AMOC collapse risk now over 50%, scientists warn
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- New research published in Science Advances combined real-world ocean observations with climate models and found a projected AMOC slowdown of 42-58% by 2100, a level described as "almost certain to end in collapse."
- Dr. Valentin Portmann at the Inria Centre de recherche Bordeaux Sud-Ouest led the study, which used ridge regression — a method "little used in climate science before now" — to identify the models that best match observed surface salinity in the south Atlantic.
- Prof Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research called the result "important and very concerning," said the risk of an AMOC shutdown was previously estimated at "maybe 5%" but now looks "more than 50%," and warned the tipping point may be passed by mid-century.
- The AMOC is already at its weakest in 1,600 years, and a collapse would plunge western Europe into extreme cold winters and summer droughts, shift tropical rainfall belts that millions rely on for food, and add 50-100cm to sea levels around the Atlantic.
- Greenland's ice cap meltwater — which is freshening the ocean and is not included in the climate models — means the real-world slowdown could exceed even the new pessimistic 42-58% estimate, Rahmstorf said.
- The slowing mechanism is a self-reinforcing feedback loop: rapid Arctic warming means surface water cools and sinks more slowly, while increased rainfall in the salty surface layer further reduces density and further slows the deep return current.
Why it matters: Western Europe, parts of Africa, and the Americas face potentially catastrophic and irreversible climate disruption if the AMOC tips into collapse — from extreme cold and drought in Europe to 50-100cm of additional sea level rise around the Atlantic. Rahmstorf, who has studied the system for 35 years, now puts shutdown probability above 50%, up from an earlier ~5% estimate, and says the tipping point could come within decades. Even the new pessimistic projections exclude Greenland meltwater, meaning the actual risk is likely higher than stated.
