Running Amoc

An ocean current that regulates global temperatures and rainfall is weakening and could collapse.

- BY ANDREA GRAVES

There are many things we don't appreciate unless they slip away. Crops that don't fail. Pleasant temperatures. The right amount of rain.

An underappreciated helper with all those things is Amoc - the Atlantic Meridional Overturning Circulation. It moderates climate at a global scale, and its future seems dubious.

Amoc is a conveyor belt of ocean currents that drags immense volumes of warm water from the Southern Hemisphere to the northern Atlantic. In return, cold water flows south. The flow is driven by the classic rule that heavy stuff sinks and light stuff rises - and similarly, cold drops and heat rises.