There is a patch of the North Atlantic, south of Greenland, that has been getting colder while the rest of the planet warms. Oceanographers call it the "cold blob," and they read it as a symptom: the great conveyor that carries tropical heat northward — the Atlantic Meridional Overturning Circulation, or AMOC — is slowing. In work reported this year, one of the field's leading researchers argues the deceleration is arriving earlier and faster than the mainstream climate models projected, and that a shutdown this century can no longer be dismissed as a low-probability event.
What makes the AMOC different from most climate stories is not speed but permanence. The circulation is understood to be "bistable" — it has two possible states, running and collapsed — and a 2026 review concluded the present-day system sits in exactly that regime, where a crossing, once made, does not simply reverse when emissions fall. A separate 2026 study modelled the consequences of a full collapse: not the deep-freeze of disaster films, but a cascade — up to 0.2°C of additional global warming as the Southern Ocean flips from carbon sink to source, sharp cooling across the North Atlantic and Europe, monsoons pulled out of place. And fresh modelling finds the West Antarctic ice sheet and the AMOC are coupled, each capable of nudging the other over its edge.
None of this is settled. The largest climate models still project gradual weakening rather than abrupt collapse this century, and two camps — those reading early-warning signals in the data, those trusting the models — genuinely disagree about timing. But the disagreement is now about when, not whether, the current is weakening, and about how close the threshold lies. What sets this apart is the door at the end of it: cross the line and, on any timescale that matters to human civilisation, there is no going back — no policy, no carbon drawdown, no treaty that reopens it. The task is not to reverse the current, but to keep it from crossing at all.
Sources
The cold blob and the pace: the Boston Globe on the 2026 finding that the AMOC is decelerating earlier than modelled. Why a crossing would be permanent: Carbon Brief's 2026 review of the evidence that the AMOC is bistable and presently in that regime. What a collapse would do: Down To Earth on the 2026 modelling of an AMOC shutdown — extra warming, Arctic cooling, the Southern Ocean turning from sink to source. The ice-sheet coupling: Science Advances on West Antarctic meltwater and AMOC resilience.
Further Reading
The gradualist case: Carbon Brief's explainer on why many climate models still project a slow weakening rather than an abrupt collapse this century — the mainstream counter to the early-warning camp.