Limited impact of Greenland meltwater on abruptness and reversibility of future Atlantic overturning changes

Abstract

All climate models project that the Atlantic Meridional Overturning Circulation (AMOC) will weaken in the 21st century, but most models neglect increasing runoff from the Greenland ice sheet. Greenland meltwater is expected to exacerbate AMOC weakening, and omitting it increases the uncertainty in assessing the possibility of a future abrupt collapse or tipping of the AMOC. Here, we test the abruptness and reversibility of AMOC changes under strong future global warming in a state-of-the-art climate model with and without physically plausible Greenland meltwater forcing. While Greenland meltwater significantly exacerbates future AMOC weakening, modeled long-term AMOC changes are neither abrupt nor irreversible. While accounting for Greenland meltwater will increase the accuracy of climate projections, our results suggest that the importance of Greenland meltwater for assessing the risk of future AMOC tipping may be smaller than previously thought.