AMOC Collapse Could Flip Southern Ocean to Carbon Source
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- AMOC collapse would release stored ocean carbon into the atmosphere, adding between 0.17°C and 0.27°C of additional global warming across all scenarios analyzed in the new study.
- The Potsdam Institute for Climate Impact Research (PIK) published the findings in Communications Earth & Environment, with lead author Da Nian, co-author Matteo Willeit, and PIK Director Johan Rockström.
- At CO₂ levels of 350 ppm or higher — well below today's ~430 ppm — a collapsed AMOC stays permanently in the 'off' state, whereas at pre-industrial 280 ppm the circulation fully recovers once freshwater forcing ends.
- The mechanism is enhanced Southern Ocean mixing that brings carbon-rich deep waters to the surface, converting the region — which currently absorbs roughly a quarter of human-made CO₂ emissions — into a net carbon source.
- Regional impacts are stark: in a 450 ppm CO₂ scenario, Antarctic temperatures rise 6°C while Arctic temperatures drop 7°C due to AMOC collapse.
- Rockström framed it bluntly: rising emissions today increase the likelihood of a stronger climate response down the line, since higher atmospheric CO₂ at the time of shutdown correlates with greater additional warming.
Why it matters: The ocean has absorbed roughly a quarter of human-caused CO₂ emissions, so converting the Southern Ocean from sink to source would not just add 0.2°C of warming on its own — it would also remove a critical buffer against further emissions, a feedback loop that strengthens with every ppm of CO₂ added before any potential AMOC tipping point.
