🌊 Is the great current carrying heat toward Europe on the verge of collapse?

The Atlantic’s great system of ocean currents could tip much faster than previously thought.

This system is known as the Atlantic Meridional Overturning Circulation, or AMOC. It transports warm water northward, then brings colder water back southward at depth. This movement helps redistribute heat between regions of the globe, particularly around the North Atlantic. Its collapse would cause a sudden and lasting change in the climate, especially in Europe.

To study its stability, René van Westen, Reyk Börner and Henk Dijkstra used climate simulations. The researchers compared several ways of reaching a warmer climate, with increases occurring at different rates.

This distinction greatly changes the outcome. In two scenarios where the change is relatively rapid, the AMOC collapses in the model after global warming of approximately 2.2°C and 2.8°C. These values correspond to the increase in average global temperature compared with the reference climate used in the simulations.

With a much slower rise in CO2, the behavior is different. Its atmospheric concentration then increases by only 0.5 parts per million each year. In this simulation, the AMOC remains stable up to approximately 5.5°C of global warming.

To understand this difference, it is necessary to consider the time the ocean needs to reorganize. When the change is slow, its surface waters and deep layers can evolve together. The simulations also show more evaporation and less sea ice. These changes help maintain the circulation despite warming.

A rapid change does not leave as much time for this stabilizing mechanism. The ocean may then be unable to follow the stable state that would be possible at the same temperatures under slower change. In other words, two trajectories reaching comparable warming do not necessarily lead to the same state of the Atlantic.

This result comes from simulations and does not establish a date for the collapse of the AMOC in the real world. However, it opens a concrete avenue for future climate projections: incorporating the rate of change more fully, rather than considering only the final temperature, when assessing the future stability of this ocean circulation.