Mitigation of 21st century Antarctic sea ice loss by stratospheric ozone recovery

We investigate the effect of stratospheric ozone recovery on Antarctic sea ice in the next half-century, by comparing two ensembles of WACCM4 (The Whole Atmosphere Community Climate Model, Version 4) integrations, from 2001 to 2065. WACCM is a stratosphere-resolving atmospheric model, with fully interactive stratospheric chemistry, coupled to land, ocean and sea-ice components. One ensemble of integrations is performed by specifying all forcings as per the Representative Concentration Pathway 4.5; the second ensemble is identical in all respects, except for the surface concentration of ozone depleting substances, which are held fixed at year 2000 levels, thus preventing stratospheric ozone recovery. In both ensembles sea ice extent declines, as a consequence of the increasing greenhouse gas concentrations. However, we find that sea ice loss is greater when stratospheric ozone recovery does not take place, and this effect is statistically significant in all seasons. In summer, greater sea ice loss is driven by enhanced equatorward Ekman drift leading to greater sea ice export and sea ice thinning. In the remainder of the year, sea ice loss results from persistent warming of the upper ocean. Our results, which confirm a previous study dealing with ozone depletion, suggest that ozone recovery will substantially mitigate Antarctic sea ice loss in the coming decades.