The Atlantic’s vital currents could collapse. Scientists are racing to understand the dangers. | MIT Tech Review

by James Temple for the MIT Technology Review, 14th Dec 2021 | https://www.technologyreview.com/2021/12/14/1041321/climate-change-ocean-atlantic-circulation/

You may never have heard of one of the most important forces in the planet’s climate system: a network of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC).

The Atlantic circulation is, effectively, one leg of the world’s mightiest river. It runs tens of thousands of miles from the Southern Ocean to Greenland and back, ping-ponging between the southwestern coast of Africa, the southeastern US, and Western Europe.

The system carries warm, shallow, salty water northward, and it’s a major factor in why Western Europe is warmer than eastern Canada even though they lie at roughly the same latitude. The waters become cooler and denser as they reach the high latitudes, forcing the currents to dive miles below the surface, spread outward, and bend back southward. That sinking of the water deep into the ocean helps propel the system.

The problem is the Atlantic circulation seems to be weakening, transporting less water and heat. Because of climate change, melting ice sheets are pouring fresh water into the ocean at the higher latitudes, and the surface waters are retaining more of their heat. Warmer and fresher waters are less dense and thus not as prone to sink, which may be undermining one of the currents’ core driving forces.

If the system collapsed, it would be a climate disaster, freezing the far north of Europe, cutting crop production across the continent, and pushing up sea levels on the Eastern Seaboard.

That’s why a new international research expedition is underway to better understand the AMOC, how global warming is changing it, and how much more it could shift in the coming decades. Read the full story.

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