UC Santa Cruz

Abstract: The ice–albedo feedback associated with sea ice loss contributes to polar amplification, while the water vapor feedback contributes to tropical amplification of surface warming. However, these feedbacks are not independent of atmospheric energy transport, raising the possibility of complex interactions that may obscure the drivers of polar amplification, in particular its manifestation across the seasonal cycle. Here, we apply a radiative transfer hierarchy to an idealized aquaplanet global climate model coupled to a thermodynamic sea ice model. The climate responses and radiative feedbacks are decomposed into the contributions from sea ice loss, including both retreat and thinning, and the radiative effect of water vapor changes. We find that summer sea ice retreat causes winter polar amplification through ocean heat uptake and release, and the resulting decrease in dry energy transport weakens the magnitude of warming. Moreover, sea ice thinning is found to suppress summer warming and enhance winter warming, additionally contributing to winter amplification. The water vapor radiative effect produces seasonally symmetric polar warming via offsetting effects: enhanced moisture in the summer hemisphere induces the summer water vapor feedback and simultaneously strengthens the winter latent energy transport in the winter hemisphere by increasing the meridional moisture gradient. These results reveal the importance of changes in atmospheric energy transport induced by sea ice retreat and increased water vapor to seasonal polar amplification, elucidating the interactions among these physical processes.