"The research found “an almost complete loss of stability over the last century” of the currents that researchers call the Atlantic meridional overturning circulation (AMOC). The currents are already at their slowest point in at least 1,600 years, but the new analysis shows they may be nearing a shutdown.
Such an event would have catastrophic consequences around the world, severely disrupting the rains that billions of people depend on for food in India, South America and West Africa; increasing storms and lowering temperatures in Europe; and pushing up the sea level off eastern North America. It would also further endanger the Amazon rainforest and Antarctic ice sheets."
It’s quite a complex and not well understood phenomenon. Here’s a research paper from 2019 with some robust reasoning. As far as I understand, it’s a consequence of the fact that the AMOC transports a huge quantity of heat north from the tropics along the Atlantic coast of the US, and as this heat transfer slows down, that will lead to changes in the temperature of the ocean along the eastern seaboard, which hence causes thermal expansion of the water, and that is part of what drives this effect. But as I said, it’s not super well understood - this is an effect that our observations see is happening already, and which our numerical computer models of the Atlantic ocean also show occuring with a slowdown in AMOC.
