Evolution of heat fluxes at the Arctic sea-ice edge

We analyze the evolution of heat fluxes and the resulting surface energy balance at the Arctic sea-ice edge in CMIP6 model simulations. We build on the study of Notz and Stroeve (2016), in which they show the existence of a strong linear relationship between Arctic sea-ice area and cumulative anthropogenic CO₂ emissions. In explaining this linear relationship, the authors claim that the surface energy balance at the sea-ice edge remains constant, following the conceptual idea of the sea-ice edge retreating northwards to compensate for the increasing longwave radiative input due to global warming by a decrease in shortwave radiation at higher latitudes. We examine the validity of this hypothesis by first identifying the sea-ice edge in the model data, and then scrutinize whether or not the surface energy balance at that location stays constant under future sea-ice retreat. Furthermore, we decompose the energy balance into its constituents to explore dynamical effects and oceanic influence.

We find that the annual mean surface energy balance shows stronger spatial than temporal variations. Looking at individual months, we find that the surface energy balance is negative in winter and positive in summer along the ice edge. Towards the end of the 21^st century, the surface energy balance enters a new regime, becoming less negative in winter, and more positive in summer. By showing a consistently negative relation between downwelling shortwave radiation and downwelling longwave radiation, we finally confirm the idea of the compensation of increasing longwave input by a decrease in shortwave incoming radiation due to a northward migration of the sea-ice edge.