Scientists at Utrecht University have published findings indicating that the stability of the Atlantic Meridional Overturning Circulation (AMOC) depends not solely on how much the planet warms, but also on the speed at which warming occurs. The research, appearing in Nature Climate Change, challenges the prevailing assumption that a fixed temperature threshold exists beyond which the AMOC would inevitably collapse.
The AMOC is a major ocean circulation system that transports warm water northward from tropical regions, playing a significant role in regulating global climate patterns and maintaining relatively temperate conditions in Western Europe. Researchers have long considered this system vulnerable to crossing a tipping point that could trigger its collapse into a much weaker state within decades. The study findings suggest this concern may need reconsideration based on warming rate as well as magnitude.
To examine the importance of warming speed, researchers ran climate model simulations with two different rates of atmospheric carbon dioxide increase. Under a slow warming scenario, the AMOC remained stable even beyond 5 degrees Celsius of warming. When warming occurred at faster rates comparable to current conditions, the circulation collapsed at approximately 2 degrees Celsius. The researchers identified a critical warming threshold of around 0.3 degrees Celsius per decade, which the world is already approaching.
The difference reflects the ocean’s capacity to adapt to changing conditions. Gradual warming allows the entire ocean structure to reorganize throughout its depth over time. Rapid warming outpaces the ocean’s ability to adjust, leaving circulation patterns more susceptible to instability. This distinction carries implications for climate policy, suggesting that the pathway toward a temperature target may be as important as the target itself.
The findings help explain variations in earlier estimates for when the AMOC might reach a tipping point. Rather than possessing a universal temperature threshold for collapse, the system’s stability appears partly dependent on warming velocity. The research suggests that slowing the pace of global warming could reduce near-term risks to this critical ocean circulation system.
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