What is the Atlantic Meridional Overturning Circulation, and why are scientists worried about it slowing down?

https://i.cbc.ca/ais/3af3b751-69b0-48ed-8db1-6b839513f63a,1777059512089/full/max/0/default.jpg?im=Crop%2Crect%3D%280%2C333%2C5500%2C3093%29%3BResize%3D%28620%29" title="Waves crash on the coast as post-tropical Cyclone Gabrielle crosses the Atlantic Ocean, in Sao Caetano, Pico island in the Azores, Portugal September 26, 2025." width="620" />

The Atlantic Meridional Overturning Circulation (AMOC) helps nourish aquatic ecosystems and is part of the reason Europe has milder temperatures than places in Canada at the same latitude.

But lately scientists are concerned that it is slowing down and could even potentially collapse.