Climate scientists have detected warning signs that the Gulf Stream, a crucial ocean current system, could be nearing a catastrophic collapse. The research, published in Nature Climate Change, reveals “an almost complete loss of stability over the last century” of the Atlantic meridional overturning circulation (AMOC), which is already at its weakest point in at least 1,600 years.
A shutdown would have devastating global consequences, including severe disruptions to monsoon rains in India, South America and West Africa, increased storms and temperature drops in Europe, and rising sea levels off eastern North America. It would also further endanger the Amazon rainforest and Antarctic ice sheets.
“The signs of destabilisation being visible already is something that I wouldn’t have expected and that I find scary,” said Niklas Boers from the Potsdam Institute for Climate Impact Research. “It’s something you just can’t [allow to] happen.” The exact timing of any collapse remains uncertain – it could occur within decades or centuries – but Boers stressed that “the likelihood of this extremely high-impact event happening increases with every gram of CO2 that we put into the atmosphere”.
The study used eight independently measured datasets of ocean temperature and salinity going back 150 years to show that global heating is increasing the instability of the currents. Ice-core and other data reveal that the AMOC has two states: a fast, strong one and a slow, weak one, with rising temperatures capable of causing an abrupt switch over one to five decades. The melting of Greenland’s ice sheet is adding fresh water to the Arctic, slowing the sinking of dense salty seawater that drives the system.
Experts not involved in the research voiced concern. Levke Caesar from Maynooth University said the analysis “presents evidence that the AMOC has already lost stability, which I take as a warning that we might be closer to an AMOC tipping than we think”. David Thornalley at University College London added: “These signs of decreasing stability are concerning. But we still don’t know if a collapse will occur, or how close we might be to it.”
