Scientists have issued a stark warning that the Atlantic Meridional Overturning Circulation (Amoc), a crucial component of the global climate system, is weakening at a faster rate than previously anticipated. New research indicates that the most pessimistic climate models, which predict a significant slowdown by 2100, are the most realistic. This finding raises the likelihood of a collapse, which would have catastrophic consequences for Europe, Africa, and the Americas.
The study, published in Science Advances, combined real-world ocean observations with climate models to reduce uncertainty. It found that the Amoc could slow by 42% to 58% by 2100, a level almost certain to lead to collapse. This is a much steeper decline than the average of all models suggested. Dr Valentin Portmann, lead author from the Inria Centre de Recherche Bordeaux Sud-Ouest, said: 'We found that the Amoc is going to decline more than expected... This means we have an Amoc that is closer to a tipping point.'
A collapse of the Amoc would have devastating impacts. It would shift the tropical rainfall belt, endangering food production for millions, plunge western Europe into extreme cold winters and summer droughts, and add 50-100cm to rising sea levels around the Atlantic. Prof Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research described the results as 'very concerning' and warned that the tipping point could be reached as early as mid-century. 'I now am increasingly worried that we may well pass that Amoc shutdown tipping point... in the middle of this century, which is quite close,' he said.
The Amoc is slowing because rapid Arctic warming reduces the cooling of ocean waters, making them less dense and slowing the sinking process that drives the current. This feedback loop is further exacerbated by increased rainfall in the North Atlantic. While precise predictions remain challenging due to the system's complexity, the new research provides a more reliable estimate by focusing on models that accurately reflect surface salinity in the South Atlantic. Rahmstorf emphasised that the actual slowdown could be even greater than the study suggests, as computer models may not fully capture all relevant processes.
