The Possible Collapse of Oceanic Circulation

This map, via Down to Earth shows the Atlantic Meridional Overturning Circulation (AMOC).

The AMOC is like a "heat conveyor belt". It moderates temperatures on the planet by moving warmer air to northern latitudes while returning cooler air to the tropics. It has already slowed down by about 15%, according to a 2021 study published in Nature Geoscience. This current could come to a halt sometime this century due to global warming. 

The effects of this would be pretty devastating to much of the planet. It would mean more heat in the tropics, possibly drying out the Amazon Basin, more melting of Antarctic ice and limiting monsoons in India and Africa which are relied upon for growing crops. In Europe a collapse would mean a major cooling of average temperatures. We might even see a reverse of the current migration situation where climate refugees begin moving south instead of north. For much more details, see downtoearth.org.