Scientists mapped what happens if a crucial system of ocean currents collapses. The weather impact would be extreme

CNN

a day ago

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The collapse of a crucial network of Atlantic Ocean currents could push parts of the world into a deep freeze, with winter temperatures plunging to around minus 55 degrees Fahrenheit in some cities, bringing 'profound climate and societal impacts,' according to a new study.
There is increasing concern about the future of the Atlantic Meridional Overturning Circulation — known as the AMOC — a system of currents that works like a giant conveyor belt, pulling warm water from the Southern Hemisphere and tropics to the Northern Hemisphere, where it cools, sinks and flows back south.
Multiple studies suggest the AMOC is weakening with some projecting it could even collapse this century as global warming disrupts the balance of heat and salinity that keeps it moving. This would usher in huge global weather and climate shifts — including plunging temperatures in Europe, which relies on the AMOC for its mild climate.
What's less clear, however, is how these impacts will unfold in a world heated up by humans burning fossil fuels.
'What if the AMOC collapses and we have climate change? Does the cooling win or does the warming win?' asked René van Westen, a marine and atmospheric researcher at Utrecht University in the Netherlands and co-author of the paper published Wednesday in the Geophysical Research Letters journal.
This new study is the first to use a modern, complex climate model to answer the question, he told CNN.
The researchers looked at a scenario where the AMOC weakens by 80% and the Earth is around 2 degrees Celsius warmer than the period before humans began burning large amounts of fossil fuels. The planet is currently at 1.2 degrees of warming.
They focused on what would happen as the climate stabilized post-collapse, multiple decades into the future.
Even in this hotter world, they found 'substantial cooling' over Europe with sharp drops in average winter temperatures and more intense cold extremes — a very different picture than the United States, where the study found temperatures would continue to increase even with an AMOC collapse.
Sea ice would spread southward as far as Scandinavia, parts of the United Kingdom and the Netherlands, the research found. This would have a huge impact on cold extremes as the white surface of the ice reflects the sun's energy back into space, amplifying cooling.
The scientists have created an interactive map to visualize the impacts of an AMOC collapse across the globe.
London, for example, could see winter cold extremes of minus 2.2 Fahrenheit , while Oslo could see temperatures as low as minus 55 Fahrenheit and endure maximum temperatures below 32 Fahrenheit for 46% of the year.
Parts of Europe will also become stormier, the study found. The increased temperature difference between northern and southern Europe will strengthen the jet stream and increase storm intensity over northwestern Europe.
It 'completely shifts the narrative, right?' van Westen said. 'Because now policy is planning for a warmer future, but maybe instead, we need to also prepare for a colder future.'
While cooling on an ever-hotter planet may sound like good news, van Westen warns it's anything but.
Society in many parts of the Northern Hemisphere 'is not built for these kind of cold extremes,' he said. Crops would die, threatening food security, and infrastructure could buckle.
What's more, the impacts of an AMOC collapse would mostly be felt in Europe's winter; it would still endure increasingly deadly heat waves in the summer as the climate crisis intensifies.
The Southern Hemisphere, meanwhile, is projected to experience increased warming.
The scientists also looked at the impacts of an AMOC collapse in an even hotter world. If global temperatures reach around 4 degrees Celsius above pre-industrial levels, the heat outweighs the cooling impact of an AMOC collapse in Europe, van Westen said. 'The warming signal actually wins.'
But, he added, an AMOC collapse won't only affect temperatures. Other impacts include increased sea level rise, which will particularly affect the US, where a weaker AMOC is already driving significantly increased flooding on the northeastern coast, according to recent research.
Stefan Rahmstorf, a physical oceanographer at Potsdam University in Germany who was not involved in the latest research, said the study confirms 'an AMOC collapse would have massive impacts on European climate.'
The research uses only one climate model; others will rely on different models and will likely come up with a variety of scenarios, he told CNN. What ultimately happens will depend on the how the two opposing trends play out: AMOC-induced cooling and climate change-induced heating. A 'large uncertainty' remains, he said.
The study is 'by no means the last word' especially as huge questions remain over whether the AMOC could be on course to collapse, said Richard Allen, a climate science professor at the University of Reading, also not involved in the research. 'But even the mere possibility of this dire storyline unfolding over coming centuries underscores the need to forensically monitor what is happening in our oceans,' he said.
What is crystal clear is that an AMOC collapse would be very bad for society, van Westen said. 'We want to avoid it at all costs.'