As the world careens past our hoped-for target of 1.5 degrees Celsius warming, scientists are growing increasingly alarmed that we may be nearing a dramatic, long-feared “tipping point” for a key Atlantic current— a moment when the main ocean current in the Atlantic Ocean becomes destined to shut down, clamping off the primary source of warmth for northern Europe and playing havoc with the global climate.

Such a scenario has been a concern for many decades, but the issue is now heating up. “I have personally researched this for 35 years,” says Stefan Rahmstorf, a physical oceanographer at the Potsdam Institute for Climate Impact Research in Germany, about the fate of the key Atlantic current. “For the first 30 years we considered this a low likelihood event — I would have said a 5 percent chance of occurring. It’s more like 50/50 now. I would even say more likely than not.”

The key Atlantic current and main current in the Atlantic Ocean — the Atlantic Meridional Overturning Circulation — is one of the most powerful drivers of heat around the globe. The AMOC is the reason that northern Europe is so temperate, a couple of degrees warmer than it ought to be given its latitude.

In November, Iceland made the unusual move of designating the risk of an AMOC shutdown a national security threat.

If the AMOC, a key Atlantic current, shuts down, its flow slowing to a near halt, the modeled consequences are catastrophic: Europe dries out, affecting agriculture and wildfires; the temperature difference between northern and southern Europe jacks up by a whopping 7 degrees F (4 degrees C), supercharging storms; the vital African and Asian monsoons weaken; and more. An AMOC collapse is also predicted to stir up the Southern Ocean, which could spew out more of its deep carbon into the air, further warming the globe.

Back in 2021, when the Intergovernmental Panel on Climate Change (IPCC) released its most recent assessment of climate science, experts concluded that the AMOC, a key Atlantic current, will “very likely” slow down, but that the current’s future wasn’t likely to involve an abrupt collapse before 2100. But more recently several studies have hinted that researchers have been overcautious. “Two or three high-impact papers have come out since then warning that we’re approaching a tipping point and approaching a collapse,” says physical oceanographer Neil Fraser of the Scottish Association for Marine Science in Oban. One of them, published last month, predicts that the AMOC will slow to half of its current flow by the end of the century.

Read the full article about the Atlantic Meridional Overturning Circulation by Nicola Jones at Yale Environment 360.