the models and their results have more credence - hence this article. I briefly review relevant hypotheses, how models are being used to incarnate and sometimes test those hypotheses, and key principles of biogeochemical cycling models should embody. Then I critically review the use of biogeochemical models in: inferring key variables from proxies; reconstructing ancient biogeochemical cycling; and examining how complex life affected biogeochemical cycling. Problems are found in published model results purporting to demonstrate long-term stable states of very low Proterozoic atmospheric pO 2 and ocean P levels. I explain what they stem from and highlight key empirical uncertainties that need to be resolved. Then I suggest how models and data can be better combined to advance our scientific understanding of the relationship between Earth system processes and the rise of complex life.
Abstract.
Guilbaud R, Poulton SW, Thompson J, Husband KF, Zhu M, Zhou Y, Shields GA, Lenton TM (2020). Phosphorus-limited conditions in the early Neoproterozoic ocean maintained low levels of atmospheric oxygen. Nature Geoscience, 13(4), 296-301.
von der Heydt A, Ashwin P, Camp C, Crucifix M, Dijkstra H, Ditlevsen P, Lenton T (2020). Quantification and interpretation of the climate variability record.
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.
Keane A, Krauskopf B, Lenton TM (2020). Signatures consistent with multi-frequency tipping in the Atlantic. meridional overturning circulation.
Abstract:
Signatures consistent with multi-frequency tipping in the Atlantic. meridional overturning circulation
The early detection of tipping points, which describe a rapid departure from
a stable state, is an important theoretical and practical challenge. Tipping
points are most commonly associated with the disappearance of steady-state or
periodic solutions at fold bifurcations. We discuss here multi-frequency
tipping (M-tipping), which is tipping due to the disappearance of an attracting
torus. M-tipping is a generic phenomenon in systems with at least two intrinsic
or external frequencies that can interact and, hence, is relevant to a wide
variety of systems of interest. We show that the more complicated sequence of
bifurcations involved in M-tipping provides a possible consistent explanation
for as yet unexplained behavior observed near tipping in climate models for the
Atlantic meridional overturning circulation. More generally, this work provides
a path towards identifying possible early-warning signs of tipping in
multiple-frequency systems.
Abstract.
Author URL.
Winkelmann R, Donges JF, Smith EK, Milkoreit M, Eder C, Heitzig J, Katsanidou A, Wiedermann M, Wunderling N, Lenton TM, et al (2020). Social tipping processes for sustainability: an analytical framework.
Ecological Economics,
192Abstract:
Social tipping processes for sustainability: an analytical framework
Societal transformations are necessary to address critical global challenges,
such as mitigation of anthropogenic climate change and reaching UN sustainable
development goals. Recently, social tipping processes have received increased
attention, as they present a form of social change whereby a small change can
shift a sensitive social system into a qualitatively different state due to
strongly self-amplifying (mathematically positive) feedback mechanisms. Social
tipping processes have been suggested as key drivers of sustainability
transitions emerging in the fields of technological and energy systems,
political mobilization, financial markets and sociocultural norms and
behaviors.
. Drawing from expert elicitation and comprehensive literature review, we
develop a framework to identify and characterize social tipping processes
critical to facilitating rapid social transformations. We find that social
tipping processes are distinguishable from those of already more widely studied
climate and ecological tipping dynamics. In particular, we identify human
agency, social-institutional network structures, different spatial and temporal
scales and increased complexity as key distinctive features underlying social
tipping processes. Building on these characteristics, we propose a formal
definition for social tipping processes and filtering criteria for those
processes that could be decisive for future trajectories to global
sustainability in the Anthropocene. We illustrate this definition with the
European political system as an example of potential social tipping processes,
highlighting the potential role of the FridaysForFuture movement.
. Accordingly, this analytical framework for social tipping processes can be
utilized to illuminate mechanisms for necessary transformative climate change
mitigation policies and actions.
Abstract.
Author URL.
Baldwin MP, Lenton TM (2020). Solving the climate crisis: Lessons from ozone depletion and COVID-19.
Global Sustainability,
3Abstract:
Solving the climate crisis: Lessons from ozone depletion and COVID-19
The ‘climate crisis’ describes human-caused global warming and climate change and its consequences. It conveys the sense of urgency surrounding humanity’s failure to take sufficient action to slow down, stop and reverse global warming. The leading direct cause of the climate crisis is carbon dioxide (CO2) released as a by-product of burning fossil fuels,i which supply ∼87% of the world’s energy. The second most important cause of the climate crisis is deforestation to create more land for crops and livestock. The solutions have been stated as simply ‘leave the fossil carbon in the ground’ and ‘end deforestation’. Rather than address fossil fuel supplies, climate policies focus almost exclusively on the demand side, blaming fossil fuel users for greenhouse gas emissions. The fundamental reason that we are not solving the climate crisis is not a lack of green energy solutions. It is that governments continue with energy strategies that prioritize fossil fuels. These entrenched energy policies subsidize the discovery, extraction, transport and sale of fossil fuels, with the aim of ensuring a cheap, plentiful, steady supply of fossil energy into the future. This paper compares the climate crisis to two other environmental crises: ozone depletion and the COVID-19 pandemic. Halting and reversing damage to the ozone layer is one of humanity’s greatest environmental success stories. The world’s response to COVID-19 demonstrates that it is possible for governments to take decisive action to avert an imminent crisis. The approach to solving both of these crises was the same: (1) identify the precise cause of the problem through expert scientific advice; (2) with support by the public, pass legislation focused on the cause of the problem; and (3) employ a robust feedback mechanism to assess progress and adjust the approach. This is not yet being done to solve the climate crisis, but working within the 2015 Paris Climate Agreement framework, it could be. Every nation can contribute to solving the climate crisis by: (1) changing their energy strategy to green energy sources instead of fossil fuels; and (2) critically reviewing every law, policy and trade agreement (including transport, food production, food sources and land use) that affects the climate crisis. Social media summary to solve the climate crisis, governments must end policies that support fossil fuels, not just support renewable energy.
Abstract.
Steffen W, Richardson K, Rockström J, Schellnhuber HJ, Dube OP, Dutreuil S, Lenton TM, Lubchenco J (2020). The emergence and evolution of Earth System Science. Nature Reviews Earth & Environment, 1(1), 54-63.
Steffen W, Richardson K, Rockstrom J, Schellnhuber HJ, Dube OP, Dutreuil S, Lenton TM, Lubchenco J (2020). The emergence and evolution of Earth System Science (vol 1, pg 54, 2020).
NATURE REVIEWS EARTH & ENVIRONMENT,
1(10), 554-554.
Author URL.
Wood R, Donoghue PCJ, Lenton TM, Liu AG, Poulton SW (2020). The origin and rise of complex life: progress requires interdisciplinary integration and hypothesis testing.
INTERFACE FOCUS,
10(4).
Author URL.
Burton K, Hopkinson P, Lenton T, Benson D, Galloway T, Godley B, Nelms S, Short R, Xiaoyu Y, Boehm S, et al (2020). Towards a new Regional Circular Economy for Plastics - Progress in South West England. Dr Kerry Burton. 8th - 12th Jun 2020.
Abstract:
Towards a new Regional Circular Economy for Plastics - Progress in South West England
Abstract.
Zhang F, Shen SZ, Cui Y, Lenton TM, Dahl TW, Zhang H, Zheng QF, Wang W, Krainer K, Anbar AD, et al (2020). Two distinct episodes of marine anoxia during the Permian-Triassic crisis evidenced by uranium isotopes in marine dolostones.
Geochimica et Cosmochimica Acta,
287, 165-179.
Abstract:
Two distinct episodes of marine anoxia during the Permian-Triassic crisis evidenced by uranium isotopes in marine dolostones
The end-Permian mass extinction (EPME; ca. 251.94 Ma) is the most severe mass extinction in the geological record. Detailed paleobiological investigations show a very rapid EPME event, and recently published δ238U data show a large negative excursion and thus a massive shift to globally expanded anoxia at the main extinction phase in the latest Permian. The negative shift in δ238U is in correlation with a globally characterized negative δ13C excursion near the Permian-Triassic boundary (PTB). In some highly expanded PTB carbonate sections, however, there are two distinct negative δ13C excursions whereas uranium isotopes (δ238U) from such sections have not yet been examined, leaving a gap in the understanding of the global perturbations of marine redox conditions immediately following the EPME. Here, we present a new δ238U study of syn-depositional dolostones from a well-characterized and highly expanded drill core, which recorded two pronounced negative δ13C excursions across the PTB, from the Carnic Alps, Austria. This drill core extends 331-meters across the PTB and provides a unique opportunity to explore the detailed timing, duration, and extent of marine redox chemistry changes before, during, and immediately after the EPME. Our new δ238U record shows two negative shifts, which are correlated with the two negative δ13C excursions. The first negative δ238U excursion preceding the EPME confirms the recently published δ238U records from across the EPME and support that syndepositional marine dolostones can record δ238U trends of seawater similar to that of limestones. Modeling of uranium isotope cycling in the latest Permian and earliest Triassic oceans suggests two distinct stages of expanded marine anoxia separated by a brief interval (∼100 kyr) of reoxygenation across the PTB. The first anoxic episode lasted for ∼ 60 kyr while anoxic seafloor area expanded to cover >18% of the entire seafloor, coeval with the main EPME horizon, agreeing with marine anoxia as a proximate kill mechanism for the EPME. The second anoxic event was less intense compared to the first anoxic pulse but sustained for a longer duration. A global modeling of coupled C, P, and U cycles show that two pulses of volcanic carbon injection that drives global warming and increased phosphorus weathering rate can reasonably reproduce our data to match two phases of anoxia. The model also demonstrates that the loss of terrestrial vegetation in the EPME is crucial to generating an intervening interval of oxygenated ocean. Our new study adds to a growing body of evidence that the global marine redox conditions underwent rapid oscillations during the EPME event and continued afterward, which may have played a central role in delaying the marine ecosystem recovery in the Early Triassic.
Abstract.
Zhang F, Lenton TM, del Rey Á, Romaniello SJ, Chen X, Planavsky NJ, Clarkson MO, Dahl TW, Lau KV, Wang W, et al (2020). Uranium isotopes in marine carbonates as a global ocean paleoredox proxy: a critical review. Geochimica et Cosmochimica Acta, 287, 27-49.
Ullmann C, Boyle R, Duarte LV, Hesselbo SP, Kasemann SA, Klein T, Lenton TM, Piazza V, Aberhan M (2020). Warm afterglow from the Toarcian Oceanic Anoxic Event drives the success of deep-adapted brachiopods. Scientific Reports, 10
Nicholson AE (2020). What mechanisms have produced a self-regulating Earth system?.
Abstract:
What mechanisms have produced a self-regulating Earth system?
The Gaia Hypothesis postulates that life and the oceans, crust, and atmosphere of the Earth form a self-regulating planetary-scale system with stabilising properties. Gaia helps to explain the long history of uninterrupted habitability on Earth. Previous Gaian models have uncovered mechanisms for self-regulation in life-environment coupled systems, such as the Earth, and the work in this thesis adds to our understanding on how and when self-regulation can emerge on a planet hosting life, and what conditions help maintain such regulation once established. To place the models presented in this thesis into their proper context this thesis contains background on Earth's history, the history of the Gaia hypothesis and some key Gaian models and known Gaian regulation mechanisms, and a discussion on habitability of exoplanets and our search for alien life.
In this thesis I explore a new variant of a pre-existing Gaian model (the flask model) which demonstrates a new regulation mechanism which I call 'single-rein control'. I then adapt this model to explore the hypothesis of 'selection by survival'. This hypothesis suggests that the longer a life harbouring planet survives, the longer it has to acquire further persistence mechanisms. Therefore over time the only planets hosting life still existing will be those that have acquired several self-regulation mechanisms like those present on Earth. The results of this model demonstrate that selection by survival can promote long term persistence of biospheres compared to a null model.
In the second part of this thesis I consider how the Gaia hypothesis can inform our search for inhabited exoplanets and I introduce the ExoGaia model, a new model of atmospheric regulation where microbes must 'catch' a window of habitability on their host planet, and quickly form self-regulating feedback loops to prevent the planetary temperature from rising to inhospitable levels.
The ExoGaia model demonstrates global regulation and the underlying geochemistry on the planet turns out to be key in determining how robust this regulation is. ExoGaia also demonstrates 'Gaian bottlenecks' where for the same planet life either quickly establishes self-regulating feedback loops and enjoys long term habitability, or fails and becomes extinct, with the host plane quickly reverting to an inhospitable state. This model agrees with the hypothesis that inhabitance and habitability are two sides to the same coin -- that a planet is highly unlike to be in a habitable state, without being inhabited.
This thesis argues a case for 'Probable Homeostatic Gaia' -- that not only is the Earth-system homeostatic but that homeostatic regulation is an expected result of a life-environment coupled system. If true, this would would increase our chances of finding other Gaian worlds.
Abstract.
2019
Boulton CA, Lenton TM (2019). A new method for detecting abrupt shifts in time series.
F1000Research,
8, 746-746.
Abstract:
A new method for detecting abrupt shifts in time series
Abrupt shifts in time series are a topic of growing interest in a number of research areas. They can be caused by a range of different underlying dynamics, for example, via a mathematical bifurcation, or potentially as the result of an auto-correlated stochastic process (i.e. ‘red’ noise). Here we present a method that detects abrupt shifts by searching for gradient changes that occur over a short space of time. It can be automated, allowing many time series to be analysed by the user at once, such as from high spatial resolution data. Our method detects abrupt shifts regardless of their origin (which it cannot deduce). We present a comparison with the method of abrupt shift detection from the changepoint R package, which is based on changes in mean over the time series. Our method performs better on data with an underlying trend where comparisons of means may fail.
Abstract.
Williams JJ, Mills BJW, Lenton TM (2019). A tectonically driven Ediacaran oxygenation event.
Nat Commun,
10(1).
Abstract:
A tectonically driven Ediacaran oxygenation event.
The diversification of complex animal life during the Cambrian Period (541-485.4 Ma) is thought to have been contingent on an oxygenation event sometime during ~850 to 541 Ma in the Neoproterozoic Era. Whilst abundant geochemical evidence indicates repeated intervals of ocean oxygenation during this time, the timing and magnitude of any changes in atmospheric pO2 remain uncertain. Recent work indicates a large increase in the tectonic CO2 degassing rate between the Neoproterozoic and Paleozoic Eras. We use a biogeochemical model to show that this increase in the total carbon and sulphur throughput of the Earth system increased the rate of organic carbon and pyrite sulphur burial and hence atmospheric pO2. Modelled atmospheric pO2 increases by ~50% during the Ediacaran Period (635-541 Ma), reaching ~0.25 of the present atmospheric level (PAL), broadly consistent with the estimated pO2 > 0.1-0.25 PAL requirement of large, mobile and predatory animals during the Cambrian explosion.
Abstract.
Author URL.
Lenton TM (2019). Biodiversity and global change: from creator to victim. In (Ed)
Biological Extinction: New Perspectives, 34-79.
Abstract:
Biodiversity and global change: from creator to victim
Abstract.
Lenton TM, Rockström J, Gaffney O, Rahmstorf S, Richardson K, Steffen W, Schellnhuber HJ (2019). Climate tipping points - too risky to bet against.
Nature,
575(7784), 592-595.
Author URL.
Quinn C (2019). Delayed effects and critical transitions in climate models.
Abstract:
Delayed effects and critical transitions in climate models
There is a continuous demand for new and improved methods of understanding our climate system. The work in this thesis focuses on the study of delayed feedback and critical transitions. There is much room to develop upon these concepts in their application to the climate system. We explore the two concepts independently, but also note that the two are not mutually exclusive.
The thesis begins with a review of delay differential equation (DDE) theory and the use of delay models in climate, followed by a review of the literature on critical transitions and examples of critical transitions in climate. We introduce various methods of deriving delay models from more complex
systems. Our main results center around the Saltzman and Maasch (1988) model for the Pleistocene climate (`Carbon cycle instability as a cause of the late Pleistocene ice age oscillations: modelling the asymmetric response.' Global biogeochemical cycles, 2(2):177-185, 1988). We observe that the model contains a chain of. first-order reactions. Feedback chains of this type limits to a discrete delay for long chains. We can then approximate the chain by a delay, resulting in scalar DDE for ice mass. Through bifurcation analysis under varying the delay, we discover a previously unexplored bistable
region and consider solutions in this parameter region when subjected to periodic and astronomical forcing. The astronomical forcing is highly quasiperiodic, containing many overlapping frequencies from variations in the Earth's orbit. We. find that under the astronomical forcing, the model exhibits a transition in time that resembles what is seen in paleoclimate records, known as the Mid-Pleistocene Transition. This transition is a distinct feature of the quasiperiodic forcing, as confi rmed by the change in sign of the leading. nite-time Lyapunov exponent. Additional results involve a box model of the Atlantic meridional overturning circulation under a future climate scenario and time-dependent freshwater forcing. We. find that the model exhibits multiple types of critical transitions, as well as recovery from potential critical transitions. We conclude with an outlook on how the work presented in this thesis can be utilised for further studies of the climate system and beyond.
Abstract.
Latour B, Lenton TM (2019). Extending the domain of freedom, or why gaia is so hard to understand. Critical Inquiry, 45(3), 659-680.
Zhang F, Xiao S, Romaniello SJ, Hardisty D, Li C, Melezhik V, Pokrovsky B, Cheng M, Shi W, Lenton TM, et al (2019). Global marine redox changes drove the rise and fall of the Ediacara biota.
Geobiology,
17(6), 594-610.
Abstract:
Global marine redox changes drove the rise and fall of the Ediacara biota.
The role of O2 in the evolution of early animals, as represented by some members of the Ediacara biota, has been heavily debated because current geochemical evidence paints a conflicting picture regarding global marine O2 levels during key intervals of the rise and fall of the Ediacara biota. Fossil evidence indicates that the diversification the Ediacara biota occurred during or shortly after the Ediacaran Shuram negative C-isotope Excursion (SE), which is often interpreted to reflect ocean oxygenation. However, there is conflicting evidence regarding ocean oxygen levels during the SE and the middle Ediacaran Period. To help resolve this debate, we examined U isotope variations (δ238 U) in three carbonate sections from South China, Siberia, and USA that record the SE. The δ238 U data from all three sections are in excellent agreement and reveal the largest positive shift in δ238 U ever reported in the geologic record (from ~ -0.74‰ to ~ -0.26‰). Quantitative modeling of these data suggests that the global ocean switched from a largely anoxic state (26%-100% of the seafloor overlain by anoxic waters) to near-modern levels of ocean oxygenation during the SE. This episode of ocean oxygenation is broadly coincident with the rise of the Ediacara biota. Following this initial radiation, the Ediacara biota persisted until the terminal Ediacaran period, when recently published U isotope data indicate a return to more widespread ocean anoxia. Taken together, it appears that global marine redox changes drove the rise and fall of the Ediacara biota.
Abstract.
Author URL.
Ritchie PDL, Harper AB, Smith GS, Kahana R, Kendon EJ, Lewis H, Fezzi C, Halleck-Vega S, Boulton CA, Bateman IJ, et al (2019). Large changes in Great Britain’s vegetation and agricultural land-use predicted under unmitigated climate change.
Environmental Research Letters,
14(11), 114012-114012.
Abstract:
Large changes in Great Britain’s vegetation and agricultural land-use predicted under unmitigated climate change
Abstract
. The impact of climate change on vegetation including agricultural production has been the focus of many studies. Climate change is expected to have heterogeneous effects across locations globally, and the diversity of land uses characterising Great Britain (GB) presents a unique opportunity to test methods for assessing climate change effects and impacts. GB is a relatively cool and damp country, hence, the warmer and generally drier growing season conditions projected for the future are expected to increase arable production. Here we use state-of-the-art, kilometre-scale climate change scenarios to drive a land surface model (JULES; Joint UK Land Environment Simulator) and an ECOnometric AGricultural land use model (ECO-AG). Under unmitigated climate change, by the end of the century, the growing season in GB is projected to get >5 °C warmer and 140 mm drier on average. Rising levels of atmospheric CO2 are predicted to counteract the generally negative impacts of climate change on vegetation productivity in JULES. Given sufficient precipitation, warming favours higher value arable production over grassland agriculture, causing a predicted westward expansion of arable farming in ECO-AG. However, drying in the East and Southeast, without any CO2 fertilisation effect, is severe enough to cause a predicted reversion from arable to grassland farming. Irrigation, if implemented, could maintain this land in arable production. However, the predicted irrigation demand of ∼200 mm (per growing season) in many locations is comparable to annual predicted runoff, potentially demanding large-scale redistribution of water between seasons and/or across the country. The strength of the CO2 fertilisation effect emerges as a crucial uncertainty in projecting the impact of climate change on GB vegetation, especially farming land-use decisions.
Abstract.
Mills BJW, Krause AJ, Scotese CR, Hill DJ, Shields GA, Lenton TM (2019). Modelling the long-term carbon cycle, atmospheric CO2, and Earth surface temperature from late Neoproterozoic to present day. Gondwana Research, 67, 172-186.
Carnicer J, Domingo-Marimon C, Ninyerola M, Camarero JJ, Bastos A, López-Parages J, Blanquer L, Rodríguez-Fonseca B, Lenton TM, Dakos V, et al (2019). Regime shifts of Mediterranean forest carbon uptake and reduced resilience driven by multidecadal ocean surface temperatures.
Glob Chang Biol,
25(8), 2825-2840.
Abstract:
Regime shifts of Mediterranean forest carbon uptake and reduced resilience driven by multidecadal ocean surface temperatures.
The mechanisms translating global circulation changes into rapid abrupt shifts in forest carbon capture in semi-arid biomes remain poorly understood. Here, we report unprecedented multidecadal shifts in forest carbon uptake in semi-arid Mediterranean pine forests in Spain over 1950-2012. The averaged carbon sink reduction varies between 31% and 37%, and reaches values in the range of 50% in the most affected forest stands. Regime shifts in forest carbon uptake are associated with climatic early warning signals, decreased forest regional synchrony and reduced long-term carbon sink resilience. We identify the mechanisms linked to ocean multidecadal variability that shape regime shifts in carbon capture. First, we show that low-frequency variations of the surface temperature of the Atlantic Ocean induce shifts in the non-stationary effects of El Niño Southern Oscillation (ENSO) on regional forest carbon capture. Modelling evidence supports that the non-stationary effects of ENSO can be propagated from tropical areas to semi-arid Mediterranean biomes through atmospheric wave trains. Second, decadal changes in the Atlantic Multidecadal Oscillation (AMO) significantly alter sea-air heat exchanges, modifying in turn ocean vapour transport over land and land surface temperatures, and promoting sustained drought conditions in spring and summer that reduce forest carbon uptake. Third, we show that lagged effects of AMO on the winter North Atlantic Oscillation also contribute to the maintenance of long-term droughts. Finally, we show that the reported strong, negative effects of ocean surface temperature (AMO) on forest carbon uptake in the last decades are unprecedented over the last 150 years. Our results provide new, unreported explanations for carbon uptake shifts in these drought-prone forests and review the expected impacts of global warming on the profiled mechanisms.
Abstract.
Author URL.
Lewis K (2019). The role of climate science in understanding Climate Security.
Abstract:
The role of climate science in understanding Climate Security
Climate change is widely recognised to represent a threat to human security, but understanding how this threat may manifest itself is a non-trivial task. Climate Security spans natural and social science boundaries, where differences in analytical methods, language and scale between disciplines can result in barriers to accessing climate science knowledge. This thesis attempts to address some of these knowledge problems and demonstrate the potential to improve the integration and utilisation of climate science in understanding climate and security. Using a systems-based approach, the example of long term food insecurity in Ethiopia is explored. Despite large increases in national cereal production in recent decades, Ethiopia continues to experience regular acute food insecurity crises, often associated with drought events. However, the meteorology of these events is poorly defined and local populations frequently experience food insecurity crises in years when national rainfall and cereal production totals are high. The on-going recurrence of acute food insecurity is a feature of the heterogeneity of climate and climate variability in Ethiopia, but only in the context of a food system dominated by smallholder farming and climate-sensitive livelihoods. Over climate change timescales both the climate and the food system will be subject to change, and so information on climate change needs to be provided in the context of food system changes. To explore the potential for climate change to threaten longer term food security, a simple ‘toy’ model of the food system in Ethiopia was developed. The model was run with a number of climate model projections and under different scenarios of transformational change to the food system. The results showed that climate change will have a negative impact on achieving food security in Ethiopia, but that the scale of this impact is smaller than potential positive food system changes. However, climate change does substantially off-set much of the modelled improvement associated with system interventions, and without ambitious system changes the food security situation in Ethiopia will become more challenging. In addition, the model shows an increase in food system variability associated with increased climate variability, which is amplified by the multiplicative effect of the food system changes. This suggests that substantial policy interventions are required if Ethiopia is to meet its food security needs long term, and that incremental adaptation to improve resilience to climate variability is required alongside transformational system change. The simple food system model was then run over Botswana, Tanzania and Mali for comparison. For Tanzania and Mali the scale of positive system changes was again larger than the negative climate change impacts, but as in Ethiopia climate change both exacerbated system variability and made transformational change necessary. In Botswana, where there is a strong signal for drying and the potential for transformational system change is more limited, the long term food security outlook under climate change is less optimistic. The simple systems model approach shows the potential for climate model projections to be better utilised in evaluating the scale and direction of the climate security threat, and that a systems approach can facilitate trans-disciplinary research in Climate Security aimed at policy-relevance.
Abstract.
Shields GA, Mills BJW, Zhu M, Raub TD, Daines SJ, Lenton TM (2019). Unique Neoproterozoic carbon isotope excursions sustained by coupled evaporite dissolution and pyrite burial.
Nature Geoscience,
12(10), 823-827.
Abstract:
Unique Neoproterozoic carbon isotope excursions sustained by coupled evaporite dissolution and pyrite burial
The Neoproterozoic era witnessed a succession of biological innovations that culminated in diverse animal body plans and behaviours during the Ediacaran–Cambrian radiations. Intriguingly, this interval is also marked by perturbations to the global carbon cycle, as evidenced by extreme fluctuations in climate and carbon isotopes. The Neoproterozoic isotope record has defied parsimonious explanation because sustained 12C-enrichment (low δ13C) in seawater seems to imply that substantially more oxygen was consumed by organic carbon oxidation than could possibly have been available. We propose a solution to this problem, in which carbon and oxygen cycles can maintain dynamic equilibrium during negative δ13C excursions when surplus oxidant is generated through bacterial reduction of sulfate that originates from evaporite weathering. Coupling of evaporite dissolution with pyrite burial drives a positive feedback loop whereby net oxidation of marine organic carbon can sustain greenhouse forcing of chemical weathering, nutrient input and ocean margin euxinia. Our proposed framework is particularly applicable to the late Ediacaran ‘Shuram’ isotope excursion that directly preceded the emergence of energetic metazoan metabolisms during the Ediacaran–Cambrian transition. Here we show that non-steady-state sulfate dynamics contributed to climate change, episodic ocean oxygenation and opportunistic radiations of aerobic life during the Neoproterozoic era.
Abstract.
2018
Bathiany S, Scheffer M, van Nes EH, Williamson MS, Lenton TM (2018). Abrupt Climate Change in an Oscillating World.
Sci Rep,
8(1).
Abstract:
Abrupt Climate Change in an Oscillating World.
The notion that small changes can have large consequences in the climate or ecosystems has become popular as the concept of tipping points. Typically, tipping points are thought to arise from a loss of stability of an equilibrium when external conditions are slowly varied. However, this appealingly simple view puts us on the wrong foot for understanding a range of abrupt transitions in the climate or ecosystems because complex environmental systems are never in equilibrium. In particular, they are forced by diurnal variations, the seasons, Milankovitch cycles and internal climate oscillations. Here we show how abrupt and sometimes even irreversible change may be evoked by even small shifts in the amplitude or time scale of such environmental oscillations. By using model simulations and reconciling evidence from previous studies we illustrate how these phenomena can be relevant for ecosystems and elements of the climate system including terrestrial ecosystems, Arctic sea ice and monsoons. Although the systems we address are very different and span a broad range of time scales, the phenomena can be understood in a common framework that can help clarify and unify the interpretation of abrupt shifts in the Earth system.
Abstract.
Author URL.
Nicholson AE, Wilkinson DM, Williams HTP, Lenton TM (2018). Alternative mechanisms for Gaia.
J Theor Biol,
457, 249-257.
Abstract:
Alternative mechanisms for Gaia.
A long-standing objection to the Gaia hypothesis has been a perceived lack of plausible mechanisms by which life on Earth could come to regulate its abiotic environment. A null hypothesis is survival by pure chance, by which any appearance of regulation on Earth is illusory and the persistence of life simply reflects the weak anthropic principle - it must have occurred for intelligent observers to ask the question. Recent work has proposed that persistence alone increases the chance that a biosphere will acquire further persistence-enhancing properties. Here we use a simple quantitative model to show that such 'selection by survival alone' can indeed increase the probability that a biosphere will persist in the future, relative to a baseline of pure chance. Adding environmental feedback to this model shows either an increased or decreased survival probability depending on the initial conditions. Feedback can hinder early life becoming established if initial conditions are poor, but feedback can also prevent systems from diverging too far from optimum environmental conditions and thus increase survival rates. The outstanding question remains the relative importance of each mechanism for the historical and continued persistence of life on Earth.
Abstract.
Author URL.
Lenton TM (2018). Can emergency geoengineering really prevent climate tipping points?. In (Ed)
Geoengineering our Climate?: Ethics, Politics, and Governance, 43-46.
Abstract:
Can emergency geoengineering really prevent climate tipping points?
Abstract.
Bathiany S, Dakos V, Scheffer M, Lenton TM (2018). Climate models predict increasing temperature variability in poor countries.
Sci Adv,
4(5).
Abstract:
Climate models predict increasing temperature variability in poor countries.
Extreme events such as heat waves are among the most challenging aspects of climate change for societies. We show that climate models consistently project increases in temperature variability in tropical countries over the coming decades, with the Amazon as a particular hotspot of concern. During the season with maximum insolation, temperature variability increases by ~15% per degree of global warming in Amazonia and Southern Africa and by up to 10%°C-1 in the Sahel, India, and Southeast Asia. Mechanisms include drying soils and shifts in atmospheric structure. Outside the tropics, temperature variability is projected to decrease on average because of a reduced meridional temperature gradient and sea-ice loss. The countries that have contributed least to climate change, and are most vulnerable to extreme events, are projected to experience the strongest increase in variability. These changes would therefore amplify the inequality associated with the impacts of a changing climate.
Abstract.
Author URL.
van de Velde S, Mills BJW, Meysman FJR, Lenton TM, Poulton SW (2018). Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing.
Nat Commun,
9(1).
Abstract:
Early Palaeozoic ocean anoxia and global warming driven by the evolution of shallow burrowing.
The evolution of burrowing animals forms a defining event in the history of the Earth. It has been hypothesised that the expansion of seafloor burrowing during the Palaeozoic altered the biogeochemistry of the oceans and atmosphere. However, whilst potential impacts of bioturbation on the individual phosphorus, oxygen and sulphur cycles have been considered, combined effects have not been investigated, leading to major uncertainty over the timing and magnitude of the Earth system response to the evolution of bioturbation. Here we integrate the evolution of bioturbation into the COPSE model of global biogeochemical cycling, and compare quantitative model predictions to multiple geochemical proxies. Our results suggest that the advent of shallow burrowing in the early Cambrian contributed to a global low-oxygen state, which prevailed for ~100 million years. This impact of bioturbation on global biogeochemistry likely affected animal evolution through expanded ocean anoxia, high atmospheric CO2 levels and global warming.
Abstract.
Author URL.
Lenton TM, Latour B (2018). Gaia 2.0 Could humans add some level of self-awareness to Earth's self-regulation?. Science, 361(6407), 1066-1068.
Nicholson AE, Wilkinson DM, Williams HTP, Lenton TM (2018). Gaian bottlenecks and planetary habitability maintained by evolving. model biospheres: the ExoGaia model.
Monthly Notices of the Royal Astronomical SocietyAbstract:
Gaian bottlenecks and planetary habitability maintained by evolving. model biospheres: the ExoGaia model
The search for habitable exoplanets inspires the question - how do habitable
planets form? Planet habitability models traditionally focus on abiotic
processes and neglect a biotic response to changing conditions on an inhabited
planet. The Gaia hypothesis postulates that life influences the Earth's
feedback mechanisms to form a self-regulating system, and hence that life can
maintain habitable conditions on its host planet. If life has a strong
influence, it will have a role in determining a planet's habitability over
time. We present the ExoGaia model - a model of simple 'planets' host to
evolving microbial biospheres. Microbes interact with their host planet via
consumption and excretion of atmospheric chemicals. Model planets orbit a
'star' which provides incoming radiation, and atmospheric chemicals have either
an albedo, or a heat-trapping property. Planetary temperatures can therefore be
altered by microbes via their metabolisms. We seed multiple model planets with
life while their atmospheres are still forming and find that the microbial
biospheres are, under suitable conditions, generally able to prevent the host
planets from reaching inhospitable temperatures, as would happen on a lifeless
planet. We find that the underlying geochemistry plays a strong role in
determining long-term habitability prospects of a planet. We find five distinct
classes of model planets, including clear examples of 'Gaian bottlenecks' - a
phenomenon whereby life either rapidly goes extinct leaving an inhospitable
planet, or survives indefinitely maintaining planetary habitability. These
results suggest that life might play a crucial role in determining the
long-term habitability of planets.
Abstract.
Nicholson AE, Wilkinson DM, Williams HTP, Lenton TM (2018). Gaian bottlenecks and planetary habitability maintained by evolving. model biospheres: the ExoGaia model.
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.
Lu W, Ridgwell A, Thomas E, Hardisty DS, Luo G, Algeo TJ, Saltzman MR, Gill BC, Shen Y, Ling HF, et al (2018). Late inception of a resiliently oxygenated upper ocean.
Science,
361(6398), 174-177.
Abstract:
Late inception of a resiliently oxygenated upper ocean
Rising oceanic and atmospheric oxygen levels through time have been crucial to enhanced habitability of surface Earth environments. Few redox proxies can track secular variations in dissolved oxygen concentrations around threshold levels for metazoan survival in the upper ocean. We present an extensive compilation of iodine-to-calcium ratios (I/Ca) in marine carbonates. Our record supports a major rise in the partial pressure of oxygen in the atmosphere at ~400 million years (Ma) ago and reveals a step change in the oxygenation of the upper ocean to relatively sustainable near-modern conditions at ~200 Ma ago. An Earth system model demonstrates that a shift in organic matter remineralization to greater depths, which may have been due to increasing size and biomineralization of eukaryotic plankton, likely drove the I/Ca signals at ~200 Ma ago.
Abstract.
McKay DIA, Lenton TM (2018). Reduced carbon cycle resilience across the Palaeocene-Eocene Thermal Maximum.
CLIMATE OF THE PAST,
14(10), 1515-1527.
Author URL.
Lenton TM, Daines SJ, Dyke JG, Nicholson AE, Wilkinson DM, Williams HTP (2018). Selection for Gaia across Multiple Scales.
Trends in Ecology and Evolution,
33(8), 633-645.
Abstract:
Selection for Gaia across Multiple Scales
Recently postulated mechanisms and models can help explain the enduring ‘Gaia’ puzzle of environmental regulation mediated by life. Natural selection can produce nutrient recycling at local scales and regulation of heterogeneous environmental variables at ecosystem scales. However, global-scale environmental regulation involves a temporal and spatial decoupling of effects from actors that makes conventional evolutionary explanations problematic. Instead, global regulation can emerge by a process of ‘sequential selection’ in which systems that destabilize their environment are short-lived and result in extinctions and reorganizations until a stable attractor is found. Such persistence-enhancing properties can in turn increase the likelihood of acquiring further persistence-enhancing properties through ‘selection by survival alone’. Thus, Earth system feedbacks provide a filter for persistent combinations of macroevolutionary innovations.
Abstract.
Krause AJ, Mills BJW, Zhang S, Planavsky NJ, Lenton TM, Poulton SW (2018). Stepwise oxygenation of the Paleozoic atmosphere.
Nat Commun,
9(1).
Abstract:
Stepwise oxygenation of the Paleozoic atmosphere.
Oxygen is essential for animal life, and while geochemical proxies have been instrumental in determining the broad evolutionary history of oxygen on Earth, much of our insight into Phanerozoic oxygen comes from biogeochemical modelling. The GEOCARBSULF model utilizes carbon and sulphur isotope records to produce the most detailed history of Phanerozoic atmospheric O2 currently available. However, its predictions for the Paleozoic disagree with geochemical proxies, and with non-isotope modelling. Here we show that GEOCARBSULF oversimplifies the geochemistry of sulphur isotope fractionation, returning unrealistic values for the O2 sourced from pyrite burial when oxygen is low. We rebuild the model from first principles, utilizing an improved numerical scheme, the latest carbon isotope data, and we replace the sulphur cycle equations in line with forwards modelling approaches. Our new model, GEOCARBSULFOR, produces a revised, highly-detailed prediction for Phanerozoic O2 that is consistent with available proxy data, and independently supports a Paleozoic Oxygenation Event, which likely contributed to the observed radiation of complex, diverse fauna at this time.
Abstract.
Author URL.
Quinn C, Sieber J, Heydt ASVD, Lenton TM (2018). The Mid-Pleistocene Transition induced by delayed feedback and. bistability.
Dynamics and Statistics of the Climate SystemAbstract:
The Mid-Pleistocene Transition induced by delayed feedback and. bistability
The Mid-Pleistocene Transition, the shift from 41 kyr to 100 kyr
glacial-interglacial cycles that occurred roughly 1 Myr ago, is often
considered as a change in internal climate dynamics. Here we revisit the model
of Quaternary climate dynamics that was proposed by Saltzman and Maasch (1988).
We show that it is quantitatively similar to a scalar equation for the ice
dynamics only when combining the remaining components into a single delayed
feedback term. The delay is the sum of the internal times scales of ocean
transport and ice sheet dynamics, which is on the order of 10 kyr. We find
that, in the absence of astronomical forcing, the delayed feedback leads to
bistable behaviour, where stable large-amplitude oscillations of ice volume and
an equilibrium coexist over a large range of values for the delay. We then
apply astronomical forcing. We perform a systematic study to show how the
system response depends on the forcing amplitude. We find that over a wide
range of forcing amplitudes the forcing leads to a switch from small-scale
oscillations of 41 kyr to large-amplitude oscillations of roughly 100 kyr
without any change of other parameters. The transition in the forced model
consistently occurs near the time of the Mid-Pleistocene Transition as observed
in data records. This provides evidence that the MPT could have been primarily
a forcing-induced switch between attractors of the internal dynamics. Small
additional random disturbances make the forcing-induced transition near 800 kyr
BP even more robust. We also find that the forced system forgets its initial
history during the small-scale oscillations, in particular, nearby initial
conditions converge prior to transitioning. In contrast to this, in the regime
of large-amplitude oscillations, the oscillation phase is very sensitive to
random perturbations, which has a strong effect on the timing of the
deglaciation events.
Abstract.
Lenton TM, Daines S (2018). The effects of marine eukaryote evolution on phosphorus, carbon and oxygen cycling across the Proterozoic–Phanerozoic transition. Emerging Topics in Life Sciences
Steffen W, Rockström J, Richardson K, Lenton TM, Folke C, Liverman D, Summerhayes CP, Barnosky AD, Cornell SE, Crucifix M, et al (2018). Trajectories of the Earth System in the Anthropocene.
Proceedings of the National Academy of Sciences of the United States of America,
115(33), 8252-8259.
Abstract:
Trajectories of the Earth System in the Anthropocene
We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a “Hothouse Earth” pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System—biosphere, climate, and societies—and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values.
Abstract.
Clarkson MO, Stirling CH, Jenkyns HC, Dickson AJ, Porcelli D, Moy CM, Von Strandmann PPAE, Cooke IR, Lenton TM (2018). Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2.
Proceedings of the National Academy of Sciences of the United States of America,
115(12), 2918-2923.
Abstract:
Uranium isotope evidence for two episodes of deoxygenation during Oceanic Anoxic Event 2
Oceanic Anoxic Event 2 (OAE 2), occurring ∼94 million years ago, was one of the most extreme carbon cycle and climatic perturbations of the Phanerozoic Eon. It was typified by a rapid rise in atmospheric CO2, global warming, and marine anoxia, leading to the widespread devastation of marine ecosystems. However, the precise timing and extent to which oceanic anoxic conditions expanded during OAE 2 remains unresolved. We present a record of global ocean redox changes during OAE 2 using a combined geochemical and carbon cycle modeling approach. We utilize a continuous, high-resolution record of uranium isotopes in pelagic and platform carbonate sediments to quantify the global extent of seafloor anoxia during OAE 2. This dataset is then compared with a dynamic model of the coupled global carbon, phosphorus, and uranium cycles to test hypotheses for OAE 2 initiation. This unique approach highlights an intra-OAE complexity that has previously been underconstrained, characterized by two expansions of anoxia separated by an episode of globally significant reoxygenation coincident with the "Plenus Cold Event." Each anoxic expansion event was likely driven by rapid atmospheric CO2 injections from multiphase Large Igneous Province activity.
Abstract.
2017
Mander L, Dekker SC, Li M, Mio W, Punyasena S, Lenton TM (2017). A morphometric analysis of vegetation patterns in dryland ecosystems.
Royal Society Open Science,
4(2).
Abstract:
A morphometric analysis of vegetation patterns in dryland ecosystems
Vegetation in dryland ecosystems often forms remarkable spatial patterns. These range from regular bands of vegetation alternating with bare ground, to vegetated spots and labyrinths, to regular gaps of bare ground within an otherwise continuous expanse of vegetation. It has been suggested that spotted vegetation patterns could indicate that collapse into a bare ground state is imminent, and the morphology of spatial vegetation patterns, therefore, represents a potentially valuable source of information on the proximity of regime shifts in dryland ecosystems. In this paper, we have developed quantitative methods to characterize the morphology of spatial patterns in dryland vegetation. Our approach is based on algorithmic techniques that have been used to classify pollen grains on the basis of textural patterning, and involves constructing feature vectors to quantify the shapes formed by vegetation patterns. We have analysed images of patterned vegetation produced by a computational model and a small set of satellite images from South Kordofan (South Sudan), which illustrates that our methods are applicable to both simulated and real-world data. Our approach provides a means of quantifying patterns that are frequently described using qualitative terminology, and could be used to classify vegetation patterns in large-scale satellite surveys of dryland ecosystems.
Abstract.
Alexander P, Prestele R, Verburg PH, Arneth A, Baranzelli C, Batista e Silva F, Brown C, Butler A, Calvin K, Dendoncker N, et al (2017). Assessing uncertainties in land cover projections.
GLOBAL CHANGE BIOLOGY,
23(2), 767-781.
Author URL.
Daines SJ, Mills BJW, Lenton TM (2017). Atmospheric oxygen regulation at low Proterozoic levels by incomplete oxidative weathering of sedimentary organic carbon.
Nature Communications,
8Abstract:
Atmospheric oxygen regulation at low Proterozoic levels by incomplete oxidative weathering of sedimentary organic carbon
It is unclear why atmospheric oxygen remained trapped at low levels for more than 1.5 billion years following the Paleoproterozoic Great Oxidation Event. Here, we use models for erosion, weathering and biogeochemical cycling to show that this can be explained by the tectonic recycling of previously accumulated sedimentary organic carbon, combined with the oxygen sensitivity of oxidative weathering. Our results indicate a strong negative feedback regime when atmospheric oxygen concentration is of order pO 2 â 1/40.1 PAL (present atmospheric level), but that stability is lost at pO 2
Abstract.
Lenton TM, Daines SJ (2017). Biogeochemical Transformations in the History of the Ocean.
Annual Review of Marine Science,
9(1), 31-58.
Abstract:
Biogeochemical Transformations in the History of the Ocean
The ocean has undergone several profound biogeochemical transformations in its 4-billion-year history, and these were an integral part of the coevolution of life and the planet. This review focuses on changes in ocean redox state as controlled by changes in biological activity, nutrient concentrations, and atmospheric O2. Motivated by disparate interpretations of available geochemical data, we aim to show how quantitative modeling--spanning microbial mats, shelf seas, and the open ocean--can help constrain past ocean biogeochemical redox states and show what caused transformations between them. We outline key controls on ocean redox structure and review pertinent proxies and their interpretation. We then apply this quantitative framework to three key questions: How did the origin of oxygenic photosynthesis transform ocean biogeochemistry? How did the Great Oxidation transform ocean biogeochemistry? and how was ocean biogeochemistry transformed in the Neoproterozoic-Paleozoic?
Abstract.
Lenton TM, Daines S, Mills B (2017). COPSE reloaded: an improved model of biogeochemical cycling over Phanerozoic time. Earth-Science Reviews
Baker SJ, Hesselbo SP, Lenton TM, Duarte LV, Belcher CM (2017). Charcoal evidence that rising atmospheric oxygen terminated Early Jurassic ocean anoxia. Nature Communications
Williamson MS, collins M, drijfhout S, kahana R, mecking J, lenton TM (2017). Effect of AMOC collapse on ENSO in a high resolution general
circulation model. Climate Dynamics
Mills BJW, Scotese CR, Walding NG, Shields GA, Lenton TM (2017). Elevated CO<inf>2</inf> degassing rates prevented the return of Snowball Earth during the Phanerozoic.
Nature Communications,
8(1).
Abstract:
Elevated CO2 degassing rates prevented the return of Snowball Earth during the Phanerozoic
The Cryogenian period (~720-635 Ma) is marked by extensive Snowball Earth glaciations. These have previously been linked to CO2 draw-down, but the severe cold climates of the Cryogenian have never been replicated during the Phanerozoic despite similar, and sometimes more dramatic changes to carbon sinks. Here we quantify the total CO2 input rate, both by measuring the global length of subduction zones in plate tectonic reconstructions, and by sea-level inversion. Our results indicate that degassing rates were anomalously low during the Late Neoproterozoic, roughly doubled by the Early Phanerozoic, and remained comparatively high until the Cenozoic. Our carbon cycle modelling identifies the Cryogenian as a unique period during which low surface temperature was more easily achieved, and shows that the shift towards greater CO2 input rates after the Cryogenian helped prevent severe glaciation during the Phanerozoic. Such a shift appears essential for the development of complex animal life.
Abstract.
Lenton TM, Pogge von Strandmann PAE, Desrochers A, Murphy MJ, Finlay AJ, Selby D (2017). Global climate stabilisation by chemical weathering during the Hirnantian glaciation. Geochemical Perspectives
Lenton TM, Daines SJ (2017). Matworld - the biogeochemical effects of early life on land.
New Phytol,
215(2), 531-537.
Abstract:
Matworld - the biogeochemical effects of early life on land.
Contents 531 I. 531 II. 532 III. 534 IV. 535 V. 535 VI. 535 Acknowledgements 536 References 536 SUMMARY: There is growing evidence that life has been on land for billions of years. Microbial mats fuelled by oxygenic photosynthesis were probably present in terrestrial habitats from c. 3.0 billion yr ago (Ga) onwards, creating localized 'oxygen oases' under a reducing atmosphere, which left a characteristic oxidative weathering signal. After the Great Oxidation c. 2.4 Ga, the now oxidizing atmosphere masked that redox signal, but ancient soils record the mobilization of phosphorus and other elements by organic acids in weathering profiles. Evidence for Neoproterozoic 'greening of the land' and intensification of weathering c. 0.85-0.54 Ga is currently equivocal. However, the mid-Palaeozoic c. 0.45-0.4 Ga shows global atmospheric changes consistent with increased terrestrial productivity and intensified weathering by the first land plants.
Abstract.
Author URL.
Nicholson AE, Wilkinson DM, Williams HTP, Lenton TM (2017). Multiple states of environmental regulation in well-mixed model biospheres.
J Theor Biol,
414, 17-34.
Abstract:
Multiple states of environmental regulation in well-mixed model biospheres.
The Gaia hypothesis postulates that life influences Earth's feedback mechanisms to form a self regulating system. This provokes the question: how can global self-regulation evolve? Most models demonstrating environmental regulation involving life have relied on alignment between local selection and global regulation. In these models environment-improving individuals or communities spread to outcompete environment degrading individuals/communities, leading to global regulation, but this depends on local differences in environmental conditions. In contrast, well-mixed components of the Earth system, such as the atmosphere, lack local environmental differentiation. These previous models do not explain how global regulation can emerge in a system with no well defined local environment, or where the local environment is overwhelmed by global effects. We present a model of self-regulation by 'microbes' in an environment with no spatial structure. These microbes affect an abiotic 'temperature' as a byproduct of metabolism. We demonstrate that global self-regulation can arise in the absence of spatial structure in a diverse ecosystem without localised environmental effects. We find that systems can exhibit nutrient limitation and two temperature limitation regimes where the temperature is maintained at a near constant value. During temperature regulation, the total temperature change caused by the microbes is kept near constant by the total population expanding or contracting to absorb the impacts of new mutants on the average affect on the temperature per microbe. Dramatic shifts between low temperature regulation and high temperature regulation can occur when a mutant arises that causes the sign of the temperature effect to change. This result implies that self-regulating feedback loops can arise without the need for spatial structure, weakening criticisms of the Gaia hypothesis that state that with just one Earth, global regulation has no mechanism for developing because natural selection requires selection between multiple entities.
Abstract.
Author URL.
Lenton TM, Dakos V, Bathiany S, Scheffer M (2017). Observed trends in the magnitude and persistence of monthly temperature variability.
Scientific Reports,
7(1).
Abstract:
Observed trends in the magnitude and persistence of monthly temperature variability
Climate variability is critically important for nature and society, especially if it increases in amplitude and/or fluctuations become more persistent. However, the issues of whether climate variability is changing, and if so, whether this is due to anthropogenic forcing, are subjects of ongoing debate. Increases in the amplitude and persistence of temperature fluctuations have been detected in some regions, e.g. the North Pacific, but there is no agreed global signal. Here we systematically scan monthly surface temperature indices and spatial datasets to look for trends in variance and autocorrelation (persistence). We show that monthly temperature variability and autocorrelation increased over 1957-2002 across large parts of the North Pacific, North Atlantic, North America and the Mediterranean. Furthermore, (multi)decadal internal climate variability appears to influence trends in monthly temperature variability and autocorrelation. Historically-forced climate models do not reproduce the observed trends in temperature variance and autocorrelation, consistent with the models poorly capturing (multi)decadal internal climate variability. Based on a review of established spatial correlations and corresponding mechanistic 'teleconnections' we hypothesise that observed slowing down of sea surface temperature variability contributed to observed increases in land temperature variability and autocorrelation, which in turn contributed to persistent droughts in North America and the Mediterranean.
Abstract.
Watson AJ, Lenton TM, Mills BJW (2017). Ocean deoxygenation, the global phosphorus cycle and the possibility of human-caused large-scale ocean anoxia.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences,
375(2102).
Abstract:
Ocean deoxygenation, the global phosphorus cycle and the possibility of human-caused large-scale ocean anoxia
The major biogeochemical cycles that keep the present-day Earth habitable are linked by a network of feedbacks, which has led to a broadly stable chemical composition of the oceans and atmosphere over hundreds of millions of years. This includes the processes that control both the atmospheric and oceanic concentrations of oxygen. However, one notable exception to the generally well-behaved dynamics of this system is the propensity for episodes of ocean anoxia to occur and to persist for 105-106 years, these ocean anoxic events (OAEs) being particularly associated with warm 'greenhouse' climates. A powerful mechanism responsible for past OAEs was an increase in phosphorus supply to the oceans, leading to higher ocean productivity and oxygen demand in subsurface water. This can be amplified by positive feedbacks on the nutrient content of the ocean, with low oxygen promoting further release of phosphorus from ocean sediments, leading to a potentially self-sustaining condition of deoxygenation. We use a simple model for phosphorus in the ocean to explore this feedback, and to evaluate the potential for humans to bring on global-scale anoxia by enhancing P supply to the oceans. While this is not an immediate global change concern, it is a future possibility on millennial and longer time scales, when considering both phosphate rock mining and increased chemical weathering due to climate change. Ocean deoxygenation, once begun, may be self-sustaining and eventually could result in long-lasting and unpleasant consequences for the Earth's biosphere. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.
Abstract.
Quinn C, Sieber J, von der Heydt AS, Lenton TM (2017). The Mid-Pleistocene Transition induced by delayed feedback and. bistability.
Boysen LR, Lucht W, Gerten D, Heck V, Lenton TM, Schellnhuber HJ (2017). The limits to global-warming mitigation by terrestrial carbon removal.
Earth's Future,
5(5), 463-474.
Abstract:
The limits to global-warming mitigation by terrestrial carbon removal
Massive near-term greenhouse gas emissions reduction is a precondition for staying “well below 2°C” global warming as envisaged by the Paris Agreement. Furthermore, extensive terrestrial carbon dioxide removal (tCDR) through managed biomass growth and subsequent carbon capture and storage is required to avoid temperature “overshoot” in most pertinent scenarios. Here, we address two major issues: First, we calculate the extent of tCDR required to “repair” delayed or insufficient emissions reduction policies unable to prevent global mean temperature rise of 2.5°C or even 4.5°C above pre-industrial level. Our results show that those tCDR measures are unable to counteract “business-as-usual” emissions without eliminating virtually all natural ecosystems. Even if considerable (Representative Concentration Pathway 4.5 [RCP4.5]) emissions reductions are assumed, tCDR with 50% storage efficiency requires >1.1 Gha of the most productive agricultural areas or the elimination of >50% of natural forests. In addition, >100 MtN/yr fertilizers would be needed to remove the roughly 320 GtC foreseen in these scenarios. Such interventions would severely compromise food production and/or biosphere functioning. Second, we reanalyze the requirements for achieving the 160–190 GtC tCDR that would complement strong mitigation action (RCP2.6) in order to avoid 2°C overshoot anytime. We find that a combination of high irrigation water input and/or more efficient conversion to stored carbon is necessary. In the face of severe trade-offs with society and the biosphere, we conclude that large-scale tCDR is not a viable alternative to aggressive emissions reduction. However, we argue that tCDR might serve as a valuable “supporting actor” for strong mitigation if sustainable schemes are established immediately.
Abstract.
2016
Dale AW, Boyle RA, Lenton TM, Ingall ED, Wallmann K (2016). A model for microbial phosphorus cycling in bioturbated marine sediments: Significance for phosphorus burial in the early Paleozoic.
Geochimica et Cosmochimica Acta,
189, 251-268.
Abstract:
A model for microbial phosphorus cycling in bioturbated marine sediments: Significance for phosphorus burial in the early Paleozoic
A diagenetic model is used to simulate the diagenesis and burial of particulate organic carbon (Corg) and phosphorus (P) in marine sediments underlying anoxic versus oxic bottom waters. The latter are physically mixed by animals moving through the surface sediment (bioturbation) and ventilated by burrowing, tube-dwelling organisms (bioirrigation). The model is constrained using an empirical database including burial ratios of Corg with respect to organic P (Corg:Porg) and total reactive P (Corg:Preac), burial efficiencies of Corg and Porg, and inorganic carbon-to-phosphorus regeneration ratios. If Porg is preferentially mineralized relative to Corg during aerobic respiration, as many previous studies suggest, then the simulated Porg pool is found to be completely depleted. A modified model that incorporates the redox-dependent microbial synthesis of polyphosphates and Porg (termed the microbial P pump) allows preferential mineralization of the bulk Porg pool relative to Corg during both aerobic and anaerobic respiration and is consistent with the database. Results with this model show that P burial is strongly enhanced in sediments hosting fauna. Animals mix highly labile Porg away from the aerobic sediment layers where mineralization rates are highest, thereby mitigating diffusive PO43- fluxes to the bottom water. They also expand the redox niche where microbial P uptake occurs. The model was applied to a hypothetical shelf setting in the early Paleozoic; a time of the first radiation of benthic fauna. Results show that even shallow bioturbation at that time may have had a significant impact on P burial. Our model provides support for a recent study that proposed that faunal radiation in ocean sediments led to enhanced P burial and, possibly, a stabilization of atmospheric O2 levels. The results also help to explain Corg:Porg ratios in the geological record and the persistence of Porg in ancient marine sediments.
Abstract.
Mills BJW, Belcher CM, Lenton TM, Newton RJ (2016). A modeling case for high atmospheric oxygen concentrations during the Mesozoic and Cenozoic.
Geology,
44(12), 1023-1026.
Abstract:
A modeling case for high atmospheric oxygen concentrations during the Mesozoic and Cenozoic
Changes in atmospheric oxygen concentration over Earth history are commonly related to the evolution of animals and plants. But there is no direct geochemical proxy for O2 levels, meaning that estimations rely heavily on modeling approaches. The results of such studies differ greatly, to the extent that today's atmospheric mixing ratio of 21% might be either the highest or lowest level during the past 200 m.y. Long term oxygen sources, such as the burial in sediments of reduced carbon and sulfur species, are calculated in models by representation of nutrient cycling and estimation of productivity, or by isotope mass balance (IMB)-a technique in which burial rates are inferred in order to match known isotope records. Studies utilizing these different techniques produce conflicting estimates for paleoatmospheric O2, with nutrient-weathering models estimating concentrations close to, or above, that of the present day, and IMB models estimating low O2, especially during the Mesozoic. Here we reassess the IMB technique using the COPSE biogeochemical model. IMB modelling is confirmed to be highly sensitive to assumed carbonate δ13C, and when this input is defined following recent compilations, predicted O2 is significantly higher and in reasonable agreement with that of non-IMB techniques. We conclude that there is no model-based support for low atmospheric oxygen concentrations during the past 200 m.y. High Mesozoic O2 is consistent with wildfire records and the development of plant fire adaptions, but links between O2 and mammal evolution appear more tenuous.
Abstract.
Bathiany S, Dijkstra H, Crucifix M, Dakos V, Brovkin V, Williamson MS, Lenton TM, Scheffer M (2016). Beyond bifurcation: using complex models to understand and predict abrupt climate change. Dynamics and Statistics of the Climate System, dzw004-dzw004.
Mock T, Daines SJ, Geider R, Collins S, Metodiev M, Millar AJ, Moulton V, Lenton TM (2016). Bridging the gap between omics and earth system science to better understand how environmental change impacts marine microbes.
Glob Chang Biol,
22(1), 61-75.
Abstract:
Bridging the gap between omics and earth system science to better understand how environmental change impacts marine microbes.
The advent of genomic-, transcriptomic- and proteomic-based approaches has revolutionized our ability to describe marine microbial communities, including biogeography, metabolic potential and diversity, mechanisms of adaptation, and phylogeny and evolutionary history. New interdisciplinary approaches are needed to move from this descriptive level to improved quantitative, process-level understanding of the roles of marine microbes in biogeochemical cycles and of the impact of environmental change on the marine microbial ecosystem. Linking studies at levels from the genome to the organism, to ecological strategies and organism and ecosystem response, requires new modelling approaches. Key to this will be a fundamental shift in modelling scale that represents micro-organisms from the level of their macromolecular components. This will enable contact with omics data sets and allow acclimation and adaptive response at the phenotype level (i.e. traits) to be simulated as a combination of fitness maximization and evolutionary constraints. This way forward will build on ecological approaches that identify key organism traits and systems biology approaches that integrate traditional physiological measurements with new insights from omics. It will rely on developing an improved understanding of ecophysiology to understand quantitatively environmental controls on microbial growth strategies. It will also incorporate results from experimental evolution studies in the representation of adaptation. The resulting ecosystem-level models can then evaluate our level of understanding of controls on ecosystem structure and function, highlight major gaps in understanding and help prioritize areas for future research programs. Ultimately, this grand synthesis should improve predictive capability of the ecosystem response to multiple environmental drivers.
Abstract.
Author URL.
Baker SJ, Belcher CM, Hesselbo SP, Lenton TM (2016). CHARCOAL EVIDENCE THAT RISING ATMOSPHERIC OXYGEN TERMINATED EARLY JURASSIC OCEAN ANOXIA.
Lenton TM, Dahl TW, Daines SJ, Mills BJW, Ozaki K, Saltzman MR, Porada P (2016). Earliest land plants created modern levels of atmospheric oxygen.
Proceedings of the National Academy of Sciences of the United States of America,
113(35), 9704-9709.
Abstract:
Earliest land plants created modern levels of atmospheric oxygen
The progressive oxygenation of the Earth's atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (∼21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435-392 Ma, and the appearance of fossil charcoal indicates O2>15-17% by 420-400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ∼470 Ma onward, were responsible for this mid-Paleozoic oxygenation event, through greatly increasing global organic carbon burial- the net long-term source of O2.We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today's global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2% increase in the carbonate carbon isotope (δ13C) record by ∼445 Ma, and predict a corresponding rise in O2to present levels by 420-400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2levels.
Abstract.
Williamson MS, Bathiany S, M Lenton T (2016). Early warning signals of tipping points in periodically forced systems.
Earth System Dynamics,
7(2), 313-326.
Abstract:
Early warning signals of tipping points in periodically forced systems
The prospect of finding generic early warning signals of an approaching tipping point in a complex system has generated much interest recently. Existing methods are predicated on a separation of timescales between the system studied and its forcing. However, many systems, including several candidate tipping elements in the climate system, are forced periodically at a timescale comparable to their internal dynamics. Here we use alternative early warning signals of tipping points due to local bifurcations in systems subjected to periodic forcing whose timescale is similar to the period of the forcing. These systems are not in, or close to, a fixed point. Instead their steady state is described by a periodic attractor. For these systems, phase lag and amplification of the system response can provide early warning signals, based on a linear dynamics approximation. Furthermore, the Fourier spectrum of the system's time series reveals harmonics of the forcing period in the system response whose amplitude is related to how nonlinear the system's response is becoming with nonlinear effects becoming more prominent closer to a bifurcation. We apply these indicators as well as a return map analysis to a simple conceptual system and satellite observations of Arctic sea ice area, the latter conjectured to have a bifurcation type tipping point. We find no detectable signal of the Arctic sea ice approaching a local bifurcation.
Abstract.
Lenton T (2016).
Earth System Science a Very Short Introduction., Oxford University Press.
Abstract:
Earth System Science a Very Short Introduction
Abstract.
Porada P, Lenton TM, Pohl A, Weber B, Mander L, Donnadieu Y, Beer C, Pöschl U, Kleidon A (2016). High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician.
Nature Communications,
7Abstract:
High potential for weathering and climate effects of non-vascular vegetation in the Late Ordovician
It has been hypothesized that predecessors of today's bryophytes significantly increased global chemical weathering in the Late Ordovician, thus reducing atmospheric CO 2 concentration and contributing to climate cooling and an interval of glaciations. Studies that try to quantify the enhancement of weathering by non-vascular vegetation, however, are usually limited to small areas and low numbers of species, which hampers extrapolating to the global scale and to past climatic conditions. Here we present a spatially explicit modelling approach to simulate global weathering by non-vascular vegetation in the Late Ordovician. We estimate a potential global weathering flux of 2.8 (km 3 rock) yr'1, defined here as volume of primary minerals affected by chemical transformation. This is around three times larger than today's global chemical weathering flux. Moreover, we find that simulated weathering is highly sensitive to atmospheric CO 2 concentration. This implies a strong negative feedback between weathering by non-vascular vegetation and Ordovician climate.
Abstract.
Clark JR, Cole M, Lindeque PK, Fileman E, Blackford J, Lewis C, Lenton TM, Galloway TS (2016). Marine microplastic debris: a targeted plan for understanding and quantifying interactions with marine life. Frontiers in Ecology and the Environment, 14, 317-324.
Saltzman MR, Edwards CT, Leslie SA, Mills BJ, Lenton TM, Williams J (2016). NEODYMIUM (ND) AND STRONTIUM (SR) ISOTOPE EVIDENCE FOR WEATHERING OF ARC VOLCANICS DURING THE ORDOVICIAN GREENHOUSE-ICEHOUSE TRANSITION.
Lenton TM, Pichler PP, Weisz H (2016). Revolutions in energy input and material cycling in Earth history and human history. Earth System Dynamics Discussions, 1-30.
Lenton TM, Pichler PP, Weisz H (2016). Revolutions in energy input and material cycling in Earth history and human history.
Earth System Dynamics,
7(2), 353-370.
Abstract:
Revolutions in energy input and material cycling in Earth history and human history
Major revolutions in energy capture have occurred in both Earth and human history, with each transition resulting in higher energy input, altered material cycles and major consequences for the internal organization of the respective systems. In Earth history, we identify the origin of anoxygenic photosynthesis, the origin of oxygenic photosynthesis, and land colonization by eukaryotic photosynthesizers as step changes in free energy input to the biosphere. In human history we focus on the Palaeolithic use of fire, the Neolithic revolution to farming, and the Industrial revolution as step changes in free energy input to human societies. In each case we try to quantify the resulting increase in energy input, and discuss the consequences for material cycling and for biological and social organization. For most of human history, energy use by humans was but a tiny fraction of the overall energy input to the biosphere, as would be expected for any heterotrophic species. However, the industrial revolution gave humans the capacity to push energy inputs towards planetary scales and by the end of the 20th century human energy use had reached a magnitude comparable to the biosphere. By distinguishing world regions and income brackets we show the unequal distribution in energy and material use among contemporary humans. Looking ahead, a prospective sustainability revolution will require scaling up new renewable and decarbonized energy technologies and the development of much more efficient material recycling systems – thus creating a more autotrophic social metabolism. Such a transition must also anticipate a level of social organization that can implement the changes in energy input and material cycling without losing the large achievements in standard of living and individual liberation associated with industrial societies.
Abstract.
Cai Y, Lenton TM, Lontzek TS (2016). Risk of multiple interacting tipping points should encourage rapid CO² emission reduction. Nature Climate Change, 520-520.
Bathiany S, Van Der Bolt B, Williamson MS, Lenton TM, Scheffer M, Van Nes EH, Notz D (2016). Statistical indicators of Arctic sea-ice stability-prospects and limitations.
Cryosphere,
10(4), 1631-1645.
Abstract:
Statistical indicators of Arctic sea-ice stability-prospects and limitations
We examine the relationship between the mean and the variability of Arctic sea-ice coverage and volume in a large range of climates from globally ice-covered to globally ice-free conditions. Using a hierarchy of two column models and several comprehensive Earth system models, we consolidate the results of earlier studies and show that mechanisms found in simple models also dominate the interannual variability of Arctic sea ice in complex models. In contrast to predictions based on very idealised dynamical systems, we find a consistent and robust decrease of variance and autocorrelation of sea-ice volume before summer sea ice is lost. We attribute this to the fact that thinner ice can adjust more quickly to perturbations. Thereafter, the autocorrelation increases, mainly because it becomes dominated by the ocean water's large heat capacity when the ice-free season becomes longer. We show that these changes are robust to the nature and origin of climate variability in the models and do not depend on whether Arctic sea-ice loss occurs abruptly or irreversibly. We also show that our climate is changing too rapidly to detect reliable changes in autocorrelation of annual time series. Based on these results, the prospects of detecting statistical early warning signals before an abrupt sea-ice loss at a "tipping point" seem very limited. However, the robust relation between state and variability can be useful to build simple stochastic climate models and to make inferences about past and future sea-ice variability from only short observations or reconstructions.
Abstract.
Daines SJ, Lenton TM (2016). The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation.
Earth and Planetary Science Letters,
434, 42-51.
Abstract:
The effect of widespread early aerobic marine ecosystems on methane cycling and the Great Oxidation
The balance of evidence suggests that oxygenic photosynthesis had evolved by 3.0-2.7 Ga, several hundred million years prior to the Great Oxidation ≈2.4 Ga. Previous work has shown that if oxygenic photosynthesis spread globally prior to the Great Oxidation, this could have supported widespread aerobic ecosystems in the surface ocean, without oxidising the atmosphere. Here we use a suite of models to explore the implications for carbon cycling and the Great Oxidation. We find that recycling of oxygen and carbon within early aerobic marine ecosystems would have restricted the balanced fluxes of methane and oxygen escaping from the ocean, lowering the atmospheric concentration of methane in the Great Oxidation transition and its aftermath. This in turn would have minimised any bi-stability of atmospheric oxygen, by weakening a stabilising feedback on oxygen from hydrogen escape to space. The result would have been a more reversible and probably episodic rise of oxygen at the Great Oxidation transition, consistent with existing geochemical evidence. The resulting drop in methane levels to ≈10 ppm is consistent with climate cooling at the time but adds to the puzzle of what kept the rest of the Proterozoic warm. A key test of the scenario of abundant methanotrophy in oxygen oases before the Great Oxidation is its predicted effects on the organic carbon isotope (δ13Corg) record. Our open ocean general circulation model predicts δCorg13≈-30 to -45‰ consistent with most data from 2.65 to 2.45 Ga. However, values of δCorg13≈-50‰ require an extreme scenario such as concentrated methanotroph production where shelf-slope upwelling of methane-rich water met oxic shelf water.
Abstract.
Bathiany S, Bolt BVD, Williamson MS, Lenton TM, Scheffer M, Nes EV, Notz D (2016). Trends in sea-ice variability on the way to an ice-free Arctic.
The CryosphereAbstract:
Trends in sea-ice variability on the way to an ice-free Arctic
It has been widely debated whether Arctic sea-ice loss can reach a tipping
point beyond which a large sea-ice area disappears abruptly. The theory of
dynamical systems predicts a slowing down when a system destabilises towards a
tipping point. In simple stochastic systems this can result in increasing
variance and autocorrelation, potentially yielding an early warning of an
abrupt change. Here we aim to establish whether the loss of Arctic sea ice
would follow these conceptual predictions, and which trends in sea ice
variability can be expected from pre-industrial conditions toward an Arctic
that is ice-free during the whole year. To this end, we apply a model hierarchy
consisting of two box models and one comprehensive Earth system model. We find
a consistent and robust decrease of the ice volume's annual relaxation time
before summer ice is lost because thinner ice can adjust more quickly to
perturbations. Thereafter, the relaxation time increases, mainly because the
system becomes dominated by the ocean water's large heat capacity when the
ice-free season becomes longer. Both trends carry over to the autocorrelation
of sea ice thickness in time series. These changes are robust to the nature and
origin of climate variability in the models and hardly depend on the balance of
feedbacks. Therefore, characteristic trends can be expected in the future. As
these trends are not specific to the existence of abrupt ice loss, the
prospects for early warnings seem very limited. This result also has
implications for statistical indicators in other systems whose effective mass
changes over time, affecting the trend of their relaxation time. However, the
robust relation between state and variability would allow an estimate of
sea-ice variability from only short observations. This could help one to
estimate the likelihood and persistence of extreme events in the future.
Abstract.
Bathiany S, van der Bolt B, Williamson MS, Lenton TM, Scheffer M, van Nes E, Notz D (2016). Trends in sea-ice variability on the way to an ice-free Arctic.
2015
Lomax G, Lenton TM, Adeosun A, Workman M (2015). COMMENTARY: Investing in negative emissions.
NATURE CLIMATE CHANGE,
5(6), 498-500.
Author URL.
Sillmann J, Lenton TM, Levermann A, Ott K, Hulme M, Benduhn F, Horton JB (2015). COMMENTARY: No emergency argument for climate engineering.
NATURE CLIMATE CHANGE,
5(4), 290-292.
Author URL.
Van Nes EH, Scheffer M, Brovkin V, Lenton TM, Ye H, Deyle E, Sugihara G (2015). Causal feedbacks in climate change.
Nature Climate Change,
5(5), 445-448.
Abstract:
Causal feedbacks in climate change
The statistical association between temperature and greenhouse gases over glacial cycles is well documented, but causality behind this correlation remains difficult to extract directly from the data. A time lag of CO 2 behind Antarctic temperature - originally thought to hint at a driving role for temperature - is absent at the last deglaciation, but recently confirmed at the last ice age inception and the end of the earlier termination II (ref.). We show that such variable time lags are typical for complex nonlinear systems such as the climate, prohibiting straightforward use of correlation lags to infer causation. However, an insight from dynamical systems theory now allows us to circumvent the classical challenges of unravelling causation from multivariate time series. We build on this insight to demonstrate directly from ice-core data that, over glacial-interglacial timescales, climate dynamics are largely driven by internal Earth system mechanisms, including a marked positive feedback effect from temperature variability on greenhouse-gas concentrations.
Abstract.
Sillmann J, Lenton TM, Levermann A, Ott K, Hulme M, Benduhn F, Horton JB (2015). Climate emergencies do not justify engineering the climate.
Nature Climate Change,
5(4), 290-292.
Abstract:
Climate emergencies do not justify engineering the climate
Current climate engineering proposals do not come close to addressing the complex and contested nature of conceivable 'climate emergencies' resulting from unabated greenhouse-gas emissions.
Abstract.
Lenton TM, Livina VN (2015). Detecting and Anticipating Climate Tipping Points. In (Ed)
Extreme Events: Observations, Modeling, and Economics, 51-62.
Abstract:
Detecting and Anticipating Climate Tipping Points
Abstract.
Williamson MS, Lenton TM (2015). Detection of bifurcations in noisy coupled systems from multiple time series.
Chaos,
25(3).
Abstract:
Detection of bifurcations in noisy coupled systems from multiple time series
We generalize a method of detecting an approaching bifurcation in a time series of a noisy system from the special case of one dynamical variable to multiple dynamical variables. For a system described by a stochastic differential equation consisting of an autonomous deterministic part with one dynamical variable and an additive white noise term, small perturbations away from the system's fixed point will decay slower the closer the system is to a bifurcation. This phenomenon is known as critical slowing down and all such systems exhibit this decay-type behaviour. However, when the deterministic part has multiple coupled dynamical variables, the possible dynamics can be much richer, exhibiting oscillatory and chaotic behaviour. In our generalization to the multi-variable case, we find additional indicators to decay rate, such as frequency of oscillation. In the case of approaching a homoclinic bifurcation, there is no change in decay rate but there is a decrease in frequency of oscillations. The expanded method therefore adds extra tools to help detect and classify approaching bifurcations given multiple time series, where the underlying dynamics are not fully known. Our generalisation also allows bifurcation detection to be applied spatially if one treats each spatial location as a new dynamical variable. One may then determine the unstable spatial mode(s). This is also something that has not been possible with the single variable method. The method is applicable to any set of time series regardless of its origin, but may be particularly useful when anticipating abrupt changes in the multi-dimensional climate system.
Abstract.
Thomas ZA, Kwasniok F, Boulton CA, Cox PM, Jones RT, Lenton TM, Turney CSM (2015). Early warnings and missed alarms for abrupt monsoon transitions.
Climate of the Past,
11(12), 1621-1633.
Abstract:
Early warnings and missed alarms for abrupt monsoon transitions
Palaeo-records from China demonstrate that the East Asian Summer Monsoon (EASM) is dominated by abrupt and large magnitude monsoon shifts on millennial timescales, switching between periods of high and weak monsoon rains. It has been hypothesized that over these timescales, the EASM exhibits two stable states with bifurcation-Type tipping points between them. Here we test this hypothesis by looking for early warning signals of past bifurcations in speleothem δ18O records from Sanbao Cave and Hulu Cave, China, spanning the penultimate glacial cycle. We find that although there are increases in both autocorrelation and variance preceding some of the monsoon transitions during this period, it is only immediately prior to the abrupt monsoon shift at the penultimate deglaciation (Termination II) that statistically significant increases are detected. To supplement our data analysis, we produce and analyse multiple model simulations that we derive from these data. We find hysteresis behaviour in our model simulations with transitions directly forced by solar insolation. However, signals of critical slowing down, which occur on the approach to a bifurcation, are only detectable in the model simulations when the change in system stability is sufficiently slow to be detected by the sampling resolution of the data set. This raises the possibility that the early warning "alarms" were missed in the speleothem data over the period 224-150 kyr and it was only at the monsoon termination that the change in the system stability was sufficiently slow to detect early warning signals.
Abstract.
Cai Y, Judd KL, Lenton TM, Lontzek TS, Narita D (2015). Environmental tipping points significantly affect the cost-benefit assessment of climate policies.
Proc Natl Acad Sci U S A,
112(15), 4606-4611.
Abstract:
Environmental tipping points significantly affect the cost-benefit assessment of climate policies.
Most current cost-benefit analyses of climate change policies suggest an optimal global climate policy that is significantly less stringent than the level required to meet the internationally agreed 2 °C target. This is partly because the sum of estimated economic damage of climate change across various sectors, such as energy use and changes in agricultural production, results in only a small economic loss or even a small economic gain in the gross world product under predicted levels of climate change. However, those cost-benefit analyses rarely take account of environmental tipping points leading to abrupt and irreversible impacts on market and nonmarket goods and services, including those provided by the climate and by ecosystems. Here we show that including environmental tipping point impacts in a stochastic dynamic integrated assessment model profoundly alters cost-benefit assessment of global climate policy. The risk of a tipping point, even if it only has nonmarket impacts, could substantially increase the present optimal carbon tax. For example, a risk of only 5% loss in nonmarket goods that occurs with a 5% annual probability at 4 °C increase of the global surface temperature causes an immediate two-thirds increase in optimal carbon tax. If the tipping point also has a 5% impact on market goods, the optimal carbon tax increases by more than a factor of 3. Hence existing cost-benefit assessments of global climate policy may be significantly underestimating the needs for controlling climate change.
Abstract.
Author URL.
Lomax G, Lenton TM, Adeosun A, Workman M (2015). Investing in negative emissions. Nature Climate Change, 5(6), 498-500.
Lewis KH, Lenton TM (2015). Knowledge problems in climate change and security research.
Wiley Interdisciplinary Reviews: Climate Change,
6(4), 383-399.
Abstract:
Knowledge problems in climate change and security research
The demand for policy-relevant information on climate change has never been higher, but there remains a gap between the type of information climate projections provide and an understanding of the consequences for human well-being. This review explores the knowledge available to support assessments of climate change and security for a wide range of policy stakeholders. Both the climate science and social science communities undertake valuable research toward understanding climate change and the interaction of environment and security, but address different aspects of the problem. Differences in the types of knowledge produced include analytical methods, language, and scale issues. This makes research conclusions difficult to reconcile and provides a barrier to knowledge sharing. It is largely left to policy and security analysts to bring these two very different types of information together in accessible, policy-relevant assessments. Often this is done by considering the potential implications of existing climate change projections, with little or no input from social scientists on the complexities of the relationship between environment and security. An alternative approach to climate change and security assessments is to consider the problem from a systems perspective. This approach has the potential to offer new insight across disciplines and improve the utility of research outcomes to inform action on climate change and security.
Abstract.
Lewis KH, Lenton TM (2015). Knowledge problems in climate change and security research.
Wiley Interdisciplinary Reviews: Climate ChangeAbstract:
Knowledge problems in climate change and security research
The demand for policy-relevant information on climate change has never been higher, but there remains a gap between the type of information climate projections provide and an understanding of the consequences for human well-being. This review explores the knowledge available to support assessments of climate change and security for a wide range of policy stakeholders. Both the climate science and social science communities undertake valuable research toward understanding climate change and the interaction of environment and security, but address different aspects of the problem. Differences in the types of knowledge produced include analytical methods, language, and scale issues. This makes research conclusions difficult to reconcile and provides a barrier to knowledge sharing. It is largely left to policy and security analysts to bring these two very different types of information together in accessible, policy-relevant assessments. Often this is done by considering the potential implications of existing climate change projections, with little or no input from social scientists on the complexities of the relationship between environment and security. An alternative approach to climate change and security assessments is to consider the problem from a systems perspective. This approach has the potential to offer new insight across disciplines and improve the utility of research outcomes to inform action on climate change and security.
Abstract.
Clarkson MO, Kasemann SA, Wood RA, Lenton TM, Daines SJ, Richoz S, Ohnemueller F, Meixner A, Poulton SW, Tipper ET, et al (2015). Ocean acidification and the Permo-Triassic mass extinction.
Science,
348(6231), 229-232.
Abstract:
Ocean acidification and the Permo-Triassic mass extinction.
Ocean acidification triggered by Siberian Trap volcanism was a possible kill mechanism for the Permo-Triassic Boundary mass extinction, but direct evidence for an acidification event is lacking. We present a high-resolution seawater pH record across this interval, using boron isotope data combined with a quantitative modeling approach. In the latest Permian, increased ocean alkalinity primed the Earth system with a low level of atmospheric CO2 and a high ocean buffering capacity. The first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.
Abstract.
Author URL.
Lomax G, Workman M, Lenton T, Shah N (2015). Reframing the policy approach to greenhouse gas removal technologies.
ENERGY POLICY,
78, 125-136.
Author URL.
Boulton CA, Lenton TM (2015). Slowing down of North Pacific climate variability and its implications for abrupt ecosystem change.
Proc Natl Acad Sci U S A,
112(37), 11496-11501.
Abstract:
Slowing down of North Pacific climate variability and its implications for abrupt ecosystem change.
Marine ecosystems are sensitive to stochastic environmental variability, with higher-amplitude, lower-frequency--i.e. "redder"--variability posing a greater threat of triggering large ecosystem changes. Here we show that fluctuations in the Pacific Decadal Oscillation (PDO) index have slowed down markedly over the observational record (1900-present), as indicated by a robust increase in autocorrelation. This "reddening" of the spectrum of climate variability is also found in regionally averaged North Pacific sea surface temperatures (SSTs), and can be at least partly explained by observed deepening of the ocean mixed layer. The progressive reddening of North Pacific climate variability has important implications for marine ecosystems. Ecosystem variables that respond linearly to climate forcing will have become prone to much larger variations over the observational record, whereas ecosystem variables that respond nonlinearly to climate forcing will have become prone to more frequent "regime shifts." Thus, slowing down of North Pacific climate variability can help explain the large magnitude and potentially the quick succession of well-known abrupt changes in North Pacific ecosystems in 1977 and 1989. When looking ahead, despite model limitations in simulating mixed layer depth (MLD) in the North Pacific, global warming is robustly expected to decrease MLD. This could potentially reverse the observed trend of slowing down of North Pacific climate variability and its effects on marine ecosystems.
Abstract.
Author URL.
Lontzek TS, Cai Y, Judd KL, Lenton TM (2015). Stochastic integrated assessment of climate tipping points indicates the need for strict climate policy.
Nature Climate Change,
5(5), 441-444.
Abstract:
Stochastic integrated assessment of climate tipping points indicates the need for strict climate policy
Perhaps the most 'dangerous'aspect of future climate change is the possibility that human activities will push parts of the climate system past tipping points, leading to irreversible impacts. The likelihood of such large-scale singular events is expected to increase with global warming, but is fundamentally uncertain. A key question is how should the uncertainty surrounding tipping events affect climate policy? We address this using a stochastic integrated assessment model, based on the widely used deterministic DICE model. The temperature-dependent likelihood of tipping is calibrated using expert opinions, which we find to be internally consistent. The irreversible impacts of tipping events are assumed to accumulate steadily over time (rather than instantaneously), consistent with scientific understanding. Even with conservative assumptions about the rate and impacts of a stochastic tipping event, today's optimal carbon tax is increased by 1/450%. For a plausibly rapid, high-impact tipping event, today's optimal carbon tax is increased by >200%. The additional carbon tax to delay climate tipping grows at only about half the rate of the baseline carbon tax. This implies that the effective discount rate for the costs of stochastic climate tipping is much lower than the discount rate for deterministic climate damages. Our results support recent suggestions that the costs of carbon emission used to inform policy are being underestimated, and that uncertain future climate damages should be discounted at a low rate.
Abstract.
Colbourn G, Ridgwell A, Lenton TM (2015). The time scale of the silicate weathering negative feedback on atmospheric CO<inf>2</inf>.
Global Biogeochemical Cycles,
29(5), 583-596.
Abstract:
The time scale of the silicate weathering negative feedback on atmospheric CO<inf>2</inf>
©2015. American Geophysical Union. All Rights Reserved. The ultimate fate of CO < inf > 2 < /inf >. added to the ocean-atmosphere system is chemical reaction with silicate minerals and burial as marine carbonates. The time scale of this silicate weathering negative feedback on atmospheric pCO < inf > 2 < /inf >. will determine the duration of perturbations to the carbon cycle, be they geological release events or the current anthropogenic perturbation. However, there has been little previous work on quantifying the time scale of the silicate weathering feedback, with the primary estimate of 300-400 kyr being traceable to an early box model study by Sundquist (1991). Here we employ a representation of terrestrial rock weathering in conjunction with the "GENIE" (Grid ENabled Integrated Earth system) model to elucidate the different time scales of atmospheric CO < inf > 2 < /inf >. regulation while including the main climate feedbacks on CO < inf > 2 < /inf >. uptake by the ocean. In this coupled model, the main dependencies of weathering - runoff, temperature, and biological productivity - were driven from an energy-moisture balance atmosphere model and parameterized plant productivity. Long-term projections (1 Myr) were conducted for idealized scenarios of 1000 and 5000 PgC fossil fuel emissions and their sensitivity to different model parameters was tested. By fitting model output to a series of exponentials we determined the e-folding time scale for atmospheric CO < inf > 2 < /inf >. drawdown by silicate weathering to be ∼240 kyr (range 170-380 kyr), significantly less than existing quantifications. Although the time scales for reequilibration of global surface temperature and surface ocean pH are similar to that for CO < inf > 2 < /inf > , a much greater proportion of the peak temperature anomaly persists on this longest time scale; ∼21% compared to ∼10% for CO < inf > 2 < /inf >.
Abstract.
Colbourn G, Ridgwell A, Lenton TM (2015). The time scale of the silicate weathering negative feedback on atmospheric CO<inf>2</inf>.
Global Biogeochemical CyclesAbstract:
The time scale of the silicate weathering negative feedback on atmospheric CO<inf>2</inf>
©2015. American Geophysical Union. The ultimate fate of CO < inf > 2 < /inf >. added to the ocean-atmosphere system is chemical reaction with silicate minerals and burial as marine carbonates. The time scale of this silicate weathering negative feedback on atmospheric pCO < inf > 2 < /inf >. will determine the duration of perturbations to the carbon cycle, be they geological release events or the current anthropogenic perturbation. However, there has been little previous work on quantifying the time scale of the silicate weathering feedback, with the primary estimate of 300-400 kyr being traceable to an early box model study by Sundquist (1991). Here we employ a representation of terrestrial rock weathering in conjunction with the "GENIE" (Grid ENabled Integrated Earth system) model to elucidate the different time scales of atmospheric CO < inf > 2 < /inf >. regulation while including the main climate feedbacks on CO < inf > 2 < /inf >. uptake by the ocean. In this coupled model, the main dependencies of weathering-runoff, temperature, and biological productivity-were driven from an energy-moisture balance atmosphere model and parameterized plant productivity. Long-term projections (1Myr) were conducted for idealized scenarios of 1000 and 5000PgC fossil fuel emissions and their sensitivity to different model parameters was tested. By fitting model output to a series of exponentials we determined the e-folding time scale for atmospheric CO < inf > 2 < /inf >. drawdown by silicate weathering to be ∼240kyr (range 170-380kyr), significantly less than existing quantifications. Although the time scales for reequilibration of global surface temperature and surface ocean pH are similar to that for CO < inf > 2 < /inf > , a much greater proportion of the peak temperature anomaly persists on this longest time scale; ∼21% compared to ∼10% for CO < inf > 2 < /inf >.
Abstract.
2014
Lenton T (2014). A Rough Ride to the Future: the Next Evolution of Gaia.
NATURE,
508(7494), 41-42.
Author URL.
Barrett S, Lenton TM, Millner A, Tavoni A, Carpenter S, Anderies JM, III CFS, Crepin A-S, Daily G, Ehrlich P, et al (2014). COMMENTARY: Climate engineering reconsidered.
NATURE CLIMATE CHANGE,
4(7), 527-529.
Author URL.
Mills B, Daines SJ, Lenton TM (2014). Changing tectonic controls on the long-term carbon cycle from Mesozoic to present.
Geochemistry, Geophysics, GeosystemsAbstract:
Changing tectonic controls on the long-term carbon cycle from Mesozoic to present
Tectonic drivers of degassing and weathering processes are key long-term controls on atmospheric CO2. However, there is considerable debate over the changing relative importance of different carbon sources and sinks. Existing geochemical models have tended to rely on indirect methods to derive tectonic drivers, such as inversion of the seawater 87Sr/86Sr curve to estimate uplift or continental basalt area. Here we use improving geologic data to update the representation of tectonic drivers in the COPSE biogeochemical model. The resulting model distinguishes CO2 sinks from terrestrial granite weathering, total basalt weathering, and seafloor alteration. It also distinguishes CO2 sources from subduction zone metamorphism and from igneous intrusions. We reconstruct terrestrial basaltic area from data on the extent of large igneous provinces and use their volume to estimate their contribution to degassing. We adopt a recently published reconstruction of subduction-related degassing, and relate seafloor weathering to ocean crust creation rate. Revised degassing alone tends to produce unrealistically high CO2, but this is counteracted by the inclusion of seafloor alteration and global basalt weathering, producing a good overall fit to Mesozoic-Cenozoic proxy CO2 estimates and a good fit to 87Sr/86Sr data. The model predicts that seafloor alteration and terrestrial weathering made similar contributions to CO2 removal through the Triassic and Jurassic, after which terrestrial weathering increased and seafloor weathering declined. We predict that basalts made a greater contribution to silicate weathering than granites through the Mesozoic, before the contribution of basalt weathering declined over the Cenozoic due to decreasing global basaltic area.
Abstract.
Mills B, Daines SJ, Lenton TM (2014). Changing tectonic controls on the long-term carbon cycle from Mesozoic to present.
Geochemistry, Geophysics, Geosystems,
15(12), 4866-4884.
Abstract:
Changing tectonic controls on the long-term carbon cycle from Mesozoic to present
Tectonic drivers of degassing and weathering processes are key long-term controls on atmospheric CO2. However, there is considerable debate over the changing relative importance of different carbon sources and sinks. Existing geochemical models have tended to rely on indirect methods to derive tectonic drivers, such as inversion of the seawater 87Sr/86Sr curve to estimate uplift or continental basalt area. Here we use improving geologic data to update the representation of tectonic drivers in the COPSE biogeochemical model. The resulting model distinguishes CO2 sinks from terrestrial granite weathering, total basalt weathering, and seafloor alteration. It also distinguishes CO2 sources from subduction zone metamorphism and from igneous intrusions. We reconstruct terrestrial basaltic area from data on the extent of large igneous provinces and use their volume to estimate their contribution to degassing. We adopt a recently published reconstruction of subduction-related degassing, and relate seafloor weathering to ocean crust creation rate. Revised degassing alone tends to produce unrealistically high CO2, but this is counteracted by the inclusion of seafloor alteration and global basalt weathering, producing a good overall fit to Mesozoic-Cenozoic proxy CO2 estimates and a good fit to 87Sr/86Sr data. The model predicts that seafloor alteration and terrestrial weathering made similar contributions to CO2 removal through the Triassic and Jurassic, after which terrestrial weathering increased and seafloor weathering declined. We predict that basalts made a greater contribution to silicate weathering than granites through the Mesozoic, before the contribution of basalt weathering declined over the Cenozoic due to decreasing global basaltic area.
Abstract.
Barrett S, Lenton TM, Millner A, Tavoni A, Carpenter S, Anderies JM, Chapin FS, Crépin AS, Daily G, Ehrlich P, et al (2014). Climate engineering reconsidered. Nature Climate Change, 4(7), 527-529.
Lenton TM, Boyle RA, Poulton SW, Shields-Zhou GA, Butterfield NJ (2014). Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era.
Nature Geoscience,
7(4), 257-265.
Abstract:
Co-evolution of eukaryotes and ocean oxygenation in the Neoproterozoic era
The Neoproterozoic era (about 1,000 to 542 million years ago) was a time of turbulent environmental change. Large fluctuations in the carbon cycle were associated with at least two severe-possible Snowball Earth-glaciations. There were also massive changes in the redox state of the oceans, culminating in the oxygenation of much of the deep oceans. Amid this environmental change, increasingly complex life forms evolved. The traditional view is that a rise in atmospheric oxygen concentrations led to the oxygenation of the ocean, thus triggering the evolution of animals. We argue instead that the evolution of increasingly complex eukaryotes, including the first animals, could have oxygenated the ocean without requiring an increase in atmospheric oxygen. We propose that large eukaryotic particles sank quickly through the water column and reduced the consumption of oxygen in the surface waters. Combined with the advent of benthic filter feeding, this shifted oxygen demand away from the surface to greater depths and into sediments, allowing oxygen to reach deeper waters. The decline in bottom-water anoxia would hinder the release of phosphorus from sediments, potentially triggering a potent positive feedback: phosphorus removal from the ocean reduced global productivity and ocean-wide oxygen demand, resulting in oxygenation of the deep ocean. That, in turn, would have further reinforced eukaryote evolution, phosphorus removal and ocean oxygenation. © 2014 Macmillan Publishers Limited. All rights reserved.
Abstract.
Boulton CA, Allison LC, Lenton TM (2014). Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model.
Nat Commun,
5Abstract:
Early warning signals of Atlantic Meridional Overturning Circulation collapse in a fully coupled climate model.
The Atlantic Meridional Overturning Circulation (AMOC) exhibits two stable states in models of varying complexity. Shifts between alternative AMOC states are thought to have played a role in past abrupt climate changes, but the proximity of the climate system to a threshold for future AMOC collapse is unknown. Generic early warning signals of critical slowing down before AMOC collapse have been found in climate models of low and intermediate complexity. Here we show that early warning signals of AMOC collapse are present in a fully coupled atmosphere-ocean general circulation model, subject to a freshwater hosing experiment. The statistical significance of signals of increasing lag-1 autocorrelation and variance vary with latitude. They give up to 250 years warning before AMOC collapse, after ~550 years of monitoring. Future work is needed to clarify suggested dynamical mechanisms driving critical slowing down as the AMOC collapse is approached.
Abstract.
Author URL.
Lenton TM (2014). Game theory: Tipping climate cooperation. Nature Climate Change, 4(1), 14-15.
Daines SJ, Clark JR, Lenton TM (2014). Multiple environmental controls on phytoplankton growth strategies determine adaptive responses of the N:P ratio.
Ecology Letters,
17(4), 414-425.
Abstract:
Multiple environmental controls on phytoplankton growth strategies determine adaptive responses of the N:P ratio
The controls on the 'Redfield' N : P stoichiometry of marine phytoplankton and hence the N : P ratio of the deep ocean remain incompletely understood. Here, we use a model for phytoplankton ecophysiology and growth, based on functional traits and resource-allocation trade-offs, to show how environmental filtering, biotic interactions, and element cycling in a global ecosystem model determine phytoplankton biogeography, growth strategies and macromolecular composition. Emergent growth strategies capture major observed patterns in marine biomes. Using a new synthesis of experimental RNA and protein measurements to constrain per-ribosome translation rates, we determine a spatially variable lower limit on adaptive rRNA:protein allocation and hence on the relationship between the largest cellular P and N pools. Comparison with the lowest observed phytoplankton N : P ratios and N : P export fluxes in the Southern Ocean suggests that additional contributions from phospholipid and phosphorus storage compounds play a fundamental role in determining the marine biogeochemical cycling of these elements. © 2014 John Wiley & Sons Ltd/CNRS.
Abstract.
Daines SJ, Clark JR, Lenton TM (2014). Multiple environmental controls on phytoplankton growth strategies determine adaptive responses of the N : P ratio.
Ecol Lett,
17(4), 414-425.
Abstract:
Multiple environmental controls on phytoplankton growth strategies determine adaptive responses of the N : P ratio.
The controls on the 'Redfield' N : P stoichiometry of marine phytoplankton and hence the N : P ratio of the deep ocean remain incompletely understood. Here, we use a model for phytoplankton ecophysiology and growth, based on functional traits and resource-allocation trade-offs, to show how environmental filtering, biotic interactions, and element cycling in a global ecosystem model determine phytoplankton biogeography, growth strategies and macromolecular composition. Emergent growth strategies capture major observed patterns in marine biomes. Using a new synthesis of experimental RNA and protein measurements to constrain per-ribosome translation rates, we determine a spatially variable lower limit on adaptive rRNA:protein allocation and hence on the relationship between the largest cellular P and N pools. Comparison with the lowest observed phytoplankton N : P ratios and N : P export fluxes in the Southern Ocean suggests that additional contributions from phospholipid and phosphorus storage compounds play a fundamental role in determining the marine biogeochemical cycling of these elements.
Abstract.
Author URL.
Mills B, Lenton TM, Watson AJ (2014). Proterozoic oxygen rise linked to shifting balance between seafloor and terrestrial weathering.
Proc Natl Acad Sci U S A,
111(25), 9073-9078.
Abstract:
Proterozoic oxygen rise linked to shifting balance between seafloor and terrestrial weathering.
A shift toward higher atmospheric oxygen concentration during the late Proterozoic has been inferred from multiple indirect proxies and is seen by many as a prerequisite for the emergence of complex animal life. However, the mechanisms controlling the level of oxygen throughout the Proterozoic and its eventual rise remain uncertain. Here we use a simple biogeochemical model to show that the balance between long-term carbon removal fluxes via terrestrial silicate weathering and ocean crust alteration plays a key role in determining atmospheric oxygen concentration. This balance may be shifted by changes in terrestrial weatherability or in the generation rate of oceanic crust. As a result, the terrestrial chemical weathering flux may be permanently altered--contrasting with the conventional view that the global silicate weathering flux must adjust to equal the volcanic CO2 degassing flux. Changes in chemical weathering flux in turn alter the long-term supply of phosphorus to the ocean, and therefore the flux of organic carbon burial, which is the long-term source of atmospheric oxygen. Hence we propose that increasing solar luminosity and a decrease in seafloor spreading rate over 1,500-500 Ma drove a gradual shift from seafloor weathering to terrestrial weathering, and a corresponding steady rise in atmospheric oxygen. Furthermore, increased terrestrial weatherability during the late Neoproterozoic may explain low temperature, increases in ocean phosphate, ocean sulfate, and atmospheric oxygen concentration at this time.
Abstract.
Author URL.
Boucher O, Forster PM, Gruber N, Ha-Duong M, Lawrence MG, Lenton TM, Maas A, Vaughan NE (2014). Rethinking climate engineering categorization in the context of climate change mitigation and adaptation.
Wiley Interdisciplinary Reviews: Climate Change,
5(1), 23-35.
Abstract:
Rethinking climate engineering categorization in the context of climate change mitigation and adaptation
The portfolio of approaches to respond to the challenges posed by anthropogenic climate change has broadened beyond mitigation and adaptation with the recent discussion of potential climate engineering options. How to define and categorize climate engineering options has been a recurring issue in both public and specialist discussions. We assert here that current definitions of mitigation, adaptation, and climate engineering are ambiguous, overlap with each other and thus contribute to confusing the discourse on how to tackle anthropogenic climate change. We propose a new and more inclusive categorization into five different classes: anthropogenic emissions reductions (AER), territorial or domestic removal of atmospheric CO2 and other greenhouse gases (D-GGR), trans-territorial removal of atmospheric CO2 and other greenhouse gases (T-GGR), regional to planetary targeted climate modification (TCM), and climate change adaptation measures (including local targeted climate and environmental modification, abbreviated CCAM). Thus, we suggest that techniques for domestic greenhouse gas removal might better be thought of as forming a separate category alongside more traditional mitigation techniques that consist of emissions reductions. Local targeted climate modification can be seen as an adaptation measure as long as there are no detectable remote environmental effects. In both cases, the scale and intensity of action are essential attributes from the technological, climatic, and political viewpoints. While some of the boundaries in this revised classification depend on policy and judgement, it offers a foundation for debating on how to define and categorize climate engineering options and differentiate them from both mitigation and adaptation measures to climate change. © 2013 John Wiley & Sons, Ltd.
Abstract.
Dearing JA, Wang R, Zhang K, Dyke JG, Haberl H, Hossain MS, Langdon PG, Lenton TM, Raworth K, Brown S, et al (2014). Safe and just operating spaces for regional social-ecological systems.
GLOBAL ENVIRONMENTAL CHANGE-HUMAN AND POLICY DIMENSIONS,
28, 227-238.
Author URL.
Boyle RA, Dahl TW, Dale AW, Shields-Zhou GA, Zhu M, Brasier MD, Canfield DE, Lenton TM (2014). Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation.
Nature Geoscience,
7(9), 671-676.
Abstract:
Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation
Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary, initiating a transition between the stratified Precambrian and more well-mixed Phanerozoic sedimentary records, against the backdrop of a variable global oxygen reservoir probably smaller in size than present. Phosphorus is the long-term limiting nutrient for oxygen production via burial of organic carbon, and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation. Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir - the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments. Bioturbation also reduces steady-state marine phosphate levels, but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations. The introduction of oxygen-sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop: the intensity of bioturbation is limited by the oxygen decrease it initially causes. The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation, leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles. © 2014 Macmillan Publishers Limited. All rights reserved.
Abstract.
Lenton T (2014). The Meaning of Human Existence.
NATURE,
513(7518), 310-311.
Author URL.
Lenton TM (2014). The global potential for carbon dioxide removal.
Issues in Environmental Science and Technology,
2014-January(38), 52-79.
Abstract:
The global potential for carbon dioxide removal
The global physical potential of different methods of carbon dioxide removal (CDR) from the atmosphere is reviewed. A new categorisation into plant-based, algal-based and alkalinity-based approaches to CDR is proposed. Within these categories, the key flux-limiting resources for CDR are identified and the potential CO2 removal flux that each technology could generate is quantitatively assessed - with a focus on the present, 2050 and 2100. This reveals, for example, that use of waste nutrient flows to feed macro-algae for biomass energy with carbon capture and storage (algal BECCS), shows significant CDR potential, without needing the large land areas or freshwater supplies of plant biomass energy crops. Adding up the potentials of different CDR methods, the total CDR potential at present is 1.5-3 PgC yr-1 (Petagram of carbon per year), comparable in size to either the natural land or ocean carbon sinks. Already 0.55-0.76 PgC yr-1 of this potential has been realised through afforestation and inadvertent ocean fertilisation. The total CDR potential (without including direct air capture) grows such that by mid-century it is 4-9 PgC yr-1 and by the end of the century it is 9-26 PgC yr-1, comparable with current total CO2 emissions of 10 PgC yr-1. The CDR that can be realised under social, economic and engineering constraints is always going to be less than the physical potential. Nevertheless, if combined with reducing CO2 emissions (conventional mitigation), CDR has the physical potential to help stabilise atmospheric CO2 by the middle of this century.
Abstract.
Dahl TW, Boyle RA, Canfield DE, Connelly JN, Gill BC, Lenton TM, Bizzarro M (2014). Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event.
Earth and Planetary Science Letters,
401, 313-326.
Abstract:
Uranium isotopes distinguish two geochemically distinct stages during the later Cambrian SPICE event
Anoxic marine zones were common in early Paleozoic oceans (542-400 Ma), and present a potential link to atmospheric pO2 via feedbacks linking global marine phosphorous recycling, primary production and organic carbon burial. Uranium (U) isotopes in carbonate rocks track the extent of ocean anoxia, whereas carbon (C) and sulfur (S) isotopes track the burial of organic carbon and pyrite sulfur (primary long-term sources of atmospheric oxygen). In combination, these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million-year time scales. Here we report high-precision uranium isotopic data in marine carbonates deposited during the Late Cambrian 'SPICE' event, at ca. 499 Ma, documenting a well-defined -0.18‰ negative δ238U excursion that occurs at the onset of the SPICE event's positive δ13C and δ34S excursions, but peaks (and tails off) before them. Dynamic modelling shows that the different response of the U reservoir cannot be attributed solely to differences in residence times or reservoir sizes - suggesting that two chemically distinct ocean states occurred within the SPICE event. The first ocean stage involved a global expansion of euxinic waters, triggering the spike in U burial, and peaking in conjunction with a well-known trilobite extinction event. During the second stage widespread euxinia waned, causing U removal to tail off, but enhanced organic carbon and pyrite burial continued, coinciding with evidence for severe sulfate depletion in the oceans (Gill et al. 2011). We discuss scenarios for how an interval of elevated pyrite and organic carbon burial could have been sustained without widespread euxinia in the water column (both non-sulfidic anoxia and/or a more oxygenated ocean state are possibilities). Either way, the SPICE event encompasses two different stages of elevated organic carbon and pyrite burial maintained by high nutrient fluxes to the ocean, and potentially sustained by internal marine geochemical feedbacks. © 2014 Elsevier B.V.
Abstract.
2013
Bellamy R, Chilvers J, Vaughan NE, Lenton TM (2013). 'Opening up' geoengineering appraisal: Multi-Criteria Mapping of options for tackling climate change. Global Environmental Change
Bellamy R, Chilvers J, Vaughan NE, Lenton TM (2013). 'Opening up' geoengineering appraisal: Multi-Criteria Mapping of options for tackling climate change.
Global Environmental Change,
23(5), 926-937.
Abstract:
'Opening up' geoengineering appraisal: Multi-Criteria Mapping of options for tackling climate change
Concerted efforts have begun to appraise deliberate, large-scale interventions in the Earth's climate system known as 'geoengineering' in order to provide critical decision support to policy makers around the world. To date geoengineering appraisals have employed narrowly framed inputs (such as context, options, methods and criteria) and 'closed' output reflexivity often amounting to unitary and prescriptive policy recommendations. For the first time, in this paper we begin to address these limitations by 'opening up' appraisal inputs and outputs to a wider diversity of framings, knowledges and future pathways. We use a Multi-Criteria Mapping methodology to appraise carbon and solar geoengineering proposals alongside a range of other options for responding to climate change with a select but diverse group of experts and stakeholders. Overall option rankings are found to vary considerably between participant perspectives and criteria. Despite these differences, the ranks of geoengineering proposals are most often lower than options for mitigating climate change (including voluntary behaviour change and low carbon technologies). The performance of all options is beset by uncertainty, albeit to differing degrees, and it can often be seen that better performing options are outperformed under their pessimistic scores by poorer performing options under their optimistic scores. Several findings contrast with those of other published appraisals. In particular, where stratospheric aerosol injection has previously outperformed other geoengineering options, when assessed against a broader diversity of criteria (spanning all the identified criteria groups) and other options for responding to climate change it performs relatively poorly. We end by briefly exploring the implications of our analysis for geoengineering technologies, their governance, and appraisal. © 2013 Elsevier Ltd.
Abstract.
Livina VN, Lenton TM (2013). A recent tipping point in the Arctic sea-ice cover: abrupt and. persistent increase in the seasonal cycle since 2007.
The CryosphereAbstract:
A recent tipping point in the Arctic sea-ice cover: abrupt and. persistent increase in the seasonal cycle since 2007
There is ongoing debate over whether Arctic sea-ice has already passed a
`tipping point', or whether it will do so in the future. Several recent studies
argue that the loss of summer sea ice does not involve an irreversible
bifurcation, because it is highly reversible in models. However, a broader
definition of a `tipping point' also includes other abrupt, non-linear changes
that are neither bifurcations nor necessarily irreversible. Examination of
satellite data for Arctic sea-ice area reveals an abrupt increase in the
amplitude of seasonal variability in 2007 that has persisted since then. We
identified this abrupt transition using recently developed methods that can
detect multi-modality in time-series data and sometimes forewarn of
bifurcations. When removing the mean seasonal cycle (up to 2008) from the
satellite data, the residual sea-ice fluctuations switch from uni-modal to
multi-modal behaviour around 2007. We originally interpreted this as a
bifurcation in which a new lower ice cover attractor appears in deseasonalised
fluctuations and is sampled in every summer-autumn from 2007 onwards. However,
this interpretation is clearly sensitive to how the seasonal cycle is removed
from the raw data, and to the presence of continental land masses restricting
winter-spring ice fluctuations. Furthermore, there was no robust early warning
signal of critical slowing down prior to the hypothesized bifurcation. Early
warning indicators do however show destabilization of the summer-autumn sea-ice
cover since 2007. Thus, the bifurcation hypothesis lacks consistent support,
but there was an abrupt and persistent increase in the amplitude of the
seasonal cycle of Arctic sea-ice cover in 2007, which we describe as a
(non-bifurcation) `tipping point'. Our statistical methods detect this `tipping
point' and its time of onset.
Abstract.
Rockström J, Steffen W, Noone K, Persson A, Chapin FS, Lambin EF, Lenton TM, Scheffer M, Folke C, Joachim H, et al (2013). A safe operating space for humanity. , 491-501.
Boulton CA, Good P, Lenton TM (2013). Early warning signals of simulated Amazon rainforest dieback.
Theoretical Ecology,
6(3), 373-384.
Abstract:
Early warning signals of simulated Amazon rainforest dieback
We test proposed generic tipping point early warning signals in a complex climate model (HadCM3) which simulates future dieback of the Amazon rainforest. The equation governing tree cover in the model suggests that zero and non-zero stable states of tree cover co-exist, and a transcritical bifurcation is approached as productivity declines. Forest dieback is a non-linear change in the non-zero tree cover state, as productivity declines, which should exhibit critical slowing down. We use an ensemble of versions of HadCM3 to test for the corresponding early warning signals. However, on approaching simulated Amazon dieback, expected early warning signals of critical slowing down are not seen in tree cover, vegetation carbon or net primary productivity. The lack of a convincing trend in autocorrelation appears to be a result of the system being forced rapidly and non-linearly. There is a robust rise in variance with time, but this can be explained by increases in inter-annual temperature and precipitation variability that force the forest. This failure of generic early warning indicators led us to seek more system-specific, observable indicators of changing forest stability in the model. The sensitivity of net ecosystem productivity to temperature anomalies (a negative correlation) generally increases as dieback approaches, which is attributable to a non-linear sensitivity of ecosystem respiration to temperature. As a result, the sensitivity of atmospheric CO2 anomalies to temperature anomalies (a positive correlation) increases as dieback approaches. This stability indicator has the benefit of being readily observable in the real world. © 2013 the Author(s).
Abstract.
Lenton T (2013). Earthmasters: the dawn of the age of climate engineering.
GEOGRAPHY,
98, 160-161.
Author URL.
Clark JR, Lenton TM, Williams HTP, Daines SJ (2013). Environmental selection and resource allocation determine spatial patterns in picophytoplankton cell size.
Limnology and Oceanography,
58(3), 1008-1022.
Abstract:
Environmental selection and resource allocation determine spatial patterns in picophytoplankton cell size
Here we describe a new trait-based model for cellular resource allocation that we use to investigate the relative importance of different drivers for small cell size in phytoplankton. Using the model, we show that increased investment in nonscalable structural components with decreasing cell size leads to a trade-off between cell size, nutrient and light affinity, and growth rate. Within the most extreme nutrient-limited, stratified environments, resource competition theory then predicts a trend toward larger minimum cell size with increasing depth. We demonstrate that this explains observed trends using a marine ecosystem model that represents selection and adaptation of a diverse community defined by traits for cell size and subcellular resource allocation. This framework for linking cellular physiology to environmental selection can be used to investigate the adaptive response of the marine microbial community to environmental conditions and the adaptive value of variations in cellular physiology. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.
Abstract.
Lenton TM (2013). Environmental tipping points.
Annual Review of Environment and Resources,
38, 1-29.
Abstract:
Environmental tipping points
Tipping points-where a small perturbation triggers a large response-can occur in many complex environmental systems. They produce abrupt and sometimes irreversible change, are inherently difficult to predict, and thus pose considerable challenges to the occupants and managers of those systems. However, tipping points can also represent opportunities. Here, different mathematical types of tipping points and different environmental processes that can give rise to them are distinguished. Then, I chart the crucial role that tipping points played in creating the modern Earth system. Looking ahead, potential large-scale tipping points are briefly reviewed before highlighting systems that could harbor tipping points across mechanisms and scales. The prospects for anticipating tipping points, avoiding dangerous ones, and encouraging others are outlined. Finally, a series of virtuous tipping points are identified, which can help transform the relationships between human societies and the environmental systems we depend upon. © 2013 by Annual Reviews. All rights reserved.
Abstract.
Lenton TM (2013). Fire Feedbacks on Atmospheric Oxygen.
, 289-308.
Abstract:
Fire Feedbacks on Atmospheric Oxygen
This chapter provides answer to the question of how much have atmospheric oxygen concentrations varied since the advent of land plants. The answer clearly depends on the nature and strength of fire feedbacks. The chapter starts by summarizing the oxygen puzzle: the fact that atmospheric oxygen concentrations have exhibited remarkably little variation over the past 370 million years or so. Then it examines the feedbacks proposed to stabilize (or in some cases, destabilize) atmospheric oxygen-particularly those involving fires. Next, existing models for atmospheric oxygen variation, including or excluding these fire feedbacks, are examined, with some explanation of why their predictions differ. Then, some new results are presented, using one such model, COPSE, to examine the sensitivity of atmospheric oxygen predictions to changing the sensitivity and nature of fire feedbacks. © 2013 John Wiley & Sons, Ltd.
Abstract.
Livina VN, Lohmann G, Mudelsee M, Lenton TM (2013). Forecasting the underlying potential governing the time series of a dynamical system.
Physica A: Statistical Mechanics and its Applications,
392(18), 3891-3902.
Abstract:
Forecasting the underlying potential governing the time series of a dynamical system
We introduce a technique of time series analysis, potential forecasting, which is based on dynamical propagation of the probability density of time series. We employ polynomial coefficients of the orthogonal approximation of the empirical probability distribution and extrapolate them in order to forecast the future probability distribution of data. The method is tested on artificial data, used for hindcasting observed climate data, and then applied to forecast Arctic sea-ice time series. The proposed methodology completes a framework for 'potential analysis' of tipping points which altogether serves anticipating, detecting and forecasting nonlinear changes including bifurcations using several independent techniques of time series analysis. Although being applied to climatological series in the present paper, the method is very general and can be used to forecast dynamics in time series of any origin. © 2013 the Authors. Published by Elsevier B.V. All rights reserved.
Abstract.
Lenton TN, Bercaw JE, Panchenko VN, Zakharov VA, Babushkin DE, Soshnikov IE, Talsi EP, Brintzinger HH (2013). Formation of Trivalent Zirconocene Complexes from ansa-Zirconocene-Based Olefin-Polymerization Precatalysts: an EPR- and NMR-Spectroscopic Study.
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY,
135(29), 10710-10719.
Author URL.
Hoogakker BAA, Downy F, Andersson MA, Chapman MR, Elderfield H, McCave IN, Lenton TM, Grützner J (2013). Gulf Stream - subtropical gyre properties across two Dansgaard-Oeschger cycles.
Quaternary Science Reviews,
81, 105-113.
Abstract:
Gulf Stream - subtropical gyre properties across two Dansgaard-Oeschger cycles
Salinity increase in the subtropical gyre system may have pre-conditioned the North Atlantic Ocean for a rapid return to stronger overturning circulation and high-latitude warming following meltwater events during the Last Glacial period. Here we investigate the Gulf Stream - subtropical gyre system properties over Dansgaard-Oeschger (DO) cycles 14 to 12, including Heinrich ice-rafting event 5. During the Holocene and Last Glacial Maximum a positive gradient in surface dwelling planktonic foraminifera δ18O (Globigerinoides ruber) can be observed between the Gulf Stream and subtropical gyre, due to decreasing temperature, increasing salinity, and a change from summer to year-round occurrence of G.ruber. We assess whether this gradient was a common feature during stadial-interstadial climate oscillations of Marine Isotope Stage 3, by comparing existing G.ruber δ18O from ODP Site 1060 (subtropical gyre location) and new data from ODP Site 1056 (Gulf Stream location) between 54 and 46ka. Our results suggest that this gradient was largely absent during the period studied. During the major warm DO interstadials 14 and 12 we infer a more zonal and wider Gulf Stream, influencing both ODP Sites 1056 and 1060. A Gulf Stream presence during these major interstadials is also suggested by the large vertical δ18O gradient between shallow dwelling planktonic foraminifera species, especially G.ruber, and the deep dwelling species Globorotalia inflata at site 1056, which we associate with strong summer stratification and Gulf Stream presence. A major reduction in this vertical δ18O gradient from 51ka until the end of Heinrich event 5 at 48.5ka suggests site 1056 was situated within the subtropical gyre in this mainly cold period, from which we infer a migration of the Gulf Stream to a position nearer to the continental shelf, indicative of a narrower Gulf Stream with possibly reduced transport. © 2013 Elsevier Ltd.
Abstract.
Lenton TM, Ciscar JC (2013). Integrating tipping points into climate impact assessments.
Climatic Change,
117(3), 585-597.
Abstract:
Integrating tipping points into climate impact assessments
There is currently a huge gulf between natural scientists' understanding of climate tipping points and economists' representations of climate catastrophes in integrated assessment models (IAMs). In particular, there are multiple potential tipping points and they are not all low-probability events; at least one has a significant probability of being passed this century under mid-range (2-4 °C) global warming, and they cannot all be ruled out at low ( 4 °C) or very high (> 8 °C) global warming. This discrepancy could qualitatively alter the predictions of IAMs, including estimates of the social cost of carbon. To address this discrepancy and assess the economic impact of crossing different climate tipping points, we highlight a list of scientific points that should be considered, at least in a stylised form, in simplified IAMs. For nine different tipping events, the range of expected physical climate impacts is summarised and some suggestions are made for how they may translate into socio-economic impacts on particular sectors or regions. We also consider how passing climate tipping points could affect economic growth. © 2012 Springer Science+Business Media B.V.
Abstract.
Hesselbo SP, Bjerrum CJ, Hinnov LA, MacNiocaill C, Miller KG, Riding JB, van de Schootbrugge B, Mochras Revisited Science Team (2013). Mochras borehole revisited: a new global standard for Early Jurassic earth history. Scientific Drilling, 16, 81-91.
Bercaw JE, Labinger JA, Tonks I, Winston MS, Klet RC, Lenton TN, Despagnet-Ayoub E (2013). New precatalysts for olefin polymerization having LX2 pincer ligands.
Author URL.
Boyle RA, Clark JR, Poulton SW, Shields-Zhou G, Canfield DE, Lenton TM (2013). Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean.
Nat Commun,
4Abstract:
Nitrogen cycle feedbacks as a control on euxinia in the mid-Proterozoic ocean.
Geochemical evidence invokes anoxic deep oceans until the terminal Neoproterozoic ~0.55 Ma, despite oxygenation of Earth's atmosphere nearly 2 Gyr earlier. Marine sediments from the intervening period suggest predominantly ferruginous (anoxic Fe(II)-rich) waters, interspersed with euxinia (anoxic H(2)S-rich conditions) along productive continental margins. Today, sustained biotic H(2)S production requires NO(3)(-) depletion because denitrifiers outcompete sulphate reducers. Thus, euxinia is rare, only occurring concurrently with (steady state) organic carbon availability when N(2)-fixers dominate the production in the photic zone. Here we use a simple box model of a generic Proterozoic coastal upwelling zone to show how these feedbacks caused the mid-Proterozoic ocean to exhibit a spatial/temporal separation between two states: photic zone NO(3)(-) with denitrification in lower anoxic waters, and N(2)-fixation-driven production overlying euxinia. Interchange between these states likely explains the varying H(2)S concentration implied by existing data, which persisted until the Neoproterozoic oxygenation event gave rise to modern marine biogeochemistry.
Abstract.
Author URL.
Huntingford C, Jones PD, Livina VN, Lenton TM, Cox PM (2013). No increase in global temperature variability despite changing regional patterns.
Nature,
500(7462), 327-330.
Abstract:
No increase in global temperature variability despite changing regional patterns
Evidence from Greenland ice cores shows that year-to-year temperature variability was probably higher in some past cold periods, but there is considerable interest in determining whether global warming is increasing climate variability at present. This interest is motivated by an understanding that increased variability and resulting extreme weather conditions may be more difficult for society to adapt to than altered mean conditions. So far, however, in spite of suggestions of increased variability, there is considerable uncertainty as to whether it is occurring. Here we show that although fluctuations in annual temperature have indeed shown substantial geographical variation over the past few decades, the time-evolving standard deviation of globally averaged temperature anomalies has been stable. A feature of the changes has been a tendency for many regions of low variability to experience increases, which might contribute to the perception of increased climate volatility. The normalization of temperature anomalies creates the impression of larger relative overall increases, but our use of absolute values, which we argue is a more appropriate approach, reveals little change. Regionally, greater year-to-year changes recently occurred in much of North America and Europe. Many climate models predict that total variability will ultimately decrease under high greenhouse gas concentrations, possibly associated with reductions in sea-ice cover. Our findings contradict the view that a warming world will automatically be one of more overall climatic variation. © 2013 Macmillan Publishers Limited. All rights reserved.
Abstract.
Huntingford C, Jones PD, Livina VN, Lenton TM, Cox PM (2013). No increase in global temperature variability despite changing regional patterns.
Nature,
500(7462), 327-330.
Abstract:
No increase in global temperature variability despite changing regional patterns.
Evidence from Greenland ice cores shows that year-to-year temperature variability was probably higher in some past cold periods, but there is considerable interest in determining whether global warming is increasing climate variability at present. This interest is motivated by an understanding that increased variability and resulting extreme weather conditions may be more difficult for society to adapt to than altered mean conditions. So far, however, in spite of suggestions of increased variability, there is considerable uncertainty as to whether it is occurring. Here we show that although fluctuations in annual temperature have indeed shown substantial geographical variation over the past few decades, the time-evolving standard deviation of globally averaged temperature anomalies has been stable. A feature of the changes has been a tendency for many regions of low variability to experience increases, which might contribute to the perception of increased climate volatility. The normalization of temperature anomalies creates the impression of larger relative overall increases, but our use of absolute values, which we argue is a more appropriate approach, reveals little change. Regionally, greater year-to-year changes recently occurred in much of North America and Europe. Many climate models predict that total variability will ultimately decrease under high greenhouse gas concentrations, possibly associated with reductions in sea-ice cover. Our findings contradict the view that a warming world will automatically be one of more overall climatic variation.
Abstract.
Author URL.
Lenton TM, Williams HTP (2013). On the origin of planetary-scale tipping points.
Trends in Ecology and Evolution,
28(7), 380-382.
Abstract:
On the origin of planetary-scale tipping points
Tipping points are recognised in many systems, including ecosystems and elements of the climate system. But can the biosphere as a whole tip and, if so, how? Past global tipping points were rare and occurred in the coupled planetary-scale dynamics of the Earth system, not in the local-scale dynamics of its weakly interacting component ecosystems. Yet, evolutionary innovations have triggered past global transformations, suggesting that tipping point theory needs to go beyond bifurcations and networks to include evolution. © 2013 Elsevier Ltd.
Abstract.
Lenton TM, Williams HTP (2013). On the origin of planetary-scale tipping points.
Trends Ecol Evol,
28(7), 380-382.
Abstract:
On the origin of planetary-scale tipping points.
Tipping points are recognised in many systems, including ecosystems and elements of the climate system. But can the biosphere as a whole tip and, if so, how? Past global tipping points were rare and occurred in the coupled planetary-scale dynamics of the Earth system, not in the local-scale dynamics of its weakly interacting component ecosystems. Yet, evolutionary innovations have triggered past global transformations, suggesting that tipping point theory needs to go beyond bifurcations and networks to include evolution.
Abstract.
Author URL.
Moore CM, Mills MM, Arrigo KR, Berman-Frank I, Bopp L, Boyd PW, Galbraith ED, Geider RJ, Guieu C, Jaccard SL, et al (2013). Processes and patterns of oceanic nutrient limitation.
Nature Geoscience,
6(9), 701-710.
Abstract:
Processes and patterns of oceanic nutrient limitation
Microbial activity is a fundamental component of oceanic nutrient cycles. Photosynthetic microbes, collectively termed phytoplankton, are responsible for the vast majority of primary production in marine waters. The availability of nutrients in the upper ocean frequently limits the activity and abundance of these organisms. Experimental data have revealed two broad regimes of phytoplankton nutrient limitation in the modern upper ocean. Nitrogen availability tends to limit productivity throughout much of the surface low-latitude ocean, where the supply of nutrients from the subsurface is relatively slow. In contrast, iron often limits productivity where subsurface nutrient supply is enhanced, including within the main oceanic upwelling regions of the Southern Ocean and the eastern equatorial Pacific. Phosphorus, vitamins and micronutrients other than iron may also (co-)limit marine phytoplankton. The spatial patterns and importance of co-limitation, however, remain unclear. Variability in the stoichiometries of nutrient supply and biological demand are key determinants of oceanic nutrient limitation. Deciphering the mechanisms that underpin this variability, and the consequences for marine microbes, will be a challenge. But such knowledge will be crucial for accurately predicting the consequences of ongoing anthropogenic perturbations to oceanic nutrient biogeochemistry. © 2013 Macmillan Publishers Limited. All rights reserved.
Abstract.
Powell TWR, Lenton TM (2013). Scenarios for future biodiversity loss due to multiple drivers reveal conflict between mitigating climate change and preserving biodiversity.
Environmental Research Letters,
8(2).
Abstract:
Scenarios for future biodiversity loss due to multiple drivers reveal conflict between mitigating climate change and preserving biodiversity
We assess the potential for future biodiversity loss due to three interacting factors: energy withdrawal from ecosystems due to biomass harvest, habitat loss due to land-use change, and climate change. We develop four scenarios to 2050 with different combinations of high or low agricultural efficiency and high or low meat diets, and use species-energy and species-area relationships to estimate their effects on biodiversity. In our scenarios, natural ecosystems are protected except when additional land is necessary to fulfil the increasing dietary demands of the global population. Biomass energy with carbon capture and storage (BECCS) is used as a means of carbon dioxide removal (CDR) from the atmosphere (and offsetting fossil fuel emissions). BECCS is based on waste biomass, with the addition of bio-energy crops only when already managed land is no longer needed for food production. Forecast biodiversity loss from natural biomes increases by more than a factor of five in going from high to low agricultural efficiency scenarios, due to destruction of productive habitats by the expansion of pasture. Biodiversity loss from energy withdrawal on managed land varies by a factor of two across the scenarios. Biodiversity loss due to climate change varies only modestly across the scenarios. Climate change is lowest in the 'low meat high efficiency' scenario, in which by 2050 around 660 million hectares of pasture are converted to biomass plantation that is used for BECCS. However, the resulting withdrawal of energy from managed ecosystems has a large negative impact on biodiversity. Although the effects of energy withdrawal and climate change on biodiversity cannot be directly compared, this suggests that using bio-energy to tackle climate change in order to limit biodiversity loss could instead have the opposite effect. © 2013 IOP Publishing Ltd.
Abstract.
Colbourn G, Ridgwell A, Lenton TM (2013). The Rock Geochemical Model (RokGeM) v0.9.
Geoscientific Model Development,
6(5), 1543-1573.
Abstract:
The Rock Geochemical Model (RokGeM) v0.9
A new model of terrestrial rock weathering - the Rock Geochemical Model (RokGeM) - was developed for incorporation into the GENIE Earth System modelling framework. In this paper we describe the model. We consider a range of previously devised parameterizations, ranging from simple dependencies on global mean temperature following Berner et al. (1983), to spatially explicit dependencies on run-off and temperature (GKWM, Bluth and Kump, 1994; GEM-CO2, Amiotte-Suchet et al. 2003) - fields provided by the energy-moisture balance atmosphere model component in GENIE. Using long-term carbon cycle perturbation experiments, we test the effects of a wide range of model parameters, including whether or not the atmosphere was "short-circuited" in the carbon cycle; the sensitivity and feedback strength of temperature and run-off on carbonate and silicate weathering; different river-routing schemes; 0-D (global average) vs. 2-D (spatially explicit) weathering schemes; and the lithology dependence of weathering. Included are details of how to run the model and visualize the results. © Author(s) 2013.
Abstract.
Toseland A, Daines SJ, Clark JR, Kirkham A, Strauss J, Uhlig C, Lenton TM, Valentin K, Pearson GA, Moulton V, et al (2013). The impact of temperature on marine phytoplankton resource allocation and metabolism. Nature Climate Change
2012
Bellamy R, Chilvers J, Vaughan NE, Lenton TM (2012). A review of climate geoengineering appraisals.
Wiley Interdisciplinary Reviews: Climate Change,
3(6), 597-615.
Abstract:
A review of climate geoengineering appraisals
Deliberate large-scale interventions in the Earth's climate system-known collectively as 'geoengineering'-have been proposed in order to moderate anthropogenic climate change. Amidst a backdrop of many ways of framing the supposed normative rationales for or against their use, geoengineering proposals are undergoing serious consideration. To support decision makers in the multitude of governance considerations a growing number of appraisals are being conducted to evaluate their pros and cons. Appraisals of geoengineering are critically reviewed here for the first time using a systematic literature search and screen strategy. Substantial variability between different appraisals' outputs originates from usually hidden framing effects relating to contextual and methodological choices. Geoengineering has largely been appraised in contextual isolation, ignoring the wider portfolio of options for tackling climate change-spanning mitigation and adaptation-and creating an artificial choice between geoengineering proposals. Most existing appraisal methods do not adequately respond to the post-normal scientific context in which geoengineering resides and show a strong emphasis on closed and exclusive 'expert-analytic' techniques. These and other framing effects invariably focus-or close down-upon particular sets of problem definition, values, assumptions, and courses of action. This produces a limited range of decision options which seem preferable given those framing effects that are privileged, and could ultimately contribute to the closing down of governance commitments. Emergent closure around particular geoengineering proposals is identified and argued to be premature given the need for more anticipatory, responsible, and reflexive forms of governing what is an 'upstream' domain of scientific and technological development. © 2012 John Wiley & Sons, Ltd.
Abstract.
Duarte CM, Lenton TM, Wadhams P, Wassmann P (2012). Abrupt climate change in the Arctic. Nature Climate Change, 2(2), 60-62.
Livina VN, Ditlevsen PD, Lenton TM (2012). An independent test of methods of detecting system states and bifurcations in time-series data.
Physica A: Statistical Mechanics and its Applications,
391(3), 485-496.
Abstract:
An independent test of methods of detecting system states and bifurcations in time-series data
We present an independent test of recently developed methods of potential analysis and degenerate fingerprinting which aim, respectively, to identify the number of states in a system, and to forecast bifurcations. Several samples of modelled data of unknown origin were provided by one author, and the methods were used by the two other authors to investigate these properties. The main idea of the test was to investigate whether the techniques are capable to identify the character of the data of unknown origin, which includes potentiality, possible transitions and bifurcations. Based on the results of the analysis, models were proposed that simulated data equivalent to the test samples. The results obtained were compared with the initial simulations for critical evaluation of the performance of the methods. In most cases, the methods successfully detected the number of states in a system, and the occurrence of transitions between states. The derived models were able to reproduce the test data accurately. However, noise-induced abrupt transitions between existing states cannot be forecast due to the lack of any change in the underlying potential. © 2011 Elsevier B.V. All rights reserved.
Abstract.
Scheffer M, Carpenter SR, Lenton TM, Bascompte J, Brock W, Dakos V, van de Koppel J, van de Leemput IA, Levin SA, van Nes EH, et al (2012). Anticipating critical transitions.
Science,
338(6105), 344-348.
Abstract:
Anticipating critical transitions.
Tipping points in complex systems may imply risks of unwanted collapse, but also opportunities for positive change. Our capacity to navigate such risks and opportunities can be boosted by combining emerging insights from two unconnected fields of research. One line of work is revealing fundamental architectural features that may cause ecological networks, financial markets, and other complex systems to have tipping points. Another field of research is uncovering generic empirical indicators of the proximity to such critical thresholds. Although sudden shifts in complex systems will inevitably continue to surprise us, work at the crossroads of these emerging fields offers new approaches for anticipating critical transitions.
Abstract.
Author URL.
Wadhams P (2012). Arctic Ice Cover, Ice Thickness and Tipping Points.
AMBIO,
41(1), 23-33.
Author URL.
Lenton TM (2012). Arctic climate tipping points.
Ambio,
41(1), 10-22.
Abstract:
Arctic climate tipping points.
There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a long history of natural, abrupt climate changes, which together with current observations and model projections, can help us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes in the Arctic are briefly reviewed. Then, the current behaviour of a range of Arctic systems is summarised. Looking ahead, a range of potential tipping phenomena are described. This leads to a revised and expanded list of potential Arctic climate tipping elements, whose likelihood is assessed, in terms of how much warming will be required to tip them. Finally, the available responses are considered, especially the prospects for avoiding Arctic climate tipping points.
Abstract.
Author URL.
Wassmann P, Lenton TM (2012). Arctic tipping points in an Earth System perspective.
Ambio,
41(1), 1-9.
Abstract:
Arctic tipping points in an Earth System perspective
We provide an introduction to the volume the Arctic in the Earth System perspective: the role of tipping points. The terms tipping point and tipping element are described and their role in current science, general debates, and the Arctic are elucidated. From a wider perspective, the volume focuses upon the role of humans in the Arctic component of the Earth system and in particular the envelope for human existence, the Arctic ecosystems. The Arctic climate tipping elements, the tipping elements in Arctic ecosystems and societies, and the challenges of governance and anticipation are illuminated through short summaries of eight publications that derive from the Arctic Frontiers conference in 2011 and the EU FP7 project Arctic Tipping Points. Then some ideas based upon resilience thinking are developed to show how wise system management could ease pressures on Arctic systems in order to keep them away from tipping points. © 2012 Royal Swedish Academy of Sciences.
Abstract.
Wassmann P, Lenton TM (2012). Arctic tipping points in an Earth system perspective.
Ambio,
41(1), 1-9.
Abstract:
Arctic tipping points in an Earth system perspective.
We provide an introduction to the volume the Arctic in the Earth System perspective: the role of tipping points. The terms tipping point and tipping element are described and their role in current science, general debates, and the Arctic are elucidated. From a wider perspective, the volume focuses upon the role of humans in the Arctic component of the Earth system and in particular the envelope for human existence, the Arctic ecosystems. The Arctic climate tipping elements, the tipping elements in Arctic ecosystems and societies, and the challenges of governance and anticipation are illuminated through short summaries of eight publications that derive from the Arctic Frontiers conference in 2011 and the EU FP7 project Arctic Tipping Points. Then some ideas based upon resilience thinking are developed to show how wise system management could ease pressures on Arctic systems in order to keep them away from tipping points.
Abstract.
Author URL.
Lenton T (2012). Chapter 17 Future Climate Surprises. In (Ed) The Future of the World's Climate, 489-507.
Lenton TM, Livina VN, Dakos V, Scheffer M (2012). Climate bifurcation during the last deglaciation?.
Climate of the Past,
8(4), 1127-1139.
Abstract:
Climate bifurcation during the last deglaciation?
There were two abrupt warming events during the last deglaciation, at the start of the Bølling-Allerød and at the end of the Younger Dryas, but their underlying dynamics are unclear. Some abrupt climate changes may involve gradual forcing past a bifurcation point, in which a prevailing climate state loses its stability and the climate tips into an alternative state, providing an early warning signal in the form of slowing responses to perturbations, which may be accompanied by increasing variability. Alternatively, short-term stochastic variability in the climate system can trigger abrupt climate changes, without early warning. Previous work has found signals consistent with slowing down during the last deglaciation as a whole, and during the Younger Dryas, but with conflicting results in the run-up to the Bølling-Allerød. Based on this, we hypothesise that a bifurcation point was approached at the end of the Younger Dryas, in which the cold climate state, with weak Atlantic overturning circulation, lost its stability, and the climate tipped irreversibly into a warm interglacial state. To test the bifurcation hypothesis, we analysed two different climate proxies in three Greenland ice cores, from the Last Glacial Maximum to the end of the Younger Dryas. Prior to the Bølling warming, there was a robust increase in climate variability but no consistent slowing down signal, suggesting this abrupt change was probably triggered by a stochastic fluctuation. The transition to the warm Bølling-Allerød state was accompanied by a slowing down in climate dynamics and an increase in climate variability. We suggest that the Bølling warming excited an internal mode of variability in Atlantic meridional overturning circulation strength, causing multi-centennial climate fluctuations. However, the return to the Younger Dryas cold state increased climate stability. We find no consistent evidence for slowing down during the Younger Dryas, or in a longer spliced record of the cold climate state before and after the Bølling-Allerød. Therefore, the end of the Younger Dryas may also have been triggered by a stochastic perturbation. © 2012 Author(s).
Abstract.
Lenton TM, Livina VN, Dakos V, van Nes EH, Scheffer M (2012). Early warning of climate tipping points from critical slowing down: comparing methods to improve robustness.
Philos Trans a Math Phys Eng Sci,
370(1962), 1185-1204.
Abstract:
Early warning of climate tipping points from critical slowing down: comparing methods to improve robustness.
We address whether robust early warning signals can, in principle, be provided before a climate tipping point is reached, focusing on methods that seek to detect critical slowing down as a precursor of bifurcation. As a test bed, six previously analysed datasets are reconsidered, three palaeoclimate records approaching abrupt transitions at the end of the last ice age and three models of varying complexity forced through a collapse of the Atlantic thermohaline circulation. Approaches based on examining the lag-1 autocorrelation function or on detrended fluctuation analysis are applied together and compared. The effects of aggregating the data, detrending method, sliding window length and filtering bandwidth are examined. Robust indicators of critical slowing down are found prior to the abrupt warming event at the end of the Younger Dryas, but the indicators are less clear prior to the Bølling-Allerød warming, or glacial termination in Antarctica. Early warnings of thermohaline circulation collapse can be masked by inter-annual variability driven by atmospheric dynamics. However, rapidly decaying modes can be successfully filtered out by using a long bandwidth or by aggregating data. The two methods have complementary strengths and weaknesses and we recommend applying them together to improve the robustness of early warnings.
Abstract.
Author URL.
Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012). First plants cooled the Ordovician. Nature Geoscience, 5(2), 86-89.
Lenton TM, Crouch M, Johnson M, Pires N, Dolan L (2012). First plants cooled the Ordovician.
NATURE GEOSCIENCE,
5(2), 86-89.
Author URL.
Powell TWR, Lenton TM (2012). Future carbon dioxide removal via biomass energy constrained by agricultural efficiency and dietary trends.
Energy and Environmental Science,
5(8), 8116-8133.
Abstract:
Future carbon dioxide removal via biomass energy constrained by agricultural efficiency and dietary trends
We assess the quantitative potential for future land management to help rebalance the global carbon cycle by actively removing carbon dioxide (CO 2) from the atmosphere with simultaneous bio-energy offsets of CO2 emissions, whilst meeting global food demand, preserving natural ecosystems and minimising CO2 emissions from land use change. Four alternative future scenarios are considered out to 2050 with different combinations of high or low technology food production and high or low meat diets. Natural ecosystems are protected except when additional land is necessary to fulfil the dietary demands of the global population. Dedicated bio-energy crops can only be grown on land that is already under management but is no longer needed for food production. We find that there is only room for dedicated bio-energy crops if there is a marked increase in the efficiency of food production (sustained annual yield growth of 1%, shifts towards more efficient animals like pigs and poultry, and increased recycling of wastes and residues). If there is also a return to lower meat diets, biomass energy with carbon storage (BECS) as CO2 and biochar could remove up to 5.2 Pg C per year in 2050 and lower atmospheric CO2 in 2050 by 25 ppm. With the current trend to higher meat diets there is only room for limited expansion of bio-energy crops after 2035 and instead BECS must be based largely on biomass residues, removing up to 3.6 Pg C per year in 2050 and lowering atmospheric CO2 in 2050 by 13 ppm. A high-meat, low-efficiency future would be a catastrophe for natural ecosystems (and thus for the humans that depend on their services) with around 9.3 Gha under cultivation in 2050 and a net increase in atmospheric CO2 in 2050 by 55 ppm due to land use changes. We conclude that future improvements in agricultural efficiency, especially in the livestock sector, could make a decisive contribution to tackling climate change, but this would be maximised if the global trend towards more meat intensive diets can be reversed. © the Royal Society of Chemistry 2012.
Abstract.
Lenton TM (2012). Future climate surprises. In Henderson-Sellers A, McGuffie K (Eds.) Future climates of the world.
Lenton TM, Ciscar J-C (2012). Integrating tipping points into climate impact assessments. Climatic Change, 1-13.
Vaughan NE, Lenton TM (2012). Interactions between reducing CO2 emissions, CO2 removal and solar radiation management.
Philos Trans a Math Phys Eng Sci,
370(1974), 4343-4364.
Abstract:
Interactions between reducing CO2 emissions, CO2 removal and solar radiation management.
We use a simple carbon cycle-climate model to investigate the interactions between a selection of idealized scenarios of mitigated carbon dioxide emissions, carbon dioxide removal (CDR) and solar radiation management (SRM). Two CO(2) emissions trajectories differ by a 15-year delay in the start of mitigation activity. SRM is modelled as a reduction in incoming solar radiation that fully compensates the radiative forcing due to changes in atmospheric CO(2) concentration. Two CDR scenarios remove 300 PgC by afforestation (added to vegetation and soil) or 1000 PgC by bioenergy with carbon capture and storage (removed from system). Our results show that delaying the start of mitigation activity could be very costly in terms of the CDR activity needed later to limit atmospheric CO(2) concentration (and corresponding global warming) to a given level. Avoiding a 15-year delay in the start of mitigation activity is more effective at reducing atmospheric CO(2) concentrations than all but the maximum type of CDR interventions. The effects of applying SRM and CDR together are additive, and this shows most clearly for atmospheric CO(2) concentration. SRM causes a significant reduction in atmospheric CO(2) concentration due to increased carbon storage by the terrestrial biosphere, especially soils. However, SRM has to be maintained for many centuries to avoid rapid increases in temperature and corresponding increases in atmospheric CO(2) concentration due to loss of carbon from the land.
Abstract.
Author URL.
Boyle RA, Williams HTP, Lenton TM (2012). Natural selection for costly nutrient recycling in simulated microbial metacommunities.
J Theor Biol,
312, 1-12.
Abstract:
Natural selection for costly nutrient recycling in simulated microbial metacommunities.
Recycling of essential nutrients occurs at scales from microbial communities to global biogeochemical cycles, often in association with ecological interactions in which two or more species utilise each others' metabolic by-products. However, recycling loops may be unstable; sequences of reactions leading to net recycling may be parasitised by side-reactions causing nutrient loss, while some reactions in any closed recycling loop are likely to be costly to participants. Here we examine the stability of nutrient recycling loops in an individual-based ecosystem model based on microbial functional types that differ in their metabolism. A supplied nutrient is utilised by a "source" functional type, generating a secondary nutrient that is subsequently used by two other types-a "mutualist" that regenerates the initial nutrient at a growth rate cost, and a "parasite" that produces a refractory waste product but does not incur any additional cost. The three functional types are distributed across a metacommunity in which separate patches are linked by a stochastic diffusive migration process. Regions of high mutualist abundance feature high levels of nutrient recycling and increased local population density leading to greater export of individuals, allowing the source-mutualist recycling loop to spread across the system. Individual-level selection favouring parasites is balanced by patch-level selection for high productivity, indirectly favouring mutualists due to the synergistic productivity benefits of the recycling loop they support. This suggests that multi-level selection may promote nutrient cycling and thereby help to explain the apparent ubiquity and stability of nutrient recycling in nature.
Abstract.
Author URL.
Levermann A, Bamber JL, Drijfhout S, Ganopolski A, Haeberli W, Harris NRP, Huss M, Krueger K, Lenton TM, Lindsay RW, et al (2012). Potential climatic transitions with profound impact on Europe Review of the current state of six 'tipping elements of the climate system'.
CLIMATIC CHANGE,
110(3-4), 845-878.
Author URL.
Lenton TN, VanderVelde DG, Bercaw JE (2012). Synthesis of a Bis(thiophenolate)pyridine Ligand and its Titanium, Zirconium, and Tantalum Complexes.
ORGANOMETALLICS,
31(21), 7492-7499.
Author URL.
Van Der Giezen M, Lenton TM (2012). The rise of oxygen and complex life.
Journal of Eukaryotic Microbiology,
59(2), 111-113.
Abstract:
The rise of oxygen and complex life
Mitochondria have been put forward as the saviours of anaerobes when their environment became oxygenated. However, despite oxygenic photosynthesis evolving around 2.7 billion years ago (Ga), followed by the "Great Oxidation" of the atmosphere ∼ 2.4 Ga, the deep oceans remained largely anoxic and either iron-enriched or sulphidic until 580 million years ago, when the eukaryotic radiation was well underway. Atmospheric oxygen probably remained at an intermediate concentration (1-10% of the present level) from ∼ 2.4 until ∼ 0.8 Ga when a "lesser oxidation" began. This drastically changes the textbook view of the ecological conditions under which the mitochondrial endosymbiont established itself. It could explain the widespread distribution of anaerobic biochemistry in every eukaryotic supergroup: anaerobic biochemistry is hard-wired into the eukaryotes. © 2012 International Society of Protistologists.
Abstract.
Van Der Giezen M, Lenton TM (2012). The rise of oxygen and complex life.
J Eukaryot Microbiol,
59(2), 111-113.
Abstract:
The rise of oxygen and complex life.
Mitochondria have been put forward as the saviours of anaerobes when their environment became oxygenated. However, despite oxygenic photosynthesis evolving around 2.7 billion years ago (Ga), followed by the "Great Oxidation" of the atmosphere ~ 2.4 Ga, the deep oceans remained largely anoxic and either iron-enriched or sulphidic until 580 million years ago, when the eukaryotic radiation was well underway. Atmospheric oxygen probably remained at an intermediate concentration (1-10% of the present level) from ~ 2.4 until ~ 0.8 Ga when a "lesser oxidation" began. This drastically changes the textbook view of the ecological conditions under which the mitochondrial endosymbiont established itself. It could explain the widespread distribution of anaerobic biochemistry in every eukaryotic supergroup: anaerobic biochemistry is hard-wired into the eukaryotes.
Abstract.
Author URL.
Duarte CM, Agusti S, Wassmann P, Arrieta JM, Alcaraz M, Coello A, Marba N, Hendriks IE, Holding J, Garcia-Zarandona I, et al (2012). Tipping Elements in the Arctic Marine Ecosystem.
AMBIO,
41(1), 44-55.
Author URL.
Mills BJW (2012). Weathering pathways and limitations in biogeochemical models: Application to Earth system evolution.
Lenton TM (2012). What early warning systems are there for environmental shocks?.
Environmental Science and PolicyAbstract:
What early warning systems are there for environmental shocks?
This paper offers a new classification of environmental shocks from a dynamical systems perspective, and reviews early warning systems for environmental shocks, particularly in climate systems and ecosystems. Three main categories of environmental shock are identified; extreme events, abrupt swings, and tipping points. The factors determining the predictability of different shocks and hence the prospects for early warning are outlined. Lessons from existing early warning systems for extreme events and abrupt climate swings are summarised. Then the potential for early warning of bifurcation-type tipping points is explained, and contrasted with the lack of warning when stochastic internal variability triggers a shift in the state of a system. The scientific and technological progress needed to improve early warning capability is outlined. Then the framework is applied to the Foresight project on Migration and Global Environmental Change, with its focal eco-regions of drylands, low-elevation coastal zones, and mountainous regions. Priority targets for early warning systems are identified and the need for an integrated approach to early warning is highlighted, which considers the interactions between different types of environmental shock. © 2012 Elsevier Ltd. All rights reserved.
Abstract.
2011
Lenton T (2011). 2 degrees C or not 2 degrees C? That is the climate question.
NATURE,
473(7345), 7-7.
Author URL.
Lenton TM (2011). 2 °C or not 2 °C? That is the climate question. Nature, 473
Vaughan NE, Lenton TM (2011). A review of climate geoengineering proposals.
Climatic Change,
109(3-4), 745-790.
Abstract:
A review of climate geoengineering proposals
Climate geoengineering proposals seek to rectify the current radiative imbalance via either (1) reducing incoming solar radiation (solar radiation management) or (2) removing CO2 from the atmosphere and transferring it to long-lived reservoirs (carbon dioxide removal). For each option, we discuss its effectiveness and potential side effects, also considering lifetime of effect, development and deployment timescale, reversibility, and failure risks. We present a detailed review that builds on earlier work by including the most recent literature, and is more extensive than previous comparative frameworks. Solar radiation management propsals are most effective but short-lived, whilst carbon dioxide removal measures gain effectiveness the longer they are pursued. Solar radiation management could restore the global radiative balance, but must be maintained to avoid abrupt warming, meanwhile ocean acidification and residual regional climate changes would still occur. Carbon dioxide removal involves less risk, and offers a way to return to a pre-industrial CO2 level and climate on a millennial timescale, but is potentially limited by the CO2 storage capacity of geological reservoirs. Geoengineering could complement mitigation, but it is not an alternative to it. We expand on the possible combinations of mitigation, carbon dioxide removal and solar radiation management that might be used to avoid dangerous climate change. © 2011 Springer Science+Business Media B.V.
Abstract.
Lenton TM (2011). Beyond 2°C: Redefining dangerous climate change for physical systems. Wiley Interdisciplinary Reviews: Climate Change, 2(3), 451-461.
Livina VN, Kwasniok F, Lohmann G, Kantelhardt JW, Lenton TM (2011). Changing climate states and stability: from Pliocene to present. Climate Dynamics, 37, 2437-2453.
Lenton TM (2011). Early warning of climate tipping points. Nature Climate Change, 1, 201-209.
Clark JR, Daines S, Lenton TM, Watson AJ, Williams HTP (2011). Individual-based modelling of adaptation in marine microbial populations using genetically defined physiological parameters. Ecological Modelling
Thomas MA, Suntharalingam P, Pozzoli L, Devasthale A, Kloster S, Rast S, Feichter J, Lenton TM (2011). Non-linearity in DMS aerosol-cloud-climate interactions. Atmospheric Chemistry and Physics Discussions, 11(5), 15227-15253.
Goodwin P, Oliver KIC, Lenton TM (2011). Observational constraints on the causes of Holocene CO <inf>2</inf> change.
Global Biogeochemical Cycles,
25(3).
Abstract:
Observational constraints on the causes of Holocene CO 2 change
The mechanisms that controlled past atmospheric CO 2 levels are not directly measurable, hence many proxy data sources are combined when reconstructing past carbon cycling. The accuracy of Holocene modeling reconstructions is checked by seeking consistency between data-based observables and their numerically simulated counterparts. A new framework is presented to evaluate which combinations of observables can best constrain carbon cycle mechanisms with the minimum of uncertainty. We show that when previous studies have combined ocean temperatures, ocean [CO 32-], and the δ 13C of atmospheric CO 2 as observables, uncertainties in the data sources are amplified by over 2 orders of magnitude when reconstructing the mechanisms responsible for CO 2 increase. However, incorporating mean δ 13C of ocean DIC since 8000 years ago as an additional data source reduces the uncertainties by more than a factor of 5, making this observable a priority for future research. Our analysis indicates that the 20 ppm increase in CO 2 between 8000 years BP and preindustrial was caused by significant CaCO 3 precipitation and a reduction in the ocean soft tissue pump. Meanwhile, an increase in terrestrial carbon storage opposed the CO 2 increase. The methods presented here are useful for investigating a range of paleoclimate events. Copyright 2011 by the American Geophysical Union.
Abstract.
Thomas MA, Suntharalingam P, Pozzoli L, Devasthale A, Kloster S, Rast S, Feichter J, Lenton TM (2011). Rate of non-linearity in DMS aerosol-cloud-climate interactions.
Atmospheric Chemistry and Physics,
11(21), 11175-11183.
Abstract:
Rate of non-linearity in DMS aerosol-cloud-climate interactions
The degree of non-linearity in DMS-cloud-climate interactions is assessed using the ECHAM5-HAMMOZ model by taking into account end-to-end aerosol chemistry-cloud microphysics link. The evaluation is made over the Southern oceans in austral summer, a region of minimal anthropogenic influence. In this study, we compare the DMS-derived changes in the aerosol and cloud microphysical properties between a baseline simulation with the ocean DMS emissions from a prescribed climatology, and a scenario where the DMS emissions are doubled. Our results show that doubling the DMS emissions in the current climate results in a non-linear response in atmospheric DMS burden and subsequently, in SO 2 and H2SO4 burdens due to inadequate OH oxidation. The aerosol optical depth increases by only ∼20 % in the 30° S-75° S belt in the SH summer months. This increases the vertically integrated cloud droplet number concentrations (CDNC) by 25 %. Since the vertically integrated liquid water vapor is constant in our model simulations, an increase in CDNC leads to a reduction in cloud droplet radius of 3.4 % over the Southern oceans in summer. The equivalent increase in cloud liquid water path is 10.7 %. The above changes in cloud microphysical properties result in a change in global annual mean radiative forcing at the TOA of-1.4 W m -2. The results suggest that the DMS-cloud microphysics link is highly non-linear. This has implications for future studies investigating the DMS-cloud climate feedbacks in a warming world and for studies evaluating geoengineering options to counteract warming by modulating low level marine clouds. © 2011 Author(s).
Abstract.
Lenton TM, Watson AJ (2011). Revolutions that made the Earth. Oxford, Oxford University Press.
Williams HTP, Boyle RA, Lenton TM (2011). Spatial structure creates community-level selection for nutrient recycling. Eleventh European Conference on the Synthesis and Simulation of Living Systems (ECAL2011). 8th - 12th Aug 2011.
Boyle RA, Lenton TM, Watson AJ (2011). Symbiotic physiology promotes homeostasis in Daisyworld.
J Theor Biol,
274(1), 170-182.
Abstract:
Symbiotic physiology promotes homeostasis in Daisyworld.
A connection is hypothesized between the physiological consequences of mutualistic symbiosis and life's average long-term impact on certain highly biologically conserved environmental variables. This hypothesis is developed analytically and with a variant of the Daisyworld model. Biological homeostasis is frequently effective due to co-ordination between opposing physiological "rein" functions, which buffer an organism in response to an external (often environmental) perturbation. It is proposed that during evolutionary history the pooling of different species' physiological functions in mutualistic symbioses increased the range of suboptimal environmental conditions that could be buffered against--a mutual tolerance benefit sometimes sufficient to outweigh the cost of cooperation. A related argument is that for a small number of biologically-crucial physical variables (i) the difference between organism interiors and the life-environment interface is relatively low, and (ii) the biologically optimum level of that variable is relatively highly conserved across different species. For such variables, symbiosis tends to cause (at a cost) an increase in the number of environmental buffering functions per unit of selection, which in turn biases the overall impact of the biota on the state of the variable towards the biological optimum. When a costly but more temperature-tolerant and physiologically versatile symbiosis between one black (warming) and one white (cooling) "daisy" is added to the (otherwise unaltered) Daisyworld parable, four new results emerge: (1) the extension of habitability to a wider luminosity range, (2) resistance to the impact of "cheater" white daisies with cold optima, that derive short-term benefit from environmental destabilisation, (3) the capacity to maintain residual, oscillatory regulation in response to forcings that change more rapidly than allele frequencies and (crucially) (4) "succession"-type dynamics in which the tolerant symbiosis colonises and to an extent makes habitable an otherwise lifeless environment, but is later displaced by free-living genotypes that have higher local fitness once conditions improve. The final result is arguably analogous to lichen colonisation of the Neoproterozoic land surface, followed by the Phanerozoic rise of vascular plants. Caution is necessary in extrapolating from the Daisyworld parable to real ecology/geochemistry, but sufficiently conserved variables may be water potential, macronutrient stoichiometry and (to a lesser extent) the temperature window for metabolic activity.
Abstract.
Author URL.
Mills B, Watson AJ, Goldblatt C, Boyle R, Lenton TM (2011). Timing of Neoproterozoic glaciations linked to transport-limited global weathering.
Nature Geoscience,
4(12), 861-864.
Abstract:
Timing of Neoproterozoic glaciations linked to transport-limited global weathering
The Earth underwent several snowball glaciations between 1,000 and 542 million years ago. The termination of these glaciations is thought to have been triggered by the accumulation of volcanic CO2 in the atmosphere over millions of years1,2. Subsequent high temperatures and loss of continental ice would increase silicate weathering and in turn draw down atmospheric CO 2(ref.3). Estimates of the post-snowball weathering rate indicate that equilibrium between CO2 input and removal would be restored within several million years4, potentially triggering a new glaciation. However the transition between deglaciation and the onset a new glaciation was on the order of 107 years. Over long timescales, the availability of fresh rock can become a limiting factor for silicate weathering rates. Here we show that when this transport-determined limitation is incorporated into the COPSE biogeochemical model6, the stabilization time is substantially longer, >10 7 years. When we include a simple ice-albedo feedback, the model produces greenhouse-icehouse oscillations on this timescale that are compatible with observations. Our simulations also indicate positive carbon isotope excursions and an increased flux of oxygen to the atmosphere during interglacials, both of which are consistent with the geological record7,8. We conclude that the long gaps between snowball glaciations can be explained by limitations on silicate weathering rates. copy; 2011 Macmillan Publishers Limited. All rights reserved.
Abstract.
Lenton TM, Schellnhuber HJ (2011). Tipping Elements: Jokers in the Pack. In Richardson K, Steffen W, Liverman D (Eds.) Climate Change: Global Risks, Challenges and Decisions, Cambridge University Press, 163-201.
2010
Holden PB, Edwards NR, Oliver KIC, Lenton TM, Wilkinson RD (2010). A probabilistic calibration of climate sensitivity and terrestrial carbon change in GENIE-1.
Climate Dynamics,
35(5), 785-806.
Abstract:
A probabilistic calibration of climate sensitivity and terrestrial carbon change in GENIE-1
In order to investigate Last Glacial Maximum and future climate, we "precalibrate" the intermediate complexity model GENIE-1 by applying a rejection sampling approach to deterministic emulations of the model. We develop ~1,000 parameter sets which reproduce the main features of modern climate, but not precise observations. This allows a wide range of large-scale feedback response strengths which generally encompass the range of GCM behaviour. We build a deterministic emulator of climate sensitivity and quantify the contributions of atmospheric (±0.93°C, 1σ) vegetation (±0.32°C), ocean (±0.24°C) and sea-ice (±0.14°C) parameterisations to the total uncertainty. We then perform an LGM-constrained Bayesian calibration, incorporating data-driven priors and formally accounting for structural error. We estimate climate sensitivity as likely (66% confidence) to lie in the range 2.6-4. 4°C, with a peak probability at 3.6°C. We estimate LGM cooling likely to lie in the range 5.3-7. 5°C, with a peak probability at 6.2°C. In addition to estimates of global temperature change, we apply our ensembles to derive LGM and 2xCO2 probability distributions for land carbon storage, Atlantic overturning and sea-ice coverage. Notably, under 2xCO2 we calculate a probability of 37% that equilibrium terrestrial carbon storage is reduced from modern values, so the land sink has become a net source of atmospheric CO2. © 2009 Springer-Verlag.
Abstract.
Williams HTP, Lenton TM (2010). Evolutionary regime shifts in simulated ecosystems.
Oikos,
119(12), 1887-1899.
Abstract:
Evolutionary regime shifts in simulated ecosystems
Catastrophic regime shifts in ecosystems occur when the system is tipped into a new attractor state under some external forcing. Here we consider whether evolutionary adaptations within ecosystems can trigger similar transitions. We use an individual-based, evolutionary model of interconnected ecosystems to analyze nonlinear changes in global state resulting from local adaptations. Transitions between periods of stability occur when new traits arise that allow exploitation of under-utilized resources. Subsequent rapid growth of the population carrying the new trait causes abrupt environmental change that drives incumbent species extinct. We call these transitions 'evolutionary regime shifts'. These internally generated perturbations can result in ecosystem collapse, followed by recovery to an alternate stable state, or occasionally system-wide extinction. While these disruptions may have a negative impact on ecosystem productivity in individual simulation runs, mean results over many simulations show a trend for increasing ecosystem productivity and stability over time. Feedback between life and the abiotic environment in the model creates a 'long-tailed' distribution of extinction sizes without any external trigger for large extinction events. © 2010 the Authors.
Abstract.
Livina V, Kwasniok F, Lenton T (2010). Potential analysis reveals changing number of climate states during the last 60 kyr. Climate of the Past, 6, 77-82.
Thomas MA, Suntharalingam P, Pozzoli L, Rast S, Devasthale A, Kloster S, Feichter J, Lenton TM (2010). Quantification of DMS aerosol-cloud-climate interactions using ECHAM5-HAMMOZ model in current climate scenario. Atmospheric Chemistry and Physics Discussions, 10(2), 3087-3187.
Thomas MA, Suntharalingam P, Pozzoli L, Rast S, Devasthale A, Kloster S, Feichter J, Lenton TM (2010). Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario.
Atmospheric Chemistry and Physics,
10(15), 7425-7438.
Abstract:
Quantification of DMS aerosol-cloud-climate interactions using the ECHAM5-HAMMOZ model in a current climate scenario
The contribution of ocean dimethyl sulfide (DMS) emissions to changes in cloud microphysical properties is quantified seasonally and globally for present day climate conditions using an aerosol-chemistry-climate general circulation model, ECHAM5-HAMMOZ, coupled to a cloud microphysics scheme. We evaluate DMS aerosol-cloud-climate linkages over the southern oceans where anthropogenic influence is minimal. The changes in the number of activated particles, cloud droplet number concentration (CDNC), cloud droplet effective radius, cloud cover and the radiative forcing are examined by analyzing two simulations: a baseline simulation with ocean DMS emissions derived from a prescribed climatology and one in which the ocean DMS emissions are switched off. Our simulations show that the model realistically simulates the seasonality in the number of activated particles and CDNC, peaking during Southern Hemisphere (SH) summer coincident with increased phytoplankton blooms and gradually declining with a minimum in SH winter. In comparison to a simulation with no DMS, the CDNC level over the southern oceans is 128% larger in the baseline simulation averaged over the austral summer months. Our results also show an increased number of smaller sized cloud droplets during this period. We estimate a maximum decrease of up to 15-18% in the droplet radius and a mean increase in cloud cover by around 2.5% over the southern oceans during SH summer in the simulation with ocean DMS compared to when the DMS emissions are switched off. The global annual mean top of the atmosphere DMS aerosol all sky radiative forcing is-2.03 W/m2, whereas, over the southern oceans during SH summer, the mean DMS aerosol radiative forcing reaches 9.32 W/m2. © 2010 Author(s).
Abstract.
Lenton TM (2010). The potential for land-based biological CO2 removal to lower future atmospheric CO2 concentration. Carbon Management, 1(1), 145-160.
Mills B, Boyle R, Goldblatt C, Lenton T, Watson A (2010). What happened in the Neoproterozoic? Investigations using a simplified Earth system model.
Author URL.
2009
Rockström J, Steffen W, Noone K, Persson A, Chapin FS, Lambin EF, Lenton TM, Scheffer M, Folke C, Schellnhuber HJ, et al (2009). A safe operating space for humanity.
Nature,
461(7263), 472-475.
Author URL.
Clark JR, Williams HTP, Lenton TM, Watson AJ (2009). Agent-based modelling of Archean biogeochemistry and the Great Oxidation.
Author URL.
Goldblatt C, Lenton TM, Watson AJ (2009). An evaluation of the long-wave radiative transfer code used in the Met Office Unified Model.
Quarterly Journal of the Royal Meteorological Society,
135(640), 619-633.
Abstract:
An evaluation of the long-wave radiative transfer code used in the Met Office Unified Model
A detailed evaluation of the radiative transfer code used in the Met Office Unified Climate/Forecast Model is performed, comparing it with a line-by-line model and testing the climatic effects of errors in a radiative-convective model. The radiative forcing at the tropopause due to CO2 changes within SRES scenarios and across Quaternary glacial cycles is represented with reasonable accuracy, suggesting that surface temperature will be correctly predicted. However, this is achieved by partial cancellation of opposing errors in upward and downward fluxes. The changes in the vertical profiles of radiative fluxes and the changes to surface and top-of-atmosphere fluxes all show significant errors, even at twice pre-industrial CO2. This causes a sign error in the change in the convective flux in the radiative-convective model. Performance of the code deteriorates rapidly above four times pre-industrial CO2. For less-abundant greenhouse gases, CH4 and N2O, the errors are larger as a proportion of their radiative forcings. Errors for surface and top-of-atmosphere fluxes for CO2 are similar to those from the mean of the general circulation model (GCM) codes submitted to the intercomparison of radiation codes for IPCC AR4, implying that errors as found here may not be uncommon in climate models. A renewed emphasis on accuracy in radiative transfer calculations and openness in intercomparison studies is necessary to improve the modelling of climate change. © 2009 Royal Meteorological Society.
Abstract.
Livina V, Kwasniok F, Sapronov Y, Lenton T (2009). Bifurcation analysis of geophysical time series.
Goldblatt C, Watson AJ, Lenton TM (2009). Bistability of Atmospheric Oxygen and the Great Oxidation: Implications for Life Detection.
Author URL.
Vaughan NE, Lenton TM, Shepherd JG (2009). Climate change mitigation: Trade-offs between delay and strength of action required.
Climatic Change,
96(1), 29-43.
Abstract:
Climate change mitigation: Trade-offs between delay and strength of action required
Climate change mitigation via a reduction in the anthropogenic emissions of carbon dioxide (CO2) is the principle requirement for reducing global warming, its impacts, and the degree of adaptation required. We present a simple conceptual model of anthropogenic CO2 emissions to highlight the trade off between delay in commencing mitigation, and the strength of mitigation then required to meet specific atmospheric CO2 stabilization targets. We calculate the effects of alternative emission profiles on atmospheric CO2 and global temperature change over a millennial timescale using a simple coupled carbon cycle-climate model. For example, if it takes 50 years to transform the energy sector and the maximum rate at which emissions can be reduced is -2.5% year-1, delaying action until 2020 would lead to stabilization at 540 ppm. A further 20 year delay would result in a stabilization level of 730 ppm, and a delay until 2060 would mean stabilising at over 1,000 ppm. If stabilization targets are met through delayed action, combined with strong rates of mitigation, the emissions profiles result in transient peaks of atmospheric CO2 (and potentially temperature) that exceed the stabilization targets. Stabilization at 450 ppm requires maximum mitigation rates of -3% to -5% year-1, and when delay exceeds 2020, transient peaks in excess of 550 ppm occur. Consequently tipping points for certain Earth system components may be transgressed. Avoiding dangerous climate change is more easily achievable if global mitigation action commences as soon as possible. Starting mitigation earlier is also more effective than acting more aggressively once mitigation has begun. © Springer Science + Business Media B.V. 2009.
Abstract.
Vaughan NE, Lenton TM, Shepherd JG (2009). Climate change mitigation: trade-offs between delay and strength of action required.
CLIMATIC CHANGE,
96(1-2), 29-43.
Author URL.
Fairman MJ, Price AR, Xue G, Molinari M, Nicole DA, Lenton TM, Marsh R, Takeda K, Cox SJ (2009). Earth system modelling with Windows Workflow Foundation.
Future Generation Computer Systems,
25(5), 586-597.
Abstract:
Earth system modelling with Windows Workflow Foundation
The GENIE project has built a Grid-enabled Earth system modelling framework that facilitates the integration, execution and management of component models for the study of the Earth system over millennial timescales. The existing framework supports collaborative study of GENIE models across heterogeneous compute grids through scripted workflows in the Matlab environment. While the scripting approach achieves simplicity and flexibility, it suffers from an essentially passive approach to work unit management and from a heavy reliance on a central database to provide fault tolerance. The Windows Workflow Foundation (WF) technology provides a rich set of features to support the authoring and execution of workflows, tracking services that enable the monitoring of a running workflow, and state persistence services that allow workflows to be recovered and resumed upon failure. We demonstrate how the Windows Workflow Foundation has been applied to build a complementary simulation management system which provides rapid composition, event driven logic and reliable hosting of the scientific workflows while interfacing to existing infrastructure. We also describe how the adoption of WF enables the application of a number of associated technologies to provide better interoperability and accessibility for the simulation system. These improvements are demonstrated through a parametric study of the bi-stability of the oceanic thermohaline circulation in a GENIE model where the effects of a new carbon cycle are studied. © 2008 Elsevier B.V. All rights reserved.
Abstract.
Lenton TM, Williams HTP (2009). Gaia and Evolution. In Crist E, Rinker B (Eds.) Gaia in Turmoil, Boston: MIT Press, 61-84.
Lenton TM, Williams HTP (2009). Gaia and evolution. In Crist E, Rinker HB (Eds.) Gaia in turmoil, the MIT Press.
Lenton TM, Footitt A, Dlugolecki A (2009). Major Tipping Points in the Earth’s Climate System and Consequences for the Insurance Sector., Tyndall Centre for Climate Change Research.
Goldblatt C, Claire MW, Lenton TM, Matthews AJ, Watson AJ, Zahnle KJ (2009). Nitrogen-enhanced greenhouse warming on earlyEarth.
Nature Geoscience,
2(12), 891-896.
Abstract:
Nitrogen-enhanced greenhouse warming on earlyEarth
Early in Earths history, the Sun provided less energy to the Earth than it does today. However, the Earth was not permanently glaciated, an apparent contradiction known as the faint young Sun paradox. By implication, the Earth must have been warmed by a stronger greenhouse effect or a lower planetary albedo. Here we use a radiative-convective climate model to show that more N 2 in the atmosphere would have increased the warming effect of existing greenhouse gases by broadening their absorption lines. With the atmospheric CO 2 and CH 4 levels estimated for 2.5 billion years ago, a doubling of the present atmospheric nitrogen (PAN) level would cause a warming of 4.4 C. Our new budget of Earths geological nitrogen reservoirs indicates that there is a sufficient quantity of nitrogen in the crust (0.5PAN) and mantle (1.4 PAN) to have supported this, and that this nitrogen was previously in the atmosphere. In the mantle, N correlates with 40 Ar, the daughter product of 40 K, indicating that the source of mantle N is subducted crustal rocks in which NH 4 + has been substituted for K +. We thus conclude that a higher nitrogen level probably helped warm the early Earth, and suggest that the effects of N 2 should be considered in assessing the habitable zone for terrestrial planets. © 2009 Macmillan Publishers Limited. All rights reserved.
Abstract.
Daines SJ, Lenton TM (2009). Oxygen oases and the Great Oxidation.
Author URL.
Rockström J, Steffen W, Noone K, Persson A, Chapin FS, Lambin E, Lenton TM, Scheffer M, Folke C, Schellnhuber HJ, et al (2009). Planetary boundaries: Exploring the safe operating space for humanity.
Ecology and Society,
14(2).
Abstract:
Planetary boundaries: Exploring the safe operating space for humanity
Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. We have identified nine planetary boundaries and, drawing upon current scientific understanding, we propose quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere
Abstract.
Livina VN, Kwasniok F, Lenton TM (2009). Potential analysis reveals changing number of climate states during the last 60 kyr. , 5(5), 2223-2237.
Livina VN, Kwasniok F, Lenton TM (2009). Potential analysis reveals changing number of climate states during the last 60 kyr. Climate of the Past Discussions, 5(5), 2223-2237.
Thomas MA, Suntharalingam P, Rast S, Pozzoli L, Feichter H, Lenton T (2009). Quantifying DMS-cloud-climate interactions using the ECHAM5-HAMMOZ model.
Author URL.
Goodwin P, Lenton TM (2009). Quantifying the feedback between ocean heating and CO<inf>2</inf> solubility as an equivalent carbon emission.
Geophysical Research Letters,
36(15).
Abstract:
Quantifying the feedback between ocean heating and CO2 solubility as an equivalent carbon emission
There are inherent difficulties in quantifying carbon cycle-climate feedbacks over the 21st century because the system is in a transient state. The conventional approach of deriving gain factors only strictly applies at equilibrium, and they differ with scenario and with respect to different climate variables (e.g. CO2, radiative forcing, and temperature) which have different time lags. Here we show that the positive feedback whereby ocean heating reduces the solubility of CO2 can be quantified in a. scenario-independent way, directly from ocean heat content changes, by expressing it as an 'equivalent carbon emission'. On annual to centennial timescales, the feedback has the same impact on atmospheric CO2 as an equivalent emission flux of fossil fuel carbon. From ocean heat-content data we quantify the ocean heating-CO2 solubility positive feedback, which increased in average strength from an equivalent emission of ∼0.08 PgC yr-I oyer 1961-2003 to ∼0.19 PgC yr-1 during 1993-2003. Copyright 2009 by the American Geophysical Union.
Abstract.
Williams HTP, Lenton TM (2009). Rebels with a cause. NERC Planet Earth(Winter 2009).
Miles CJ, Bell TG, Lenton TM (2009). Testing the relationship between the solar radiation dose and surface DMS concentrations using in situ data.
Biogeosciences,
6(9), 1927-1934.
Abstract:
Testing the relationship between the solar radiation dose and surface DMS concentrations using in situ data
The proposed strong positive relationship between dimethylsulphide (DMS) concentration and the solar radiation dose (SRD) received into the surface ocean is tested using data from the Atlantic Meridional Transect (AMT) programme. In situ, daily data sampled concurrently with DMS concentrations is used for the component variables of the SRD (mixed layer depth, MLD, surface insolation, I0, and a light attenuation coefficient, k) to calculate SRDinsitu. This is the first time in situ data for all of the components, including k, has been used to test the SRDDMS relationship over large spatial scales. We find a significant correlation (p=0.55 n=65 p
Abstract.
Veron JEN, Hoegh-Guldberg O, Lenton TM, Lough JM, Obura DO, Pearce-Kelly P, Sheppard CRC, Spalding M, Stafford-Smith MG, Rogers AD, et al (2009). The coral reef crisis: the critical importance of<350 ppm CO2.
Mar Pollut Bull,
58(10), 1428-1436.
Abstract:
The coral reef crisis: the critical importance of<350 ppm CO2.
Temperature-induced mass coral bleaching causing mortality on a wide geographic scale started when atmospheric CO(2) levels exceeded approximately 320 ppm. When CO(2) levels reached approximately 340 ppm, sporadic but highly destructive mass bleaching occurred in most reefs world-wide, often associated with El Niño events. Recovery was dependent on the vulnerability of individual reef areas and on the reef's previous history and resilience. At today's level of approximately 387 ppm, allowing a lag-time of 10 years for sea temperatures to respond, most reefs world-wide are committed to an irreversible decline. Mass bleaching will in future become annual, departing from the 4 to 7 years return-time of El Niño events. Bleaching will be exacerbated by the effects of degraded water-quality and increased severe weather events. In addition, the progressive onset of ocean acidification will cause reduction of coral growth and retardation of the growth of high magnesium calcite-secreting coralline algae. If CO(2) levels are allowed to reach 450 ppm (due to occur by 2030-2040 at the current rates), reefs will be in rapid and terminal decline world-wide from multiple synergies arising from mass bleaching, ocean acidification, and other environmental impacts. Damage to shallow reef communities will become extensive with consequent reduction of biodiversity followed by extinctions. Reefs will cease to be large-scale nursery grounds for fish and will cease to have most of their current value to humanity. There will be knock-on effects to ecosystems associated with reefs, and to other pelagic and benthic ecosystems. Should CO(2) levels reach 600 ppm reefs will be eroding geological structures with populations of surviving biota restricted to refuges. Domino effects will follow, affecting many other marine ecosystems. This is likely to have been the path of great mass extinctions of the past, adding to the case that anthropogenic CO(2) emissions could trigger the Earth's sixth mass extinction.
Abstract.
Author URL.
Lenton TM, Vaughan NE (2009). The radiative forcing potential of different climate geoengineering options.
Atmospheric Chemistry and Physics,
9(15), 5539-5561.
Abstract:
The radiative forcing potential of different climate geoengineering options
Climate geoengineering proposals seek to rectify the Earth's current and potential future radiative imbalance, either by reducing the absorption of incoming solar (shortwave) radiation, or by removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on energy balance considerations and pulse response functions for the decay of CO2 perturbations. This aids transparency compared to calculations with complex numerical models, but is not intended to be definitive. It allows us to compare the relative effectiveness of a range of proposals. We consider geoengineering options as additional to large reductions in CO2 emissions. By 2050, some land carbon cycle geoengineering options could be of comparable magnitude to mitigation "wedges", but only stratospheric aerosol injections, albedo enhancement of marine stratocumulus clouds, or sunshades in space have the potential to cool the climate back toward its pre-industrial state. Strong mitigation, combined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO2 sinks, might be able to bring CO2 back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alternatively, strong mitigation stabilising CO2 at 500 ppm, combined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settlements might achieve a patchy cancellation of radiative forcing. Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition may have greater long-term potential than iron or nitrogen fertilisation. Enhancing ocean upwelling or downwelling have trivial effects on any meaningful timescale. Our approach provides a common framework for the evaluation of climate geoengineering proposals, and our results should help inform the prioritisation of further research into them.
Abstract.
Goldblatt C, Matthews AJ, Claire M, Lenton TM, Watson AJ, Zahnle KJ (2009). There was probably more nitrogen in the Archean atmosphere - This would have helped resolve the Faint Young Sun paradox.
Author URL.
Lenton TM, Myerscough RJ, Marsh R, Livina VN, Price AR, Cox SJ, Genie Team (2009). Using GENIE to study a tipping point in the climate system.
Philos Trans a Math Phys Eng Sci,
367(1890), 871-884.
Abstract:
Using GENIE to study a tipping point in the climate system.
We have used the Grid ENabled Integrated Earth system modelling framework to study the archetypal example of a tipping point in the climate system; a threshold for the collapse of the Atlantic thermohaline circulation (THC). eScience has been invaluable in this work and we explain how we have made it work for us. Two stable states of the THC have been found to coexist, under the same boundary conditions, in a hierarchy of models. The climate forcing required to collapse the THC and the reversibility or irreversibility of such a collapse depends on uncertain model parameters. Automated methods have been used to assimilate observational data to constrain the pertinent parameters. Anthropogenic climate forcing leads to a robust weakening of the THC and increases the probability of crossing a THC tipping point, but some ensemble members collapse readily, whereas others are extremely resistant. Hence, we test general methods that have been developed to directly diagnose, from time-series data, the proximity of a 'tipping element', such as the THC to a bifurcation point. In a three-dimensional ocean-atmosphere model exhibiting THC hysteresis, despite high variability in the THC driven by the dynamical atmosphere, some early warning of an approaching tipping point appears possible.
Abstract.
Author URL.
2008
Livina VN, Edwards NR, Goswami S, Lenton TM (2008). A wavelet-coefficient score for comparison of two-dimensional climatic-data fields.
QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY,
134(633), 941-955.
Author URL.
Marinelli LW, Lipford KA, Lenton TN, Haines DR (2008). CHED 1290-Determining the reactive properties of GLP-1.
Author URL.
Lenton TN, Haines DR (2008). CHED 1315-Quantitative structure-activity relationship (QSAR) study of the N-terminal histidine of GLP-1.
Author URL.
Wood AJ, Ackland GJ, Dyke JG, Williams HTP, Lenton TM (2008). Daisyworld: a review.
Reviews of Geophysics,
46(1).
Abstract:
Daisyworld: a review
Daisyworld is a simple planetary model designed to show the long-term effects of coupling between life and its environment. Its original form was introduced by James Lovelock as a defense against criticism that his Gaia theory of the Earth as a self-regulating homeostatic system requires teleological control rather than being an emergent property. The central premise, that living organisms can have major effects on the climate system, is no longer controversial. The Daisyworld model has attracted considerable interest from the scientific community and has now established itself as a model independent of, but still related to, the Gaia theory. Used widely as both a teaching tool and as a basis for more complex studies of feedback systems, it has also become an important paradigm for the understanding of the role of biotic components when modeling the Earth system. This paper collects the accumulated knowledge from the study of Daisyworld and provides the reader with a concise account of its important properties. We emphasize the increasing amount of exact analytic work on Daisyworld and are able to bring together and summarize these results from different systems for the first time. We conclude by suggesting what a more general model of life-environment interaction should be based on. Copyright 2008 by the American Geophysical Union.
Abstract.
Lenton TM, Livina VN (2008). Developing a long-term business-as-usual climate change scenario for engineers.
Lenton T (2008). Engines of life - Review of 'Energy in Nature and Society' by Vaclav Smil. Nature, 452, 691-692.
Williams HTP, Lenton TM (2008). Environmental regulation in a network of simulated microbial ecosystems.
Proc Natl Acad Sci U S A,
105(30), 10432-10437.
Abstract:
Environmental regulation in a network of simulated microbial ecosystems.
The Earth possesses a number of regulatory feedback mechanisms involving life. In the absence of a population of competing biospheres, it has proved hard to find a robust evolutionary mechanism that would generate environmental regulation. It has been suggested that regulation must require altruistic environmental alterations by organisms and, therefore, would be evolutionarily unstable. This need not be the case if organisms alter the environment as a selectively neutral by-product of their metabolism, as in the majority of biogeochemical reactions, but a question then arises: Why should the combined by-product effects of the biota have a stabilizing, rather than destabilizing, influence on the environment? Under certain conditions, selection acting above the level of the individual can be an effective adaptive force. Here we present an evolutionary simulation model in which environmental regulation involving higher-level selection robustly emerges in a network of interconnected microbial ecosystems. Spatial structure creates conditions for a limited form of higher-level selection to act on the collective environment-altering properties of local communities. Local communities that improve their environmental conditions achieve larger populations and are better colonizers of available space, whereas local communities that degrade their environment shrink and become susceptible to invasion. The spread of environment-improving communities alters the global environment toward the optimal conditions for growth and tends to regulate against external perturbations. This work suggests a mechanism for environmental regulation that is consistent with evolutionary theory.
Abstract.
Author URL.
Lenton TM (2008). TIPPING POINTS OR GRADUAL CLIMATE CHANGE?.
Author URL.
Lenton TM, Held H, Kriegler E, Hall JW, Lucht W, Rahmstorf S, Schellnhuber HJ (2008). Tipping elements in the Earth's climate system.
Proc Natl Acad Sci U S A,
105(6), 1786-1793.
Abstract:
Tipping elements in the Earth's climate system.
The term "tipping point" commonly refers to a critical threshold at which a tiny perturbation can qualitatively alter the state or development of a system. Here we introduce the term "tipping element" to describe large-scale components of the Earth system that may pass a tipping point. We critically evaluate potential policy-relevant tipping elements in the climate system under anthropogenic forcing, drawing on the pertinent literature and a recent international workshop to compile a short list, and we assess where their tipping points lie. An expert elicitation is used to help rank their sensitivity to global warming and the uncertainty about the underlying physical mechanisms. Then we explain how, in principle, early warning systems could be established to detect the proximity of some tipping points.
Abstract.
Author URL.
Johnson MT, Vaughan NE, Goodwin P, Goldblatt C, Roudesli S, Lenton TM (2008). Why NH<inf>3</inf> is not a candidate reagent for ambient CO<inf>2</inf> fixation: a response to "alternative solution to global warming arising from CO<inf>2</inf> Emissions - Partial neutralization of tropospheric H <inf>2</inf>CO<inf>3</inf> with NH<inf>3</inf>".
Environmental Progress,
27(3), 412-417.
Abstract:
Why NH3 is not a candidate reagent for ambient CO2 fixation: a response to "alternative solution to global warming arising from CO2 Emissions - Partial neutralization of tropospheric H 2CO3 with NH3"
It has been proposed that application of urea, or ammonium sulfate (phis lime) to nonagricultural land to evolve ammonia may provide a "solution" to increasing CO2 concentrations by neutralizing atmospheric carbonic acid to ammonium bicarbonate at ambient concentrations and subsequent storage in the surface ocean (Apak [2007]: Environmental Progress 26, 355-359). We identify a series of major flaws in this hypothesis, which indicate that the approach is unfeasible and would not succeed if attempted at any scale: (i) ne phenomenal energy cost associated with breaking the N≡N bond and evolving H2 for NH3 production (and associated fossil fuel CO2 emissions under the current energy generation market); (ii) the radiative forcing associated with substantially increasing the concentration of ammonia in the atmosphere, and (iii) a number of unwanted indirect effects, including eutrophication, enhanced N2O emissions, and the inhibition of the oxidation of strong green-house gases such as methane in the atmosphere. We strongly urge future efforts to be directed away from this approach and suggest that engagement with the climate, earth-system, and biogeochemtetry communities is essential when putting forward ideas for potential geoengineering approaches to mitigate global climate change. © 2008 American Institute of Chemical Engineers.
Abstract.
2007
Livina VN, Lenton TM (2007). A modified method for detecting incipient bifurcations in a dynamical system.
Geophysical Research Letters,
34(3).
Abstract:
A modified method for detecting incipient bifurcations in a dynamical system
We assess the proximity of a system to a bifurcation point, using a degenerate fingerprinting method that estimates the declining decay rate of fluctuations in a time series as an indicator of approaching a critical state. The method is modified by employing Detrended Fluctuation Analysis (DFA) which improves the estimation of short-term decay, especially in climate records which generally possess power-law correlations. When the modified method is applied to GENIE-1 model output that simulates collapse of the Atlantic thermohaline circulation, the bifurcation point is correctly anticipated. In Greenland ice core paleotemperature data, for which the conventional degenerate fingerprinting is not applicable due to the short length of the series, the modified method detects the transition from glacial to interglacial conditions. The technique could in principle be used to anticipate future bifurcations in the climate system, but this will require high-resolution time series of the relevant data. Copyright 2007 by the American Geophysical Union.
Abstract.
Williams HTP, Lenton TM (2007). Artificial ecosystem selection for evolutionary optimisation.
Abstract:
Artificial ecosystem selection for evolutionary optimisation
Abstract.
Williams HTP, Lenton TM (2007). Artificial selection of simulated microbial ecosystems.
Proc Natl Acad Sci U S A,
104(21), 8918-8923.
Abstract:
Artificial selection of simulated microbial ecosystems.
Recent work with microbial communities has demonstrated an adaptive response to artificial selection at the level of the ecosystem. The reasons for this response and the level at which adaptation occurs are unclear: does selection act implicitly on traits of individual species, or are higher-level traits genuinely being selected? If the ecosystem response is just the additive combination of the responses of the constituent species, then the ecosystem response could be predicted a priori, and the ecosystem-level selection process is superfluous. However, if the ecosystem response results from ecological interactions among species, then selection at a higher level is necessary. Here we perform artificial ecosystem selection experiments on an individual-based evolutionary simulation model of microbial ecology and observe a similar response to that seen with real ecosystems. We demonstrate that a significant fraction of artificially selected ecosystem responses cannot be accounted for by implicit lower-level selection of a single type of organism within the community, and that interactions among different types of organism contribute significantly to the response in the majority of cases. However, when the ecological problem posed by the artificial ecosystem selection process can be easily solved by a single dominant species, it often is.
Abstract.
Author URL.
Ridgwell A, Zondervan I, Hargreaves JC, Bijma J, Lenton TM (2007). Assessing the potential long-term increase of oceanic fossil fuel CO <inf>2</inf> uptake due to CO<inf>2</inf>-calcification feedback.
Biogeosciences,
4(4), 481-492.
Abstract:
Assessing the potential long-term increase of oceanic fossil fuel CO 2 uptake due to CO2-calcification feedback
Plankton manipulation experiments exhibit a wide range of sensitivities of biogenic calcification to simulated anthropogenic acidification of the ocean, with the "lab rat" of planktic calcifiers, Emiliania huxleyi apparently not representative of calcification generally. We assess the implications of this observational uncertainty by creating an ensemble of realizations of an Earth system model that encapsulates a comparable range of uncertainty in calcification response to ocean acidification. We predict that a substantial reduction in marine carbonate production is possible in the future, with enhanced ocean CO2 sequestration across the model ensemble driving a 4-13% reduction in the year 3000 atmospheric fossil fuel CO 2 burden. Concurrent changes in ocean circulation and surface temperatures in the model contribute about one third to the increase in CO 2 uptake. We find that uncertainty in the predicted strength of CO2-calcification feedback seems to be dominated by the assumption as to which species of calcifier contribute most to carbonate production in the open ocean.
Abstract.
Lenton TM, Klausmeier CA (2007). Biotic stoichiometric controls on the deep ocean N:P ratio.
Biogeosciences,
4(3), 353-367.
Abstract:
Biotic stoichiometric controls on the deep ocean N:P ratio
We re-examine what controls the deep ocean N:P ratio in the light of recent findings that the C:N:P stoichiometry of phytoplankton varies with growth rate, nutrient and light limitation, species and phylum, and that N 2-fixation may be limited by Fe, temperature and/or light in large parts of the world ocean. In particular, we assess whether a systematic change in phytoplankton stoichiometry can alter the deep ocean N:P ratio. To do this we adapt recent models to include non-Redfieldian stoichiometry of phytoplankton and restriction of N2-fixers to a fraction of the surface ocean. We show that a systematic change in phytoplankton C:N:P can alter the concentrations of NO3 and PO4 in the deep ocean but cannot greatly alter their ratio, unless it also alters the N:P threshold for N 2-fixation. This occurs if competitive dynamics set the N:P threshold for N2-fixation, in which case it remains close to the N:P requirement of non-fixers (rather than that of 2N-fixers) and consequently so does the deep ocean N:P ratio. Then, even if N 2-fixers are restricted to a fraction of the surface ocean, they reach higher densities there, minimising variations in deep ocean N:P. Theoretical limits on the N:P requirements of phytoplankton suggest that whilst the deep ocean has been well oxygenated (i.e. since the Neoproterozoic, with the possible exception of Oceanic Anoxic Events), its N:P ratio is unlikely to have varied by more than a factor of two in either direction. Within these bounds, evolutionary changes in phytoplankton composition, and increased phosphorus weathering due to the biological colonisation of the land surface, are predicted to have driven long-term changes in ocean composition.
Abstract.
Lenton TM, Klausmeier CA (2007). Biotic stoichiometric controls on the deep ocean N:P ratio. Biogeosciences Discussions, 4(1), 417-454.
Goldblatt C, Lenton TM, Watson AJ (2007). Bistability of atmospheric oxygen and the Great Oxidation.
Author URL.
Goldblatt C, Lenton TM, Watson AJ (2007). Bistability of atmospheric oxygen and the great oxidation: Implications for life detection.
ASTROBIOLOGY,
7(3), 483-483.
Author URL.
Fairman MJ, Price AR, Xue G, Molinari M, Nicole DA, Lenton TM, Marsh R, Takeda K, Cox SJ (2007). Building scientific workflows for earth system modelling with windows workflow foundation.
Abstract:
Building scientific workflows for earth system modelling with windows workflow foundation
Abstract.
Lenton TM, Marsh R, Price AR, Lunt DJ, Aksenov Y, Annan JD, Cooper-Chadwick T, Cox SJ, Edwards NR, Goswami S, et al (2007). Effects of atmospheric dynamics and ocean resolution on bi-stability of the thermohaline circulation examined using the Grid ENabled Integrated Earth system modelling (GENIE) framework.
Climate Dynamics,
29(6), 591-613.
Abstract:
Effects of atmospheric dynamics and ocean resolution on bi-stability of the thermohaline circulation examined using the Grid ENabled Integrated Earth system modelling (GENIE) framework
We have used the Grid ENabled Integrated Earth system modelling (GENIE) framework to undertake a systematic search for bi-stability of the ocean thermohaline circulation (THC) for different surface grids and resolutions of 3-D ocean (GOLDSTEIN) under a 3-D dynamical atmosphere model (IGCM). A total of 407,000 years were simulated over a three month period using Grid computing. We find bi-stability of the THC despite significant, quasi-periodic variability in its strength driven by variability in the dynamical atmosphere. The position and width of the hysteresis loop depends on the choice of surface grid (longitude-latitude or equal area), but is less sensitive to changes in ocean resolution. For the same ocean resolution, the region of bi-stability is broader with the IGCM than with a simple energy-moisture balance atmosphere model (EMBM). Feedbacks involving both ocean and atmospheric dynamics are found to promote THC bi-stability. THC switch-off leads to increased import of freshwater at the southern boundary of the Atlantic associated with meridional overturning circulation. This is counteracted by decreased freshwater import associated with gyre and diffusive transports. However, these are localised such that the density gradient between North and South is reduced tending to maintain the THC off state. THC switch-off can also generate net atmospheric freshwater input to the Atlantic that tends to maintain the off state. The ocean feedbacks are present in all resolutions, across most of the bi-stable region, whereas the atmosphere feedback is strongest in the longitude-latitude grid and around the transition where the THC off state is disappearing. Here the net oceanic freshwater import due to the overturning mode weakens, promoting THC switch-on, but the atmosphere counteracts this by increasing net freshwater input. This increases the extent of THC bi-stability in this version of the model. © Springer-Verlag 2007.
Abstract.
Ridgwell A, Hargreaves JC, Edwards NR, Annan JD, Lenton TM, Marsh R, Yool A, Watson A (2007). Marine geochemical data assimilation in an efficient Earth system model of global biogeochemical cycling.
Biogeosciences,
4(1), 87-104.
Abstract:
Marine geochemical data assimilation in an efficient Earth system model of global biogeochemical cycling
We have extended the 3-D ocean based "Grid EN-abled Integrated Earth system model" (GENIE-1) to help understand the role of ocean biogeochemistry and marine sediments in the long-term (∼100 to 100000 year) regulation of atmospheric CO2, and the importance of feedbacks between CO2 and climate. Here we describe the ocean carbon cycle, which in its first incarnation is based around a simple single nutrient (phosphate) control on biological productivity. The addition of calcium carbonate preservation in deep-sea sediments and its role in regulating atmospheric CO2 is presented elsewhere (Ridgwell and Hargreaves, 2007). We have calibrated the model parameters controlling ocean carbon cycling in GENIE-1 by assimilating 3-D observational datasets of phosphate and alkalinity using an ensemble Kalman filter method. The calibrated (mean) model predicts a global export production of particulate organic carbon (POC) of 8.9 PgC yr-1, and reproduces the main features of dissolved oxygen distributions in the ocean. For estimating biogenic calcium carbonate (CaCO 3) production, we have devised a parameterization in which the CaCO3POC export ratio is related directly to ambient saturation state. Calibrated global CaCO3 export production (1.2 PgC yr -1) is close to recent marine carbonate budget estimates. The GENIE-1 Earth system model is capable of simulating a wide variety of dissolved and isotopic species of relevance to the study of modern global biogeochemical cycles as well as past global environmental changes recorded in paleoceanographic proxies. Importantly, even with 12 active biogeochemical tracers in the ocean and including the calculation of feedbacks between atmospheric CO2 and climate, we achieve better than 1000 years per (2.4 GHz) CPU hour on a desktop PC. The GENIE-1 model thus provides a viable alternative to box and zonally-averaged models for studying global biogeochemical cycling over all but the very longest (> 1000000 year) time-scales.
Abstract.
Williams HTP, Lenton TM (2007). Microbial Gaia: a new model for the evolution of environmental regulation. Gaia Circular
Boyle RA, Lenton TM, Williams HTP (2007). Neoproterozoic 'snowball Earth' glaciations and the evolution of altruism.
Geobiology,
5(4), 337-349.
Abstract:
Neoproterozoic 'snowball Earth' glaciations and the evolution of altruism
We hypothesize that a demographic and ecological effect of Neoproterozoic 'snowball Earth' glaciations was to increase the fitness of group-level traits and consequently the likelihood of the evolution of macroscopic form. Extreme and repeated founder effects raised genetic relatedness - and therefore the influence of kin selection on the individuals within a group. This was permissive for the evolution of some highly costly altruistic traits, including those for macroscopic differentiation. In some eukaryotic species, the harsh and fluctuating abiotic conditions made a macroscopic physiology advantageous, perhaps necessary, for collective survival. This caused population-wide group viability selection, whereby non-altruist 'cheat' genotypes killed the groups they were in, and therefore themselves, by reaching fixation. Furthermore, dispersal between refugia would reach zero under anything near a 'hard snowball', which would protect altruists at high local frequency from the influx of cheats from neighbouring groups. We illustrate our hypothesis analytically and with a simple spatial model. We show how removal of between-group dispersal, in a population with initial between-group variation in cheat frequency, causes the relative frequency of altruists to increase while the population as a whole decreases in size, as a result of group death caused by cheat invasion. This may be of particular relevance to animal multicellularity because irreversible differentiation (highly altruistic in that it imposes a high fitness cost on the individual cell) is more prevalent than in other multicellular eukaryotes. The relevance of our hypothesis should be scaled by any future consensus on the severity of snowball Earth, but it is theoretically plausible that global-scale glaciations had a systematic influence on the level of selection during Earth history. © 2007 the Authors.
Abstract.
Price AR, Xue G, Yool A, Lunt DJ, Valdes PJ, Lenton TM, Wason JL, Pound GE, Cox SJ (2007). Optimization of integrated Earth System Model components using Grid-enabled data management and computation.
Concurrency and Computation: Practice and Experience,
19(2), 153-165.
Abstract:
Optimization of integrated Earth System Model components using Grid-enabled data management and computation
In this paper, we present the Grid enabled data management system that has been deployed for the Grid ENabled Integrated Earth system model (GENIE) project. The database system is an augmented version of the Geodise Database Toolbox and provides a repository for scripts, binaries and output data in the GENIE framework. By exploiting the functionality available in the Geodise toolboxes we demonstrate how the database can be employed to tune parameters of coupled GENIE Earth System Model components to improve their match with observational data. A Matlab client provides a common environment for the project Virtual Organization and allows the scripting of bespoke tuning studies that can exploit multiple heterogeneous computational resources. We present the results of a number of tuning exercises performed on GENIE model components using multi-dimensional optimization methods. In particular, we find that it is possible to successfully tune models with up to 30 free parameters using Kriging and Genetic Algorithm methods. Copyright © 2006 John Wiley & Sons, Ltd.
Abstract.
Marinelli LW, Lenton TN, Lipford KA, Haines DR (2007). Structure-activity study of the N-terminal histidine of GLP-1.
Author URL.
Lenton TN, Vij A, Grabow W, Mabry JM, Haddad TS (2007). Structures of vinyl polyhedral oligomeric silsesquioxanes (ViSiO1.5)n with n=8, 10, 12 and 14.
Author URL.
Williams HTP, Lenton TM (2007). The Flask model: Emergence of nutrient-recycling microbial ecosystems and their disruption by environment-altering 'rebel' organisms.
Oikos,
116(7), 1087-1105.
Abstract:
The Flask model: Emergence of nutrient-recycling microbial ecosystems and their disruption by environment-altering 'rebel' organisms
Here we introduce a new model of life-environment interaction, which simulates an evolving microbial community in a 'Fask' of liquid with prescribed inputs of nutrients. The flask is seeded with a clonal population of 'microbes' that are subject to mutation on genetic loci that determine their nutrient uptake patterns, release patterns, and their effects on, and response to, other environmental variables. In contrast to existing models of life-environment interaction, notably Daisyworld, what benefits the individual organisms is decoupled from their 'global' (system-level) effects. A robust property of the model is the emergence of ecosystems that tend toward a state where nutrients are efficiently utilised and differentially recycled, with a correlated increase in total population. Organisms alter the environment as a free 'by-product' of their growth, and their growth is constrained by adverse environmental effects. This introduces environmental feedback, which can disrupt the model ecosystems, even though there are no constraints on the conditions to which the organisms can theoretically adapt. 'Rebel' organisms can appear that grow rapidly by exploiting an under-utilised resource, but in doing so shift the environment away from the state to which the majority of the community are adapted. The result can be a population crash with lossof recycling, followed by later recovery, or in extreme cases, a total extinction of the system. Numerous runs of these 'flask' ecosystems show that tighter environmental constraints on growth make the system more vulnerable to internally generated ecosystem extinction. © Oikos.
Abstract.
2006
Williamson MS, Lenton TM, Shepherd JG, Edwards NR (2006). An efficient numerical terrestrial scheme (ENTS) for Earth system modelling.
Ecological Modelling,
198(3-4), 362-374.
Abstract:
An efficient numerical terrestrial scheme (ENTS) for Earth system modelling
We present a minimal spatial model of vegetation carbon, soil carbon and soil water storage and the exchange of energy, water and carbon with the atmosphere. The efficient numerical terrestrial scheme (ENTS) is designed for long time period simulations and large ensemble studies in Earth system models of intermediate complexity (EMICs). ENTS includes new parameterisations of vegetation fractional cover and roughness length as functions of vegetation carbon, and a relationship between soil carbon storage and soil water holding capacity. We make and justify the approximation that when the solar forcing is a diurnal average, as in our EMIC, the land radiation balance equilibrates with the atmosphere within a few days. This allows us to solve directly for equilibrium land temperature, making ENTS very computationally efficient and avoiding problems of numerical instability that beset many land surface schemes. We tune the carbon cycle parameters towards observed values of global carbon storage in vegetation and soil and estimated global fluxes of net photosynthesis, vegetation respiration, leaf litter and soil respiration. When the model is forced with long term monthly mean fields of NCEP reanalysis climate data, we find ENTS yields broadly accurate patterns of vegetation and soil carbon storage, vegetation fraction, surface albedo, land temperature and evaporation. © 2006 Elsevier B.V. All rights reserved.
Abstract.
Goldblatt C, Lenton TM, Watson AJ (2006). Bistability of atmospheric oxygen and the Great Oxidation.
Nature,
443(7112), 683-686.
Abstract:
Bistability of atmospheric oxygen and the Great Oxidation.
The history of the Earth has been characterized by a series of major transitions separated by long periods of relative stability. The largest chemical transition was the 'Great Oxidation', approximately 2.4 billion years ago, when atmospheric oxygen concentrations rose from less than 10(-5) of the present atmospheric level (PAL) to more than 0.01 PAL, and possibly to more than 0.1 PAL. This transition took place long after oxygenic photosynthesis is thought to have evolved, but the causes of this delay and of the Great Oxidation itself remain uncertain. Here we show that the origin of oxygenic photosynthesis gave rise to two simultaneously stable steady states for atmospheric oxygen. The existence of a low-oxygen (less than 10(-5) PAL) steady state explains how a reducing atmosphere persisted for at least 300 million years after the onset of oxygenic photosynthesis. The Great Oxidation can be understood as a switch to the high-oxygen (more than 5 x 10(-3) PAL) steady state. The bistability arises because ultraviolet shielding of the troposphere by ozone becomes effective once oxygen levels exceed 10(-5) PAL, causing a nonlinear increase in the lifetime of atmospheric oxygen. Our results indicate that the existence of oxygenic photosynthesis is not a sufficient condition for either an oxygen-rich atmosphere or the presence of an ozone layer, which has implications for detecting life on other planets using atmospheric analysis and for the evolution of multicellular life.
Abstract.
Author URL.
Lenton TM, Loutre MF, Williamson MS, Warren R, Goodess CM, Swann M, Cameron D, Hankin R, Marsh R, Shepherd JG, et al (2006). Climate change on the millennial timescale., Environment Agency.
Lenton TM, Williamson MS, Warren R, Loutre MF, Goodess CM, Swann M, Cameron D, Hankin R, Marsh R, Shepherd JG, et al (2006). Climate change on the millennial timescale. Norwich, Tyndall Centre.
Lenton TM (2006). Climate change to the end of the millennium: an editorial review essay.
Climatic Change,
76(1-2), 7-29.
Abstract:
Climate change to the end of the millennium: an editorial review essay
Anthropogenic climate change will continue long after anthropogenic CO 2 emissions cease. Atmospheric CO2, global warming and ocean circulation will approach equilibrium on the millennial timescale, whereas thermal expansion of the ocean, ice sheet melt and their contributions to sea level rise are unlikely to be complete. Atmospheric CO2 in year 3000 depends non-linearly on the total amount of CO2 emitted and is very likely to exceed the present level of ∼380 ppmv. CO2 is doubled for ∼2500 GtC emitted, quadrupled if all ∼5000 GtC of conventional fossil fuel resources are emitted, and increases by a factor of ∼32 if a further 20,000 GtC of exotic fossil fuel resources are emitted. Global warming in year 3000 will also depend on climate sensitivity to doubling CO2, which is most probably ∼3°C but highly uncertain. Thermal expansion will contribute 0.5-2 m to millennial sea level rise for each doubling of CO2. The Greenland ice sheet could melt completely within the millennium under > 8 x CO2, adding a further ∼7 m to sea level. The rate of melt depends on the magnitude of forcing above a regional warming threshold of 1-3°C. The West Antarctic ice sheet could be threatened by 4-10°C local warming, and its potential contribution to millennial sea level rise exceeds current maximum estimates of ∼1 m. The fate of the ocean thermohaline circulation may depend on the rate as well as the magnitude of forcing. © Springer 2006.
Abstract.
Lenton TM, Klausmeier CA (2006). Co-evolution of phytoplankton C:N:P stoichiometry and the deep ocean N:P ratio. Biogeosciences Discussions, 3(4), 1023-1047.
Price AR, Jiao Z, Voutchkov II, Lenton TM, Williams G, Lunt DJ, Marsh R, Valdes PJ, Cox SJ, Team GENIE, et al (2006). Collaborative study of GENIEfy earth system models using scripted database workflows in a grid-enabled PSE.
Author URL.
Lunt DJ, Williamson MS, Valdes PJ, Lenton TM, Marsh R (2006). Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model.
Climate of the Past,
2(2), 221-235.
Abstract:
Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model
We examine several aspects of the ocean-atmosphere system over the last 30000 years, by carrying out simulations with prescribed ice sheets, atmospheric CO2 concentration, and orbital parameters. We use the GENIE-1 model with a frictional geostrophic ocean, dynamic sea ice, an energy balance atmosphere, and a land-surface scheme with fixed vegetation. A transient simulation, with boundary conditions derived from ice-core records and ice sheet reconstructions, is compared with equilibrium snapshot simulations, including the Last Glacial Maximum (21000 years before present; 21 kyrBP), mid-Holocene (6 kyrBP) and preindustrial. The equilibrium snapshot simulations are all very similar to their corresponding time period in the transient simulation, indicating that over the last 30000 years, the model's ocean-atmosphere system is close to equilibrium with its boundary conditions. However, our simulations neglect the transfer of fresh water from and to the ocean, resulting from the growth and decay of ice sheets, which would, in reality, lead to greater disequilibrium. Additionally, the GENIE-1 model exhibits a rather limited response in terms of its Atlantic Meridional Overturning Circulation (AMOC) over the 30000 years; a more sensitive AMOC would also be likely to lead to greater disequilibrium. We investigate the method of accelerating the boundary conditions of a transient simulation and find that the Southern Ocean is the region most affected by the acceleration. The Northern Hemisphere, even with a factor of 10 acceleration, is relatively unaffected. The results are robust to changes to several tunable parameters in the model. They also hold when a higher vertical resolution is used in the ocean.
Abstract.
Lunt DJ, Williamson MS, Valdes PJ, Lenton TM (2006). Comparing transient, accelerated, and equilibrium simulations of the last 30 000 years with the GENIE-1 model. Climate of the Past Discussions, 2(3), 267-283.
Lenton TM, Britton C (2006). Enhanced carbonate and silicate weathering accelerates recovery from fossil fuel CO<inf>2</inf> perturbations.
Global Biogeochemical Cycles,
20(3).
Abstract:
Enhanced carbonate and silicate weathering accelerates recovery from fossil fuel CO2 perturbations
Increasing atmospheric CO2 and surface temperatures should increase carbonate and silicate weathering rates, directly via warming, and indirectly via the CO2 fertilization effect enhancing plant productivity. Enhanced weathering should in turn increase alkalinity input to the ocean and accelerate long-term CO2 uptake. We added silicate and carbonate weathering and carbonate sediments to an existing global carbon cycle and surface temperature model and subjected it to a range of long-term fossil fuel emissions scenarios, spanning 1100-15,000 GtC in total. Emissions of≥7350 GtC dissolve all carbonate sediments, and enhanced carbonate and silicate weathering accelerate subsequent CO2 removal from the atmosphere by up to a factor of 4. For 1100-4000 GtC emissions, enhanced weathering accelerates CO2 removal by a factor of 1.5-2.5. However, it takes >1 Myr for silicate weathering to stabilize atmospheric CO 2. If land use tends to suppress vegetation and weathering rates on this timescale, then CO2 will stabilize above preindustrial levels. Copyright 2006 by the American Geophysical Union.
Abstract.
Boyle RA, Lenton TM (2006). Fluctuation in the physical environment as a mechanism for reinforcing evolutionary transitions.
J Theor Biol,
242(4), 832-843.
Abstract:
Fluctuation in the physical environment as a mechanism for reinforcing evolutionary transitions.
We hypothesize a mechanism for reinforcing transitions between levels of selection, involving physiological homeostasis and amplification of variation in the physical environment. Groups experience a stronger selection pressure than individuals for homeostasis with respect to reproductively limiting variables, because their greater longevity exposes them more often to suboptimal physical conditions, and greater physical size means they encompass a larger fraction of any resource/nutrient gradient. Groups achieve homeostasis by differentiation into microcosms with specialist functions, e.g. cell types. Such differentiation is more limited in individuals due to their smaller size and shorter lifespan. Hence tolerance of fluctuation in certain physical variables is proposed to be weaker in individuals than in groups. We show that a trait providing increased tolerance (alpha) to fluctuation (V-V(opt)) in a limiting abiotic variable (V), at relative fitness cost (C), can increase from rarity if the condition alpha.mid R:V-V(opt)|>C is met. Groups also sequester larger absolute quantities of resource than individuals, and group death is less frequent, hence the population dynamics of groups cause resource/nutrient availability to fluctuate with greater amplitude than that of individuals. Increasing the amplitude of fluctuation in a reproductively limiting environmental variable is proposed as a mechanism by which a group can limit reproduction of parasitic "cheat" individuals. Enhancing physical fluctuation is frequency dependent, hence only an increase in tolerance to fluctuation can explain the group's increase from rarity. However, once groups reach intermediate frequencies, a positive feedback process can be initiated in which a differentiated group enhances physical fluctuation beyond the tolerance of any "cheat", and in so doing enhances the selection pressure it experiences for homeostasis. This may help explain the persistence of transitions in individuality, and the coincidence of some such transitions with periods of change and oscillation in global scale environmental variables.
Abstract.
Author URL.
Ridgwell A, Hargreaves JC, Edwards NR, Annan JD, Lenton TM, Marsh R, Yool A, Watson A (2006). Marine geochemical data assimilation in an efficient Earth system model of global biogeochemical cycling. Biogeosciences Discussions, 3(4), 1313-1354.
Lenton TM, Williamson MS, Edwards NR, Marsh R, Price AR, Ridgwell AJ, Shepherd JG, Cox SJ (2006). Millennial timescale carbon cycle and climate change in an efficient Earth system model.
Climate Dynamics,
26(7-8), 687-711.
Abstract:
Millennial timescale carbon cycle and climate change in an efficient Earth system model
A new Earth system model, GENIE-1, is presented which comprises a 3-D frictional geostrophic ocean, phosphate-restoring marine biogeochemistry, dynamic and thermodynamic sea-ice, land surface physics and carbon cycling, and a seasonal 2-D energy-moisture balance atmosphere. Three sets of model climate parameters are used to explore the robustness of the results and for traceability to earlier work. The model versions have climate sensitivity of 2.8-3.3°C and predict atmospheric CO2 close to present observations. Six idealized total fossil fuel CO2 emissions scenarios are used to explore a range of 1,100-15,000 GtC total emissions and the effect of rate of emissions. Atmospheric CO2 approaches equilibrium in year 3000 at 420-5,660 ppmv, giving 1.5-12.5°C global warming. The ocean is a robust carbon sink of up to 6.5 GtC year-1. Under "business as usual", the land becomes a carbon source around year 2100 which peaks at up to 2.5 GtC year-1. Soil carbon is lost globally, boreal vegetation generally increases, whilst under extreme forcing, dieback of some tropical and sub-tropical vegetation occurs. Average ocean surface pH drops by up to 1.15 units. A Greenland ice sheet melt threshold of 2.6°C local warming is only briefly exceeded if total emissions are limited to 1,100 GtC, whilst 15,000 GtC emissions cause complete Greenland melt by year 3000, contributing 7 m to sea level rise. Total sea-level rise, including thermal expansion, is 0.4-10 m in year 3000 and ongoing. The Atlantic meridional overturning circulation shuts down in two out of three model versions, but only under extreme emissions including exotic fossil fuel resources. © Springer-Verlag 2006.
Abstract.
Marsh R, Smith MPLM, Rohling EJ, Lunt DJ, Lenton TM, Williamson MS, Yool A (2006). Modelling ocean circulation, climate and oxygen isotopes in the ocean over the last 120000 years. Climate of the Past Discussions, 2(5), 657-709.
Price AR, Voutchkov II, Pound GE, Edwards NR, Lenton TM, Cox SJ (2006). Multiobjective tuning of Grid-enabled earth system models using a Non-dominated Sorting Genetic Algorithm (NSGA-II).
e-Science 2006 - Second IEEE International Conference on e-Science and Grid ComputingAbstract:
Multiobjective tuning of Grid-enabled earth system models using a Non-dominated Sorting Genetic Algorithm (NSGA-II)
The tuning of parameters in climate models is essential to provide reliable long-term forecasts of Earth system behaviour. In this paper we present the first application of the multiobjective non-dominated sorting genetic algorithm (NSGA-II) to the GENIE-1 Earth System Model (ESM). Twelve model parameters are tuned to improve four objective measures of fitness to observational data. Grid computing and data handling technology is harnessed to perform the concurrent simulations that comprise the generations of the genetic algorithm. Recent advances in the method exploit Response Surface Modelling to provide surrogate models of each objective. This enables more extensive and efficient searching of the design space. We assess the performance of the NSGA-II using surrogates by repeating a tuning exercise that has been performed using a proximal analytical centre plane cutting method and the Ensemble Kalman Filter on the GENIE-1 model. We find that the multiobjective algorithm locates Pareto-optimal solutions which are of comparable quality to those obtained using the single objective optimisation methods. © 2006 IEEE.
Abstract.
Wood AJ, Ackland GJ, Lenton TM (2006). Mutation of albedo and growth response produces oscillations in a spatial Daisyworld.
J Theor Biol,
242(1), 188-198.
Abstract:
Mutation of albedo and growth response produces oscillations in a spatial Daisyworld.
We extended a two-dimensional cellular automaton (CA) Daisyworld to include mutation of optimal growth temperature as well as mutation of albedo. Thus, the organisms (daisies) can adapt to prevailing environmental conditions or evolve to alter their environment. We find the resulting system oscillates with a period of hundreds of daisy generations. Weaker and less regular oscillations exist in previous daisyworld models, but they become much stronger and more regular here with mutation in the growth response. Despite the existence of a particular combination of mean albedo and optimum individual growth temperature which maximises growth, we find that this global state is unstable with respect to mutations which lower absolute growth rate, but increase marginal growth rate. The resulting system oscillates with a period that is found to decrease with increasing death rate, and to increase with increasing heat diffusion and heat capacity. We speculate that the origin of this oscillation is a Hopf bifurcation, previously predicted in a zero-dimensional system.
Abstract.
Author URL.
Ridgwell A, Zondervan I, Hargreaves JC, Bijma J, Lenton TM (2006). Significant long-term increase of fossil fuel CO2 uptake from reduced marine calcification. Biogeosciences Discussions, 3(6), 1763-1780.
2005
Toniazzo T, Lenton TM, Cox PM, Gregory J (2005). 17 Entropy and Gaia: is There a Link Between MEP and Self-Regulation in the Climate System?. In (Ed) Non-equilibrium Thermodynamics and the Production of Entropy, 223-241.
Cameron DR, Lenton TM, Ridgwell AJ, Shepherd JG, Marsh R, Yool A (2005). A factorial analysis of the mar
