2024-02-09 00:53:00
(CNN) — A crucial system of ocean currents could already be on the verge of collapse, according to a new report, with alarming implications for sea level rise and global climate, leading to temperatures falling sharply in some regions and rising in others.
Scientists have found a new way to detect an early warning sign of the collapse of these currents using exceptionally complex and expensive computer systems, according to the study published this Friday in the academic journal Science Advances. And as the planet warms, there are already signs that it is heading in that direction.
The Atlantic Southern Circulation (AMOC), of which the Gulf Stream is a part, functions as a gigantic global conveyor belt, carrying warm water from the tropics to the far north of the Atlantic, where the water It cools, becomes saltier and sinks into the depths of the ocean, before spreading southward.
Currents transport heat and nutrients to different areas of the planet and play a vital role in maintaining a relatively temperate climate in large areas of the Northern Hemisphere.
For decades, scientists have warned about the stability of the circulation as climate change warms the ocean and melts ice, altering the balance of heat and salt that determines the strength of currents.
Although many scientists believe that the AMOC will slow down with climate change, and could even stop, there remains great uncertainty about when and how quickly it could occur. The AMOC has only had continuous monitoring since 2004.
Scientists know that, thanks to ice cores and ocean sediments, the AMOC stopped more than 12,000 years ago as a result of rapid melting of glaciers.
Now they are trying to find out if this phenomenon could be repeated.
According to René van Westen, a marine and atmospheric researcher at Utrecht University, the Netherlands, and co-author of the study, this represents an “important advance.”
The scientists used a supercomputer to run complex climate models over a three-month period, simulating a gradual increase in freshwater in the AMOC, which accounted for snowmelt, as well as precipitation and river runoff, which can dilute ocean salinity and weaken the currents.
By slowly increasing the freshwater in the model, they saw the AMOC gradually weaken until it abruptly collapsed.
It is the first time a collapse has been detected using these complex models, which represents “bad news for the climate system and humanity,” the report says.
What the study does not do, however, is give timelines for a possible collapse. Van Westen explained to CNN that more research is needed, including models that also mimic the effects of climate change, such as increasing pollution levels that warm the planet, something that was not done in this study.
“But at least we can say that we are heading towards the tipping point of climate change,” van Westen said.
The repercussions of the collapse of the AMOC current could be catastrophic. According to the study, in some parts of Europe temperatures could drop by up to 30°C over a century, leading to a completely different climate within one or two decades.
“No realistic adaptation measures can cope with such rapid temperature changes,” the study authors write.
Countries in the southern hemisphere, for their part, could suffer increased warming, while the Amazon’s wet and dry seasons could reverse, causing serious disruption to the ecosystem.
The collapse of the AMOC current could also cause a sea level rise of one meter, according to van Westen.
Stefan Rahmstorf, a physical oceanographer at the University of Potsdam, Germany, who was not involved in the study, said it was “a major advance in the science of AMOC stability.”
“It confirms that the AMOC has a tipping point beyond which it breaks if the North Atlantic Ocean is diluted with fresh water,” he told CNN.
Previous studies that had found the AMOC tipping point used much simpler models, he said, giving some scientists hope that more complex models would not be found.
According to Rahmstorf, this study dashes those hopes.
Joel Hirschi, associate head of marine systems modeling at the UK’s National Oceanography Centre, said the study was the first to use complex climate models to show that the AMOC current can go from “on” to “off” in response to the entry of relatively small amounts of fresh water into the ocean.
But there are reasons to be cautious, he added.
Although a complex model was used in the study, it is still low resolution, meaning there could be limitations in the representation of some parts of the currents.
This study adds to the growing body of evidence that the AMOC may be approaching a tipping point, and might even be close.
And study 2021 revealed that the AMOC was weaker than at any time in the last 1,000 years. And an especially alarming, and somewhat controversial, report published in July of last year concluded that the AMOC could be about to collapse by 2025.
However, enormous uncertainties remain. Jeffrey Kargel, senior scientist at the Planetary Science Institute in Arizona, said he suspected the theory of a potentially imminent AMOC shutdown “will remain somewhat controversial until, a year from now, we know it’s happening.”
He compared its possible collapse to the “wild gyrations of a stock market that precede a big crash”: It is almost impossible to decipher which changes are reversible and which are harbingers of disaster.
According to Hirschi, current data shows that the AMOC’s strength is fluctuating, but no sign of decline has yet been seen. “Whether abrupt changes in the AMOC similar to those observed in the past will occur as our climate continues to warm is an important open question.”
This study is one piece of that puzzle, Rahmstorf said. “(It) adds significantly to the growing concern about a collapse of the AMOC in the not-too-distant future,” he said. “We will ignore this at our own peril.”
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