Abstract
Abstract. The Antarctic ice sheet's contribution to global sea level rise over the 21st century is of primary societal importance and remains largely uncertain as of yet. In particular, in the recent literature, the contribution of the Antarctic ice sheet by 2100 can be negative (sea level fall) by a few centimetres or positive (sea level rise), with some estimates above 1 m. The Ice Sheet Model Intercomparison Project for the Coupled Model Intercomparison Project – phase 6 (ISMIP6) aimed at reducing the uncertainties in the fate of the ice sheets in the future by gathering various ice sheet models in a common framework. Here, we present the GRISLI-LSCE (Grenoble Ice Sheet and Land Ice model of the Laboratoire des Sciences du Climat et de l'Environnement) contribution to ISMIP6-Antarctica. We show that our model is strongly sensitive to the climate forcing used, with a contribution of the Antarctic ice sheet to global sea level rise by 2100 that ranges from −50 to +150 mm sea level equivalent (SLE). Future oceanic warming leads to a decrease in thickness of the ice shelves, resulting in grounding-line retreat, while increased surface mass balance partially mitigates or even overcompensates the dynamic ice sheet contribution to global sea level rise. Most of the ice sheet changes over the next century are dampened under low-greenhouse-gas-emission scenarios. Uncertainties related to sub-ice-shelf melt rates induce large differences in simulated grounding-line retreat, confirming the importance of this process and its representation in ice sheet models for projections of the Antarctic ice sheet's evolution.
Highlights
The Greenland and Antarctic ice sheets are the largest source for the observed global mean sea level rise behind the thermosteric and the glacier contributions (Nerem et al, 2018)
We have presented the GRISLI-LSCE contribution to Intercomparison Project for Coupled Model Intercomparison Project – phase 6 (CMIP6) (ISMIP6)-Antarctica, providing the means to investigate the impact of the climate forcing on one individual ice sheet model
We showed that the total mass change simulated by 2100 is strongly dependant on the general circulation model used to force the ice sheet model
Summary
The Greenland and Antarctic ice sheets are the largest source for the observed global mean sea level rise behind the thermosteric and the glacier contributions (Nerem et al, 2018). While the ice sheet was probably in a quasi mass equilibrium in the 1980s (Rignot et al, 2019), it has since lost ice at an accelerated pace, contributing 7.6 mm to the global sea level rise over 1992–2017 (The IMBIE team, 2018). The largest changes are observed in West Antarctica, with increased ice discharge (Gardner et al, 2018) and increased ice shelf mass loss (Paolo et al, 2015). These recent changes might have already triggered mechanical instabilities (Favier et al, 2014) that could lead to an irreversible retreat of the grounding line over large sectors of the ice sheet. While the acceleration of mass loss is mostly associated with ocean warming, the increased precipitation related to climate change can partially mitigate the ice sheet contribution to sea level rise in the future (Palerme et al, 2017; Medley and Thomas, 2019)
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