Danish model finds Atlantic current can recover if warming reverses

No tipping point in the model

The Atlantic Meridional Overturning Circulation could recover from severe weakening if global temperatures fall, according to a Danish Meteorological Institute study published in Science Advances. The study found no sign of an irreversible tipping point in its model, contrary to some earlier research. It was presented on Wednesday 14 October, Reuters reported.

The AMOC brings warm water from the tropics northward toward the Arctic, and the flow helps keep Europe's winters mild. It moves heat around the planet and shapes weather far beyond the Atlantic. A weaker current would change European winters, rainfall and sea level.

In the simulation, the AMOC weakens to about 6 million cubic metres of water per second from around 17 million at roughly 7C of global warming, about a third of its strength. The decline is gradual rather than a threshold, the study said.

Lead author Chuncheng Guo said:

"In our model, we do not see a tipping point leading to a collapse. The AMOC gradually weakens, but we find that it also immediately regains its strength if global warming is reversed."

A stress test, not a forecast

The 7C of warming is far beyond current projections for the warming trend and far beyond the 1.5C threshold governments committed to under the 2015 Paris Agreement. The study used it to examine the system under severe conditions.

Guo also said the cooling rate needed to reverse the AMOC exceeds what current technology could achieve. The work rests on a single climate model, and the authors called for it to be tested against others. Recovery, even when it starts, could take several centuries, and the effects of a weakened current would persist.

What the model does not restore

The Greenland ice sheet weakens the current by pouring cold freshwater into the North Atlantic. It cannot be restored once it has melted, even if the warming trend reverses, the study said. The researchers estimated around 20 cm of long-term sea-level rise from Greenland melt after a 1.5C rise.

A disrupted AMOC would still destabilise global rainfall patterns and accelerate coastal sea-level rise, the study said. Willem Huiskamp of the Potsdam Institute for Climate Impact Research, who was not involved, said a more stable AMOC would be good news. He doubted the real-world current was as stable as some models suggest.

Why the result matters

The result adds to a debate over whether the AMOC faces an irreversible collapse. A 2023 paper in Nature Communications put a possible collapse window between 2037 and 2109. The Danish study does not settle the timing, but it suggests the circulation can regain strength if warming is reversed.

The UN's environmental body said in September that global temperature rises are set to exceed 1.5C within a few years. The researchers urged faster action to rein in emissions. Guo said relying on future cooling would be riskier than preventing warming now.

"Instead of relying on the global cooling to happen, it's a much, much safer strategy to not have warming in the first place."