The finding raises the urgency for drastic reductions in global carbon emissions, with researchers warning that humanity may be closer to crossing a climate tipping point than previously believed.

A climate engine at risk

The Atlantic meridional overturning circulation (Amoc) is one of the planet's key climate regulators. Driven by the sinking of cold, dense water in the North Atlantic, it acts like a giant conveyor belt: carrying warm tropical waters northward, where they cool and sink, before flowing back south in the deep ocean. This circulation helps distribute heat across the globe, keeping Europe relatively mild, stabilising rainfall in the tropics, and supporting global weather patterns.

But the Amoc has already weakened to its lowest level in at least 1,600 years due to human-driven warming, and scientists have long feared that further destabilisation could tip it into collapse.

The tipping point may be decades away

Until recently, most climate models suggested that a shutdown was unlikely before 2100. But the new study, published in Environmental Research Letters, extended those models into the 23rd and 25th centuries. It found that while the collapse itself may not unfold until 50–100 years after a tipping point is crossed, that critical threshold could be breached within the next 10 to 20 years.

The risk is not marginal. If emissions continue to rise, 70% of models simulated a collapse. Under moderate emissions, the risk was 37%, and even with low emissions aligned with the Paris climate agreement, one in four models still showed the system shutting down.

"This is quite shocking," said Prof Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, a co-author of the study. "I used to say the chance of collapse this century was less than 10%. Now, even in a low-emission scenario, it looks closer to 25%. And even a 10% chance would be far too high when the consequences are so grave."

What collapse would mean

The consequences of an Amoc shutdown would be profound. Western Europe could face freezing winters and scorching summer droughts. The tropical rainfall belt, on which hundreds of millions rely for food, would shift dramatically. Sea levels along the North Atlantic coastlines would surge by up to 50 centimetres on top of existing rises.

The last time the Amoc collapsed — during the last Ice Age — it triggered abrupt temperature swings of up to 10°C in parts of the Northern Hemisphere within just a few decades.

"Even in intermediate and low-emission scenarios, the Amoc slows drastically by 2100," said Prof Sybren Drijfhout of the Royal Netherlands Meteorological Institute, another member of the research team. "That shows the risk is far more serious than many people assume."

A dangerous feedback loop

The research highlights how global heating is destabilising the North Atlantic. Rapid warming in the Arctic means the ocean there cools more slowly. Meanwhile, the influx of rainfall and meltwater from Greenland reduces the saltiness — and therefore the density — of surface waters, slowing their ability to sink. This triggers a self-reinforcing feedback: the weaker the sinking, the weaker the circulation becomes.

Observational data already show a downward trend in deep-water formation over the past decade, aligning with model predictions.

Rahmstorf warned that the true risk might be even greater than the study suggests, since many models do not yet fully account for Greenland's accelerating ice melt — one of the most important drivers of fresh water into the Atlantic.

Scientific caution — but little comfort

Not all experts agree on the precise timeline. Dr Aixue Hu of the US National Center for Atmospheric Research, who was not involved in the study, described the results as important but emphasised the uncertainty: "It is still very unclear exactly when the tipping point will be crossed, due to limited direct observations and differences between models."

Other researchers also called for caution, noting that relatively few models have been run beyond 2100, meaning the sample size is small. "The risk rises significantly after 2100, but we need more long-term simulations to pin this down," said Dr Jonathan Baker of the UK's Met Office Hadley Centre, whose earlier work suggested collapse this century was unlikely.

Still, Baker agreed that major weakening of the circulation was almost certain: "Even without a complete shutdown, the changes projected could have serious impacts on Europe's climate and global weather systems in the coming decades."

A narrowing window

For scientists, the new findings sharpen what has long been a warning: avoiding Amoc collapse is non-negotiable.

"The tipping point may only be decades away," said Rahmstorf. "That's why we must act quickly and decisively to cut emissions. Because once this system passes its threshold, there is no way to bring it back."

The future of the Atlantic's great climate engine, researchers say, is still in human hands — but only if fossil fuel burning is curbed far faster than current policies allow.