North Atlantic carbon uptake modulates warming rate of the future Northern Hemisphere

The North Atlantic is a pacemaker of global climate through the Atlantic meridional overturning circulation (AMOC) and a large anthropogenic carbon uptake. Removal of anthropogenic carbon in the atmosphere by the ocean is key mechanism for modulating warming rate of globe. But, there is a large uncertainty in climate models for simulating AMOC and anthropogenic carbon uptake. To reduce the uncertainties in anthropogenic carbon uptake and its associated Northern Hemisphere surface warming, here we apply an emergent constraint. Sea surface salinity is often used to represent ocean circulations through its strong relationship with ocean density. The results suggest that the present-day sea surface salinity in the North Atlantic subpolar region constrains the future warming of the Northern Hemisphere by modulating anthropogenic carbon uptake in the North Atlantic. Models that generate a present-day higher SSS in the North Atlantic subpolar region systematically tend to a greater uptake of anthropogenic carbon, resulting in a slower warming in the Northern Hemisphere.