Regionally-Dependent Arctic Sea Ice Recovery to CO2 Removal

Abstract

The decline of Arctic sea ice area (SIA) has accelerated in recent decades and is projected to continue in a warming climate. This trend can be reversed by reducing atmospheric CO2 concentrations. A large-ensemble model experiment, in which atmospheric CO2 concentrations are quadrupled and then reduced to the initial state, shows an overall recovery of Arctic SIA by CO2 removal, but at a slower rate than its decline to CO2 increase. The exception is the North Atlantic, where SIA increases rapidly with decreasing CO2 concentrations. The under-recovery of Central Arctic SIA can be attributed to a slow decrease in Arctic ocean heat storage, due to a lagged ocean cooling and heat transport, and enhanced downward longwave radiation in the Arctic atmosphere, partly due to frequent atmospheric rivers across the Arctic Circle. In contrast, the over-recovery of North Atlantic SIA is primarily attributed to weakened ocean heat transport by a delayed recovery of the Atlantic Meridional Overturning Circulation (AMOC). This over-recovery is shown to be model dependent, following each model's AMOC change. Full recovery of Arctic SIA takes over 300 years after CO2 removal. This result suggests that the response of Arctic sea ice to CO2 removal may be spatially inhomogeneous, with different impacts on regional climate, potentially affecting the climate of the Northern Hemisphere mid-latitudes.