Quantifying the role of local and remote processes in polar amplification
The surface temperature response to greenhouse gas forcing displays a characteristic polar amplification (PA) pattern, particularly in the Northern Hemisphere. The relative importance of individual processes in causing it are still debated. While some studies highlight the importance of the surface albedo feedback, others dispute its dominance and stress larger contributions from long-wave feedbacks, specifically the lapse rate feedback. Additionally, northward atmospheric and oceanic heat transport has been proposed to be important. Here we use a prognostic model hierarchy simulating CO2 forcing in different geographical regions to determine the respective roles of remote and local radiative forcing for PA. We quantify the individual feedback processes, as well as the role of heat uptake and transport. The climate response to forcing and associated feedbacks in different regions is largely linear, even when accounting for ocean circulation feedback. Importantly, PA is found to be dominated by polar forcing, while forcing from the tropics and midlatitudes make negligible contributions. The relative contribution of each feedback, as well as the role of meridional heat transport, to polar warming strongly depend on the forcing pattern. The dominant feedback for PA is the lapse rate, while Planck and albedo contribute less. The cloud feedback has a small contribution to Arctic warming in our simulations. We propose that using a similar experiment hierarchy in different models should strengthen our confidence in the quantification of feedbacks in response to different radiative forcing patterns.