Decomposing the Drivers of Polar Amplification with a Single-Column Model

Abstract

The precise mechanisms driving Arctic amplification are still under debate. Previous attribution methods based on top-of-atmosphere energy budgets have assumed all forcings and feedbacks lead to vertically-uniform temperature changes, with any departures from this collected into the lapse-rate feedback. We propose an alternative attribution method using a single column model that accounts for the forcing-dependence of high latitude lapse-rate changes. We test this method in an idealized General Circulation Model (GCM), finding that, even though the column-integrated carbon dioxide (CO2) forcing and water vapor feedback are stronger in the tropics, they contribute to polar-amplified surface warming as they lead to bottom-heavy warming in high latitudes. A separation of atmospheric temperature changes into local and remote contributors shows that, in the absence of polar surface forcing (e.g., sea-ice retreat), changes in energy transport are primarily responsible for the polar amplified pattern of warming. The addition of surface forcing substantially increases polar surface warming and reduces the contribution of atmospheric dry static energy transport. This physically-based attribution method can be applied to comprehensive GCMs to provide a clearer view of the mechanisms behind Arctic amplification.