Multimodel Evidence for an Atmospheric Circulation Response to Arctic Sea Ice Loss in the CMIP5 Future Projections

Previous single-model experiments have found that Arctic sea ice loss can influence the atmospheric circulation. To evaluate this process in a multimodel ensemble, a novel methodology is here presented and applied to infer the influence of Arctic sea ice loss in the CMIP5 future projections. Sea ice influence is estimated by comparing the circulation response in the RCP8.5 scenario against the circulation response to sea surface warming and CO2 increase inferred from the AMIPFuture and AMIP4xCO2 experiments, where sea ice is unperturbed. Multimodel evidence of the impact of sea ice loss on midlatitude atmospheric circulation is identified in late winter (January-March), when the sea ice-related surface heat flux perturbation is largest. Sea ice loss acts to suppress the projected poleward shift of the North Atlantic jet, to increase surface pressure in northern Siberia, and to lower it in North America. These features are consistent with previous single-model studies, and the present results indicate that they are robust to model formulation. Plain Language Summary How the atmospheric circulation will respond to climate change in the coming decades remains uncertain. The loss of Arctic sea ice has been identified as one of the factors that can influence atmospheric circulation, and a better understanding of this connection is important to improve our confidence in the regional impacts of climate change. To do this, we have analyzed future climate projections from computer simulations based on a large set of different climate models. Using a novel approach, we were able to demonstrate that Arctic sea ice loss exerts a consistent and nonnegligible impact on the atmospheric circulation response. In particular, in late winter and in the North Atlantic and Euro-Asian sector, Arctic sea ice loss tends to oppose the poleward shift of the midlatitude westerly winds, which is a common feature of the future projections of atmospheric circulation change. These results are important as they provide the first assessment that Arctic sea ice loss is important for the atmospheric circulation response to climate change based on a large number of climate models.