A growing body of evidence suggests that a massive change is underway in the sensitive circulation system of the Atlantic Ocean, a group of scientists said Thursday. The Atlantic meridional overturning circulation (AMOC), a system of currents that includes the Florida Current and the Gulf Stream, is now “in its weakest state in over a millennium,” these experts say. This has implications for everything from the climate of Europe to the rates of sea-level rise along the U.S. East Coast.

Although evidence of the system’s weakening has been published before, the new research cites 11 sources of “proxy” evidence of the circulation’s strength, including clues hidden in seafloor mud as well as patterns of ocean temperatures. The enormous flow has been directly measured only since 2004, too short a period to definitively establish a trend, which makes these indirect measures critical for understanding its behavior.
https://www.washingtonpost.com/climate-environment/2021/02/25/atlantic-ocean-currents-weakening-amoc-gulf-stream/

The general conception of a tipping point is that there’s some fixed physical threshold beyond which the system trips into a different state. But they found that a lesser-known phenomenon known as a rate-­induced tipping point, triggered by a sudden increase in the system’s rate of change, might halt the currents as well. In other words, too much change occurring too fast could cause the system to break down. The Atlantic circulation could be susceptible to this if the water flowing from ice sheets increases rapidly enough, according to the study, which was published in the Proceedings of the National Academy of Sciences in March.

It’s just one model and one study, but it suggests that the climate system could be more fragile than previously appreciated. These “chaotic dynamics” mean that “we maybe cannot expect, even if our models get much better, to be able to predict with 100% confidence whether such an element of the climate system will go into another state or not,” Lohmann says.

https://www.technologyreview.com/2021/12/14/1041321/climate-change-ocean-atlantic-circulation/