AMOC, which encompasses part of the Gulf Stream and other powerful currents, is a marine conveyer belt that carries heat, carbon and nutrients from the tropics towards the Arctic Circle, where it cools and sinks into the deep ocean. This churning helps to distribute energy around the Earth and modulates the impact of human-caused global heating.
AMOC has declined 15% since 1950 and is in its weakest state in more than a millennium.
Researchers found AMOC is already on track towards an abrupt shift, which has not happened for more than 10,000 years and would have dire implications for large parts of the world.
The paper said the results provided a “clear answer” about whether such an abrupt shift was possible: “This is bad news for the climate system and humanity as up till now one could think that AMOC tipping was only a theoretical concept and tipping would disappear as soon as the full climate system, with all its additional feedbacks, was considered.”
It also mapped some of the consequences of AMOC collapse. Sea levels in the Atlantic would rise by a metre in some regions, inundating many coastal cities. The wet and dry seasons in the Amazon would flip, potentially pushing the already weakened rainforest past its own tipping point. Temperatures around the world would fluctuate far more erratically. The southern hemisphere would become warmer. Europe would cool dramatically and have less rainfall. While this might sound appealing compared with the current heating trend, the changes would hit 10 times faster than now, making adaptation almost impossible.
“What surprised us was the rate at which tipping occurs,” said the paper’s lead author, René van Westen, of Utrecht University. “It will be devastating.”
He said there was not yet enough data to say whether this would occur in the next year or in the coming century, but when it happens, the changes are irreversible on human timescales.
Until now there has been no consensus about how severe this will be. One study last year, based on changes in sea surface temperatures, suggested the tipping point could happen between 2025 and 2095.