Distinct impacts of diverse forcing agents on Arctic sea ice since the mid-twentieth century

Arctic sea ice has undergone non-monotonic changes since the middle of the last century. Here, we investigate the cause of this behavior by isolating and quantifying the effects of anthropogenic aerosols, well-mixed greenhouse gases, and biomass burning on sea ice dynamics through climate model simulations. We find minimal changes in Arctic sea ice from 1956 to 1980, which largely reflect a balance between the warming effect of greenhouse gases and the cooling effect of aerosols. This balance, however, is disrupted in subsequent decades. Both sea ice area and volume exhibit marked declines between 1981 and 2005, owing primarily to intensified warming by greenhouse gases and a shift in aerosols’ role from mitigating to exacerbating sea ice loss. Our sea ice volume budget analysis demonstrates that sea ice changes since 1956 are mostly driven by thermodynamic processes: greenhouse gases significantly promote surface melting, whereas aerosols and biomass burning diminish surface melting by reducing surface shortwave radiation during boreal summer. From 1956–1980 to 1981–2005, the transitional effects of aerosols are associated with increased bottom ice melting and decreased bottom ice formation, which are primarily driven by changes in the Atlantic meridional overturning circulation.