Rapid warming may tip Atlantic circulation at 2°C, while slower warming may avert collapse

For several years, climate scientists have shown that the Atlantic Meridional Overturning Circulation (AMOC) could come to a halt if the world warms too much. New research from Utrecht University shows that this picture is incomplete: The pace of warming also determines whether the AMOC stays stable.

The study was published in the journal Nature Climate Change.

AMOC is the system of ocean currents that transports warm water from the tropics northward. It plays a major role in redistributing heat across the planet and helps keep the climate in Western Europe relatively mild.

Scientists have long suspected that this "heat engine" of the Atlantic Ocean could reach a tipping point. This means that the system would shift from its present-day strong state to a much weaker state within decades. Such a tipping event could be triggered by external influences, such as an increasing amount of meltwater from the polar regions or global warming itself.

Until now, the AMOC was thought to tip and collapse around +4°C of warming. Researchers at the Institute for Marine and Atmospheric Research Utrecht now show that there's more to the story. "Our results show there is not necessarily a fixed temperature beyond which the AMOC inevitably collapses," says lead author René van Westen. "The stability of the circulation depends on how fast the climate is changing."

Slow versus fast warming

To investigate how the rate of climate change affects the strength of the AMOC, van Westen and his colleagues ran a climate model twice. In their simulations, they used a gradually increasing amount of atmospheric CO2, but at different speeds. In one simulation, CO2 concentrations rose slowly (0.5 ppm per year); in the other, much faster (2.5 ppm per year), comparable to today's rate.

Under slow warming, the AMOC remained stable well beyond +4°C, and it did not collapse even at +5°C of warming. Under fast warming, the AMOC collapsed at around +2°C. "We deliberately looked at a scenario that is much slower than what we're experiencing today," explains co-author Reyk Börner. "That allowed us to isolate the effect of the warming rate alone, independent of how warm it eventually gets."

The explanation lies in how the ocean is able to adjust to change. "Under slow warming, the entire ocean, from the surface down to its deepest layers, has time to gradually reorganize and adapt to the changing conditions," says co-author Henk Dijkstra, professor of dynamical oceanography. "Under faster warming, the ocean simply can't keep up."

According to the researchers, the critical warming rate lies around 0.3°C per decade, a pace the world is already approaching. Van Westen compares it to driving a car: "If you're driving toward a wall, it makes sense to steer around it. To do that, you need to brake, otherwise you fly off the road. When it comes to global warming, the world is still pressing extra hard on the accelerator right now."

In perspective

The same research group has published on AMOC stability several times in recent years, each time from a slightly different angle.

• In 2024, the group showed that an increasing amount of meltwater in the North Atlantic makes the AMOC more unstable. This mechanism had long been suspected, but this study was the first to demonstrate it in a modern, complex climate model. The results confirmed that there is a critical meltwater threshold beyond which the AMOC becomes unstable. However, this threshold is unrealistically high, meaning that the present-day AMOC is unlikely to become unstable through this contribution alone. That study did not account for global warming or its pace.
• A later study examined different global warming scenarios and concluded that the AMOC would reach a tipping point around 2060 under both intermediate- and high-emissions scenarios. In those simulations, the tipping point was reached at approximately 2.5°C of global warming.
• The new study explains why the results of such studies can differ and why estimated temperature thresholds vary between climate models and emissions scenarios. While the AMOC has a critical threshold for meltwater, no universal temperature threshold exists. Instead, AMOC stability depends on the rate of warming: The faster the climate warms, the more vulnerable the AMOC becomes, whereas slower warming allows it to remain stable under substantially higher levels of global warming.

Climate policy

The slower the warming, the more time the Atlantic Ocean has to adapt and the lower the near-term risk of an AMOC collapse. That has implications for how we think about climate policy: Much current policy, including the Paris Agreement, is aimed at limiting the eventual peak temperature. This is sometimes based on so-called overshoot pathways: temporary global warming past that limit, on the assumption that future technology could later bring the temperature back down.

According to Westen, that assumption is risky. "A tipping point that induces an AMOC collapse could already be triggered during such a temporary overshoot. Once that happens, it can't simply be undone. It's comparable to coral reefs: Once they die off due to ocean warming, they don't come back, even if the temperature drops again later."

If policy focuses only on the eventual warming peak, it may already be too late. The researchers therefore argue that emission reductions aimed at limiting the rate of global warming deserve their own place on the policy agenda.

René M. van Westen, Reyk Börner and Henk A. Dijkstra, Failure to track a stable AMOC state under rapid climate change. Nature Climate Change. DOI: doi.org/10.1038/s41558-026-02730-w

Citation: Rapid warming may tip Atlantic circulation at 2°C, while slower warming may avert collapse (2026, August 13) retrieved 13 August 2026 from https://phys.org/news/2026-08-rapid-atlantic-circulation-2c-slower.html

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Reporting from Phys.org contributed to this story.