Imagine you’re in a bar, watching a patron tilt backwards on their stool. Further and further back they lean, the stool’s feet lifting more and more off the floor, until eventually, to nobody’s surprise but their own, they fall. They’re hurt and bruised, the stool is completely broken, and the bar staff are irate.
Now imagine that wobbling stool is the second largest ocean on Earth.
Sorry to inform you but… we might be in trouble.
What is the AMOC?
AMOC stands for Atlantic Meridional Overturning Circulation, and it refers to the huge web of ocean currents moving through the Atlantic Ocean. It’s often likened to a huge conveyor belt: it brings warm, nutrient-rich water north from near the equator, and cold water south from near the pole.
These aren’t the kind of currents that you’d experience on a day at the beach, however. “Tidal currents occur close to shore and are influenced by the sun and moon,” notes the National Ocean and Atmospheric Administration (NOAA), and “surface currents are influenced by the wind.”
“However, other, much slower currents that occur from the surface to the seafloor are driven by changes in the saltiness and ocean temperature,” it explains – “a process called thermohaline circulation.”
These latter currents are the kind that form the AMOC, and it’s responsible for quite a few quirks of the Atlantic Ocean and climate. It’s why, for example, temperatures in Tromsø, within the Norwegian Arctic, can average -3°C (26.6°F) even in January, while, say, Southampton Island in Canada, some 591 kilometers closer to the equator, suffers through averages of -29 (-20.2). And “it is a key reason why Europe’s climate has been stable for thousands of years,” wrote Robert Marsh, Professor of Oceanography and Climate at the University of Southampton, in a 2023 article for The Conversation.
It’s also, seemingly paradoxically, why the weather in Europe is so unstable. “The weather and climate of Europe, and northern Europe in particular, is highly variable from day to day, week to week and year to year,” Marsh pointed out, “with competing air masses (warm and moist, cold and dry, and so on) gaining or losing influence, often guided by the high-altitude jet stream.”
It is, overall, pretty important and influential. So we should maybe be a bit worried about the fact that it seems to be breaking down.
A slow and wobbly process
The AMOC moves at a pace generously described as “leisurely” – that is, it takes about 1,000 years for any given parcel of water to complete its journey around the belt. But there’s some evidence that it’s slowing down even further: in recent years, less and less heat has been arriving in Europe, with the AMOC’s present flow being weaker than any point in the last millennium.
Is it headed for a full stop? Not imminently – but that’s not really the issue. The real fear among climate scientists is instead that, like that careless drunk on a barstool, it’s wobbling between stability and instability – and unless we do something soon, it might just collapse completely.
“The general concern that there is a risk of AMOC collapse goes back more than half a century,” explained Stefan Rahmstorf, an oceanographer who runs the Earth system analysis department at the Potsdam Institute for Climate Impact Research in Germany, in 2024. “The fact that the AMOC has a tipping point was first described in a famous study by the American oceanographer Henry Stommel in 1961; he showed that the system was unstable because of a self-amplifying feedback [system].”
“It’s been known for a long time,” he told Live Science, “but until recently it was considered as low probability but high impact. It’s like telling someone who boards a plane that it has a 5 percent probability of it crashing.”
Today, however, the outlook isn’t so optimistic. “Yet now, in light of new evidence, I think many of my colleagues, including myself, don’t really consider it low probability anymore,” Rahmstorf said.
What’s the evidence for such a prognosis? Well, that wobble we mentioned? It’s not as metaphorical as you might have thought: since the beginning of the 20th century, temperatures in the North Atlantic have quite literally been “wobbling” from above the global average for the decade, to below it, and back again.
That’s exactly the kind of behavior that precedes a wholesale collapse. “When you approach a tipping point, the system starts to wobble back and forth, so there’s more natural variability because the system is less stable,” Rahmstorf explained – “so it’s slower to pull back towards its equilibrium state when it’s just displaced by a little bit of random weather noise, for example.”
What if the AMOC collapses?
So, what’s the equivalent of a global-scale concussion in the pub? As you can probably imagine, nothing good: we should expect more extreme temperatures in Europe; more floods and droughts; colder and dryer climates in places like Ireland and Scandinavia, who thus far have been made lush by the Atlantic currents. A larger temperature differential across Europe, in turn, would drive more extreme weather events – more storms; stronger storms; tropical storms turning up where they’ve no right to.
It would be bad news for the ocean at large, too. Sea levels would rise – significantly more than they’re going to already – and the ecosystems would suffer: “The AMOC […] transports oxygen into the deep ocean,” Rahmstorf pointed out. “This is also bad news [if this process stops], because if you get an oxygen-depleted ocean it would disrupt the entire web of life in the northern Atlantic.”
That oxygen accompanies a whole lot of CO2 – up to 25 percent of the amount we produce, in fact – to the bottom of the ocean. It’s been our saving grace for a long time – and should the AMOC stop, a whole lot of that greenhouse gas will instead be hanging around in the atmosphere, contributing even further to global warming.
Overall, it paints a bleak picture. Higher temperatures everywhere except, perhaps, one little spot in the North Atlantic; droughts and floods worldwide; major storms that would destroy infrastructure and lead to huge loss of life. “We mostly know from paleoclimate data how drastic and worldwide these changes are,” Rahmstorf warned – “even reaching as far as New Zealand, which is as removed from the North Atlantic as you can possibly get.”
What can we do?
Is there any hope for the AMOC? Perhaps – but it’ll take a whole lot of political power and will. “The main thing is to prioritize sticking to what was agreed in the Paris Agreement,” advised Rahmstorf. “Namely, to limit global warming to 1.5 C [2.7 F], if possible, but certainly well below 2 C [3.6 F].”
“That means 1.7 C or maybe 1.8 C,” he added. “If we manage to do that, and all countries have committed to do that, then we can really minimize the risk of going over the tipping point.”
“No guarantee, but I think it’s very likely that we would actually avoid going across that tipping point if we stuck to the Paris Agreement.”
Source Link: The North Atlantic Is Wobbling – And It's A Warning For Us All
