Comparing the robustness of the coupled circulation response to high and low latitude forcing
Four fully coupled climate models, CESM1, CanESM2, CNRM-CM5 and GFDL-CM3Z are used to isolate the impact of Arctic sea ice loss on the atmosphere. In all models, Arctic sea ice is melted in isolation from the effects of external radiative forcing. However the method through which this melting is achieved, as well as the radiative forcing protocol, differs between the sets of experiments. Nonetheless, several aspects of the wintertime response are remarkably robust. Arctic sea ice loss in coupled models produces warming that is strongest over the Arctic Ocean and high latitude land masses alongside a weak cooling over eastern Eurasia, a dipole pattern in sea level pressure with lower pressure over North America and higher pressure over Eurasia, a strengthening of 850 hPa zonal winds in mid-latitudes along with a weakening on the poleward side, and an increase in precipitation over northern high latitudes. Because there are different amounts of warming at lower latitudes between the models, a pattern scaling approach is used to separate out the part of the pattern that scales with low-latitude warming and the part that scales with sea ice loss. The similarity in the part that scales with sea ice loss remains after applying pattern scaling, but the part of the pattern that scales with low-latitude warming is model-dependent.