This is clear from a new study conducted by scientists from Utrecht University. Concerns about the potential stalling of the Gulf Stream in the Atlantic Ocean have been around for a long time. It is widely assumed that this could have serious consequences for the Earth's climate. But so far, climate research using computer models has not provided a definitive answer about whether and when such a shutdown might occur.
The study's most important conclusion is that “abrupt transmission is indeed possible,” says lead author Rene van Westen. “We already had strong suspicions, but now we have already shown that it is possible. This means that on a very short time scale, within a hundred years, a completely different climate could arise. Western Europe could then cool significantly, with five to ten grades.”
What is AMOC?
The Gulf Stream is officially called the Atlantic Meridional Overturning Circulation, AMOC. This AMOC carries warm ocean water north toward the North Pole. There the water cools and sinks to the depths, then flows back towards the south. Because all the water in the ocean is connected to each other, this Gulf Stream affects climate around the world.
In 2021, we have already prepared the video below about the Gulf Stream. Even then, the idea was that it could sometimes reach a dead end, but it was still unclear how quickly this could happen:
If the AMOC stops, it will become colder in the Northern Hemisphere and warmer in the Southern Hemisphere. But there are consequences not only for temperature. Ecosystems and rainfall patterns can also change around the world, such as in the Amazon, where dry and wet seasons can reverse.
The potential arrival of a climate tipping point, such as the closing of the AMOC, is an important reason for scientists to call for urgent action on climate change. Further climate change can only be prevented by rapidly reducing greenhouse gas emissions.
Sea level rise
The cessation of the Gulf Stream may also cause sea levels to rise more than currently expected. According to Van Westen, sea levels could rise by an additional 80 centimetres, on top of the melting of ice caps and the expansion of warm sea water. This may lead to some coastal areas becoming uninhabitable.
In their research, the scientists looked at the salinity of ocean water between Africa and South America. “If the amount of salt in the water reaches a critical value, circulation will collapse,” says Van Westen. This means that the Gulf Stream flows at a slower speed and can stop.
The reason the water has become saltier is the amount of melting water from the Greenland ice sheet. That melt water is fresh. “If you make the water sweeter, it becomes lighter and sinks less deeply,” Van Westen explains. “As a result, the water flows less well.” The ocean water between Africa and South America also stays in the same place for a longer period, which leads to increased salinity.
“This is bad news for the climate system and humanity, because until now one might have thought that this tipping point was just a theoretical concept,” the researchers wrote in the new study. But there remain many questions that more research needs to answer. For example, researchers say it is not yet possible to predict exactly how long the AMOC will last before it reaches a tipping point.
Professor of Oceans and Climate Caroline Katzmann from TU Delft believes it is an interesting and important study. “Based on the Prediction Index, it has been confirmed that the climate is moving towards a tipping point,” she says.
Katzman: “What they showed is that about 25 years before the AMOC collapses, an important measurable indicator changes, which is the trend in freshwater transport in the South Atlantic. So the idea is that measuring this parameter provides predictability.”
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