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amoc
'Serious Risk' of Vital Ocean Current Collapse by 2100, Warn Scientists
"A string of scientific studies in the past few years suggests that this risk has so far been greatly underestimated," wrote scientists in a letter to Nordic governments.
Oct 24, 2024
A group of 44 climate scientists from 15 different countries warn there is a "serious risk" that soaring global temperatures will trigger the "catastrophic" collapse of a crucial system of ocean currents—and possibly sooner than established estimates considered likely.
The Atlantic Meridional Overturning Circulation, or AMOC, moves warm water up from the tropics to the North Atlantic, where it sinks and cools before returning south. It is, as letter signatory and oceanographer Stefan Rahmstorf toldThe Guardian, "one of our planet's largest heat transport systems." If it collapsed, it could lower temperatures in some parts of Europe by up to 30°C.
That's why the scientists sent a letter to the Council of Nordic Ministers over the weekend urging them to take action to understand and prevent a potential collapse.
"A string of scientific studies in the past few years suggests that this risk has so far been greatly underestimated," the scientists wrote. "Such an ocean circulation change would have devastating and irreversible impacts especially for Nordic countries, but also for other parts of the world."
In the letter, the scientists detailed some of the potential "catastrophic" impacts of such a collapse, including "major cooling" in northern Europe, extreme weather, and changes that would "potentially threaten the viability of agriculture in northwestern Europe."
One study cited in the letter shows that London could cool by 10°C and Bergen, Norway by 15°C.
"If Britain and Ireland become like northern Norway, (that) has tremendous consequences. Our finding is that this is not a low probability," Peter Ditlevsen, a University of Copenhagen professor who signed the letter, toldReuters. "This is not something you easily adapt to."
Globally, the scientists said, the end of AMOC could cause the ocean to absorb less carbon dioxide, thereby increasing its presence in the atmosphere. It could also further augment sea-level rise along the U.S. Atlantic coast and alter tropical rainfall patterns.
The most recent synthesis report from the Intergovernmental Panel on Climate Change (IPCC) expressed "medium confidence" that the current would not cease functioning before 2100. Since its publication in March 2023, however, a rash of studies have come out upping the risk.
"Given that the outcome would be catastrophic and impacting the entire world for centuries to come, we believe more needs to be done to minimize this risk."
A Nature Communications study, also published last year, looked at 150 years of temperature data and determined with 95% confidence that AMOC would collapse between 2025 and 2095 if greenhouse gas emissions continue to rise as currently predicted.
Another, published in Science Advances in February, concluded that AMOC was currently "on route to tipping."
There are already signs that AMOC has begun to stall over the last six to seven decades, Rahmstorf told The Guardian, such as the cold blob in the North Atlantic that is defying global warming trends. The water in North Atlantic is also becoming less salty due to meltwater from the Greenland ice sheets and increased precipitation due to climate change. Less salty water is lighter and does not sink, interrupting the process that makes AMOC flow.
"It is an amplifying feedback: As AMOC gets weaker, the subpolar oceans gets less salty, and as the oceans gets less salty then AMOC gets weaker," Rahmstorf explained. "At a certain point this becomes a vicious circle which continues by itself until AMOC has died, even if we stop pushing the system with further emissions."
"The big unknown here—the billion-dollar question—is how far away this tipping point is," Rahmstorf said.
The scientists acknowledged that the chance of the AMOC tipping "remains highly uncertain."
They continued:
The purpose of this letter is to draw attention to the fact that only 'medium confidence' in the AMOC not collapsing is not reassuring, and clearly leaves open the possibility of an AMOC collapse during this century. And there is even greater likelihood that a collapse is triggered this century but only fully plays out in the next.
Given the increasing evidence for a higher risk of an AMOC collapse, we believe it is of critical importance that Arctic tipping point risks, in particular the AMOC risk, are taken seriously in governance and policy. Even with a medium likelihood of occurrence, given that the outcome would be catastrophic and impacting the entire world for centuries to come, we believe more needs to be done to minimize this risk.
To respond to this threat, the scientists urged the council—a group that includes Denmark, Finland, Iceland, Norway, Sweden, Greenland, the Faroe Islands, and Åland—to launch a study of the risk posed to these countries by an AMOC collapse and to take measures to counter that risk.
"This could involve leveraging the strong international standing of the Nordic countries to increase pressure for greater urgency and priority in the global effort to reduce emissions as quickly as possible, in order to stay close to the 1.5°C target set by the Paris agreement," they wrote.
Johan Rockström, a letter signatory who leads the Potsdam Institute for Climate Impact Research, wrote on social media that global politics, "particularly in [the] Nordic region, can no longer exclude [the] risk of AMOC collapse."
And there is one way that political leaders can stave off such a collapse, as well as other climate tipping points, according to Rahmstorf.
"This is all driven mainly by fossil fuel emissions and also deforestation, so both must be stopped," he told The Guardian. "We must stick to the Paris agreement and limit global heating as close to 1.5°C as possible."
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'Cliff-Like' Collapse of Critical Current System More Likely Than Thought: Study
"The new study adds significantly to the rising concern about an AMOC collapse in the not-too-distant future," said one scientist. "We will ignore this at our peril."
Feb 10, 2024
A study published Friday warned that a systemic collapse of the Atlantic Ocean currents driving warm water from the tropics toward Europe could be more likely than researchers previously estimated—an event that would send temperatures plummeting in much of the continent.
The Atlantic Meridional Overturning Circulation (AMOC), which includes the Gulf Stream, could be headed for a relatively sudden shutdown that René Van Western, who led the Dutch study published in Science Advances, called "cliff-like."
"We are heading towards a tipping point."
For many millennia, the Gulf Stream has carried warm waters from the Gulf of Mexico northward along the eastern North American seaboard and across the Atlantic to Europe. As human-caused global heating melts the Greenland ice sheet, massive quantities of fresh water are released into the North Atlantic, cooling the AMOC—which delivers the bulk of the Gulf Stream's heat—toward a "tipping point" that could stop the current in its tracks.
An AMOC shutdown would cause temperatures to rise in the Southern Hemisphere but plunge dramatically in Europe. In the study's model, London cools by an average of 18°F and Bergen, Norway by 27°F. An AMOC failure would also cause sea levels to rise along North America's east coast.
"We are moving closer [to the collapse], but we we're not sure how much closer," van Westen toldThe Associated Press. "We are heading towards a tipping point."
According to the study:
Although AMOC collapses have been induced in complex global climate models by strong freshwater forcing, the processes of an AMOC tipping event have so far not been investigated. Here, we show results of the first tipping event in the Community Earth System Model, including the large climate impacts of the collapse. Using these results, we develop a physics-based and observable early warning signal of AMOC tipping: the minimum of the AMOC-induced freshwater transport at the southern boundary of the Atlantic. Reanalysis products indicate that the present-day AMOC is on route to tipping. The early warning signal is a useful alternative to classical statistical ones, which, when applied to our simulated tipping event, turn out to be sensitive to the analyzed time interval before tipping.
"The research makes a convincing case that the AMOC is approaching a tipping point based on a robust, physically based early warning indicator," said Tim Lenton, director of the University of Exeter's Global Systems Institute. "What it cannot and does not say is how close the tipping point, because... there is insufficient data to make a statistically reliable estimate of that.
"We have to plan for the worst," added Lenton, who was not involved in the Dutch study. "We should invest in collecting relevant data and improving estimation of how close a tipping point is, improving assessment of what its impacts would be, and getting pre-prepared for how we could best manage and adapt to those impacts if they start to unfold."
Stefan Rahmstorf—who leads the Earth Systems Analysis department at the Potsdam Institute for Climate Research in Germany and was not part of the new study—called the research "a major advance in AMOC stability science."
"The new study adds significantly to the rising concern about an AMOC collapse in the not-too-distant future," Rahmstorf told The Associated Press. "We will ignore this at our peril."
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'Frightening': Greenland Losing 33 Million Tons of Ice Per Hour Due to Climate Crisis
A new study finds the island's ice sheet is retreating 20% more than previously thought.
Jan 17, 2024
New research on the rate at which Greenland's glaciers are melting shed new light on how the climate emergency is rapidly raising the chance that crucial ocean current systems could soon collapse, as scientists revealed Wednesday that the vast island has lost about 20% more ice than previously understood.
Scientists at the National Aeronautics and Space Agency (NASA) Jet Propulsion Laboratory led the study, published in Nature, which showed that Greenland's ice cap is losing an average of 33 million tons of ice per hour, including from glaciers that are already below sea level.
The researchers analyzed satellite photos showing the end positions of Greenland's glaciers every month from 1985 to 2022, examining a total of about 235,000 end positions.
Over the 38-year period, Greenland lost about 1,930 square miles of ice—equivalent to one trillion metric tons and roughly the size of Delaware.
An earlier study had estimated that 221 billion metric tons had been lost since 2003, but the researchers added another 43 billion metric tons to that assessment.
Previous research had not quantified the level of ice melt and breakage from the ends of glaciers around the perimeter of Greenland.
"Almost every glacier in Greenland is retreating. And that story is true no matter where you look," Chad Greene, a glaciologist at the NASA Jet Propulsion Laboratory who led study, toldThe New York Times. "This retreat is happening everywhere and all at once."
Because the glaciers examined in the study are already below sea level, their lost ice would have been replaced by sea water and would not have contributed to sea-level rise.
But as Greene toldThe Guardian, "It almost certainly has an indirect effect, by allowing glaciers to speed up."
"These narrow fjords are the bottleneck, so if you start carving away at the edges of the ice, it's like removing the plug in the drain," he said.
The previously unaccounted-for ice melt is also an additional source of freshwater that pours into the North Atlantic Ocean, which scientists warn places the Atlantic Meridional Overturning Circulation (AMOC) at risk of collapse.
AMOC carries warm water from the tropics into the North Atlantic, allowing nutrients to rise from the bottom of the ocean and supporting phytoplankton production and the basis of the global food chain.
A collapse of the system would also disrupt weather patterns across the globe, likely leading to drier conditions and threatening food security in Asia, South America, and Africa, and increasing extreme weather events in other parts of the world.
One analysis found the collapse could take place as soon as 2025.
Charlie Angus, a member of the Canadian Parliament representing the New Democratic Party, noted that the study was released as Canada's government continues to support fossil fuel production and what experts call false solutions to the planetary heating crisis—including a $12 billion carbon capture and storage project led by tar sands oil companies.
The Environmental Voter Project in the U.S. urged Americans to consider the latest statistics on melting glaciers when choosing the candidates and political parties they will support in 2024.
"Greenland is losing 30 million tons of ice an hour," said the group. "So vote like it."
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