Utrecht study: AMOC stability hinges on warming rate, not just temperature
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Utrecht University researchers report in Nature Climate Change that the stability of the Atlantic Meridional Overturning Circulation depends on how fast the planet warms, not only how warm it gets. In model simulations, slow CO2 increases of 0.5 ppm per year left the circulation stable beyond +5°C, while faster increases of 2.5 ppm per year triggered collapse at around +2°C.
Key Facts
- Lead author René van Westen said the AMOC has no fixed temperature threshold beyond which it inevitably collapses.
- In a slow-warming model with CO2 rising 0.5 ppm per year, the AMOC remained stable beyond +5°C and did not collapse.
- In a fast-warming model with CO2 rising 2.5 ppm per year, comparable to today's rate, the AMOC collapsed at around +2°C.
- Utrecht University scientists published the findings in the journal Nature Climate Change.
- Co-author Reyk Börner said the slow scenario was much slower than today and designed to isolate the warming-rate effect.
Warming Rate Effect
Previous estimates put an AMOC tipping point at about +4°C of global warming. Utrecht University scientists found no fixed temperature beyond which the circulation inevitably collapses. Lead author René van Westen said the circulation's stability depends on how fast the climate is changing. Two worlds reaching the same eventual temperature could experience very different AMOC outcomes depending on warming speed.
Slow and Fast CO2 Paths
Researchers ran two climate model versions with CO2 rising at different rates. In the slow simulation, CO2 increased 0.5 ppm per year and the AMOC remained stable beyond +4°C and did not collapse even after warming reached +5°C. In the fast simulation, CO2 increased 2.5 ppm per year, comparable to today's rate, and the AMOC collapsed at around +2°C. Co-author Reyk Börner said the slow scenario was much slower than today and was designed to isolate the effect of warming rate alone.
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Utrecht study: AMOC stability hinges on warming rate, not just temperature
