Recent studies have focused on the short-term contribution of the Greenland ice sheet to sea-level rise, yet little is known about its long-term stability. The present best estimate of the threshold in global temperature rise leading to complete melting of the ice sheet is 3.1 °C (1.9–5.1 °C, 95% confidence interval) above the preindustrial climate1, determined as the temperature for which the modelled surface mass balance of the present-day ice sheet turns negative. Here, using a fully coupled model, we show that this criterion systematically overestimates the temperature threshold and that the Greenland ice sheet is more sensitive to long-term climate change than previously thought. We estimate that the warming threshold leading to a monostable, essentially ice-free state is in the range of 0.8–3.2 °C, with a best estimate of 1.6 °C. By testing the ice sheet’s ability to regrow after partial mass loss, we find that at least one intermediate equilibrium state is possible, though for sufficiently high initial temperature anomalies, total loss of the ice sheet becomes irreversible. Crossing the threshold alone does not imply rapid melting (for temperatures near the threshold, complete melting takes tens of millennia). However, the timescale of melt depends strongly on the magnitude and duration of the temperature overshoot above this critical threshold.
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We would like to thank R. Greve for providing us with the ice-sheet model SICOPOLIS. We are also grateful to K. Frieler for providing the AOGCM scaling coefficients and to M. Perrette and J. Rougier for support concerning statistics. We acknowledge the modelling groups, the Program for Climate Model Diagnosis and Intercomparison and the World Climate Research Programme’s Working Group on Coupled Modelling for their roles in making available the World Climate Research Programme CMIP3 multimodel data set. Support of this data set is provided by the Office of Science, US Department of Energy. A.R. was financially supported by the European Commission’s Marie Curie 6th Framework Programme and by the Spanish Ministry of the Environment under project 200800050084028. R.C. was financially supported by the Deutsche Forschungsgemeinschaft grant RA 977/6-1.
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Response of the North Atlantic surface and intermediate ocean structure to climate warming of MIS 11
Scientific Reports (2017)