It can get noticeably colder in Europe
Researchers show for the first time in a climate model that global warming could cause the Atlantic Current to collapse. The billion dollar question is: when?
NASA simulations show the warm Gulf Stream (orange) moving along the Florida coast and numerous eddies that can only be imprecisely depicted in models.
Illustration: NASA
When the disastrous film “The Day After Tomorrow” hit theaters twenty years ago, the closure of the Gulf Stream due to climate change was widely discussed publicly for the first time. Dramatically speaking, the collapse causes a new ice age in the film, which is completely exaggerated.
The collapse of the Atlantic Great Current system, in which the Gulf Stream plays an important role, was theorized in simple concepts in climate research as early as the 1960s and later confirmed in other studies. Now Dutch scientists have discovered this for the first time in a sophisticated climate model: There is actually a turning point in this giant Atlantic “conveyor belt” that transports warm water from tropical latitudes to the north and gives Europe a temperate climate.
This means that the ocean current that brings warm water from south to north could slow down and even stop. Reason: Increased flow of fresh water into the North Atlantic Ocean due to global warming. Increased precipitation, melting ice cream in Greenland, and meltwater from melting glaciers on the continents are thinning the North Atlantic Ocean. This leads to a decrease in the salinity and density of seawater. The water becomes lighter.
In the worst-case scenario, it will be noticeably colder in Europe
The result: less water flows south. This in turn means transporting less salty water from the south to the north. The “conveyor belt” engine, which researchers call for short Amoc (Atlantic Meridional Overturning Circulation), begins to stutter and may even die.
Consequences for global climate: There will not be a new ice age in the Northern Hemisphere as in the novel “The Day After Tomorrow.” But in the worst-case scenario, it will become noticeably colder in Europe because heat transport across the Atlantic from the south will stop.
Scientists give an example: According to models, in Bergen, Norway, temperatures could drop by 3.5 degrees every decade in February if the ocean current reaches a tipping point and slows significantly within 100 years. If heat transport stopped completely, depending on the region, there would be no truly warm summers in Europe. In the tropics, the rainy season will completely transform, and the rainy season will become the dry season, and vice versa.
The drastic effect has to do with the fact that the extent of Arctic sea ice is increasing dramatically again and that more solar radiation is being reflected back into space, the researchers wrote. “Until now, it was possible to assume that tipping behavior was just a theoretical concept and would disappear again in the entire climate system,” the Dutch researchers wrote in the scientific journal Science Advances, in which they recently published their study.
How close is the tipping point?
The Dutch study is the second in six months about the collapse of the Atlantic current system. Danish researchers made headlines last July because they used statistical analyzes of water surface temperature in parts of the Gulf Stream system An alarming message announced: The Gulfstream system could collapse between 2025 and 2095 if their assumptions are correct.
However, many experts criticized and questioned the reliability of this method. It's different with the new study: Independent researchers attest to the good work of the new study, but they still put the results in perspective: The positive thing about the study is that Dutch researchers at Utrecht University used a climate model for the first time that shows interactions between the ocean, atmosphere and ice. They were able to keep their model running for thousands of years thanks to access to the national supercomputer. The computing time was several months. Scientists also discovered that measuring freshwater transport in the South Atlantic could be used as an early warning signal about whether ocean currents are gradually slowing.
Satellites and marine buoys have been measuring freshwater transport in tropical latitudes since 2004. According to the researchers, observations and model calculations show that a slight slowdown can already be observed. This may be an indication that the Atlantic currents are heading towards a point of no return.
According to the models, if the Atlantic Ocean currents collapsed, temperatures in Bergen, Norway, would drop dramatically.
Photo: Getty Images
Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research does not want to deny this. “But the billion-dollar question is how far this tipping point lies,” the German climate researcher wrote in a blog post. Decades, centuries? The new study cannot provide an answer to this.
Weak points in the study
The new study is also an important contribution by Nicholas Gruber from ETH Zurich. The results should be taken seriously because they show that the Atlantic Current system is not as stable as the results of ancient simulations previously suggested. In its 2022 Global Climate Report, the Intergovernmental Panel on Climate Change (IPCC) posits that the Atlantic currents are likely to become weaker. But the extent of its power is still unclear.
ETH researcher Gruber can also support the proposal to use freshwater transport as an early warning signal. “But the discussions have not yet been resolved with this study,” he says. He sees a weakness of the study in the fact that the models used do not have sufficient spatial resolution to represent the important and highly central processes of ocean circulation. These include, for example, large-scale eddies that can extend from the sea surface to the sea floor. “These processes are important for transport and formation of deep water,” says Gruber. He is therefore skeptical about whether the data made by the model results is strong enough.
In addition, an imminent collapse cannot be predicted from these results. The reason: The tipping point in the flow regime only appears when there is an extreme influx of fresh water: about 80 times higher than the current melting rate of the Greenland ice sheet. British glaciologist Jonathan Bamber of the University of Bristol explains it this way: The assumed amount of fresh water corresponds to a sea level rise of six centimeters per year. This is greater than what happened when the ice sheet covering North America collapsed during the last ice age.
However, experts agree on one point: more measurements, improved models, and more computing power are urgently needed to understand freshwater transport in Atlantic currents. One thing is known today: historical data from ice cores show that there were collapses in the flow system tens of thousands of years ago.
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