TY - JOUR A1 - Levermann, Anders A1 - Winkelmann, Ricarda T1 - A simple equation for the melt elevation feedback of ice sheets JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - In recent decades, the Greenland Ice Sheet has been losing mass and has thereby contributed to global sea-level rise. The rate of ice loss is highly relevant for coastal protection worldwide. The ice loss is likely to increase under future warming. Beyond a critical temperature threshold, a meltdown of the Greenland Ice Sheet is induced by the self-enforcing feedback between its lowering surface elevation and its increasing surface mass loss: the more ice that is lost, the lower the ice surface and the warmer the surface air temperature, which fosters further melting and ice loss. The computation of this rate so far relies on complex numerical models which are the appropriate tools for capturing the complexity of the problem. By contrast we aim here at gaining a conceptual understanding by deriving a purposefully simple equation for the self-enforcing feedback which is then used to estimate the melt time for different levels of warming using three observable characteristics of the ice sheet itself and its surroundings. The analysis is purely conceptual in nature. It is missing important processes like ice dynamics for it to be useful for applications to sea-level rise on centennial timescales, but if the volume loss is dominated by the feedback, the resulting logarithmic equation unifies existing numerical simulations and shows that the melt time depends strongly on the level of warming with a critical slow-down near the threshold: the median time to lose 10% of the present-day ice volume varies between about 3500 years for a temperature level of 0.5 degrees C above the threshold and 500 years for 5 degrees C. Unless future observations show a significantly higher melting sensitivity than currently observed, a complete meltdown is unlikely within the next 2000 years without significant ice-dynamical contributions. Y1 - 2016 U6 - https://doi.org/10.5194/tc-10-1799-2016 SN - 1994-0416 SN - 1994-0424 VL - 10 SP - 1799 EP - 1807 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Schleussner, Carl-Friedrich A1 - Donges, Jonathan Friedemann A1 - Engemann, Denis A. A1 - Levermann, Anders T1 - Clustered marginalization of minorities during social transitions induced by co-evolution of behaviour and network structure JF - Scientific reports N2 - Large-scale transitions in societies are associated with both individual behavioural change and restructuring of the social network. These two factors have often been considered independently, yet recent advances in social network research challenge this view. Here we show that common features of societal marginalization and clustering emerge naturally during transitions in a co-evolutionary adaptive network model. This is achieved by explicitly considering the interplay between individual interaction and a dynamic network structure in behavioural selection. We exemplify this mechanism by simulating how smoking behaviour and the network structure get reconfigured by changing social norms. Our results are consistent with empirical findings: The prevalence of smoking was reduced, remaining smokers were preferentially connected among each other and formed increasingly marginalized clusters. We propose that self-amplifying feedbacks between individual behaviour and dynamic restructuring of the network are main drivers of the transition. This generative mechanism for co-evolution of individual behaviour and social network structure may apply to a wide range of examples beyond smoking. Y1 - 2016 U6 - https://doi.org/10.1038/srep30790 SN - 2045-2322 VL - 6 SP - 3407 EP - 3417 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Clark, Peter U. A1 - Shakun, Jeremy D. A1 - Marcott, Shaun A. A1 - Mix, Alan C. A1 - Eby, Michael A1 - Kulp, Scott A1 - Levermann, Anders A1 - Milne, Glenn A. A1 - Pfister, Patrik L. A1 - Santer, Benjamin D. A1 - Schrag, Daniel P. A1 - Solomon, Susan A1 - Stocker, Thomas F. A1 - Strauss, Benjamin H. A1 - Weaver, Andrew J. A1 - Winkelmann, Ricarda A1 - Archer, David A1 - Bard, Edouard A1 - Goldner, Aaron A1 - Lambeck, Kurt A1 - Pierrehumbert, Raymond T. A1 - Plattner, Gian-Kasper T1 - Consequences of twenty-first-century policy for multi-millennial climate and sea-level change JF - Nature climate change N2 - Most of the policy debate surrounding the actions needed to mitigate and adapt to anthropogenic climate change has been framed by observations of the past 150 years as well as climate and sea-level projections for the twenty-first century. The focus on this 250-year window, however, obscures some of the most profound problems associated with climate change. Here, we argue that the twentieth and twenty-first centuries, a period during which the overwhelming majority of human-caused carbon emissions are likely to occur, need to be placed into a long-term context that includes the past 20 millennia, when the last Ice Age ended and human civilization developed, and the next ten millennia, over which time the projected impacts of anthropogenic climate change will grow and persist. This long-term perspective illustrates that policy decisions made in the next few years to decades will have profound impacts on global climate, ecosystems and human societies - not just for this century, but for the next ten millennia and beyond. Y1 - 2016 U6 - https://doi.org/10.1038/NCLIMATE2923 SN - 1758-678X SN - 1758-6798 VL - 6 SP - 360 EP - 369 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Frieler, Katja A1 - Mengel, M. A1 - Levermann, Anders T1 - Delaying future sea-level rise by storing water in Antarctica JF - Earth system dynamics N2 - Even if greenhouse gas emissions were stopped today, sea level would continue to rise for centuries, with the long-term sea-level commitment of a 2 degrees C warmer world significantly exceeding 2 m. In view of the potential implications for coastal populations and ecosystems worldwide, we investigate, from an ice-dynamic perspective, the possibility of delaying sea-level rise by pumping ocean water onto the surface of the Antarctic ice sheet. We find that due to wave propagation ice is discharged much faster back into the ocean than would be expected from a pure advection with surface velocities. The delay time depends strongly on the distance from the coastline at which the additional mass is placed and less strongly on the rate of sea-level rise that is mitigated. A millennium-scale storage of at least 80% of the additional ice requires placing it at a distance of at least 700 km from the coastline. The pumping energy required to elevate the potential energy of ocean water to mitigate the currently observed 3 mmyr(-1) will exceed 7% of the current global primary energy supply. At the same time, the approach offers a comprehensive protection for entire coastlines particularly including regions that cannot be protected by dikes. Y1 - 2016 U6 - https://doi.org/10.5194/esd-7-203-2016 SN - 2190-4979 SN - 2190-4987 VL - 7 SP - 203 EP - 210 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Wenz, Leonie A1 - Levermann, Anders T1 - Enhanced economic connectivity to foster heat stress-related losses JF - Science Advances N2 - Assessing global impacts of unexpected meteorological events in an increasingly connected world economy is important for estimating the costs of climate change. We show that since the beginning of the 21st century, the structural evolution of the global supply network has been such as to foster an increase of climate-related production losses. We compute first- and higher-order losses from heat stress-induced reductions in productivity under changing economic and climatic conditions between 1991 and 2011. Since 2001, the economic connectivity has augmented in such a way as to facilitate the cascading of production loss. The influence of this structural change has dominated over the effect of the comparably weak climate warming during this decade. Thus, particularly under future warming, the intensification of international trade has the potential to amplify climate losses if no adaptation measures are taken. Y1 - 2016 U6 - https://doi.org/10.1126/sciadv.1501026 SN - 2375-2548 VL - 2 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Geiger, Tobias A1 - Frieler, Katja A1 - Levermann, Anders T1 - High-income does not protect against hurricane losses JF - Environmental research letters N2 - Damage due to tropical cyclones accounts for more than 50% of all meteorologically-induced economic losses worldwide. Their nominal impact is projected to increase substantially as the exposed population grows, per capita income increases, and anthropogenic climate change manifests. So far, historical losses due to tropical cyclones have been found to increase less than linearly with a nation's affected gross domestic product (GDP). Here we show that for the United States this scaling is caused by a sub-linear increase with affected population while relative losses scale super-linearly with per capita income. The finding is robust across a multitude of empirically derived damage models that link the storm's wind speed, exposed population, and per capita GDP to reported losses. The separation of both socio-economic predictors strongly affects the projection of potential future hurricane losses. Separating the effects of growth in population and per-capita income, per hurricane losses with respect to national GDP are projected to triple by the end of the century under unmitigated climate change, while they are estimated to decrease slightly without the separation. KW - climate change KW - tropical cyclones KW - damage KW - meteorological extremes KW - vulnerability Y1 - 2016 U6 - https://doi.org/10.1088/1748-9326/11/8/084012 SN - 1748-9326 VL - 11 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Mengel, Matthias A1 - Feldmann, Johannes A1 - Levermann, Anders T1 - Linear sea-level response to abrupt ocean warming of major West Antarctic ice basin JF - Nature climate change N2 - Antarctica’s contribution to global sea-level rise has recently been increasing1. Whether its ice discharge will become unstable and decouple from anthropogenic forcing2,3,4 or increase linearly with the warming of the surrounding ocean is of fundamental importance5. Under unabated greenhouse-gas emissions, ocean models indicate an abrupt intrusion of warm circumpolar deep water into the cavity below West Antarctica’s Filchner–Ronne ice shelf within the next two centuries6,7. The ice basin’s retrograde bed slope would allow for an unstable ice-sheet retreat8, but the buttressing of the large ice shelf and the narrow glacier troughs tend to inhibit such instability9,10,11. It is unclear whether future ice loss will be dominated by ice instability or anthropogenic forcing. Here we show in regional and continental-scale ice-sheet simulations, which are capable of resolving unstable grounding-line retreat, that the sea-level response of the Filchner–Ronne ice basin is not dominated by ice instability and follows the strength of the forcing quasi-linearly. We find that the ice loss reduces after each pulse of projected warm water intrusion. The long-term sea-level contribution is approximately proportional to the total shelf-ice melt. Although the local instabilities might dominate the ice loss for weak oceanic warming12, we find that the upper limit of ice discharge from the region is determined by the forcing and not by the marine ice-sheet instability. Y1 - 2016 U6 - https://doi.org/10.1038/NCLIMATE2808 SN - 1758-678X SN - 1758-6798 VL - 6 SP - 71 EP - + PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Schleussner, Carl-Friedrich A1 - Rogelj, Joeri A1 - Schaeffer, Michiel A1 - Lissner, Tabea A1 - Licker, Rachel A1 - Fischer, Erich M. A1 - Knutti, Reto A1 - Levermann, Anders A1 - Frieler, Katja A1 - Hare, William T1 - Science and policy characteristics of the Paris Agreement temperature goal JF - Nature climate change Y1 - 2016 U6 - https://doi.org/10.1038/NCLIMATE3096 SN - 1758-678X SN - 1758-6798 VL - 6 SP - 827 EP - 835 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Feldmann, Johannes A1 - Levermann, Anders T1 - Similitude of ice dynamics against scaling of geometry and physical parameters JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - The concept of similitude is commonly employed in the fields of fluid dynamics and engineering but rarely used in cryospheric research. Here we apply this method to the problem of ice flow to examine the dynamic similitude of isothermal ice sheets in shallow-shelf approximation against the scaling of their geometry and physical parameters. Carrying out a dimensional analysis of the stress balance we obtain dimensionless numbers that characterize the flow. Requiring that these numbers remain the same under scaling we obtain conditions that relate the geometric scaling factors, the parameters for the ice softness, surface mass balance and basal friction as well as the ice-sheet intrinsic response time to each other. We demonstrate that these scaling laws are the same for both the (two-dimensional) flow-line case and the three-dimensional case. The theoretically predicted ice-sheet scaling behavior agrees with results from numerical simulations that we conduct in flow-line and three-dimensional conceptual setups. We further investigate analytically the implications of geometric scaling of ice sheets for their response time. With this study we provide a framework which, under several assumptions, allows for a fundamental comparison of the ice-dynamic behavior across different scales. It proves to be useful in the design of conceptual numerical model setups and could also be helpful for designing laboratory glacier experiments. The concept might also be applied to real-world systems, e.g., to examine the response times of glaciers, ice streams or ice sheets to climatic perturbations. Y1 - 2016 U6 - https://doi.org/10.5194/tc-10-1753-2016 SN - 1994-0416 SN - 1994-0424 VL - 10 SP - 1753 EP - 1769 PB - Copernicus CY - Göttingen ER -