The hysteresis of the Antarctic Ice Sheet
More than half of Earth’s freshwater resources are held frozen in the Antarctic Ice Sheet, making the ice sheet the single largest potential source for global sea-level rise under future warming. At the same time, its future evolution will be determined by the interplay of several strong feedbacks between the ice and its environment, implying threshold behavior and the existence of tipping points in its response to future warming.
In this paper, which has been published a few weeks ago in Nature, researchers from the Potsdam Institute for Climate Impact Research, Potsdam University and New York’s Columbia University, led by TiPACCs co-PI Ricarda Winkelmann, present model results that show how vulnerable the Antarctic Ice Sheet is to global warming. The study identifies the ice sheet’s tipping points which are associated with the non-linear behavior of the ice flow.
Beyond these critical temperature thresholds ice loss is self-sustained: If those temperatures would last for long enough the ice loss does not stop until a new equilibrium is reached. The authors show that ice loss resulting from the passing of these thresholds is in fact irreversible. This is the ‘hysteresis’ characteristic of the ice sheet: Once one or more thresholds have been crossed the ice sheet does not regrow to its original extent even if temperatures were to sink to lower values. To restore the ice sheet to its current form would require a cooling to lower than pre-industrial levels.
Moreover, their results imply that with increasing global temperatures, the ice sheet becomes progressively more sensitive to a given amount of warming: Up to 2 degrees above preindustrial (as aimed for in the Paris Agreement), the long-term ice losses per degree of warming correspond to about 1.3 meters of equivalent sea-level rise (i.e. at 2 degrees Antarctica contributes more than 2.5 meters to global sea-level rise). Between 2 and 6 degrees this value almost doubles to 2.4 meters per degree of warming and for temperatures between 6 and 9 degrees, it is increasing to about 10 meters per degree of warming.
The results of this study emphasize the urgency to adhere to the global warming limits set out in the Paris Agreement: If they are not met, Antarctica’s long-term contribution to sea levels will dramatically increase and will be close to impossible to reverse.
Weblink to the paper: https://doi.org/10.1038/s41586-020-2727-5