Severe Atlantic Ocean current system showing first signs of collapse

(CNN) — According to a new report, a vital system of ocean currents may already be on the brink of collapse, which could have dangerous effects on sea level rise and global climate, causing temperatures in some areas to drop rapidly and Growing in others.

According to the study published this Friday in the academic journal Science Advances, scientists have discovered a new way to detect early warning signs of the collapse of these streams using exceptionally complex and expensive computer systems. And as the planet warms, there are already signs it is moving in that direction.

The Atlantic Southern Circulation (AMOC), of which the Gulf Stream is a part, acts as a giant global conveyor belt, carrying warm water from the tropics to the far north of the Atlantic, where the water is cooler, becoming saltier. Goes and drowns in water. The depths of the ocean before spreading southwards.

Currents transport heat and nutrients to different regions of the planet and play an important role in maintaining a relatively temperate climate across 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 the currents.

Although many scientists believe that the AMOC will slow, and even stop, with climate change, great uncertainty remains about when and how quickly this might happen. AMOC has conducted continuous monitoring since 2004.

Scientists know that the AMOC stopped more than 12,000 years ago as a result of the rapid melting of glaciers, caused by ice caps and marine sediments.

Now they are trying to find out if this incident can be repeated.

According to study co-author René van Westen, a marine and atmospheric researcher at Utrecht University, the Netherlands, this represents a “significant advance.”

Scientists used a supercomputer to run complex climate models over a three-month period, simulating a gradual increase in freshwater in the AMOC, which is responsible for ice melt as well as precipitation and river runoff, Which can reduce the salinity of the ocean and weaken the currents.

By gradually increasing freshwater in the model, they saw the AMOC gradually weaken until it suddenly collapsed.

The report said this is the first time that the collapse has been detected using these complex models, which represents “bad news for the climate system and humanity.”

What the study does not do, however, is provide a timeline for potential relapse. Van Westen explained to CNN that more research is needed, including models that mimic the effects of climate change, such as increased pollution levels that warm the planet, something this study did not do. it was done.

“But at least we can say that we are approaching the tipping point of climate change,” Van Westen said.

The consequences of the collapse of the AMOC current could be devastating. According to the study, temperatures in parts of Europe could drop by as much as 30 degrees Celsius over a century, leading to a completely different climate within a decade or two.

“No realistic adaptation measure can cope with such rapid temperature changes,” the study authors write.

Southern Hemisphere countries, for their part, could face increased heat, while the Amazon’s wet and dry seasons could be reversed, causing serious disruption to the ecosystem.

According to Van Westen, the collapse of the AMOC current could cause sea levels to rise by up to one metre.

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.”

“This confirms that the AMOC has a tipping point beyond which it breaks down if the North Atlantic Ocean is diluted with fresh water,” he told CNN.

Previous studies that found the AMOC tipping point used too simple models, he said, giving some scientists hope that more complex models will not be found.

According to Rahmstorf, this study dashes those expectations.

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, showing that the AMOC current switches from “on” to “off” in response to relatively low entrainment. May go. A small amount of fresh water in the sea.

But there are some reasons to be cautious, he said.

Although the study used a complex model, it is still low resolution, meaning there may be limitations in its representation of certain parts of the streams.

This study adds to the growing evidence that AMOC may be approaching, and even close to, a tipping point.

A 2021 study showed that the AMOC was weaker than at any time in the past 1,000 years. And a particularly worrying and somewhat controversial report published in July last year concluded that AMOC could be on the verge of collapse by 2025.

However, huge uncertainties remain. Jeffrey Kargel, a senior scientist at the Arizona Planetary Science Institute, said he suspects 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 potential collapse to “the wild fluctuations that occur in the stock market before a major decline”: it is almost impossible to discern which changes are reversible and which changes are destructive.

According to Hirschi, current data shows that the strength of the AMOC is fluctuating, but no signs of decline have been seen yet. “Whether the AMOC will have the same sudden changes seen in the past as our climate continues to warm is an important open question.”

This study is a piece of that puzzle, Rahmstorf said. “(This) significantly adds to the growing concern about AMOC collapse in the near future,” he said. “We will ignore it at our peril.”