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ocean currents
'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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'Very Bad News Indeed': Study Sounds Alarm on Threat of Deep Ocean Current Collapse
"It's something that is a concern because it touches on so many aspects of the Earth, including climate, sea level, and marine life," said one oceanographer.
May 25, 2023
Antarctic currents that enrich 40% of Earth's deep ocean with oxygen and nutrients that are vital for marine life have slowed dangerously in recent decades and could collapse by mid-century, a study published Thursday revealed.
The research—which was published in the journal Nature Climate Change—showed that a 30% slowdown in deep water currents around Antarctica since the early 1990s.
Currents known as Antarctic bottom waters—which are driven by cold, dense waters off the Antarctic continental shelf—power a worldwide system of currents. The most important of these, known as the Southern Ocean overturning circulation, comprises two massive cells—one subducting downward and the other upwelling—that connect the various water basins in a global circulation system.
"If the oceans had lungs, this would be one of them."
"If the oceans had lungs, this would be one of them," Matt England of the Climate Change Research Center at the University of New South Wales in Australia, a co-author of the new paper, said in a statement.
"Our modeling shows that if global carbon emissions continue at the current rate, then the Antarctic overturning will slow by more than 40% in the next 30 years—and on a trajectory that looks headed towards collapse," England added.
\u201c\ud83d\udc49\ud83d\udc49 Out today in @nature our new paper showing how meltwater increases around Antarctica are set to dramatically slowdown the Antarctic overturning circulation, with a potential collapse this century. https://t.co/p3au6k4zcK A\ud83e\uddf5on how this work came about and what we found...\u201d— Prof. Matt England (@Prof. Matt England) 1680102960
Steve Rintoul, co-author of the study and oceanographer at the Australian government's Commonwealth Scientific and Industrial Research Organisation, toldThe Guardian that "changes in the overturning circulation are a big deal."
"It's something that is a concern because it touches on so many aspects of the Earth, including climate, sea level, and marine life," he added.
England and Rintoul were part of a team of researchers who in March published a study in Nature that found the vital deep ocean current is "on a trajectory that looks headed towards collapse" over the coming decades.
\u201cIt isn't just the Gulf Stream and North Atlantic currents that are now completely unstable, something similar is happening around Antarctica.\n\nMake no mistake, this is very bad news indeed.\n\nhttps://t.co/zeFN1Gh0iM\u201d— Bill McGuire (@Bill McGuire) 1685034661
Scientists from Australia examined the deep ocean current below approximately 13,000 feet that originates in the cold, dense waters off the continental shelf of Antarctica and flows to ocean basins across the planet.
"The model projections of rapid change in the deep ocean circulation in response to melting of Antarctic ice might, if anything, have been conservative," Rintoul said Thursday. "We're seeing changes have already happened in the ocean that were not projected to happen until a few decades from now."
England toldThe Guardian in March that "in the past, these circulations have taken more than 1,000 years or so to change, but this is happening over just a few decades."
"It's way faster than we thought these circulations could slow down," he added. "We are talking about the possible long-term extinction of an iconic water mass."
\u201cA new study warns that the deep ocean current driving the Antarctic overturning circulation\u2014a network of currents that regulate ecosystems around the world\u2014could collapse due to climate change. https://t.co/GFN4K9ucyn via @USATODAY\u201d— Yale Program on Climate Change Communication (@Yale Program on Climate Change Communication) 1681509318
The new research comes after the European Union's Copernicus Climate Change Service reported in February that its analysis of satellite imagery showed Antarctic sea ice coverage was 31% below average the previous month, significantly lower than the previous January low mark set in 2017.
In January, a 600-square-mile iceberg nearly the size of Greater London broke off Antarctica's Brunt Ice Shelf, although scientists said the event will affect—but was not caused by—climate change. January is summer in the Southern Hemisphere.
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