Clouds Are Crucial to Capture Antarctic Sea Ice Variability

Abstract

Models from the Coupled Model Intercomparison Project phase 6 (CMIP6) typically struggle to reproduce observed Antarctic sea ice trends, a bias that is substantially alleviated when constraining winds. We use wind-nudged simulations from two CMIP models to investigate the influence of clouds on sea ice area (SIA). We find that nudging model winds in coupled simulations toward reanalysis, in addition to improving SIA variability, is crucial to reproduce realistic anomalies in cloud radiative effect (CRE) and cloud cover. Biases in the variability of cloud properties at sea ice edge—characterized by CRE anomalies—help explain the remaining discrepancies between simulated and observed SIA; a bias of 1 (Formula presented.) in the CRE anomaly corresponds to a negative bias of 0.43 (Formula presented.) in SIA anomaly. Finally, we find that most CMIP6 models show positive trends in CRE anomaly biases, which should contribute to enhanced SIA decline, a long-standing bias in CMIP models.