Global Coupled Climate Response to Polar Sea Ice Loss: Evaluating the Effectiveness of Different Ice-Constraining Approaches

Coupled ocean-atmosphere models have been utilized to investigate the global climate response to polar sea ice loss using different approaches to constrain ice concentration and thickness. The goal of this study is to compare two commonly used methods within a single model framework: ice albedo reduction, which is energy conserving, and ice-flux nudging, which is not energy conserving. The two approaches generate virtually identical equilibrium global climate responses to the same seasonal cycle of sea ice loss. However, while ice-flux nudging is able to control the sea ice state year-round, albedo reduction is most effective during summer and lessens the effects of climate change in winter due to the underestimation of sea ice loss. These evaluations have implications for the Polar Amplification Model Intercomparison Project (PAMIP), which proposes a set of coordinated coupled model experiments but without a defined protocol on how to constrain sea ice.