Within this century, climate change could lead to the collapse of a vital ocean current system—and it could happen as soon as 2025, according to a new study published Tuesday in Nature Communications. However, some researchers remain skeptical about the finding, which contradicts a recent assessment by United Nations climate scientists.
The system, called the Atlantic Meridional Overturning Circulation (AMOC), is part of the ocean’s global conveyor belt that moves water and nutrients across the seas. It’s a wide-reaching network of currents, including the Gulf Stream, that spans the Atlantic Ocean, and it’s a major driver of climate. If the system were to collapse, it could influence temperature and precipitation patterns around the world.
Essentially, shutting down the AMOC “would affect every person on the planet,” Peter de Menocal, president of the Woods Hole Oceanographic Institution, who was not involved in the study, tells CNN’s Laura Paddison. It would raise temperatures near the equator and deliver more extreme winters to the United States and Europe.
“While a cooling of Europe may seem less severe as the globe as a whole becomes warmer and heat waves occur more frequently, this shutdown will contribute to increased warming of the tropics, where rising temperatures have already given rise to challenging living conditions,” Peter Ditlevsen, a physicist at the University of Copenhagen and co-author of the study, says in a statement.
The AMOC is key for transporting warm water from the tropics to the northern Atlantic. This movement is driven by differences in water density—colder, saltier water is more dense and sinks deep into the ocean, while warmer and fresher water stays closer to the surface. As water from the tropics moves northward, it cools, and some of it evaporates, which increases its saltiness. This cooler, denser water then moves southward until it’s pulled back up to the surface and warms in a process called upwelling.
But as temperatures on Earth rise because of human-caused climate change, ice in Greenland is melting rapidly, and this influx of cool freshwater disrupts the sinking of salty water, weakening the AMOC, Ditlevsen tells USA Today’s Doyle Rice.
Scientists have been predicting that the AMOC would slow down or come to a complete stop since measurements of the system began around 2004, Ditlevsen tells BBC News’ Georgina Rannard. The system has shut down in the past, at several times during the last glacial period between 71,000 and 12,000 years ago.
A 2019 report by the Intergovernmental Panel on Climate Change concluded a full collapse of the AMOC would be unlikely this century. But the new study reached its opposing conclusion based on an analysis with “new and improved statistical tools,” Susanne Ditlevsen, a statistician at the University of Copenhagen who is a co-author of the study and Peter Ditlevsen’s sister, says in the statement. The researchers’ model predicted with 95 certainty that the AMOC will stop between 2025 and 2095, with the tipping point likely in 2057.
“It’s really scary,” Peter Ditlevsen tells CNN. “This is not something you would lightly put into papers. … We’re very confident that this is a robust result.”
Other scientists, however, are more skeptical of the research, calling the results of a single study inconclusive. “Whilst there is definitely a role for papers like this, the conclusions are far from settled science,” Ben Booth, a senior climate scientist at the Met Office Hadley Center, says in a statement.
In the study, the team assumed that global greenhouse gas emissions would continue to rise, as they have been since the Industrial Revolution, per the New York Times’ Raymond Zhong. They based their analysis on sea surface temperatures in a specific area of the North Atlantic from 1870 to the present. These data suggested how strong the AMOC had been during that time, since direct measurements of the system’s strength began only 15 years ago. Yet, sea surface temperatures in this area are “not a clear indicator of the state of the AMOC,” Penny Holliday, head of marine physics and ocean circulation at the National Oceanography Center in England, says in a statement. “A collapse of the AMOC would profoundly impact every person on Earth, but this study overstates the certainly in the likelihood of it taking place within the next few years.”
Still, Stefan Rahmstorf, a physicist and physical oceanographer at the University of Potsdam in Germany, says the new paper adds to existing evidence that the tipping point could be sooner than previously thought.
“As always in science, a single study provides limited evidence, but when multiple approaches lead to similar conclusions, this must be taken very seriously,” Rahmstorf says in a statement. “Especially when we’re talking about a risk that we really want to rule out with 99.9 percent certainty. The scientific evidence now is that we can’t even rule out crossing a tipping point already in the next decade or two.”