Control by the Circulation Transport Outside the Arctic on Transient Response of AMOC to Global Warming

Using the Alfred Wegener Institute Climate Model (AWI-CM 1.1 LR), we conduct sensitivity experiments separating the Arctic and extra-Arctic warming to investigate the transient response of AMOC to quadrupled carbon dioxide (4×CO2) forcings. The results suggest that AMOC weakening is primarily affected by circulation adjustment induced by the outer-Arctic warming, while the effects of Arctic warming are confined to the polar range and contribute less to AMOC changes. When warming forcing is applied outside the Arctic, the increases of northward advective heat transport dominate the weakening of deep convection in the Nordic Seas, while the reduction of heat loss from ocean to atmosphere is prevalent in Labrador Sea. Besides, the weakening of deep convection in Nordic Seas is more pronounced than in Labrador Sea, implying a leading role of Nordic Seas in the weakening of AMOC under global warming.