AMOC is part of a system of currents which move heat around the world's oceans. It delivers a stupendous flow of heat—more than 1,000 terawatts—to the North Atlantic. (Global civilisation runs at a mere 20 terawatts.) Changes in sea-surface temperature and salinity caused by global warming could conceivably make it stall; such abrupt shutdowns are clearly visible in the geological record. Both theory and models suggest that after an as-yet-unknown temperature threshold is passed, a collapse could take just a few decades. Parts of AMOC may already be in slow decline.
A complete AMOC shutdown would mean sudden, severe cooling for Europe even as the rest of the world keeps warming. Brussels could hit -20°C in a bad winter; Oslo could reach almost -50°C. February sea ice in the North Sea could extend as far south as the Humber estuary and the Frisian Islands north of the Netherlands. Average rainfall in parts of northern Europe would drop precipitously; by one estimate as much as 80% of England's arable land would no longer be farmable without irrigation. Storms would worsen; in some models, so might summer heatwaves.
Beyond Europe, an AMOC collapse would cool the northern hemisphere as a whole, pushing the tropical rain belt southward. That would be very bad for African countries on the southern edge of the Sahara and could be devastating to the Amazon.
The subpolar gyre is a circulating current in the north Atlantic that helps power AMOC. If too much fresh water from a melting Greenland ice sheet flows into the gyre, it could be disrupted, increasing the odds of AMOC collapse.
In February 2025 ARIA announced a five-year, £81m ($109m) programme involving 26 teams to build an early-warning system for climate tipping points, focusing on the Greenland ice sheet and the subpolar gyre. Teams include the British Antarctic Survey (underwater drones to map the ice face) and Oshen, a British startup deploying self-sailing robots with solar-powered sensors in the subpolar gyre. As of 2025 no government apart from possibly the Nordic countries is considering AMOC collapse with the seriousness afforded to other high-impact risks such as pandemics.
Bernard Shaw is an excellent man; he has not an enemy in the world, and none of his friends like him either.