The seasonal, polar-amplified climate response to a latent heat transport forcing

Abstract Polar amplification is a well-documented phenomenon driven by multiple feedback mechanisms, with latent heat transport (LHT) playing a role that is often underestimated. Although the total atmospheric energy transport into polar regions remains nearly unchanged in warming scenarios, compensating changes in dry static and latent energy transport interact with polar-amplified surface warming: dry static energy transport generally decreases due to a reduction in meridional temperature gradient, while the latent energy transport increases, contributing to polar warming by enhancing moisture. To isolate the impact of LHT changes, we lock the moisture advection in an idealized general circulation model (GCM) and apply it as a forcing. Simulations forced with an increase in LHT, equivalent to that which would be produced by a doubling of CO 2 , consistently demonstrate substantial polar warming, providing a different perspective from the conventional feedback analysis that attributes polar amplification predominantly to the ice-albedo feedback and lapse-rate feedback. The GCM is coupled to a thermodynamic sea ice model, which allows the role of sea ice to be examined by systematically disabling sea ice-LHT interactions. Sea ice loss strongly enhances annual mean polar amplification and wintertime polar warming, and is itself a response to the increase in LHT. We additionally provide a quantitative comparison of different metrics of LHT-induced polar amplification. These findings suggest that diagnostic decompositions, by only quantifying the enhanced LHT into polar regions and neglecting its impact on polar feedbacks, underestimate the role of LHT as a significant driver of polar amplification.