Assessing Antarctic Ice Sheet dynamics under temporary overshoot and long-term temperature stabilization scenarios

Current projections of Antarctic Ice Sheet dynamics during the next centuries are subject to large uncertainties both reflecting the ice sheet model setup as well as the climate pathways taken into consideration. Assessing both, we present ice sheet model projections of the Antarctic Ice Sheet’s evolution during the next centuries using PISM. We employ PISM at continental scale forced by Earth system model data tailored to specific global temperature scenarios via an adaptive greenhouse gas emissions approach. The scenarios reflect a range of transient temperature overshoot (during the 21st and 22nd century) and stabilization trajectories until the year 2500 resulting either in 1.5 °C or 3°C warming. We account for various ice sheet sensitivities and initialize PISM with a present-day state obtained by a paleo thermal spin-up and further tuned on present-day conditions. For each climate scenario, a wide range of physical parameterizations is explored, to consider different ice sheet responses. Comparing the results with a historical baseline control simulation, a relative loss of ice volume proportional to temperature rise is observed across all parameters in the various scenarios. Additionally, tipping points can be identified for certain parameterisations, beyond which no significant differences are observed between stabilization and overshoot scenarios indicating an already destabilised West Antarctic Ice Sheet at present. We compare these results with model projections based on a selection of the CMIP6 scenarios to illustrate the range of Antarctic Ice Sheet responses under uncertain future climate trajectories.