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Zusammenfassung:
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 Sheet1. 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 data2 we find, using the
Parallel Ice Sheet Model3,4,5, 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.