A collapse of the Atlantic Meridional Overturning Circulation (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 the ferocity of storms and send temperatures plunging in Europe [UK & Scandinavia1], while pushing up sea levels on the eastern coast of North America and further endangering the Amazon rainforest and Antarctic ice sheets. Scientists have previously said a collapse must be avoided at all costs.
Studies based on ocean measurements indicate that AMOC is becoming unstable and approaching a tipping point, beyond which a collapse will be unstoppable. They have suggested this would happen this century, but there are only 20 years of direct measurements and data inferred from earlier times bring large uncertainties.
Climate models have indicated that a collapse is not likely before 2100, but they might have been unrealistically stable compared with the actual ocean system.
The latest study is important because it uses climate models to reveal the reason that AMOC is more stable: winds in the Southern Ocean continuing to draw water up to the surface and drive the whole system. The study does not rule out an AMOC collapse after 2100, and other modelling research suggests collapses will occur after that time.
“We found that the AMOC is very likely to weaken under global warming, but it’s unlikely to collapse this century,” said Dr Jonathan Baker at the UK’s Met Office, who led the latest study. He said it was reassuring that an abrupt AMOC crash was improbable, and that the knowledge could help governments plan better for future climate impacts. AMOC weakening would still bring major climate challenges across the globe however, with more floods and droughts and faster sea level rise, he added.
“Of course, unlikely doesn’t mean impossible,” he said. “There’s still a chance that AMOC could collapse [this century], so we still need to cut greenhouse gas emissions urgently. And even a collapse in the next century would cause devastating impacts for climate and society.”
Prof Stefan Rahmstorf, an AMOC expert at PIK, said the latest study considered a collapse to be the total cessation of the currents in the North Atlantic, while previous studies have termed a greatly weakened AMOC a collapse.