Regionally-Dependent Arctic Sea Ice Recovery to CO2 Removal

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.