Climate|More than 40 scientists sent an open letter to the Nordic Council in October, emphasizing that the risk will increase as climate change progresses.
Atlantic it is not very likely that the seawater cycle will stop as climate change progresses – but the risk is greater in light of current knowledge than was estimated just a few years ago.
Without the warming sea current, average temperatures in the Nordic countries would drop by about 4–10 degrees.
“The change that is predicted in the Atlantic is faster than previously thought,” says the professor Petteri Uotila From the Center for Atmospheric Sciences of the University of Helsinki.
The Amoc (Atlantic Meridional overturning circulation), which cuts through the Atlantic in a north-south direction, which also includes the Gulf Stream, which warms the Nordic countries and Britain, has gradually weakened in recent decades. The weakening is mainly influenced by the melting of Greenland’s glaciers.
“It is also possible that Amoc will weaken and not necessarily stop,” says Uotila.
Although the probability of the Amoc cycle stopping in the next few decades is not high, the disadvantages would be significant. In October, forty scientists who were concerned about the issue published an open letter addressed to the Nordic Council, urging the country’s decision-makers to take action to reduce greenhouse gases that warm the climate.
A stoppage of the Atlantic seawater cycle would lead to a drop in the average temperature of at least four, possibly even 10 degrees.
That’s right as recently as 2021 the intergovernmental panel on climate change IPCC evaluatethat the probability of the Atlantic Amoc flow stopping within the 21st century due to climate change would be between zero and 33 percent. The assessment was based on the research up to that point.
Based on studies published in recent years, however, it seems that the probability is higher. According to Uotila, more advanced climate models and more observations and statistical analyzes have been used in the new studies.
“Newer, more advanced climate models give a more warning picture. There is quite a lot of discussion in the scientific community,” he says.
According to Uotila, it is impossible to say how many percent the risk of the Amoc cycle stopping in the light of the current information is. The results of different studies are different to that extent.
Last year, the scientific journal Nature Communications published researchaccording to which the 50 percent probability of the collapse of the Amoc current and the Gulf Stream would be exceeded already around 2060 at the current rate.
“The study was published in a good journal and peer-reviewed. Since then, there has been at least one study – also good and peer-reviewed – that criticized this and said that the reliability of the observations is not good enough,” says Uotila.
Uotila points out that when assessing risks, attention should not only be paid to the probability of a harmful event, but also to how big the risk of damage is.
The risk of major damage should be taken seriously, even if the probability does not seem high.
“It would be good to be prepared and try to do something to reduce emissions.”
A stoppage of the Amoc cycle would lead to a drop in the average temperature of at least four, possibly even 10 degrees in the Nordic countries. The climate would resemble Northern Siberia.
In the light of current knowledge, winters would be colder than summers, Uotila says. If the climate elsewhere warms up at the same time, even more violent winds and storms can be expected in the North.
Further south on Earth, the cessation of the Amoc ocean current system would at least affect the rainfall of tropical regions. The area of monsoon rains would move somewhat further south, previously rainy areas would be drier and vice versa.
Gulf Stream According to Uotila, the weakening is most strongly influenced by the melting of Greenland’s glaciers. The flow of fresh water from glaciers to the sea leads to a decrease in the density of seawater and a decrease in mixing. This in turn weakens the sea current.
“Of the world’s continental glaciers, Greenland is probably melting the fastest. In addition to Antarctica, its melting has also been the least predictable,” states Uotila.
The melting of the ice in the Arctic Ocean and the increase in the flow of Siberian rivers also have their share in the weakening of the Gulf Stream.
The underlying cause of all these causes is global warming, which is mainly caused by the use of fossil fuels. The increase in temperature in itself affects the Amoc flow.
Of the continental glaciers on Earth, Greenland seems to be melting the fastest, says Professor Petteri Uotila.
Uotila is one of the 44 climate and environmental scientists who signed the one addressed to the Nordic Council an open letter in October. The Nordic Council met in Iceland at the end of October.
“The letter emphasizes the urgency of emission reductions,” says Uotila.
The researchers state in the letter that the risk of tipping points, i.e. irreversible and relatively sudden changes, increases when the average global temperature rises by 1.5–2 degrees compared to the time before industrialization.
With current greenhouse gas emissions, we are on our way to a temperature increase of more than 2.5 degrees.
“This increases the probability of changes that can be considered unlikely but have very large adverse effects,” the letter states.
Last year, the annual average temperature of the earth rose for the first time almost 1.5 degrees higher than before industrialization, said EU:n klimapalvelu Copernicus in January. This year may be even warmer.
Correction 3.11. 8:19 p.m.: The Gulf Stream itself does not stop, but the Amoc circulation, or circulation that carries warm water to the north and cold, deep water to the south.