A vital system of ocean currents may already be collapsing, according to a new report, with alarming implications for sea level rise and global weather – causing temperatures to drop sharply in some region and that it will rise in other regions.
Using highly complex and expensive computer systems, scientists have discovered a new way to detect an early warning sign of the collapse of these streams, according to the study published Friday in the journal Science Advances. And as the planet goes, there are already indications that it is heading in this direction.
The Atlantic Overturning Overturning Transport (AMOC) — of which the Gulf Stream is a part — acts as a huge global conveyor belt, taking warm water from the tropics towards the far North Atlantic, where the water cools, becomes it is more salty and goes deep into the ocean, before spreading south.
The currents transport heat and nutrients to different areas of the world and play a vital role in keeping the climate of large parts of the Northern Hemisphere relatively mild.
For decades, scientists have been calling for the stability of the circulation as climate change warms the ocean and melts ice, disrupting the balance of heat and salt that determines the strength of currents.
Although many scientists believe that climate change will slow the AMOC, and may even stop it, there is still huge uncertainty as to when and how quickly this might happen. The AMOC has only been continuously monitored since 2004.
Scientists know – from building a picture of the past using things like ice cores and ocean sediments – that the AMOC closed more than 12,000 years ago after the rapid melting of glaciers.
Now they are scrambling to work out if it could happen again.
This new study provides “an important conclusion,” said René van Westen, a marine and atmospheric researcher at Utrecht University in the Netherlands and co-author of the study.
The scientists used a supercomputer to run complex climate models over a three-month period, simulating a gradual increase in freshwater to the AMOC – which reflects ice melt as well as rainfall and river runoff, which could dilute the salinity of the ocean and weaken the currents.
As they slowly increased the amount of fresh water in the model, they saw the AMOC gradually weaken until it suddenly collapsed. This is the first time that a fall has been detected using these complex models, which indicates “bad news for the climate system and humanity,” the report says.
What the study does not do, however, is give time frames for a possible collapse. More research is needed, van Westen told CNN, including models that also mimic the impacts of climate change, such as increased levels of planet-warming pollution, which this study did not do.
“But we can at least say that we are approaching the tipping point about climate change,” said van Westen.
The collapse of the AMOC could have a devastating impact. Temperatures could drop by up to 30 degrees Celsius in some parts of Europe over the past century, according to the study, leading to a completely different climate over a decade or two.
“No realistic adaptation measures can cope with such rapid temperature changes,” the study authors wrote.
On the other hand, the increased warming could be in countries in the Southern Hemisphere, and the wet and dry seasons of the Amazon could slip, which would seriously affect the ecosystem.
The collapse of the AMOC could cause sea levels to rise by about 1 meter (3.3 feet), van Westen said.
Stefan Rahmstorf, a physical oceanographer at the University of Potsdam in Germany, who was not involved in the study, said that “this is a major advance in the science of AMOC stability.”
“It confirms that the AMOC has a tipping point that it breaks down if the North Atlantic Ocean is diluted with fresh water,” he told CNN.
Previous studies that found the tipping point of the AMOC used much simpler models, he said, giving some scientists hope that they might not be found under more complex models.
This study puts pressure on those hopes, Rahmstorf said.
Joel Hirschi, associate head of marine systems modeling at the UK’s National Oceanographic Centre, said the study was the first to use complex climate models to show that the AMOC can slip from “on” to “off”. ” in response to relatively small amounts of fresh water entering the ocean.
But there are reasons to be cautious, he said. Although the study used a complex model, it still has low resolution, he said, which means there may be limitations in representing certain parts of the streams.
This study adds to the growing body of evidence that the AMOC may be approaching a tipping point – and may even be close.
A 2021 study found that the AMOC was weaker than at any other time in the last 1,000 years. And a very alarming – and somewhat controversial – report, published in July last year, concluded that the AMOC could be on track to collapse as early as 2025.
However, huge uncertainties remain. Jeffrey Kargel, a senior scientist at the Planetary Science Institute in Arizona, said he suspected that the theory that the AMOC could be shut down soon will remain “somewhat controversial until we know, one year, that it’s happening.” “
He compared its possible fall to the “wild gyrations of a stock market that precede a major crash” – it is almost impossible to unpick which changes are reversible, and which are the precursors to disaster.
Modern data show that the strength of the AMOC varies, but there is still no observed evidence of a decline, Hirschi said. “Whether abrupt changes in the AMOC like those seen in the past will occur as our climate continues to warm is an important open question.”
This study is a piece of that puzzle, Rahmstorf said. “(It) adds to the growing concern about an AMOC collapse in the not-too-distant future,” he said. “We will ignore this looming risk.”
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