Looking from the bridge of the Norwegian polar analysis vessel Kronprins Haakon (see principal picture), dense pack ice extends into the darkness in each course. To the east, a slim strip of purple paints the noon sky simply above the horizon.
It’s the primary signal of daylight right here in three months. Analysis ships not often enterprise into this area – 1,000km (621 miles) north of the Arctic Circle, within the Greenland Sea – throughout polar evening.
Temperatures fall under -30°C (-22°F) and ice floes greater than a metre (3.3ft) thick make it nearly impassable.
It’s February 2025, and the expedition I’ve joined is gathering important knowledge on the ocean circulation alongside Greenland’s east coast.
Beneath the icebreaker I’m travelling on, the waters flowing deep under the ice and additional out to sea feed a sprawling net of currents that run all the best way throughout the Atlantic Ocean.
Referred to as the Atlantic Meridional Overturning Circulation (AMOC), it performs a central position in controlling the Earth’s local weather, transferring warmth from the tropics to the north.
This technique helps energy the Gulf Stream and is credited with regulating Europe’s temperatures, in addition to being a key participant in international local weather stability.
One of many drivers of world ocean circulation, together with the AMOC, is the sinking of dense water plenty close to the poles.
The Nordic Seas, which join the Arctic and Atlantic oceans, are one of many main areas the place dense, deep waters form on account of floor warmth loss in winter. These waters finally spill into the abysses of the North Atlantic.
However ocean warming and freshening of the subpolar seas close to Greenland, attributable to melting ice and rising rainfalls, is making it more durable for floor waters to sink.
As CO2 emissions proceed to rise and climate change accelerates, scientists are increasingly involved that the AMOC is slowing down – and that it may weaken by as much as 50 per cent by the end of the 21st century.
What’s worse, this important present system may be nearing a tipping point. Past this level, a speedy decline may probably result in its collapse – and the results may very well be widespread.
Researchers wish to get a greater deal with on what collapse may appear like, how probably it’s and when it may occur. Which brings us to the expedition on the Kronprins Haakon.
The scientists onboard the ship are hoping to get some solutions earlier than it’s too late.
In the meantime, different researchers are racing to reply a basic query: if atmospheric CO2 ranges don’t fall rapidly, are there any viable choices for society to stop a worst-case state of affairs?
It’s a query that’s already impressed proposals for extra radical – even excessive – measures.
An enormous oceanic warmth pump
The floor currents of the AMOC deliver sun-warmed, salty water from the equatorial Atlantic to the excessive northern latitudes. Right here, the water cools down, turns into denser and sinks into the deep sea.
It then flows southward and resurfaces once more close to Antarctica, finishing the loop.
The northward transport of heat currents brings warmth to Europe. It’s why winters within the UK are a lot milder than in Labrador, in Canada, which lies at an identical latitude however has a subarctic local weather.
In reality, with out the AMOC, Europe’s local weather could be so much chillier – dropping to chilly extremes as low as -20°C (-4°F) in Western Europe.
The return circulation of the AMOC in flip traps huge amounts of atmospheric CO2, which dissolve within the chilly waters close to Greenland, earlier than being carried down into the deep sea. It additionally provides oxygen to life within the darkest depths of the ocean.
International warming, nevertheless, may jeopardise the soundness of the present system, as climate models indicate. That’s as a result of rapidly rising air temperatures scale back the quantity of warmth escaping from the ocean into the environment in winter.
Consequently, the floor water within the subpolar North Atlantic and the Nordic Seas is getting much less dense, making it much less prone to sink.
In the meantime, meltwater from Arctic sea ice and the Greenland ice sheet will increase the buoyancy of the floor ocean, hampering deep-water formation (the method the place chilly, salty and dense water sinks and drives the present alongside).
The massive danger will likely be if these adjustments speed up unpredictably, which may result in an abrupt decline or ‘tipping’ of the circulation.
“A weaker AMOC implies that much less salty water from the tropical Atlantic is reaching the north,” says Prof Henk Dijkstra, a bodily oceanographer at Utrecht College within the Netherlands. “Therefore, the density of the floor waters close to Greenland decreases even additional.”
It’s a vicious cycle that could push the system to the brink of collapse.
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Worst-case state of affairs
The impacts of an AMOC collapse could be dire, to say the least.
It could have an effect on international local weather, climate patterns and sea ranges: Northwestern Europe could experience extraordinarily chilly winters not seen for the reason that final ice age, whereas the buildup of warmth within the tropics and adjustments within the monsoon cycle may lead to severe droughts in Africa and Asia.
A disrupted AMOC is what impressed the glacial New York Metropolis imagined within the 2004 sci-fi catastrophe movie The Day After Tomorrow – however, in actuality, the results on the US could be very totally different.
The Jap US is predicted to see a dramatic surge in coastal flooding, displacing communities and destroying habitats.
In the meantime, Iceland – whose economic system and meals sector could be notably in danger – has categorized a possible collapse of the AMOC as a threat to its national security.
What’s extra, it’s probably the upshot of all this may be even more international warming.
On the identical time, open questions on the destiny of the AMOC stay: have the currents already misplaced power? Do laptop local weather fashions, which venture a future weakening, seize all of the related ocean processes in enough element?
One of many areas the place researchers have very restricted info on how the AMOC is evolving – particularly throughout winter – is the ice-choked waters of the Greenland Sea. That’s what introduced the Kronprins Haakon out right here within the first place.
In reality, it’s attainable there’s an ignored mechanism right here that would really stabilise the AMOC and curb its decline.
Prof Kjetil Våge, a bodily oceanographer on the College of Bergen in Norway and chief scientist of the expedition on the Kronprins Haakon, thinks that processes within the Arctic area, that are poorly resolved by local weather fashions, may very well be a consider the place the AMOC is headed.
With the assistance of drones and underwater robotic gliders, Våge and his workforce measured the temperature and salinity of the East Greenland Present. Beneath a layer of chilly, contemporary polar water, this present carries hotter, salty Atlantic water alongside the coast.
“The East Greenland Present is a significant supply to the deep return circulation of the overturning circulation,” says Våge. As Earth warms, sea ice on this area is lowering.
Based mostly on pilot knowledge from a earlier research, Våge believes that stronger warmth loss throughout winter from the rising ice-free space could actually enhance dense water formation.
“This might add some resilience to the overturning within the Nordic Seas,” he says – and stop the AMOC from slowing as a lot as usually feared.
Placing a date on decline
However others aren’t so optimistic. Based on a current research by Dijkstra and his colleagues utilizing an Earth system mannequin, the AMOC is already approaching a tipping point.
Of their simulations, the currents decelerate quickly inside a century after crossing it.
The consequences are dramatic:
Arctic winter sea ice extends as far south because the latitude of London. In some coastal areas within the North Atlantic, sea ranges rise by over 0.7m (2.3ft). There are main disruptions to rainfall patterns within the Amazon Basin.
Dijkstra cautions that there will likely be huge challenges as society is compelled to adapt to the intense adjustments that may happen within the occasion of a collapse.
His mannequin runs present a lower in annual imply temperatures by 10–15°C (18–27°F) in Scandinavia and Western Europe.
“I’m extra pessimistic than some years in the past, once I thought the system was way more secure,” he says. “However that’s possibly not the case.”
Different analysis findings additionally recommend a considerable weakening of the AMOC sooner or later, however the timing and extent differ relying on the mannequin and the underlying CO2 emissions.
A study published in 2025 reported that, in excessive emission situations, a tipping level will likely be triggered by the mid-century – with a complete AMOC collapse after 2100.
In distinction, researchers from the College of Exeter concluded in 2024 {that a} full shutdown is unlikely. As a substitute, sturdy winds within the Southern Ocean, which drive upwelling of Atlantic deep waters close to Antarctica, would nonetheless preserve a weak AMOC, even within the worst of instances.
However even a lack of simply 50 per cent of in the present day’s power would probably trigger main local weather upheaval.
A glimpse again in time demonstrates that the risk is actual. Analyses of glacial ice cores and marine sediments have revealed abrupt shifts in AMOC power between chilly and heat phases all through Earth’s historical past.
For instance, a pre-print study (that hasn’t but undergone peer evaluation) by researchers at College Faculty London signifies that in a heat section about 400,000 years in the past, melting of the Greenland ice sheet triggered a weakening of the AMOC by a few third, inflicting extreme cooling of the subpolar area.
Now, research based on ocean age tracers (man-made gases that permit scientists to estimate deep-water formation) means that the AMOC is certainly dropping power.
Based on the research, water plenty within the North Atlantic have turn out to be ‘older’ over the previous 30 years, an indicator that the switch of floor waters to the deep ocean is weakening.
Suspiciously chilly waters
Then once more, direct observations haven’t proven a weakening of the currents, but.
Involved by previous AMOC swings, scientists began monitoring the Atlantic Ocean within the early 2000s to trace adjustments within the circulation because the planet warms up.
These observations have proven important fluctuations, however thus far no clear proof that the AMOC is slowing down.
Figuring out definitive change is difficult due to the big pure variability of the currents, says Eleanor Frajka-Williams, a bodily oceanographer on the College of Hamburg, in Germany.
“A standard view of the overturning circulation is that of a conveyor belt, like in a grocery store, the place every part strikes with the identical velocity. Nonetheless, knowledge from the subtropical and subpolar North Atlantic present that’s not the case, at the very least not on human timescales.”
Different studies have discovered the AMOC to truly have a secure circulation over the previous many years.
However whereas there’s no clear reply on how far alongside any weakening to the AMOC is, many nonetheless assume the outcomes aren’t price risking.
“I’m not satisfied that an AMOC collapse is so imminent,” says Frajka-Williams. However the prices to watch it are minuscule in comparison with what the impacts could be, she says.
“If in case you have a 5 per cent danger that your home goes to burn down, that danger nonetheless appears fairly large. You’re going to insure your home.”
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Drastic options
Navigating at nighttime of the polar evening, between open sea and heavy pack ice over the shelf, the scientists onboard the Kronprins Haakon assume the East Greenland Present may maintain the solutions.
Along with their survey by ship, they’re additionally gathering long-term knowledge on the present flows of the Greenland Sea utilizing devices deployed in 2024. These will likely be retrieved in summer time 2026.
Protecting two full winters, these data will assist Våge’s workforce assess whether or not lack of sea ice may contribute to the soundness of the AMOC in a warming local weather.
If these outcomes present that the processes taking place deep under the ice actually are self-stabilising, it may imply collapse isn’t as probably.
What if, nevertheless, the AMOC received’t stabilise?
With CO2 and different greenhouse gases build up within the environment, international warming is on a trajectory nicely past the 1.5–2°C goal set by the 2015 Paris Settlement.
This increases the risk that important parts of the local weather system – together with the AMOC – are coming into perilous territory.
It’s for that reason that technological fixes are more and more being thought of, to keep away from catastrophic tipping factors from being triggered.
These highly controversial geoengineering ideas vary from injecting sunlight-reflecting particles into the environment to chill the planet to sucking CO2 molecules out of the air and storing them underground – and even alkalising the oceans with crushed rock to extend marine carbon storage.
Then there’s the concept of elevating massive seafloor barriers (for instance, in Greenland’s fjords), to brake the circulation of glaciers into the ocean and maintain out heat water, which may in any other case soften them from under.
One other includes placing up 100m (328ft) high underwater curtains to guard glaciers from heat currents and scale back ice loss.
Clearly, the prices, technical and logistical challenges, and required supplies for these constructions in distant areas could be large.
The schemes would additionally probably have a unfavorable impact on marine ecosystems, fisheries and tourism. That’s why many researchers consider blocking glaciers and different polar geoengineering ideas unfeasible and harmful.
An enormous dam between two oceans
But for Dijkstra it’s at the very least price investigating how the Earth’s system responds to such interventions utilizing laptop fashions. “As a result of it tells us whether or not we perceive the system nicely sufficient,” he says.
It could additionally assist to establish the least dangerous actions that – ought to climate change spiral uncontrolled – may purchase humanity a while.
In a modelling study, revealed in April 2026, he and his colleagues explored the results of 1 such ‘last-resort measure’ designed to stop an AMOC collapse: the development of an 80km (50-mile) broad dam throughout the Bering Strait that separates Alaska and Siberia.
By this slim and shallow marine channel, water from the North Pacific flows into the Arctic Ocean. It will definitely finds its means into the Labrador Sea and the Greenland Sea.
As a result of Pacific water is comparatively contemporary, it inhibits deep water formation in these areas and makes the present sluggish.
However that hasn’t at all times been the case. Earlier work suggests the AMOC was stronger through the Earth’s ice ages, when falling sea ranges created a land bridge between Asia and the Americas, and the Pacific was minimize off from the Arctic.
Dijkstra and colleagues checked out how artificially closing the strait now would have an effect on the AMOC in situations the place the North Atlantic is warming and freshening.
Blocking the influx of much less salty Pacific water by means of this bottleneck by way of the Arctic Ocean – whereas the overturning circulation was nonetheless sufficiently sturdy – elevated the salinity within the subpolar Atlantic.
“This stabilises the AMOC,” says Dijkstra.
However when the currents had weakened an excessive amount of, they noticed the alternative impact.
Now, the closure prevented comparatively contemporary Atlantic water (diluted by glacial soften, for instance) from escaping into the Pacific, reducing the salinity within the Atlantic much more and thus additional weakening the circulation.
In different phrases, the timing was essential to how efficient the closure was.
Though the Bering Strait is slim and solely 50m (164ft) deep, constructing a dam from Russia to the US wouldn’t simply face immense political obstacles.
It could even have main results on ocean chemistry and marine life, which help indigenous communities within the Bering space.
From an engineering perspective, although, Dijkstra thinks it’s attainable. He factors out one thing related exists already: the 33km (20.5-mile) lengthy Saemangeum Seawall in South Korea, the world’s largest human-made dyke.
Elsewhere, nevertheless, different researchers warn of radical geoengineering as a distraction from what ought to be the precedence for humanity: drastically reducing CO2 emissions.
“The answer for the AMOC goes to be the identical as for different impacts of local weather change that we’re going through,” says Frajka-Williams.
“We all know the way to repair the issue. It’s simply having the ability to try this within the present political local weather appears very tough.”
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