Atlantic Meridional Overturning Circulation: A Looming Climate Threat

Global warming, driven by human carbon emissions, is increasingly impacting the Atlantic Meridional Overturning Circulation (AMOC), a crucial system of ocean currents including the Gulf Stream that significantly influences Europe’s climate. A complete collapse of the AMOC could unleash vast amounts of stored carbon from the deep Southern Ocean into the atmosphere, creating a dangerous feedback loop that would exacerbate global warming.

Previous research has highlighted the potential for an AMOC shutdown to cause colder winters in Europe, disrupt monsoon patterns in Africa and Asia, and contribute to overall increases in global temperatures. However, new computer modeling reveals an even more concerning consequence: the potential release of up to 640 billion tonnes of carbon dioxide near Antarctica, leading to an additional 0.2°C warming of the planet.

The Southern Ocean’s Carbon Reservoir

“AMOC collapse could trigger significant mixing in the Southern Ocean, releasing the carbon stored in the deep water,” explains Da Nian, lead author of the study from the Potsdam Institute for Climate Impact Research in Germany. “This is a relatively new finding with potentially far-reaching implications.”

Co-author Johan Rockström emphasizes the gravity of the situation: “The key message is that a very serious event… could have even worse implications than we previously thought. We must proceed with caution, as one disruption can trigger a cascade of negative effects.”

How the AMOC Works and Why It’s Weakening

The AMOC functions due to differences in water density. Warm, salty water travels from the Gulf of Mexico towards the North Atlantic, where it cools and sinks, then returns southward along the seafloor. However, scientists believe that freshwater influx from the melting Greenland ice sheet is diluting the water, hindering the sinking process and slowing down the circulation.

Recent buoy measurements confirm that the southward flow is weakening, and the AMOC has already declined by an estimated 15%. Model projections suggest a potential collapse could occur within decades to centuries.

Irreversible Changes and a Critical Threshold

The new study modeled AMOC collapse under various future climate scenarios. The results indicate that if atmospheric CO2 concentrations reach 350 parts per million (ppm) or higher, the AMOC will not recover after a shutdown. Given that current CO2 levels are around 430 ppm, this suggests that an AMOC collapse could be irreversible.

Furthermore, the study found that an AMOC shutdown would initiate convection of deep water to the surface near Antarctica. This deep water, largely isolated beneath a layer of fresher surface water, has accumulated carbon from the atmosphere and from sinking organic matter. The model predicts that much of this carbon would be released into the atmosphere.

Cascading Effects and Global Impacts

Previous research on past AMOC collapses supports the idea that convection would begin near Antarctica. As less-salty water sinks and flows from the North Atlantic to the Southern Ocean, the waters around Antarctica also become less salty, disrupting the layering and allowing deep water to rise to the surface.

Jonathan Baker from the UK Met Office notes, “Seeing this play out in a warmer climate with such a large CO2 increase is striking. While this is an interesting study, its conclusions depend on whether Southern Ocean convection strengthens, which remains uncertain.”

Beyond carbon release, an AMOC collapse would also have dramatic regional impacts. The Arctic would cool by 7°C, potentially freezing Canada, Scandinavia, and Russia. Simultaneously, Antarctica would warm by 6°C, potentially triggering the collapse of the East Antarctic Ice Sheet and causing significant sea level rise.

Rockström warns that the commitment to this future AMOC collapse could be locked in within the next 25 to 50 years. “What right do we have to hand over to all future generations a less and less liveable planet?” he asks.

Learn more about climate change and ocean currents:

• Ocean acidification and its impact on marine ecosystems
• NOAA on the Atlantic Meridional Overturning Circulation

Journal Reference: Nature Communications Earth & Environment DOI: 10.1038/s43247-026-03427-w