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gulf stream
'Cliff-Like' Collapse of Critical Current System More Likely Than Thought: Study
"The new study adds significantly to the rising concern about an AMOC collapse in the not-too-distant future," said one scientist. "We will ignore this at our peril."
Feb 10, 2024
A study published Friday warned that a systemic collapse of the Atlantic Ocean currents driving warm water from the tropics toward Europe could be more likely than researchers previously estimated—an event that would send temperatures plummeting in much of the continent.
The Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream, could be headed for a relatively sudden shutdown that René Van Western, who led the Dutch study published in Science Advances, called "cliff-like."
"We are heading towards a tipping point."
For many millennia, 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.
An AMOC shutdown would cause temperatures to rise in the Southern Hemisphere but plunge dramatically in Europe. In the study's model, London cools by an average of 18°F and Bergen, Norway by 27°F. An AMOC failure would also cause sea levels to rise along North America's east coast.
"We are moving closer [to the collapse], but we we're not sure how much closer," van Westen told The Associated Press. "We are heading towards a tipping point."
According to the study:
Although AMOC collapses have been induced in complex global climate models by strong freshwater forcing, the processes of an AMOC tipping event have so far not been investigated. Here, we show results of the first tipping event in the Community Earth System Model, including the large climate impacts of the collapse. Using these results, we develop a physics-based and observable early warning signal of AMOC tipping: the minimum of the AMOC-induced freshwater transport at the southern boundary of the Atlantic. Reanalysis products indicate that the present-day AMOC is on route to tipping. The early warning signal is a useful alternative to classical statistical ones, which, when applied to our simulated tipping event, turn out to be sensitive to the analyzed time interval before tipping.
"The research makes a convincing case that the AMOC is approaching a tipping point based on a robust, physically based early warning indicator," said Tim Lenton, director of the University of Exeter's Global Systems Institute. "What it cannot and does not say is how close the tipping point, because... there is insufficient data to make a statistically reliable estimate of that.
"We have to plan for the worst," added Lenton, who was not involved in the Dutch study. "We should invest in collecting relevant data and improving estimation of how close a tipping point is, improving assessment of what its impacts would be, and getting pre-prepared for how we could best manage and adapt to those impacts if they start to unfold."
Stefan Rahmstorf—who leads the Earth Systems Analysis department at the Potsdam Institute for Climate Research in Germany and was not part of the new study—called the research "a major advance in AMOC stability science."
"The new study adds significantly to the rising concern about an AMOC collapse in the not-too-distant future," Rahmstorf told The Associated Press. "We will ignore this at our peril."
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Study Warns Climate-Driven Collapse of Critical Ocean Current System 'Much Closer Than We Thought'
"It is very plausible that we've fallen off a cliff already and don't know it," said one researcher.
Jul 25, 2023
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."
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."
The Washington Post reports:
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.
According to The Guardian:
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, told The New York Times. "I fear, honestly, that by the time any of this is settled science, it's way too late to act."
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.
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