Scientists have found that the Atlantic meridional overturning circulation (Amoc), a major part of the global climate system, is significantly more likely to collapse than previously thought, with new research suggesting a slowdown of 42% to 58% by 2100 – a level almost certain to end in collapse. The study, published in Science Advances, combined real-world ocean observations with climate models to determine the most reliable projections, reducing the spread of uncertainty.
Lead author Dr Valentin Portmann, of the Inria Centre de recherche Bordeaux Sud-Ouest in France, said: 'We found that the Amoc is going to decline more than expected compared to the average of all climate models. This means we have an Amoc that is closer to a tipping point.' The finding is described as 'very concerning' by scientists, as a collapse would have catastrophic consequences for Europe, Africa and the Americas.
The Amoc brings sun-warmed tropical water to Europe and the Arctic, where it cools and sinks to form a deep return current. A collapse would shift the tropical rainfall belt relied upon by millions for food, plunge western Europe into extreme cold winters and summer droughts, and add 50-100cm to already rising sea levels around the Atlantic.
Prof Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research in Germany, who has studied the Amoc for 35 years, said: 'I now am increasingly worried that we may well pass that Amoc shutdown tipping point, where it becomes inevitable, in the middle of this century.' He added that a collapse must be avoided 'at all costs', noting that the risk now appears to be more than 50%.
The Amoc is already at its weakest for 1,600 years due to the climate crisis, and is slowing because rapid Arctic warming reduces the cooling of ocean waters. Warmer water is less dense and sinks more slowly, while increased rainfall in salty surface waters further reduces density, creating a feedback loop that accelerates the slowdown.
