Atlantic Ocean current acts as Earth's 'heat valve,' and a slowdown could boost warming

A key system of Atlantic Ocean currents appears to affect more than European weather and the movement of nutrients through the ocean. Researchers say it may also determine how much heat Earth stores.

That matters because a climate-driven slowdown would do more than disrupt conditions in one region — it could add to the planet's warming.

Here's what to know

At the center of the study is the Atlantic meridional overturning circulation. This network carries warm, salty surface water north and returns colder, denser water south at depth. 

According to a news release, the researchers concluded that Earth tended to lose heat during stronger AMOC phases in the past, whereas weaker phases coincided with heat gain.

"The AMOC works like a heat valve that controls the energy budget of the planet," Christo Buizert, a paleoclimatologist at Oregon State University and lead author of the study, said.

For the last 11,700 years, the AMOC has stayed relatively strong. Even so, many climate models indicate that human-caused warming could weaken it.

The study estimates that earlier weak-AMOC intervals added about as much warming as 25 parts per million of carbon dioxide would today — roughly a decade of human pollution.

More background

Conversations about the AMOC usually focus on how it shifts heat from place to place. When that circulation slows, parts of the North Atlantic, including nearby areas such as Greenland, can cool, and abrupt changes during ice-age times were linked to sharp regional temperature drops.

The researchers say the mechanism is more than a simple transfer of warmth between north and south. Using three climate models, they found that when the AMOC weakens, heat that would normally vent in the North Atlantic instead builds up in the ocean interior.

So, a cooler ocean surface in one area can hide a broader rise in stored heat elsewhere.

Buizert explained it this way: "It's as if the whole ocean acts as a giant bucket of heat."

Ocean heat influences weather patterns, sea level rise, marine ecosystems, and the pace of warming. A system that traps more heat in the ocean can worsen climate risks even if one region cools temporarily.

What's being done?

Because the AMOC is a crucial part of Earth's large-scale circulation, researchers are watching it closely. This study used evidence from abrupt climate swings in the past to gauge how the current may behave in the future.

"Our research also shows that in a warmer world, the AMOC tends to be more stable, which would suggest that these 'tipping point' events might not occur in the future," Buizert said. "... But more research is needed to better understand the future stability of the AMOC."

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