Could hidden Atlantic current transform Europe's climate?

A vast ocean current that has helped shape Europe's climate for thousands of years is drawing increasing scientific scrutiny as global temperatures rise. 

Researchers broadly agree that the Atlantic Meridional Overturning Circulation (AMOC) is weakening, but a far more contentious question remains: could it reach a tipping point that fundamentally reshapes weather patterns across Europe and beyond? In an analysis, the BBC examines the growing scientific debate over the future of one of Earth's most important climate systems, highlighting both mounting evidence of change and deep uncertainty over what lies ahead.

The AMOC is a massive system of ocean currents that transports warm surface water northwards from the tropics before colder, denser water sinks and flows back south through the deep Atlantic. The circulation, which includes the Gulf Stream, helps explain why Britain and north-west Europe experience relatively mild climates despite their northern latitude.

Scientists widely agree that climate change is placing increasing pressure on the system. As the planet warms, higher ocean temperatures, increased rainfall and freshwater from melting ice sheets reduce the salinity and density of North Atlantic waters, making them less likely to sink — a process essential to sustaining the circulation.

The disagreement lies not over whether the AMOC will weaken, but over how quickly that weakening could occur and whether it could trigger an abrupt shift.

Some researchers argue warning signs are already emerging. They point to an unusual patch of relatively cool water south of Greenland, changing salinity levels and other observations suggesting the circulation may already be slowing.

Among those expressing growing concern is Prof Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, who has studied the AMOC for more than three decades.

"The paleoclimate evidence actually doesn't suggest that climate change would happen smoothly, but rather in some jumps and jolts and non-linear effects," he told the BBC.

His concern centres on a potential feedback loop. If the North Atlantic becomes too fresh to allow sufficient water to sink, the circulation weakens, reducing the transport of salty water northward and making further weakening more likely.

"We have this AMOC because it's salty enough in the North Atlantic. And it's salty enough because we have the AMOC. So that's a self-sustaining system," Rahmstorf said.

He argues that if a tipping point were crossed, the process could become irreversible.

"Once we have crossed the tipping point," he says, "we can't do anything to stop the further shutdown."

The BBC notes, however, that not all climate scientists interpret the evidence in the same way.

Prof Andrew Watson of the University of Exeter agrees that the AMOC has undergone major changes in the distant past.

"Clearly, its behaviour has changed in the past," he says. "So there's every chance that it can change again."

But Watson cautions against assuming today's warming will produce the same outcome observed after the last Ice Age. Rather than shutting down completely, he argues, the ocean circulation could reorganise itself in ways that current climate models struggle to simulate accurately.

A study led by the UK Met Office concluded that a complete collapse of the AMOC before the end of this century appears unlikely, although continued weakening could still alter storm tracks, rainfall patterns and seasonal weather across Europe.

Watson also stresses that any cooling linked to a weaker AMOC would occur alongside continuing global warming, making future climate impacts more complex than a simple return to colder conditions. Instead, Europe could experience greater weather variability, including hotter summers, colder winters and more frequent extremes.

By Sabina Mammadli