Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> It is virtually certain that Antarctica's contribution to sea-level rise will increase with future warming, although competing mass balance processes hamper accurate quantification of the exact magnitudes. Today, ocean-induced melting underneath the floating ice shelves dominates mass losses, but melting at the surface will gain importance as global warming continues. Meltwater at the ice surface has crucial implications for the ice sheet's stability, as it increases the risk of hydrofracturing and ice-shelf collapse that could cause enhanced glacier outflow into the ocean. Simultaneously, positive feedbacks between the atmosphere and the ice elevation and albedo can accelerate mass losses and increase the ice sheet's sensitivity to warming. However, due to long response times it may take hundreds to thousands of years until the ice sheet fully adjusts to the environmental changes. Therefore, ice sheet model simulations must be computationally fast and capture the relevant feedbacks, including the ones at the ice–atmosphere interface. Here we use the novel surface melt module dEBM-simple, coupled to the Parallel Ice Sheet Model (PISM), to estimate the impact of 21<sup>st</sup>-century atmospheric warming on Antarctic surface melt and long-term ice dynamics. As an enhancement compared to the widely adopted positive degree-day (PDD) scheme, dEBM-simple includes an implicit diurnal cycle and computes melt not only from the temperature, but also from the influence of solar radiation and changes in ice albedo, thus accounting for the melt–albedo feedback. We calibrate PISM-dEBM-simple to reproduce historical and present-day Antarctic surface melt rates given by the regional climate model RACMO2.3p2 and use the calibrated model to assess the range of possible future surface melt trajectories under SSP5-8.5 warming projections, extended beyond 2100 under fixed climatological conditions. Our findings reveal a substantial speed-up in ice flow associated with large-scale elevation reductions in sensitive ice-sheet regions, underscoring the critical role of self-reinforcing ice-sheet–atmosphere feedbacks on future mass losses and sea-level contribution from the Antarctic Ice Sheet on centennial to millennial timescales.
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