May 6, 2021

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Gulf Stream system at its weakest in a millennium due to climate change

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The Gulf Stream system has weakened at its slowest rate in more than a thousand years, scientists say, as global warming slows the powerful ocean current that controls much of the Atlantic Ocean.

Two studies published this week reveal that climate change is slowing the ocean current, which carries warm water to Europe, more dramatically than expected.

Using sediment data and temperature records to map historical trends, a to study in Nature Geoscience discovered that the Gulf Stream system, also known as the Atlantic Reversing Meridional Circulation (Amoc), is moving at its slowest rate in the past millennium.

“This is most likely caused by our greenhouse gas emissions, as there is no other plausible explanation for this slowdown,” said Stefan Rahmstorf, one of the authors and responsible for the analysis of the earth system at the Potsdam Institute for Climate Impact Research. “This is exactly what climate models have been predicting for decades.”

The Gulf Stream is a huge ocean current that carries warm water from the tropics to the east coast of North America. The current – which carries over 100 times the flow of the Amazon River – cools and descends around Greenland, carrying cooler water south into the deeper layers of the ocean.

It has already slowed down by 15% in the last century, and Rahmstorf said this is starting to affect weather conditions, such as the more frequent heat waves in southern Europe.

The Amoc not only carries hot water to Europe – it is responsible for the mild winters in the UK – but it also influences the development of storms.

The results of the new study are “worrying,” Rahmstorf said. “If this continues, we could slowly get closer to a tipping point, where this circulation could destabilize completely.”

One of the reasons why the Amoc system slows down is due to melting ice in Greenland, where large volumes of cold fresh water enter the ocean and alter the natural mechanism of the current descent.

Increasing precipitation in North America, causing more fresh water to enter rivers, streams, and the ocean, and warmer ocean temperatures that reduce the temperature gradient between the tropics and the Pole, are contributing also to slowdown.

Andrew Meijers, an oceanographer with the British Antarctic Survey, who was not involved in the research, said the study “reveals that before the era of human-induced climate change, the Atlantic overturning circulation was relatively stable and stronger than it is now ”.

“This indicates that the slowdown is probably not a natural change, but the result of human influence,” he added.

Other scientists pointed out that there was still a high degree of uncertainty about how the Gulf Stream influences Europe’s climate.

“There are many other factors explaining variations in European weather, including atmospheric chaos,” said Tim Palmer, professor of climate physics at Oxford, who was not involved in the study. “This is an interesting study and one that requires continued investigation. However, it should not be overinterpreted. “

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A separate to study published in Proceedings of the National Academy of Sciences found that if the pace of global warming accelerates, it could cause the Gulf Stream to shut down completely.

Johannes Lohmann, lead author of the study and post-doctoral fellow in physics at the University of Copenhagen, said the current was “unlikely” to reach this point in the next 100 years, unless global warming does not accelerate.

“There is still a debate on whether an Amoc tipping point is imminent,” Lohmann said. “There is strong evidence of climate change in the past, that Amoc has gone from a similar state to today. . . to the one where the Amoc was extinguished.

“There is a self-reinforcing feedback that could cause the Amoc to stop, in a runaway effect,” he said.



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