Ripples in the North Atlantic off the coast of Iceland = March 2020/Daniele Orsi/REDA&CO/Universal Images Group/Getty Images
2024.02.10 Sat posted at 20:07 JST
(CNN) The Atlantic Meridional Circulation (AMOC), in which ocean water moves northward at the surface and southward at depth, may already be on its way to collapse. A new report has been released. The collapse of the AMOC could have a serious impact on sea level rise and global climate, leading to sharp drops or rises in temperature in various regions.
Using an extremely complex and expensive computational system, a research team has discovered a new way to detect AMOC’s early signs of collapse, according to a study published in the US journal Science Advances on the 9th. .
AMOC acts like a giant global conveyor belt. When the AMOC transports warm seawater from the tropics to the North Atlantic, the water cools and becomes more salty, sinking deeper into the ocean and heading south again.
These ocean currents transport heat and nutrients to different parts of the globe, and play an essential role in keeping the climate relatively warm across large swathes of the Northern Hemisphere.
Scientists have long sounded the alarm about the stability of the AMOC, as ocean warming and ice melt caused by climate change disrupt the balance of heat and salt that determines the strength of ocean currents.
Scientists believe that the effects of climate change will slow AMOC, and in some cases it may even stop, but there are still many unknowns about when and how quickly this will happen. . Continuous observation of AMOC began only in 2004.
However, by reconstructing the past using clues such as ice cores and marine sediments, we know that the AMOC stopped more than 12,000 years ago after rapid melting of glaciers. .
Researchers are currently working to find out whether something similar to this could happen again.
This new research represents an “important breakthrough.” So says Rene van Westen, an ocean and atmosphere researcher at Utrecht University in the Netherlands and co-author of the paper.
The research team used a supercomputer to run a complex climate model for three months, gradually adding freshwater to the AMOC during the simulation. The addition of fresh water represents melting ice, rainfall, and inflowing river water. These can dilute the salinity of seawater and weaken ocean currents.
By gradually increasing the amount of fresh water in the model, the AMOC gradually weakened until it suddenly collapsed. This is the first time such a complex model has confirmed AMOC collapse, and the report says it is “bad news for the climate system and for humanity.”
However, the study does not provide a time frame for collapse. Van Westen pointed out the need for further research in an interview with CNN, saying that models that take into account the effects of climate change, including the progression of global warming, will also be needed.
Still, “we can at least say that under climate change, we are moving towards a tipping point[of the collapse of AMOC].”
The effects of AMOC’s collapse could be catastrophic. Temperatures in some parts of Europe could drop 30 degrees in 100 years, and the climate could change to a completely different climate in just 10 to 20 years.
The study’s authors point out that “no adaptation measures can realistically respond to such rapid changes in temperature.”
Meanwhile, countries in the southern hemisphere may see an acceleration of global warming. The rainy and dry seasons in the Amazon could be reversed, with serious consequences for the ecosystem.
Van Westen said sea levels could rise by about 1 meter.
Stephan Rahmstorf, a marine physicist at the University of Potsdam in Germany who was not involved in the paper, calls the research results a “major advance in the science of AMOC stability.” He “confirmed that there is a tipping point where the AMOC collapses as the North Atlantic becomes diluted with fresh water.”
Previous studies have shown the existence of tipping points, but they used much simpler models. He says the study shatters some scientists’ expectations that complex models would eliminate tipping points.
Joel Hirschi, an ocean system modeler at the UK’s National Oceanography Centre, uses complex climate models to show that relatively small amounts of freshwater entering the ocean can switch the AMOC from “on” to “off.” It was praised as the first study to show this.
However, there are some points to be aware of; even though it is a complex model, the resolution is still low, and there may be limitations as a model in some ocean currents.
In recent years, a growing number of studies have suggested that AMOC may be approaching a tipping point.
A 2021 study showed that AMOC is at its weakest in 1,000 years. A paper published in July last year caused controversy by warning that AMOC could collapse as early as 2025.
However, there is still a great deal of uncertainty. Jeffrey Gergel of the Planetary Science Institute in Arizona thinks the theory that AMOC is about to shut down will remain controversial until we know it’s happening.
The possibility of AMOC’s collapse is, so to speak, “some of the wild fluctuations in the stock market that are a harbinger of a major crash,” and it is impossible to determine which changes are reversible and which are a harbinger of a major disaster. It is recognized that it is close to .
Although recent data shows fluctuations in AMOC’s strength, there is no observational evidence that a decline has occurred yet, Hirsi said. He notes, “Whether or not the AMOC will undergo sudden changes like those that have occurred in the past as the climate continues to warm is an important question that remains unanswered.”
Rahmstorf says this research is one piece to fill in that puzzle. The study “furthers concerns that the collapse of AMOC will occur in the not-too-distant future,” he continued, “and we are doing so at our peril if we ignore this risk.”
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2024-02-10 11:07:00
