A sudden shutdown of currents from the Atlantic Ocean that could plunge large parts of Europe into a deep freeze is more likely and closer than ever as a complex new computer simulation finds a “cliff-like” tipping point in the future.
A long-worried nightmare scenario, fueled by the melting of the Greenland ice sheet from global warming, is at least decades away, but perhaps not centuries away, a new study in Science Advances finds Friday. . The study, the first to use complex simulations and include multiple factors, uses a key measurement to track the strength of the critical overall ocean circulation, which is slowing.
The collapse of the current – known as the Atlantic Meridional Overturning Circulation or AMOC – would change the weather around the world because it means shutting down one of the main forces of the planet’s climate and oceans. It would plunge the temperatures of north-west Europe by 9 to 27 degrees (5 to 15 degrees Celsius) over the years, the expansion of Arctic ice much further south, up the heat more in the Southern Hemisphere, changing global rain patterns and putting into the Amazon, the. study said. Other scientists said it would be a disaster that could cause food and water shortages around the world.
“We’re getting closer (to fall), but we’re not sure how close,” said study author Rene van Westen, a climate scientist and oceanographer at Utrecht University in the Netherlands. “We are heading towards a tipping point.”
When this global weather disaster – fictionalized in the movie “The Day After Tomorrow” – could happen is “the million dollar question, which unfortunately we can’t answer right now,” van said. Westen. He said that it is probably a hundred years away but it could still happen in his lifetime. He turned only 30 years.
“It also depends on the rate of climate change we are driving as a human race,” van Westen said.
Studies have shown that the AMOC is slowing down, but the question is whether it will collapse or shut down completely. The United Nations’ Intergovernmental Panel on Climate Change, a group of hundreds of scientists who provide regular authoritative updates on warming, said it has moderate confidence that there will be no collapse before 2100 and a general reduction in disaster scenarios. But van Westen says, some outside scientists and a study last year may not be right.
Stefan Rahmstorf, head of Global Systems Analysis at the Potsdam Institute for Climate Research in Germany, was not part of the research, but called it a “major advance in the science of AMOC stability”.
“The new study adds significantly to the growing concern about an AMOC collapse in the not-too-distant future,” Rahmstorf said in an email. “We will ignore this at risk.”
University of Exeter climate scientist Tim Lenton, who is also not part of the research, said the new study makes him more concerned about a fall.
A collapse of the AMOC would cause so many shocks to the world’s climate “so sudden and severe that in some places it would be almost impossible to adapt to them,” Lenton said.
There are signs that the AMOC has fallen in the past, but it remains uncertain when and how it will change in the future, said Wei Cheng, a US National Oceanic and Atmospheric Administration oceanographer who was not part of the research.
The AMOC is part of an intricate global conveyor belt of ocean currents that move different levels of salt and warm water around the globe at different depths in patterns that help regulate Earth’s temperature, absorb carbon dioxide and fuel the cycle water, according to NASA.
When the AMOC closes, less heat is exchanged around the globe and “it leaves a very strong impact on Europe,” van Westen said.
For thousands of years, the Earth’s oceans have depended on a circulation system that runs like a conveyor belt. It’s still going but slowing down.
The engine of this conveyor belt is off the coast of Greenland, where, as more ice melts due to climate change, more freshwater flows into the North Atlantic and slows everything down, van Westen said. In the current system, cold deeper fresh water flows south over the Americas and then east over Africa. Meanwhile the saltier and warmer sea water, coming from the Pacific and Indian Oceans, passes over the southern tip of Africa, goes to and around Florida and continues up the East Coast of the USA up to to Greenland.
The Dutch team visualized 2,200 years of its flow, adding the contribution of human-caused climate change. They discovered after 1,750 years a “sudden AMOC collapse,” but so far they have not been able to transfer that simulated timeline to the real future of the Earth. Critical to monitoring what happens is a sophisticated measurement of flow around the tip of Africa. The more negative that measurement is, the slower AMOC runs.
“This value is becoming more negative under climate change,” said van Westen. When it reaches a certain point it’s not a gradual stop but something “like a cliff,” he said.
The world should pay attention to the possible collapse of AMOC, said Joel Hirschi, head of division at the UK’s National Oceanographic Centre. But there is a larger global priority, he said.
“To me, the rapidly increasing temperatures of recent years and the associated temperature extremes are a more immediate concern than the AMOC shutdown,” Hirschi said. “Warming is not hypothetical but is already happening and affecting society now.” ___
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