AMOC collapse could turn Southern Ocean into carbon source, adding 0.2°C to global warming

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A shutdown of the Atlantic Meridional Overturning Circulation (AMOC) could trigger a substantial release of stored ocean carbon into the atmosphere over hundreds of years, according to a new study that simulated such a collapse under stable climate conditions. This would add 0.2°C of extra global warming. The new paper from researchers at the Potsdam Institute for Climate Impact Research (PIK), published in Communications Earth & Environment, highlights the AMOC's role as a key regulator of the global climate.

To assess how a collapse of the AMOC—a major Atlantic Ocean circulation system that transports warm water north and cold water south—would affect the carbon cycle and global temperatures, the authors simulated Earth's climate stabilizing at different atmospheric CO₂ levels and subsequently applied fresh water input to the Atlantic surface to induce an AMOC shutdown.

At pre-industrial atmospheric CO₂ concentrations of 280 ppm, even if the AMOC collapses under freshwater forcing, it fully recovers once the forcing ends. However, at CO₂ levels of 350ppm or higher—well below today's level of around 430ppm—once the AMOC collapses it stays in the "off" state.

"Higher CO₂ concentrations fundamentally alter the AMOC's stability, pushing the system into a bistable regime where the AMOC could weaken over hundreds of years before shifting to, and remaining in, a collapsed state. Once shutdown, we see it does not recover in the long run," says lead author Da Nian of PIK.

In all scenarios analyzed in the paper, a shift of the AMOC into an off state would see additional warming of 0.17°C to 0.27°C.

"This change in temperatures is driven by a large release of carbon from the Southern Ocean, due to enhanced mixing that brings carbon-rich deep waters to the surface," explains co-author Matteo Willeit of PIK.

Regional temperature changes would be even more pronounced than global mean temperature change. In one scenario at CO₂ concentrations of 450ppm—last experienced by Earth several million years ago, when polar ice was significantly reduced—Antarctic temperatures rise by 6°C while Arctic temperatures drop by 7°C due to AMOC collapse.

"The ocean has been our greatest ally, absorbing a quarter of human-made CO₂ emissions. Our study shows how an AMOC collapse could flip the Southern Ocean from a carbon sink into a carbon source, releasing vast amounts of CO₂ and fueling further global warming. The more CO₂ in our atmosphere at the stage of shutdown, the higher the likelihood of additional warming. Put simply, rising emissions today increase the risk of a stronger climate response down the line," says PIK Director and co-author Johan Rockström.

Publication details

Da Nian et al, Collapse of the Atlantic meridional overturning circulation would lead to substantial oceanic carbon release and additional global warming, Communications Earth & Environment (2026). DOI: 10.1038/s43247-026-03427-w

Journal information: Communications Earth & Environment

Key concepts

ocean mixingocean conveyor beltcarbon fluxocean circulationcarbon cyclingGlobal Warming

Provided by Potsdam Institute for Climate Impact Research