Large Uncertainty in Arctic Warming Driven by the Atlantic Meridional Overturning Circulation

Climate models project a weakening of the Atlantic Meridional Overturning Circulation (AMOC) that will reduce Arctic warming. However, there is substantial intermodel spread in the projected AMOC decline, and its contribution to uncertainty in projected Arctic warming has not yet been quantified. To investigate this, we perform model experiments that increase CO₂ concentrations while imposing the intermodel spread in the AMOC decline. We find that this intermodel spread in the AMOC decline reproduces 45% of the total intermodel spread in Arctic warming. A smaller AMOC decline increases Arctic warming via increased northward ocean heat transport, atmospheric moisture transport, and positive Arctic feedbacks. Arctic warming is more sensitive to AMOC differences that produce larger sea-ice changes. Combined with a strong correlation between a small AMOC decline and Arctic warming across models, these results indicate that ocean circulation is a key source of model uncertainty in projections of Arctic warming.