Collapse of critical Atlantic current is no longer low-likelihood, study finds | Oceans

The collapse of a current of the critical Atlantic can no longer be considered as a low -like event, concluded a study, making deep cuts in fossil fuel emissions even more urgent to avoid the catastrophic impact.

The circulation of southern Atlantic (AMOC) is an important part of the global climate system. It brings tropical water warmed of sun in Europe and in the Arctic, where it cools and flows to form a deep return current. The Amoc was already known to be the lowest in 1,600 years following the climate crisis.

Climate models have recently indicated that a collapse before 2100 was unlikely, but the new analysis examined the models that have been executed longer, at 2300 and 2500. These show the tilting point which makes an inevitable Amoc stop is likely to be passed in a few decades, but that the collapse itself can occur before 50 to 100 years later.

Research revealed that if carbon emissions continued to increase, 70% of model races led to collapse, while intermediate emission level has resulted in 37% of models. Even in the case of low future emissions, an Amoc closure occurred in 25% of the models.

Scientists previously warned that the collapse of the Amoc must be avoided “at all costs”. This would move the tropical belt of precipitation to which several million people count to cultivate their food, plunge Western Europe into extreme cold winters and summer droughts, and add 50 cm up the sea level.

The new results are “quite shocking because I said that the chances of collapsing Amoc due to global warming were less than 10%,” said Professor Stefan Rahmstorf, at the Potsdam Institute for Climate Impact Research in Germany, which was part of the study team. “Now, even in a low -program scenario, sticking to the Paris Agreement, it seems that it can be more at 25%.

“These figures are not very certain, but we are talking about a question of risk assessment where even 10% of the fellowship of the Amoc would be far too high. We have found that the tilting point where the closure becomes inevitable is probably in the next 10 to 20 years.

Scientists have spotted signs of warning a shift in 2021 and know that the Amoc collapsed in the past of the earth. “Observations in depth [far North Atlantic] Already display a downward trend in the last five to 10 years, in accordance with model projections, “said Professor Sybren Drijfhout, Royal Netherlands Meteorological Institute, who was also part of the team.

“Even in certain intermediate and low -emission scenarios, the Amoc slowly slows down 2100 and stops completely afterwards. This shows that the risk of stop is more serious than many people think it.”

The study, published in the journal Environmental Research Letters, analyzed the standard models used by the Intergovernmental Panel on Climate Change (IPCC). Scientists were particularly anxious to note that in many models, the tilting point is reached during the next decade or two, after which the end of the AMOC becomes inevitable due to a retroaculation of self-employment.

Air temperatures increase quickly in the Arctic due to the climate crisis, which means that the ocean cools more slowly. The warmer water is less dense and therefore sinks more slowly into the depths. This slowdown allows more precipitation to accumulate in salt surface waters, which makes it less dense and more slows down the sinking, forming the feedback loop. Another new study, using a different approach, also revealed that the tilting point will probably be reached towards the middle of this century.

Only some of the IPCC models were managed beyond 2100, so the researchers also sought to see which of those who take place until the end of this century have shown that Amoc was already in terminal decline. This produced figures by 70%, 37%and 25%. Scientists have concluded: “Such figures no longer comply with the low -free impact event which is used to discuss a brutal Amoc collapse in [the IPCC’s last report]. “”

Rahmstorf said that real figures could be even worse, because the models did not include the torrent of the melting mass of the Greenland ice cap which also refreshes the waters of the ocean.

Dr Aixue Hu to the Global Climate Dynamics Laboratory of Colorado, in the United States, which was not part of the study team, said The results were important. “But it is always very uncertain when the Amoc collapse will occur or when the switching point of the Amoc will cross due to the lack of direct observations [of the ocean] and the variable results of the models. »»

The study which revealed that a total collapse of the Amoc was unlikely this century was led by Dr. Jonathan Baker at the Met Office Hadley Center in the United Kingdom. “This new study stresses that the risk increases after 2100,” he said. “”[But] These percentages must be treated with caution – the size of the sample is small, so more simulations [beyond 2100] are necessary to better quantify the risk. »»

However, Baker said: “The ocean is already changing and changes projected in the convection of the North Atlantic is a real concern. Even if a collapse is unlikely, a major weakening is expected, and this alone could have serious effects on the European climate in the decades. But the future of Atlantic traffic is always in our hands. ”