A new analysis of Atlantic Ocean data suggests that a major ocean circulation system is weakening significantly and may be approaching a critical threshold. The Atlantic Meridional Overturning Circulation, which includes the Gulf Stream, plays a central role in global climate by transporting warm water northward and cold water southward.
Researchers have identified an unusual cold region in the North Atlantic, known as the Atlantic cold blob, as evidence of the circulation's decline. By combining real-world ocean observations with climate models, scientists determined that the AMOC is likely to slow by between 42 and 58 percent by 2100, a level almost certain to trigger collapse.
This finding represents a significant shift in scientific understanding. Climate models previously produced widely varying predictions about the AMOC's future, ranging from no further slowdown to a 65 percent deceleration. The new research dramatically reduced this uncertainty by identifying which models most accurately reflect actual ocean conditions, particularly surface salinity in the South Atlantic.
The implications are severe. A collapse of the AMOC would shift tropical rainfall patterns that millions of people depend on for agriculture, bring extreme cold winters and summer droughts to Western Europe, and raise sea levels around the Atlantic by 50 to 100 centimeters. The system would also disrupt marine ecosystems and weather patterns across multiple continents.
Scientists have expressed serious concern about these prospects. Dr. Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research stated that "the pessimistic models, which show a strong weakening of the AMOC by 2100, are unfortunately the realistic ones." He added that the collapse tipping point could potentially occur in the middle of this century.
The AMOC is weakening due to rapid air temperature increases in the Arctic. Warmer ocean water is less dense and therefore sinks more slowly into the depths. This slowing allows more rainfall to accumulate in surface waters, further reducing their density and creating a feedback loop that slows the circulation further. Additionally, freshwater from melting ice sheets adds to this problem.
Scientists have raised concerns about preparedness for potential consequences. The system has collapsed before in Earth's history, most notably during the Younger Dryas period roughly 12,000 years ago, when North Atlantic temperatures dropped sharply within decades.
Rahmstorf noted that models do not yet account for additional meltwater from the Greenland ice cap, meaning actual conditions could be even worse than current projections. He emphasized that avoiding an AMOC collapse "must be done at all costs," given the massive potential impacts on global climate and human societies.