The Hysteresis of the Antarctic Ice Sheet
Date:
Virtual poster presentation (session C062 - Modeling of the Cryosphere: Glaciers and Ice Sheets) at the AGU Fall Meeting 2020 (online).
Abstract
More than half of Earth’s freshwater resources and thus by far the largest potential to raise global sea level under future warming is held by the Antarctic Ice Sheet. Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are missing a comprehensive stability analysis of the Antarctic Ice Sheet under different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeo data we find, using the Parallel Ice Sheet Model, that at global warming levels around 2 °C above pre-industrial West Antarctica is committed to long-term partial collapse due to the marine ice sheet instability. The precise threshold temperature bears some uncertainty due to model resolution and parameters. Between 6 to 9 °C of warming, the loss of more than 70 % of the present-day ice volume is triggered, mainly due to the surface elevation feedback. Above 10 °C Antarctica is committed to becoming virtually ice free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree up to 2 °C of warming, almost doubling to 2.4 m °C-1 between 2 and 6 °C and increasing to ~10 m °C-1 between 6 and 9 °C. Each of these thresholds gives rise to hysteresis behaviour, i.e. the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least -1 °C colder than pre-industrial levels. Our results show that if the Paris Climate Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources.