State‐Dependence of Polar Amplification in an Idealized GCM

Abstract Polar amplification (PA) is a robust feature of contemporary climate change, but its state‐dependence across different climate conditions is poorly understood despite potential relevance to paleoclimate records and future projections. Here we examine the state‐dependence of PA across a wide range of climate states in an idealized moist general circulation model. We generate a phase space of climate states with different global‐mean surface temperatures and equator‐to‐pole surface temperature contrasts then perturb each with longwave radiative forcing. We find that the state‐dependence of PA is largely a superposition of two effects. Firstly, as a consequence of moist thermodynamics, latent energy transport drives stronger PA in climates with higher global‐mean surface temperatures and stronger meridional surface temperature gradients. On top of this, the ice‐albedo feedback amplifies PA in climates where the climatological ice edge sits within the polar cap.