The circulation of the Atlantic Ocean is heading towards a breakdown that will dramatically alter the climate system, a paper published on Friday (9 February) has found.
By modelling vast amounts of data, the research team headed by climate physicist René van Westenhave from the University of Utrecht created an early warning system that suggests the so-called Atlantic Meridional Overturning Circulation (Amoc) is heading towards a breakdown before the end of this century.
The Amoc is one of the most consequential climate tipping points associated with global warming. It is a vast conveyor belt that transports warm water and salt from the equator up to the North Atlantic, where it strongly modulates the regional and even global climate.
This is why western Europe’s climate is milder than other areas of the same latitude around the globe.
But earlier research has shown that the conveyor belt has already slowed by 15 percent since 1950, caused by the rapid melt-off of the Arctic and the Greenland ice sheets.
Research published in Nature last year suggested the tipping point could happen between 2025 and 2095.
In the Nature paper, abrupt changes to Amoc were found to be “very unlikely.”
But by looking at freshwater changes in the southern Atlantic between South Africa and Argentina, which they describe as a “physics-based, observable, and reliable early-warning indicator”, the Dutch paper suggests Amoc is now heading for “abrupt change.”
Scientists have yet to reach a consensus on what might happen after.
James Hansen, director of the climate science programme at Columbia University, in a 2016 study warned that the temperature differential between a much colder Europe and the equator could trigger “raging tempests” that will deposit “house-sized boulders” on European coastlines.
The Dutch team’s data suggests March sea-ice from the Arctic would extend down to the 50th parallel north under a scenario where the Amoc is strongly weakened. That means Arctic ice would effectively reach down to Normandy.
The vast ice sheet would reflect more energy from the sun, leading to further cooling of the entire northern hemisphere. The opposite would be true in the south, where temperatures are expected to rise.
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In this way, the collapse of Amoc would compensate for global warming in Europe.
But changes to the climate would happen 10 times faster than now, making it impossible for humans to adapt.
Data suggests annual surface temperature change ranges from one to 3.5 degrees per decade over a broad region in northwestern Europe.
In several European cities, temperatures would drop by 5 to 15 degrees Celsius.
“No realistic adaptation measures can deal with such rapid temperature changes,” the researchers wrote.