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Most people can probably name a few particularly prominent effects of global warming on the Earth system: the polar ice caps are melting and the permafrost is thawing. However, it is much less known that the so-called Atlantic Overturning Circulation (abbreviated Amoc for Atlantic Meridional Overturning Circulation) is weakening. The likely consequences are at least as threatening.
The situation would be particularly bad if this current system in the Atlantic Ocean, which also includes the Gulf Stream, completely collapses. Experts speak of a so-called turning point; the Amoc would come to a standstill within a few decades and would not recover even under favorable conditions.
Researchers were able to simulate a collapse
In short, the Amoc – very roughly speaking – transfers heat from the south to the North Atlantic Ocean, thus contributing to a relatively mild climate in Western and Northern Europe. Whether and under what circumstances this power system could collapse is being intensively debated among experts.
However, there is increasing evidence that this is both possible and becoming more likely. Dutch researchers recently showed in the journal ‘Science Advances’ that they can simulate a collapse of the Amoc in a more complex climate model under certain conditions. The work was considered solid by several experts, but there was also criticism of certain assumptions made by the Dutch group.
This also created a kind of early warning system that, according to the researchers, shows that the North Atlantic current is developing towards a tipping point.
15 degrees less within 100 years
According to the analyses, the consequences would be dramatic: in some European cities, the annual average temperature could drop by several to 15 degrees within 100 years, depending on the region. The temperature drops sharply, especially in winter and in the northwest. In Bergen, Norway, February can get more than three degrees colder per decade. One can only imagine the devastating consequences of such rapid and extreme changes on nature and agriculture.
In other regions, warming may be accelerated. For the Amazon region, the model shows a drastic change in precipitation patterns. “It is also predicted that the abrupt collapse of the ocean circulation will cause sea levels in Europe to rise by 100 centimeters,” said lead author René van Westen of Utrecht University, according to the statement.
To understand the effects of the climate crisis on the Amoc, you need to take a closer look at the system. Simply put, it consists of two opposing currents. Warm water is transported near the surface from the southern regions of the Atlantic Ocean to the north. There it cools and sinks near the poles. As a cold current it flows southwards again at depth.
The driving forces are differences in the density of the water
The driving forces behind this system are differences in the density of the water. Simply put, the water near the poles becomes particularly heavy because it is cold and salty. This causes it to sink into the depths and thus create dynamics.
However, according to experts, global warming is having a slowing effect on this system. On the one hand, the temperature of the surface water is rising in the far north. On the other hand, the ingress of fresh water, for example from melting ice caps, makes the water there less salty. Both phenomena reduce the water density of the northern surface water, making the Amoc’s propulsion weaker. In the worst case, the event becomes increasingly self-intensifying until the power system collapses.
The prize is under what circumstances such a collapse could occur – and especially when. Van Westen’s group – like many other experts – does not provide a direct answer to this.
Criticism from the professional world
Danish researchers, who dared to make a prediction in the journal ‘Nature Communications’ in July last year, are different. Their analyzes showed that the Amoc is very likely to collapse between 2025 and 2095. The response from experts was swift and the study was heavily criticized. Many researchers believed that the predictions were untenable for methodological reasons.
Niklas Boers of the Technical University of Munich, who conducts intensive research into weakening the Amoc, criticizes the fact that the Danish model has not taken sufficient account of existing uncertainties. The work makes far too simplistic assumptions to predict the future development of the Amoc based on historical data alone, he told German news agency DPA. On the other hand, the Dutch researchers led by van Westen write about the findings of their Danish colleagues: “Your assessment of the tipping point could well be correct.”
Johanna Baehr, head of climate modeling at the Institute of Oceanography of the University of Hamburg, also highlighted the uncertainties of a prediction in an interview with dpa: “We don’t know if and when such a collapse will come, whether in 50, 100 or 1000 years.” However, Baehr also says about the Dutch research: “The possibility of a collapse can no longer be completely excluded.” It is now the job of science to further narrow down a possible time frame.
For Baehr, the sixth assessment report of the Intergovernmental Panel on Climate Change (IPCC) remains the benchmark. It says: The Amoc will most likely decline over the course of the 21st century – regardless of the climate protection scenario. Moreover, people are relatively certain (average confidence) that this will not lead to a collapse before the year 2100.
Tilting element also creates discussions with other systems
The Amoc is not the only system that is discussed as a so-called tilting element. Late last year, the ‘Global Tipping Points Report’ highlighted five major natural systems facing potentially irreversible upheavals. However, in individual cases it is difficult or impossible to specifically indicate how close a tilting element will actually collapse. There are too many components at play.
With regard to the Amoc, Boers says it is unclear how much additional freshwater would actually enter the North Atlantic Ocean at a certain level of global warming, whether from melting polar ice caps or more input from rivers and additional rain. The exact location where the fresh water enters also plays a major role. On the other hand, there are concerns that the models portray the Amoc as too stable. The current is currently weaker than at any time in the past 1,000 years.
According to Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research (PIK), the risk of collapse must be reduced at all costs. “The question is not whether we are certain that this will happen. The problem is that we have to rule it out for 99.9 percent,” he writes in a blog article. Once there is a clear warning sign, it is too late to do anything about it. (SDA)
Source: Blick
I am Amelia James, a passionate journalist with a deep-rooted interest in current affairs. I have more than five years of experience in the media industry, working both as an author and editor for 24 Instant News. My main focus lies in international news, particularly regional conflicts and political issues around the world.
