Critical Atlantic current significantly more likely to collapse than thought

Scientists say the Atlantic meridional overturning circulation is far more likely to collapse than previously thought, based on new research combining climate models with real-world ocean observations. A collapse would be catastrophic for Europe, Africa and the Americas.

The Atlantic meridional overturning circulation (Amoc) is a major part of the global climate system and is already at its weakest point in 1,600 years due to the climate crisis. Researchers found that climate models predicting the biggest slowdown are the most realistic, narrowing previous estimates to a 42% to 58% decline by 2100—a level almost certain to trigger collapse.

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 rainfall patterns that millions depend on for food production, plunge western Europe into extreme cold winters and summer droughts, and raise sea levels around the Atlantic by 50-100 centimeters.

Dr Valentin Portmann at the Inria Centre de recherche Bordeaux Sud-Ouest in France led the research. Prof Stefan Rahmstorf at the Potsdam Institute for Climate Impact Research in Germany said the findings show the "pessimistic" models are "unfortunately, the realistic ones." Rahmstorf warned that the risk of an Amoc shutdown has risen from roughly 5% to more than 50%.

Context

The Amoc is slowing because Arctic air temperatures are rising rapidly due to global heating. Warmer ocean water sinks more slowly into the depths. This allows more rainfall to accumulate in salty surface waters, making them less dense and further slowing the sinking process—creating a feedback loop that accelerates the decline. Scientists spotted warning signs of a tipping point in 2021 and know the Amoc has collapsed during Earth's past. The new research was published in the journal Science Advances and used a method called ridge regression to identify which climate models best reflected observational data.

What's Next

Rahmstorf said the Amoc shutdown tipping point may be reached by the middle of this century if current trends continue. He emphasized that collapse must be avoided "at all costs" given the massive impacts on global climate patterns and sea levels. The findings underscore the urgency of reducing carbon emissions from fossil fuel burning to net zero.