A collapse of the Atlantic Meridional Overturning Circulation, or AMOC, could do more than reshape weather across the Northern Hemisphere. New climate modelling suggests it could also trigger a major carbon release from the Southern Ocean, adding a long-term warming feedback that scientists say has not been fully appreciated.
The study finds that if the current system shuts down, deep waters near Antarctica could rise and release up to 640 billion tonnes of carbon dioxide into the atmosphere. That extra greenhouse gas could raise global temperatures by about 0.2°C, while also increasing the risk of further ice loss and sea-level rise.
Why AMOC matters
AMOC is part of a vast ocean conveyor belt that moves warm, salty water northward before it cools, sinks, and flows back south at depth. This circulation helps keep Europe milder than it would otherwise be, and scientists have already warned that it is weakening because of climate change.
Fresh meltwater from the Greenland ice sheet is one of the main reasons for the slowdown. Recent buoy measurements show the southward return flow has weakened, and some researchers estimate the system has already declined by around 15%.
What the new model found
The research team modelled AMOC shutdown under different future climate scenarios. It found that when atmospheric carbon dioxide reaches 350 parts per million or more, the circulation does not recover after collapse.
That matters because current CO2 levels are about 430 ppm, which suggests a shutdown could become irreversible once the threshold is crossed. The model also showed that AMOC failure would weaken the ocean layering around Antarctica and allow deep water to mix upward.
How the carbon feedback could work
The deep waters around Antarctica store carbon that has built up over long periods. Some of it comes from the atmosphere, while some comes from dead plankton that sank to the ocean floor and decomposed.
When the ocean layers break down, that carbon can escape back into the air. As lead researcher Da Nian of the Potsdam Institute for Climate Impact Research put it, “AMOC collapse could trigger … big mixing and release the carbon stored in the deep water.”
Main projected effects from an AMOC collapse
- Up to 640 billion tonnes of CO2 could be released near Antarctica.
- Global temperatures could rise by an additional 0.2°C.
- The Arctic could cool by about 7°C.
- Antarctica could warm by about 6°C.
- The East Antarctic Ice Sheet could face a higher risk of instability.
The model suggests the Southern Ocean response would unfold through a chain reaction. Less-salty water flowing south from the North Atlantic would alter Antarctic surface waters, weaken the normal layering, and let deeper water rise.
Scientists urge caution, but warn of domino effects
Not all researchers view the result as settled. Jonathan Baker of the UK Met Office said the findings are striking, but noted that the strength of Southern Ocean convection remains uncertain across climate models.
Still, the broader risk is serious because AMOC collapse has already been linked to colder winters in Europe, disrupted monsoons in Africa and Asia, and wider shifts in global climate patterns. Johan Rockström, also at the Potsdam Institute, said the study shows a severe event could have “even worse implications than we previously thought.”
Why the timing matters
The carbon release itself would likely unfold over 1,000 years or more after an AMOC shutdown. But the decision point, researchers say, may come much sooner because today’s emissions could lock in the collapse within decades.
Rockström warned that the “commitment time” may fall within the next 25 to 50 years, even if the greatest impacts arrive much later. That makes the study a warning not only about ocean circulation, but also about how quickly human emissions can push the climate system toward irreversible change.
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