­­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 constraining ice concentration and thickness. The goal of this study is to compare two commonly used methods: albedo reduction, which is energy conserving, and ice-flux (or similar "ghost flux") nudging, which is not energy conserving. Through a pair of CCSM4 experiments it is shown that when given approximately the same Arctic and Antarctic sea ice loss, the albedo and nudging approaches generate virtually identical equilibrium global climate responses. However, albedo reduction is ineffective in winter and thus this approach underestimates the projected local and remote impacts of sea ice loss. The nudging approaches are effective year-round. These evaluations have implications for the Polar Amplification Model Intercomparison Project (PAMIP), which proposes a coordinated set of coupled experiments but without a defined protocol on how to constrain sea ice.