"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."
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."
Meteorologist and climate journalist Eric Holthaus called the study's findings "incredibly worrying."
The Washington Postreports:
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 toThe 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, toldThe New York Times. "I fear, honestly, that by the time any of this is settled science, it's way too late to act."
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.