Polar Amplification in Idealized Climates: The Role of Ice, Moisture, and Seasons

Abstract

The drivers of polar amplification are investigated by isolating the role of sea-ice processes, moist energy transport, and the seasonal cycle of insolation in two models, an energy balance model and an idealized general circulation model. Compared to a simple ice-albedo feedback (temperature-dependent surface albedo), the addition of thermodynamic-ice processes and the seasonal cycle of insolation profoundly affects seasonal polar warming. Climatologically limited-extent ice in the warm season permits only small increases in absorbed solar radiation, producing weak warming, while thick, cold ice in the cold season enables a large radiatively forced response. Despite this enhanced winter warming, the annual-mean polar amplification is modestly reduced by thermodynamic-ice processes. When latent heat transport is disabled, polar amplification is further reduced by a factor of 1.8 across the range of ice representations, suggestive of a nearly additive warming by ice and moist-transport processes.