Atlantic overturning collapses in global warming projections after 2100

Abstract The Atlantic Meridional Overturning Circulation (AMOC) strongly influences climate, particularly (but not exclusively) around the northern Atlantic, and its instabilities explain some of the largest abrupt regional climate shifts in Earth history1. For several decades, the risk of a collapse of this crucial circulation system in response to anthropogenic global warming has been discussed as a ‘low probability – high impact’ risk of our greenhouse gas emissions. Multiple lines of evidence have shown that this circulation is slowing down and may be at its weakest since at least a millennium2, and several studies have identified early warning signals in observations of an approaching tipping point3-6. Here we show, by analysing standard global warming simulations extended beyond the year 2100, that the circulation collapses in all IPCC-class climate models in the high emission scenarios and even in some moderate and low scenarios, despite the neglect of increasing Greenland meltwater influx. In most cases the collapse is initiated by a breakdown of deep convection already early in this century. We conclude that a collapse of the AMOC cannot be considered a low-probability event anymore.