Its collapse would have devastating consequences, causing severe droughts, Europe to freeze, sea levels to rise and the ocean – a critical carbon sink – would not take in as much of the greenhouse gases produced by our fossil fuels.
The Atlantic Meridional Overturning Circulation, also known as the AMOC, is a system of deep ocean currents that acts as the Earth’s central heating system. It sends warm water north and cold water south within the Atlantic Ocean, bringing warmth to various parts of the globe.
As a part of the global conveyor belt – a constantly moving system of deep-ocean circulation driven by temperature and salinity – it also carries nutrients necessary to sustain ocean life. Currents slow when more fresh water is injected into the ocean. Fresh water is less dense than the salt water that helps drive them.
While there have been questions regarding the rate of weakening or collapse of the AMOC during recent years, research published this year has had extremely concerning conclusions.
Now, a new study from the University of New South Wales is warning of the impact of the melting Greenland ice sheet and Canadian glaciers, which researchers say is weakening ocean circulation and speeding up warming in the southern hemisphere.
The study’s authors said the AMOC, which is weaker now than at any other time in the past millennium, is likely to become a third weaker than it was 70 years ago when the Earth passes the 2 degrees Celsius mark of global warming over preindustrial levels. A 2-degree rise in global temperatures means humans could face multiple impacts of climate change simultaneously.
And, if the additional melting of the Greenland ice sheet in the subarctic ocean is accounted for, the study says the AMOC could be 30 percent weaker by 2040: 20 years sooner than initially projected.
Reacting to these findings, Dr. Stefan Rahmstorf – who has been studying the AMOC for years – says that the world must expect a faster decline than the United Nations’ Intergovernmental Panel on Climate Change (IPCC) has predicted in annual assessments. Rahmstorf was not involved in the research.
“‘It is very likely (90–100 percent probability) that the AMOC will weaken faster than CMIP6 projections if meltwater forcing is considered.’ That’s bad news; it increases the risk of passing the AMOC tipping point,” he wrote in a thread on X.
Rahmstorf, who is a professor of physics of the oceans and head of earth system analysis at Germany’s Potsdam Institute for Climate Impact Research, told The Independent that the biggest uncertainty is knowing how far away the planet is from that tipping point.
“I’ve compared it to sailing with a ship into uncharted waters,” he said, “and you know there are rocks under the surface that you can’t see. So, it’s dangerous, but you don’t know exactly where they are. And, that’s the kind of situation we are facing here.”
The AMOC wouldn’t collapse suddenly. It would slowly wind down over 50 to 100 years after that. Passing the tipping point in a few decades, he said, would be entirely plausible.
Rahmstorf noted that the impacts of the collapse would likely be very severe, although they require further study.
“But most importantly, I think, of course it’s more important to try and prevent this from happening, rather than studying in more and more detail what it would mean. Or, of course, we can do both at the same time, hopefully,” he said.
Rahmstorf was one of 44 international scientists who recently penned an open letter to the Nordic Council of Ministers, issuing a stark warning about the dangers of crossing the tipping point.
Its authors also included UC Riverside associate professor Wei Liu and NASA’s Dr. Anastasia Romanou.
“The IPCC had said, for example, that we don’t expect this to happen before 2100. But, what people don’t realize is that the IPCC has looked at models where they don’t simulate ice sheet collapse or large extreme events – the sort that we have seen over the last two years,” Romanou told The Independent before the Australian study was released.
She said that while there is uncertainty regarding the time frame, collapse will take just decades, but “will not be much longer than that.” Whether it happens in 20, 30, or 50 years, “it will be catastrophic.”
“We have to take measures now to avoid these kinds of effects,” said Romanou.
What kinds of measures does the world need to take? For many, that’s been clear for a long time. To limit continued warming, by slashing emissions of greenhouse gases.
“I think we definitely want to take action to reduce greenhouse gas emissions,” Liu said in a separate interview, noting that the world would still feel the effects of previous carbon dioxide emissions.
Echoing Rahmstorf, he says more research is necessary to look at the global impact of a possible collapse.
This year is expected to be Earth’s warmest on record, surpassing scorching temperatures felt in 2023. The United Nations warned in October that the world is on track for a global temperature rise of up to 3.1 degrees Celsius over preindustrial levels. A previous goal to limit warming to 1.5 degrees will “soon be dead,” it said, without unprecedented mobilization.
“For AMOC, I wouldn’t place a time frame, like 2100 or 2080 or something like that. I would place something like a temperature threshold,” Romanou said. She cited a 2022 paper published in the journal Science that warned exceeding 1.5 degrees could trigger multiple climate tipping points including the AMOC’s collapse.
“When we are going to pass that, that will place the AMOC tipping much earlier than 2100,” she added.
Rahmstorf also said global warming up to 3.1 degrees would be “catastrophic” and would “increasingly endanger the AMOC.”
“You know, I try to take this professionally,” he said of climate impacts. “I sometimes think of emergency doctors who come to horrible accidents frequently. They just have to somehow distance themselves emotionally from that and just take a professional attitude. That’s what I’m trying to do, but I have two children and I do really worry about their future.”
