The Atlantic meridional overturning circulation is a major part of global climate system and is known to be at its weakest for 1,600 years as a result of climate crisis. Photograph: Henrik Egede-Lassen/Zoomedia/PA
Scientists say finding is ‘very concerning’ as collapse would be catastrophic for Europe, Africa and the Americas
The critical Atlantic current system appears significantly more likely to collapse than previously thought after new research found that climate models predicting the biggest slowdown are the most realistic. Scientists called the new finding “very concerning” as a collapse would have catastrophic consequences for Europe, Africa and the Americas.
The Atlantic meridional overturning circulation (Amoc) is a major part of the global climate system and was already known to be at its weakest for 1,600 years as a result of the climate crisis. Scientists spotted warning signs of a tipping point in 2021 and know that the Amoc has collapsed in the Earth’s past.
Climate scientists use dozens of different computer models to assess the future climate. However, for the complex Amoc system, these produce widely varying results, ranging from some that indicate no further slowdown by 2100 to those suggesting a huge deceleration of about 65%, even when carbon emissions from fossil fuel burning are gradually cut to net zero.
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Dr Valentin Portmann, at the Inria Centre de recherche Bordeaux Sud-Ouest in France and who led the new research, said: “We found that the Amoc is going to decline more than expected compared to the average of all climate models. This means we have an Amoc that is closer to a tipping point.”
Prof Stefan Rahmstorf, at the Potsdam Institute for Climate Impact Research in Germany, said: “This is an important and very concerning result. It shows that the ‘pessimistic’ models, which show a strong weakening of the Amoc by 2100, are, unfortunately, the realistic ones, in that they agree better with observational data.”
He added: “I now am increasingly worried that we may well pass that Amoc shutdown tipping point, where it becomes inevitable, in the middle of this century, which is quite close.”
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The huge ocean current known as the Atlantic Meridional Overturning Circulation (AMOC – not the Gulf Stream!) shifts vast amount of water around the world. But scientists fear that by heating the planet and melting the Greenland ice-sheet, we’re already slowing it down, with the risk that it could collapse – a potential tipping point with huge consequences around the world. And a new study (published in 2023) has tried to pin down what could happen, when. So what do we actually known about this current, does it have anything to do with the Gulf Stream, and is there anything we can do to protect ourselves?
The Gulf Stream is an ocean current that carries warm water from the Gulf of Mexico into the Atlantic Ocean. (Image: NASA)
“It is very plausible that we’ve fallen off a cliff already and don’t know it,” said one researcher.
The system of Atlantic Ocean currents that drive warm water from the tropics toward Europe is at risk of collapsing in the coming decades, an analysis of 150 years of temperature data published Tuesday concluded.
“The Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream, is a major tipping element in the climate system and a future collapse would have severe impacts on the climate in the North Atlantic region,” states the study, which was published in the scientific journal Nature Communications.
Although the analysis notes that “assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century,” the study’s authors “estimate a collapse of the AMOC to occur around mid-century under the current scenario of future emissions.”
“We show that a transition of the AMOC is most likely to occur around 2025-2095,” the paper states with “95% confidence.”
“There is still large uncertainty where the Amoc tipping point is, but the new study adds to the evidence that it is much closer than we thought.” https://t.co/KtAkaXDSC8
— David Wallace-Wells (@dwallacewells) July 25, 2023
University of Copenhagen professor Peter Ditlevsen, who led the study, told The Guardian: “I think we should be very worried. This would be a very, very large change. The AMOC has not been shut off for 12,000 years.”
Bill McKibben, co-founder of the climate action group 350.org, tweeted that “Gulf Stream collapse used to be viewed as a far-off and remote possibility… Less so now.”
Meteorologist and climate journalist Eric Holthaus called the study’s findings “incredibly worrying.”
Wow. I'm having trouble processing this news. This is incredibly worrying. https://t.co/M9A9aNkusW
The new study adds to a growing body of evidence that this crucial ocean system is in peril. Since 2004, observations from a network of ocean buoys [have shown] the AMOC getting weaker—though the limited time frame of that data set makes it hard to establish a trend. Scientists have also analyzed multiple “proxy” indicators of the current’s strength, including microscopic organisms and tiny sediments from the seafloor, to show the system is in its weakest state in more than 1,000 years.
For thousands of years, the Gulf Stream has carried warm waters from the Gulf of Mexico northward along the eastern North American seaboard and across the Atlantic to Europe. As human-caused global heating melts the Greenland ice sheet, massive quantities of fresh water are released into the North Atlantic, cooling the AMOC—which delivers the bulk of the Gulf Stream’s heat—toward a “tipping point” that could stop the current in its tracks.
A collapse of AMOC would have disastrous consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America, and West Africa. It would increase storms and drop temperatures in Europe, and lead to a rising sea level on the eastern coast of North America. It would also further endanger the Amazon rainforest and Antarctic ice sheets.
“It is very plausible that we’ve fallen off a cliff already and don’t know it,” Hali Kilbourne, an associate research professor at the University of Maryland Center for Environmental Science, toldThe New York Times. “I fear, honestly, that by the time any of this is settled science, it’s way too late to act.”
On the new AMOC study that's currently making a splash: Even fairly low odds of something dramatic happening with global ocean overturning circulations this century is still a really big deal. This new study does not singlehandedly shift understanding, but is still unsettling.
Other studies—including one published in March and another in 2021—have also concluded that the AMOC is at risk of collapsing this century.
Meanwhile in the Southern Hemisphere, Antarctic currents that enrich 40% of Earth’s deep oceans with oxygen and nutrients essential for marine life have slowed dangerously in recent decades and could also collapse by mid-century, an Australian study released in May showed.
