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Ice sheet feedbacks are underrepresented in model assessments of climate sensitivity and their magnitudes are still poorly constrained. We combine a recently published record of Earth's Energy Imbalance (EEI) with existing reconstructions of temperature, atmospheric composition, and sea level to estimate both the magnitude and timescale of the ice sheet‐albedo feedback since the Last Glacial Maximum. This facilitates the first opportunity to quantify this feedback over the most recent deglaciation using a proxy data‐driven approach. We find the ice sheet‐albedo feedback to be amplifying, increasing the total climate feedback parameter by 42% and reaching an equilibrium magnitude of 0.55 Wm−2K−1, with a 66% confidence interval of 0.45–0.63 Wm−2K−1. The timescale to equilibrium is estimated as 3.6 ka (66% confidence: 1.9–5.5 ka). These results provide new evidence for the timescale and magnitude of the amplifying ice sheet‐albedo feedback that will drive anthropogenic warming for millennia to come. During a deglacial transition, ice sheets melt and retreat, decreasing the reflectivity of the land surface and increasing the surface temperature, leading to further melting. It is agreed that this feedback amplifies global warming on millennial timescales, but the exact magnitude and timescale are still very uncertain. This is important because the stronger the feedback, the more sensitive Earth's climate is to carbon dioxide on long timescales. We use proxy data records of the past 25,000 years to quantify the ice sheet‐albedo feedback since the Last Glacial Maximum and estimate the time taken for the feedback to reach equilibrium and stabilize. We find that the ice sheet‐albedo feedback strongly amplifies warming over thousands of years, increasing our understanding of how human activity today will continue to influence our climate for generations into the future. Novel proxy data‐driven assessment of the ice sheet‐albedo feedback for the last deglaciation is presentedIce sheet‐albedo feedback is amplifying during a deglacial transition with a best estimate of 0.55 Wm−2K−1(0.45–0.63 Wm−2K−1)Ice sheet‐albedo feedback reaches equilibrium after approximately 3.6 ka (1.9–5.5 ka) Novel proxy data‐driven assessment of the ice sheet‐albedo feedback for the last deglaciation is presented Ice sheet‐albedo feedback is amplifying during a deglacial transition with a best estimate of 0.55 Wm−2K−1(0.45–0.63 Wm−2K−1) Ice sheet‐albedo feedback reaches equilibrium after approximately 3.6 ka (1.9–5.5 ka)

The surface warming response to anthropogenic forcing is highly sensitive to the strength of feedbacks in both the physical climate and carbon cycle systems. However, the definitions of climate feedback, λClimatein W·m−2·K−1, and climate sensitivity, SClimatein K/(W/m2), explicitly exclude the impact of carbon cycle feedbacks. Here we provide a new framework to incorporate carbon feedback into the definitions of climate feedback and sensitivity. Applying our framework to the Global Carbon Budget reconstructions reveals a present‐day terrestrial carbon feedback of λCarbon= 0.31 ± 0.09 W·m−2·K−1and an ocean carbon feedback of −0.06 to 0.015 W·m−2·K−1in Earth system models. Observational constraints reveal a combined climate and carbon feedback of λClimate+Carbon= 1.48 W·m−2·K−1with a 95% range of 0.76 to 2.32 W·m−2·K−1on centennial time scales, corresponding to a combined climate and carbon sensitivity of SClimate+Carbon= 0.67 K/(W/m2) with a 95% range of 0.43 to 1.32 K/(W/m2). Feedback processes in the physical climate system and the carbon cycle affect the Earth's climate response to emissions of greenhouse gases, such as carbon dioxide. Physical climate feedbacks include the responses of clouds and atmospheric water vapor to rising surface temperatures, while carbon cycle feedbacks affect how much of the emitted carbon dioxide is removed from the atmosphere and stored in the ocean and on land. Conventionally, definitions of climate feedback and climate sensitivity include all the feedbacks in the physical climate system but do not include carbon cycle feedbacks. This study provides a new framework to incorporate carbon feedback into the definitions of climate feedback and sensitivity. Evaluating the historical strengths of physical climate system and carbon cycle feedbacks suggests emissions of carbon dioxide will cause equilibrium (century time scale) surface warming to increase between 0.6 and 2.0 °C for every 1,000 PgC emitted when an equilibrium is approached between the atmosphere and the ocean over many centuries. A new method is presented for calculating the terrestrial and ocean carbon feedback from observational constraints and model simulationsThe terrestrial carbon feedback is analyzed from observational reconstructions as 0.31 ± 0.09 W·m−2·K−1The total feedback from physical climate system and carbon cycle processes is 1.48 (95% range from 0.76 to 2.32) W·m−2·K−1

The Transient Climate Response to Emissions (TCRE), the ratio of surface warming and cumulative carbon emissions, is controlled by a product of thermal and carbon contributions. The carbon contribution involves the airborne fraction and the ratio of ocean saturated and atmospheric carbon inventories, with this ratio controlled by ocean carbonate chemistry. The evolution of the carbon contribution to the TCRE is illustrated in a hierarchy of models: a box model of the atmosphere‐ocean and an Earth system model, both integrated for 1,000 years, and a suite of Earth system models integrated for 140 years. For all models, there is the same generic carbonate chemistry response: An acidifying ocean during emissions leads to a decrease in the ratio of the ocean saturated and atmospheric carbon inventories and the carbon contribution to the TCRE. Hence, ocean carbonate chemistry is important in controlling the magnitude of the TCRE and its evolution in time. The increase in surface temperature with the amount of carbon emitted to the atmosphere depends on the uptake and storage of heat and carbon. Ocean heat uptake acts to strengthen surface warming, as the ocean becomes more stratified in time. Carbon uptake by the ocean and terrestrial system acts to weaken surface warming by removing carbon from the atmosphere. The proportionality of surface warming to carbon emissions may be written in terms of a thermal contribution multiplied by a carbon contribution. The carbon contribution depends on the increase in the atmospheric carbon inventory plus the maximum amount of carbon that the ocean may hold. To understand the role of ocean chemistry, we diagnose the response of climate models of differing complexity over centennial and millennial timescales. In all the models, there is a similar carbon response: During emissions, the ocean surface acidifies and the maximum amount of carbon that the ocean can hold decreases, which weakens the carbon contribution to the proportionality of surface warming to carbon emissions. Hence, ocean carbonate chemistry is important in controlling the proportionality of surface warming to carbon emissions and its evolution in time. Transient Climate Response to Emissions (TCRE) depends on the product of thermal and carbon contributions that need not exactly compensateThe carbon contribution to the TCRE depends on the airborne fraction and the ratio of the ocean carbon saturation and atmospheric carbonAn acidifying ocean decreases the ratio of ocean carbon saturation and atmospheric carbon and so the carbon contribution to the TCRE

Climate sensitivity represents the global mean temperature change caused by changes in the radiative balance of climate; it is studied for both present/future (actuo) and past (paleo) climate variations, with the former based on instrumental records and/or various types of model simulations. Paleo-estimates are often considered informative for assessments of actuo-climate change caused by anthropogenic greenhouse forcing, but this utility remains debated because of concerns about the impacts of uncertainties, assumptions, and incomplete knowledge about controlling mechanisms in the dynamic climate system, with its multiple interacting feedbacks and their potential dependence on the climate background state. This is exacerbated by the need to assess actuo- and paleoclimate sensitivity over different timescales, with different drivers, and with different (data and/or model) limitations. Here, we visualize these impacts with idealized representations that graphically illustrate the nature of time-dependent actuo- and paleoclimate sensitivity estimates, evaluating the strengths, weaknesses, agreements, and differences of the two approaches. We also highlight priorities for future research to improve the use of paleo-estimates in evaluations of current climate change.

Climate model experiments reveal that transient global warming is nearly proportional to cumulative carbon emissions on multi-decadal to centennial timescales. However, it is not quantitatively understood how this near-linear dependence between warming and cumulative carbon emissions arises in transient climate simulations. Here, we present a theoretically derived equation of the dependence of global warming on cumulative carbon emissions over time. For an atmosphere–ocean system, our analysis identifies a surface warming response to cumulative carbon emissions of 1.5 ± 0.7 K for every 1,000 Pg of carbon emitted. This surface warming response is reduced by typically 10–20% by the end of the century and beyond. The climate response remains nearly constant on multi-decadal to centennial timescales as a result of partially opposing effects of oceanic uptake of heat and carbon. The resulting warming then becomes proportional to cumulative carbon emissions after many centuries, as noted earlier. When we incorporate estimates of terrestrial carbon uptake, the surface warming response is reduced to 1.1 ± 0.5 K for every 1,000 Pg of carbon emitted, but this modification is unlikely to significantly affect how the climate response changes over time. We suggest that our theoretical framework may be used to diagnose the global warming response in climate models and mechanistically understand the differences between their projections.

In recent years, the notion of local participation has emerged as a major force in both policy‐making and political philosophy. This paper explores the role that participation is playing in mediating relations between local people, conservation organizations and the ideas and practices of nature conservation in England. Drawing upon empirical research in the county of Kent, the paper argues that there are systematic discrepancies between the motives, experiences and understandings of the various policy actors towards the theory and practice of a participatory conservation. It argues that these apparent discrepancies have serious implications for both the credibility and the effectiveness of present initiatives, whereby participatory practice serves to reshape existing conceptions of conservation and rural space.

The climate response after cessation of carbon emissions is examined here, exploiting a single equation connecting surface warming to cumulative carbon emissions. The multicentennial response to an idealized pulse of carbon is considered by diagnosing a 1,000 year integration of an Earth system model (Geophysical Fluid Dynamics Laboratory ESM2M) and an ensemble of efficient Earth system model simulations. After emissions cease, surface temperature evolves according to (i) how much of the emitted carbon remains in the atmosphere and (ii) how much of the additional radiative forcing warms the surface rather than the ocean interior. The peak in surface temperature is delayed in time after carbon emissions cease through the decline in ocean heat uptake, which in turn increases the proportion of radiative forcing warming the surface. Eventually, after many centuries, surface temperature declines as the radiative forcing decreases through the excess atmospheric CO2being taken up by the ocean and land. Continued warming is explained using theory from a heat balance and a carbon inventory budgetPeak global warming is delayed after the cessation of carbon emissionsTiming of peak warming is controlled by the weakening of ocean heat uptake The climate response after carbon emissions cease is examined here, exploiting a combination of theory and diagnostics of an Earth system model. The multicentennial response to an idealized pulse of carbon is considered over 1,000 years. After emissions cease, surface temperature evolves according to (i) how much of the emitted carbon remains in the atmosphere and (ii) how much of the additional radiative forcing warms the surface rather than the ocean interior. Surface temperature continues to increase after carbon emissions cease through a decline in ocean heat uptake, which increases the proportion of radiative forcing warming the surface. Eventually, after many centuries, surface temperature declines as the excess atmospheric carbon dioxide is taken up by the ocean and land.

A theory for the ocean‐atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales is presented. The partial pressure of atmospheric CO2(PCO2) is related to the external CO2input (ΔΣC) at air‐sea equilibrium by: PCO2= 280 ppm exp(ΔΣC/[IA+ IO/R]), where IA, IO, and Rare the pre‐industrial values of the atmospheric CO2inventory, the oceanic dissolved inorganic carbon inventory, and the Revelle buffer factor of seawater, respectively. This analytical expression is tested with two‐ and three‐box ocean models, as well as for a version of the Massachusetts Institute of Technology general circulation model (MIT GCM) with a constant circulation field, and found to be valid by at least 10% accuracy for emissions lower than 4500 GtC. This relationship provides the stable level that PCO2reaches for a given emission size, until atmospheric carbon is reduced on weathering timescales. On the basis of the MIT GCM, future carbon emissions must be restricted to a total of 700 GtC to achieve PCO2stabilization at present‐day transient levels.

Many conservation groups operate a top down approach to public participation. Maintaining this stance will fuel further mistrust of conservation bodies amongst the public. [ABSTRACT FROM AUTHOR]