Look out, Europe: Melting Arctic ice could weaken the Gulf Stream, researchers say

Michael Walsh
Reporter

The loss of Arctic sea ice as a result of global warming could have dramatic and potentially catastrophic effects on the climate of much of the northern hemisphere, according to a new report.

Scientists at Yale University and the University of Southampton recently demonstrated that the ongoing loss of sea ice is actively changing one of Earth’s main systems for transporting water — the Atlantic Meridional Overturning Circulation (AMOC).

To put it simply, AMOC circulates cold, dense water from the north Atlantic southward and warm, salty water from the tropical Atlantic northward. This system, which includes the Gulf Stream, plays a major role in maintaining the global climate, and its deterioration could have a dramatic impact.

“We have shown that this contraction of Arctic sea ice leads over the course of several decades to the weakening of the Atlantic Meridional Overturning Circulation,” climate scientist and study co-author Alexey Fedorov told Yahoo News.

Conventional thinking maintained that a weakening of ocean water circulation would prevent warm water from reaching the Arctic — resulting in a growth of sea ice. According to the researchers, however, this overlooks the mechanism by which the loss of sea ice affects AMOC over the course of decades.

Fedorov, a professor in Yale’s department of geology and geophysics, worked on the study with Florian Sévellec, an associate professor at the University of Southampton and former Yale postdoctoral researcher, and Wei Liu, a Yale postdoctoral associate. It was published in the Nature Climate Change journal on Monday.

The sun sets over melting sea ice on Peel Sound along the Northwest Passage in the Canadian Arctic Archipelago on July 23. (Photo: David Goldman/AP)

“Previous studies found that ocean circulation change can affect sea ice, but we found another way. Sea ice was affecting circulation,” Liu told Yahoo News.

Their study was based on new calculations about the sensitivity of ocean circulation to changes in the ocean’s surface’s temperature and salinity over time. Their experiments demonstrated that Arctic sea ice loss was linked to a potential weakening of AMOC by 30 to 50 percent.

According to the researchers, changes in the sub-polar north Atlantic had the biggest impact on AMOC in the short term, but changes in the Arctic itself were having the biggest long-term impact on the system.

But how will this weakening of ocean circulation affect the climate?

According to researchers, in the short term it could lead to harsher, stormier winters and drier summers for countries in Europe, whose climate now is ameliorated by the Gulf Stream.

“Europe, especially Northern Europe, would be affected the most as it is downstream of the atmospheric jet stream. However, some of these effects may be also felt along the east coast of Canada and Northeastern U.S.,” Fedorov said.

In the long term, a total cessation of AMOC is possible with potentially catastrophic consequences. According to Fedorov, one of the scarier aspects of this possibility is that we would be entering the unknown.

“The last time the circulation collapsed like that was thousands and thousands and years ago,” he added. “It’s a risk management problem. We don’t want to induce something we don’t fully understand or that we’ve never lived through.”

A different Yale study led by Liu from last January warned that the AMOC system might not be as stable as weather models had predicted. They argued that the possibility of AMOC’s collapse under global warming had been hitherto “hugely underestimated.”

“These two studies are quite connected, and it’s very interesting coming to a better understanding of AMOC and climate change,” Liu said.

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