02/10/2024 – 19:09
A collapse of Atlantic ocean currents, which could plunge large parts of Europe into an intense cold snap, looks a little more likely and closer than before, as a new computer simulation identifies an “abrupt” tipping point if approaching in the future.
A long-feared scenario triggered by the melting of the Greenland ice sheet due to global warming is still decades away. This interval, however, is much less than the centuries of distance that were projected for a phenomenon of this type, as shown by a new study published in the journal Science Advances this Friday the 9th.
“We are getting closer (to collapse), but we are not sure how much closer,” said study lead author Rene van Westen, a climate scientist and oceanographer at Utrecht University in the Netherlands. “We are heading towards an inflection point.”
The research, the first to use complex simulations and include multiple factors, uses a key measurement to track the strength of vital general ocean circulation, which is slowing.
A collapse of the current – called the Atlantic Meridional Circulation or AMOC – would change the world's climate. This is because it would mean the shutdown of one of the main forces of the climate and the ocean. This would reduce temperatures in northwestern Europe by 5°C to 15°C over decades and extend Arctic ice much further south.
Such a transformation would also further increase heat in the Southern Hemisphere, change global rainfall patterns and disrupt the Amazon, according to the research. Other scientists say it would have the potential to cause food and water shortages around the world.
The AMOC is part of a complex global conveyor system of ocean currents that move different levels of salt and hot water around the globe, at different depths and patterns, that help regulate Earth's temperature, absorb carbon dioxide, and drive the cycle. of water, according to the American space agency, NASA.
When AMOC turns off, there is less heat exchange around the world. For thousands of years, Earth's oceans have depended on a circulation system that works like a conveyor belt. It is still moving, but slowing down.
The engine of this conveyor belt is off the coast of Greenland, where, as more ice melts because of climate change, more freshwater flows into the North Atlantic and slows everything down, van Westen said. In the current system, deeper, fresher cold water flows south past the Americas and then east past Africa.
Meanwhile, warmer, saltier ocean water from the Pacific and Indian Oceans passes around the southern tip of Africa, turns around and around Florida, and continues up the American East Coast to Greenland.
Floating robotic sensors
In recent decades, researchers have used networks of floating robotic sensors to observe the ocean in real time. As these sensors drift with the currents and swim through the water column, they collect information about the ocean's temperature and salinity and send it to satellites, which then transmit the information to scientists around the world.
These observations revealed a strange cooling spot at the southern tip of Greenland – one of the only places on the planet where the ocean is not getting warmer. This suggests that the AMOC is not delivering as much warm water to the North Atlantic and indicates that the system is slowing down.
Other studies have combined direct observations with computer simulations to conclude that the AMOC has weakened by about 15% since the 1950s.
In the new work, the researchers found that the amount of freshwater moved in the southernmost portion of the Atlantic was a good indicator of the strength of the feedback system that powers the AMOC.
When this metric was positive, it meant that the system was reinforcing itself. But when the team examined real-world data, they found that their measure of freshwater transport was negative.
“This value is becoming more negative under climate change,” van Westen said. When it reaches a certain point, it is not a gradual stop, but something “abrupt”, he warns.
The Dutch team simulated 2,200 years of its flow, adding what human-caused climate change does to it. They found, after 1,750 years, “abrupt collapse of the AMOC”, but so far they are unable to translate this simulated timeline into the real future of Earth.
Catastrophes in sight
When this global climate calamity – portrayed, crudely, in the film The Day After Tomorrow – might happen is “the $1 million question, which unfortunately we cannot answer at the moment,” van Westen said.
For him, it is likely a century away, but the researcher does not rule out being alive to see this problem take hold on Earth – van Westen has just turned 30 years old. “This also depends on the rate of climate change we are inducing as humanity,” he pointed out.
Studies have shown that AMOC is slowing down, but the question is about a collapse or complete shutdown. The IPCC, a group of hundreds of scientists that provides regular updates on global warming to the United Nations, says it has moderate confidence that there will not be a collapse before 2100. But this is not a consensus in the scientific community.
Stefan Rahmstorf, head of Earth Systems Analysis at the Potsdam Institute for Climate Research in Germany, calls the research a “major advance in the science of stability” of the Atlantic ocean current system.
“The study adds significantly to the growing concern about an AMOC collapse in the not-so-distant future,” he noted, who is not involved in the study.
Climate scientist from the University of Exeter in the United Kingdom, Tim Lenton, was also concerned. According to him, the effects would be “so abrupt and severe that they would be almost impossible to adapt to in some places”.
But in the opinion of Joel Hirschi, division leader at the UK's National Oceanography Center, there are more pressing concerns than that.
“The rapidly rising temperatures we have seen in recent years, and the associated temperature extremes, are of greater immediate concern than the AMOC shutdown,” Hirschi said. “Warming is not hypothetical: it is already happening and impacting society now.” (WITH INTERNATIONAL AGENCIES)
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