Reply on RC1

Abstract

Antarctic Ice Sheet (AIS) mass loss can be mitigated by an increase in surface mass balance (SMB) which is impacted by the ice sheet's surface climate. Because of Antarctica’s remoteness, in-situ observations of its surface climate are spatially and temporally sparse, limiting our understanding of how the surface climate, and therefore SMB, are changing. To that end, Earth System Models (ESMs) fill an important gap, allowing us to explore components of the AIS climate system, both historically and under future climate change scenarios. Here, we present and analyze output of the most recent version of the National Center for Atmospheric Research’s ESM: the Community Earth System Model version 2 (CESM2). We compare AIS surface climate and SMB as simulated by CESM2 with regional climate models and observations. We find that CESM2 substantially better represents AIS near-surface temperature, wind speed, and surface melt compared with its predecessor, CESM1, which is likely a result of the inclusion of new cloud microphysical parameterizations and changes made to the snow model. However, CESM2 SMB is shown to be biased high, particularly because of excessive precipitation. ESMs such as CESM2 are used as forcing for ice sheet models, which provide estimates and projections of ice sheet contribution to sea level rise. Thus, it is important to fully understand the limitations and biases of this climate model forcing. This study provides a comprehensive analysis of the strengths and weaknesses of CESM2 representation of AIS surface climate, which will be especially useful in preparation for CESM3, which plans to incorporate a coupled Antarctic Ice Sheet that interacts with the ocean and atmosphere.