Uncertainty in future change of the Antarctic Ice Sheet forced by climate models

Abstract:

Future projections of ice sheets in response to different climate scenarios and their associated sea level change are subject to deep uncertainty, hampering a proper risk assessment of sea level rise contributed by ice sheets and enaction of mitigation/adaptation strategies. Much effort has been made in multiple ice sheet model inter-comparison projects to understand the uncertainty associated with ice sheet models, which differ in incorporated physical processes and parameterization schemes, but limited resource has been directed to a systematic evaluation of the uncertainty originated from relevant atmospheric/oceanic fields simulated by climate models. Here we drive a 3-D ice sheet model for Antarctica with the output from 22 models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) and evaluate the change in Antarctic ice sheet (AIS), an approach complementary to existing ice sheet intercomparison projects. Simulated polar climate shows a wide spread across the models, not only in modern climatological fields, but also in the amplitude of changes in future climate scenarios. Simulations forced by climate models' modern climatological fields show substantial difference in the equilibrium state of AIS; with the forcings from a few models the West Antarctic ice sheet would partially collapse. Simulations forced by 1850-2100 transient climate fields adjusted against reanalysis data display a large spread in the changes in AIS's volume, comparable to the uncertainty originating from differing ice sheet models. These highlight the urgent need of better representations of physical processes important for polar climate in climate models.