Atlantic Ocean Circulation Indicates Abrupt Climate Change

The Atlantic Ocean's circulation, which is an important driver of precipitation and climate, is showing signs that it will soon collapse, indicating that abrupt climate change may not be so far away.

Officially known as the Atlantic Meridional Overturning Circulation (AMOC), it is like a conveyor belt in the ocean, driven by the water's salinity and temperature. The system transports heat from the tropics and Southern Hemisphere to the North Atlantic, where it is released into the atmosphere.

But researchers from the University of Exeter have found early warning signals of abrupt climate change in the form of a reorganization of the AMOC. Such long-lasting changes could result in the system's collapse and ultimately a drastic impact on the global climate.

"We found that natural fluctuations in the circulation were getting longer-lived as the collapse was approached, a phenomenon known as critical slowing down," lead author Chris Boulton said in a statement.

Based on complex model simulations, Boulton and his colleagues estimate that the AMOC will collapse approximately 250 years from now or sooner.

If the AMOC were to collapse and be "switched off" by an abundance of freshwater entering the North Atlantic, say from melting Arctic sea ice, surface air temperature in the North Atlantic region would cool by around 1-3 degrees Celsius (33.8-37.4 Fahrenheit). The worst affected regions would cool up to 8 C (46.6 F).

Drought in the Sahel - located south of the Sahara desert - and sea level rise up to 0.8 meters along the coasts of Europe and North America would also be consequences of the AMOC's collapse should the observed changes continue.

Not to mention intense rainfall and possibly subsequent flooding would be part of the picture, given that 21,000 years ago in Africa warmer temperatures, melting ice sheets and an increase in freshwater caused the AMOC to weaken and a dry spell to persist. It was when ice sheets stopped melting and the circulation regained its strength that intense rainfall in Africa rose and lasted for about 10,000 years.

"We don't know how close we are to a collapse of the circulation, but a real world early warning could help us prevent it, or at least prepare for the consequences," added co-author Professor Tim Lenton.

The study results were published in the journal Nature Communications.

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