Future cloud changes in the Arctic: what's ice got to do with it?

A fundamental uncertainty in polar climate change is the relative importance of processes within high latitudes compared with remote forcing from lower latitudes. Another key unknown is the impact of clouds in affecting future polar climate. We address these questions for the Arctic by conducting a set of enhanced greenhouse simulations utilizing both the atmosphere-only version (CAM) of NCAR's CCSM model, as well as the fully coupled version. The experiments consist of prescribed SSTs and sea ice extent, in which both of these boundary conditions in CAM are either fixed at their modern values or at the values produced from the fully coupled, 2xCO2 CCSM simulation. We decompose the Arctic cloud response produced in a simulation with future SSTs and future sea ice globally into its component regional influences by using (1) modern SSTs globally but future Arctic sea ice coverage and (2) future SSTs globally but modern Arctic sea ice coverage. Results suggest a tight coupling between the cryosphere (sea ice) and the polar atmosphere (moisture, clouds, radiation) and that the simulated Arctic cloud increase under greenhouse forcing stems largely from reduced sea ice cover.