Climate change: Researchers warn of a “devastating tipping point” in currents in the Atlantic

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Photo: Werner Thomas / CHROMORANGE / IMAGO

“Bad news for the climate system and for humanity”: This is how Dutch researchers summarize new study results on global warming and the effects on certain ocean currents in the Atlantic. The system is therefore facing a “devastating tipping point”. The consequences: a drastic drop in temperatures in Europe, a significant rise in sea levels; and at a pace that probably makes it impossible to adapt to the serious changes.

• You can read the original study here: Physics-based early warning signal shows that AMOC is on tipping course 

Specifically, the Dutch study is about the consequences of climate change for the so-called Atlantic Meridional Overturning Current (AMOC), as reported by the broadcaster CNN and the Guardian, citing the magazine Science Advances. AMOC describes a complex system of currents in the Atlantic Ocean. It is considered a key component in regulating the climatic conditions on the planet.

Using complex and expensive computer systems, scientists have developed an early warning signal for the first time, the reports say, to detect a possible collapse of this system. And: There are already signs that this is exactly what will happen.

The exact time is still unclear. “But we can at least say that we are moving towards the tipping point of climate change,” lead author René van Westen, a marine researcher at Utrecht University, is quoted as saying. “What surprised us was the speed at which the change occurred,” he says. "It will be devastating."

Temperature drop of up to 30 degrees

AMOC works like a kind of giant global conveyor belt: It transports warm, very salty water from the tropics towards the Arctic Circle, where the water cools and sinks due to its greater density. At depth it flows in a southerly direction. Ocean currents transport heat and nutrients to different areas of the world and play a key role in ensuring that the climate remains relatively mild in large parts of the Northern Hemisphere.

Scientists have been warning for decades that the stability of this special circulation is at risk due to climate change: the ocean is warming, ice is melting in the northern regions, and the additional fresh water will disrupt the relationship between temperature and salt, which in turn increases the strength of the currents. They become weaker. If the system collapses, the consequences would be catastrophic.

In some parts of Europe, the Dutch study says, temperatures could fall by up to 30 degrees Celsius within a century, leading to a completely different climate within just a decade or two. “There are no realistic adaptation measures that can deal with such rapid temperature changes,” write the authors, according to the Guardian and CNN. There would also be less rainfall.

On the other hand, warming could increase in countries in the southern hemisphere, and in the Amazon the wet and dry seasons could reverse, seriously disrupting the ecosystem. The already weakened rainforest could exceed its own tipping point. Temperatures around the world would fluctuate much more. The collapse of the AMOC could also cause sea levels to rise by around one meter, flooding many coastal cities.

Van Westen considers the study to be a “real breakthrough.” “Until now, it could be assumed that the tipping of the AMOC system was only a theoretical concept and that it would disappear as soon as the entire climate system with all its additional feedbacks was taken into account,” says the researcher in the Guardian. But the results provided a “clear answer” to the question of whether such an abrupt change was possible: Yes.

According to the Guardian, the researchers were looking for warning signs of salinity in the southern part of the Atlantic between Cape Town and Buenos Aires. By simulating changes over 2,000 years in computer models, they found that a slow decline can lead to a sudden collapse in less than 100 years.

Van Westen said there is not enough data yet to say whether this will happen next year or the next century, but if it does happen, the changes will be irreversible on human time scales. In the meantime, developments are undoubtedly moving in an alarming direction. »We're moving towards it. “It’s kind of scary,” van Westen said. “We have to take climate change much more seriously.”

Stefan Rahmstorf, a physical oceanographer at the University of Potsdam in Germany, who was not involved in the study, called the research results a major advance. "It confirms that the AMOC has a tipping point beyond which it will collapse if the North Atlantic is diluted with fresh water," he is quoted as saying by CNN.

Uncertainty remains: As with “wild fluctuations in the stock market” before the crash

Previous studies that found the AMOC tipping point had used much simpler models, Rahmstorf said. This has led some scientists to hope that this tipping point could not be found in more complex models. The new study from the Netherlands dashes these hopes.

Joel Hirschi, deputy head of marine systems modeling at the National Oceanography Center in the United Kingdom, told CNN there are reasons to be cautious. Although the study used a complex model, the resolution is still low, meaning there may be limitations in representing some parts of the flows.

The last time there were drastic changes in the AMOC was more than 10,000 years ago. The system is currently in its weakest state in more than a millennium, according to the Guardian. He cites research that shows currents have declined by 15 percent since 1950. However, it was still unclear whether and when a tipping point could be reached.

According to a controversial study from last year, the tipping point could be reached between 2025 and 2095. However, there were strong doubts about the calculations. Britain's Met Office said major, rapid changes at AMOC were "very unlikely" in the 21st century. So the topic remains fraught with a lot of uncertainty.

Jeffrey Kargel, senior scientist at the Planetary Science Institute in Arizona, told the Guardian that he suspects the theory of a possible imminent collapse of the AMOC "will remain somewhat controversial until we know in a year that it is actually happening." He likened the potential collapse to "wild stock market swings that precede a major crash."