Research indicates that rapid melting of the West Antarctic ice sheet might prevent the complete shutdown of the Atlantic Meridional Overturning Circulation, despite the slowing effects from Greenland's ice melt. However, the current would still decline significantly, with recovery taking thousands of years. This finding highlights an unexpected link between polar ice losses and global ocean dynamics.
The Atlantic Meridional Overturning Circulation (AMOC) is a critical system that transports warm surface water from the tropics to northern Europe, where it cools, sinks, and flows southward. It carries 1.2 petawatts of heat, equivalent to the output of 1 million power plants, keeping Europe warmer than regions like Labrador or Siberia at similar latitudes. However, freshwater from the melting Greenland ice sheet is expected to disrupt this sinking process by freshening the dense, salty waters, potentially slowing or collapsing the AMOC.
A collapse could bring winter temperatures as low as -50°C to northern Europe, raise sea levels along the US East Coast, and exacerbate droughts in Africa. This week, Iceland described an AMOC shutdown as an "existential" security threat. Recent studies suggest that even achieving net zero emissions by 2075 and removing CO2 afterward leaves a 25% risk of eventual collapse, with some predictions pointing to a shutdown within decades.
New simulations by Sacha Sinet at Utrecht University and colleagues, published in Science Advances, explore the role of West Antarctic ice sheet melt. The West Antarctic ice sheet has accelerated in melting recently, and its potential full collapse remains unclear in impact. The research shows timing is crucial: if Antarctic meltwater arrives about 1000 years before the peak of Greenland's melting, the AMOC would weaken for centuries but then recover over 3000 years, avoiding total shutdown. In all scenarios, the AMOC eventually recovers, but early Antarctic input prevents collapse and accelerates revival by shifting sinking southward as Antarctic melt tapers.
"I would tend to say, don’t be so quick to say that the AMOC is going to collapse," says Sinet. "But the things I show here do not change much what will happen for the next century. Probably you will not be alive to tell if the AMOC was stabilised or not by West Antarctica."
Louise Sime at the British Antarctic Survey notes the study's revelation of stronger connections between Antarctic and Greenland melts. "I don’t think we knew until this study that there was this possibility that changes in Antarctica could potentially change so much the impacts of Greenland ice sheet melt [on the AMOC]," she says. However, more complex models are needed to account for feedbacks like changing winds.
Even if Antarctic melt averts AMOC collapse, it would contribute up to 3 meters of sea-level rise, flooding coastal cities. "Unfortunately it is not a consolation if one catastrophe might perhaps reduce the risk of another catastrophe," says Stefan Rahmstorf at the University of Potsdam.