Could the Gulf Stream Collapse? Scientists Remain Deeply Divided

Reports of an imminent Gulf Stream collapse and a coming ice age have drawn attention away from how little scientists still know about the Atlantic circulation. Researchers agree that a major weakening would affect the global climate, but they remain sharply divided over whether such a change is under way.

The Atlantic Meridional Overturning Circulation, or AMOC, is a network of currents at the surface and thousands of metres below the Atlantic. Warm surface water moves north, cools at high latitudes, sinks and returns south along the ocean floor. The Gulf Stream forms part of the northbound surface flow, but winds and Earth's rotation drive it primarily. It would remain even if the AMOC weakened considerably.

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If the AMOC weakens, the climate is affected globally, not only in northern Europe.

A severe weakening or collapse could have major climate effects, particularly in Sweden and other Nordic countries, where climate models indicate much colder conditions, especially during winter. “If the AMOC weakens, the climate is affected globally, not only in northern Europe,” said Léon Chafik, an oceanographer and climate researcher at Stockholm University. He added that scientists still struggle to determine whether it is happening, when it might happen and at what rate.

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But the question is whether it is happening, when it will happen and at what rate. It is very difficult to predict.

The disagreement begins with the question of what researchers are measuring. Scientists use different mathematical definitions and study the circulation at different latitudes. Chafik said there is not one single AMOC, but several circulations that behave differently in different places.

Fabien Roquet of the University of Gothenburg said researchers lack long, robust records and cannot easily observe the circulation as a whole. Models range from showing a strong weakening to showing much smaller changes. He said the risk of collapse should be taken seriously, but the overall scientific assessment puts the probability very low and places any such event several decades in the future. His research also challenges the common view that increasing ocean stratification in the North Atlantic is weakening the AMOC. Continuous measurements began in 2004 between Florida and northwest Africa, leaving researchers with relatively short records.

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The risk should be taken seriously, but the overall scientific assessment is that the probability is very low and that, if it happens, it is several decades away.