AMOC and the Inevitable Climate Threat

Like other acronyms that slowly seeped into our consciousness — think COVID — I predict that you’ll soon be familiar with AMOC, the Atlantic Meridional Overturning Circulation. We and our children may — with a great deal of luck and statesmanship — dodge such potential global catastrophes as another pandemic (thanks to the magic of RNA vaccines — see “mRNA Vaccines vs. the Pandemic,” May 23, 2024), nuclear war, or an AI doomsday scenario. What’s inevitable, however, is the collapse of the AMOC, with far-reaching consequences. The only question is, when?

The AMOC can be thought of as a vast conveyor belt of water bringing comparatively salty warm surface water from the Southern Hemisphere northeast across the Atlantic to Northern Europe in the form of the Gulf Stream. As it cools in the northeast Atlantic, the water becomes denser and sinks before returning at depth to the tropics. This great circulation pattern has endured for at least 100,000 years (since the last Interglacial Period) and, without global warming, would continue into the far future.

The AMOC is a critical component of global weather patterns, particularly on both sides of the North Atlantic, which would otherwise be about 5 degrees C (9 degrees F) colder than they are now. That’s on average — at one extreme, Norway would be about 20 degrees C (36 degrees F) colder without the AMOC. And not just in the North Atlantic: The consequences of a collapse of the AMOC would be felt worldwide, disrupting weather patterns everywhere. These would include catastrophic shifts in annual monsoons and extreme storm events in both hemispheres. Taking one specific example of a world without the AMOC, the Organization for Economic Co-operation and Development OECD estimates that we’d lose half the land now being used to grow wheat and maize (which together supply 40 percent of global calories). Fisheries, meanwhile, would be decimated without the AMOC bringing nutrients from the depths to the surface.

Unfortunately, we humans are in the process of slowly but surely sabotaging the AMOC. Since the start of the Industrial Revolution we have been burning fossil fuels, pumping billions upon billions of tons of carbon dioxide into Earth’s atmosphere, leading to average temperatures rising exponentially due to the greenhouse effect. This, inevitably, will lead to a slowing down and eventual complete stoppage of the AMOC. It’s probably already happening — climatologists and oceanographers are divided on the existing situation — but the consensus is that the current will slow by up to one-third over the next 20 years. The main culprit of this weakening is Greenland. Global warming is currently causing huge volumes — an estimated 40 million gallons per second — of fresh water from Greenland’s melting glaciers to merge with the AMOC, diluting its salty water and thus preventing it from sinking into the depths before beginning its southwest return flow (fresh water being less dense than salty water).

Last October, 44 oceanographers representing 15 countries published an open letter warning that the risk of the AMOC totally collapsing before 2100 has been “greatly underestimated” up until now, and that such a collapse will have “devastating and irreversible” global impacts. Well, not quite irreversible. According to Stefan Rahmstorf of Germany’s Institute for Climate Impact Research (who organized the letter), a shutdown of the AMOC “won’t last forever … it would last on the order of 1,000 years before it recovers.”

The letter also refers to the latest report by the Intergovernmental Panel on Climate Change that states, “There is medium confidence that the AMOC will not collapse abruptly before 2100.” Which is my new definition of “cold comfort.”

Barry Evans (he/him, barryevans9@yahoo.com) worries about the sort of world we’re leaving to our kids.

This article appears in 2025 NCJ Pet Photo Contest Winners.