Understanding the Seasonal Cycle of Polar Warming

Using the climate feedback response analysis method, we examine the individual contributions of the anthropogenic radiative forcing and climate feedbacks to the magnitude, spatial pattern, and seasonality of the transient polar surface warming response in a 1% per year CO2 increase simulation of the NCAR CCSM4. The polar warming has a pronounced seasonal cycle, with maximum warming in fall/winter and minimum warming in summer. In summer, the large cancelations between the shortwave and longwave cloud feedbacks and between the surface albedo feedback warming and the cooling from the ocean heat storage/dynamics feedback lead to a warming minimum. In polar winter, albedo and shortwave cloud feedbacks are nearly absent due to a lack of insolation. However, the ocean heat storage feedback relays the warming due to the surface albedo feedback from summer to winter polar warming, and the longwave cloud feedback warms the polar surface. Therefore, the seasonal variations in cloud, surface albedo, and ocean heat storage/dynamics feedbacks, directly caused by the strong annual cycle of insolation, contribute primarily to the large seasonal variation of polar warming.