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New research suggests that the Atlantic meridional overturning circulation (AMOC), a critical ocean current that stabilizes monsoon patterns and helps keep the northern hemisphere warm, has become wildly unstable and dangerously weak.
“Human-caused warming has led to an ‘almost complete loss of stability’ in the system that drives Atlantic Ocean currents, a new study has found—raising the worrying prospect that this critical aquatic ‘conveyor belt’ could be close to collapse,” reports the Washington Post. After examining more than 100 years of ocean temperature and salinity data, climate physicists at the Potsdam Institute for Climate Impact Research in Germany now believe the AMOC—known widely as the Gulf Stream—is perilously close to an abrupt and irreversible shift into the “off” position.
While the workings of the sprawling and intricate AMOC are, as yet, impossible to perceive directly, the basic physics are well understood: following the dictates of “thermohaline circulation,” the warm, salty waters of the tropical Atlantic flow northeast from the U.S. coast to Greenland, growing cooler and more dense as they gain latitude and eventually sinking and pushing other waters at depth south toward Antarctica. From there, the cycle repeats—or at least it has, so far.
Now, this “self-sustaining” loop is in jeopardy, with change being driven on two fronts: as climate change warms the Atlantic its waters become lighter, and as freshwater rushes in from melting ice sheets and glaciers, it becomes less salty, less dense, and less able to sink. The Post writes that it was just such a shift that switched the AMOC into its “off” position near the end of the last ice age, when a massive volume of meltwater from icebound North America spilled into the Atlantic, stopping the current and plunging much of the northern hemisphere into deep freeze conditions that lasted 1,000 years.
Maynooth University climate physicist Levke Caesar, lead author of a previous study that warned the ocean cycle is at its weakest point in a millennium, said this recent analysis offers no certainty about when the major climate system might collapse. But “the mere possibility that the AMOC tipping point is close should be motivation enough for us to take countermeasures,” she said.
The new study constitutes a grim update to a 2019 projection by the UN Intergovernmental Panel on Climate Change (IPCC) that the AMOC “would weaken during this century, but total collapse within the next 300 years was only likely under the worst-case warming scenarios.”
Potsdam Institute lead author Niklas Boers told The Guardian he did not expect to see signs of an AMOC destabilization in his lifetime. But “that I find scary,” he said. “It’s something you just can’t [allow to] happen.”
Because it is still unknown what atmospheric concentration of carbon dioxide will trigger a collapse, and every gram sent into the atmosphere brings that moment closer, he added, “the only thing to do is keep emissions as low as possible.”