| Summary: | Observations of ocean-driven grounding line retreat in the Amundsen Sea Embayment in Antarctica raise the question of an imminent collapse of the West Antarctic Ice Sheet. Here we analyse (1) whether the Antarctic grounding lines are undergoing a Marine Ice Sheet Instability in their current position and (2) the committed evolution of Antarctic grounding lines under the present-day ocean and atmospheric conditions. To this aim, we first calibrate a sub-shelf melt parameterisation, that is derived from an ocean box model, with observed and modelled melt sensitivities to ocean temperature changes, making it suitable for present-day simulations and future sea-level projections. Using the new calibration, we conduct a systematic numerical stability analysis of all the grounding lines of the Antarctic Ice Sheet to determine if they are currently undergoing irreversible retreat. In a second step, we run an ensemble of historical simulations from 1850 to 2015 to create model instances of possible present-day ice sheet configurations. Then, we investigate the long-term ice sheet evolution and reversibility under constant bathymetry and present-day climate and ocean forcing.
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