The climate models used to date may have underestimated the risks faced by one of the key currents of the Atlantic Ocean: the so-called meridional overturning of the Atlantic circulation. An “underwater river” fundamental for the climatic balance of the planet, which transports the warm waters of the tropics towards the north, and vice versa, the cold and saline waters of the arctic towards the south. And which according to two researchers from the University of New South Wales in Sydney it would be slowing down much faster than expected, due to the effect of fresh water introduced into the oceans by the melting of Greenland’s glaciers, a variable that until now has not been adequately taken into account by climate scientists.
A fundamental current
The meridional overturning of the Atlantic circulation, better known by the English acronym Amoc (from Atlantic meridional overturning circulation), is part of the complex network of global ocean currents powered by the difference in heat and salinity (and therefore density) of the waters at different latitudes. In the case of Amoc, its existence is fundamental to keeping the climate of many areas of the Northern Hemisphere in balance. And if it were to slow down significantly, or even stop, the consequences could be devastating, leading for example to the collapse of temperatures in Europe, especially in the northernmost areas of the continent, and to the distortion of annual rainfall linked to the Asian monsoons.
Several observational studies (i.e. based on measurements and time series of climate data) in the past have indicated that the meridional overturning of the Atlantic circulation is slowing down, due to human-induced climate changes. But to date, most climate models have always given results of the opposite sign, so much so that the IPCC indicates as “extremely unlikely” the risk that it could undergo noteworthy upheavals over the next century.
The new study
Convinced that something was wrong with the climate models, given that they clash with what was observed from “field” studies, two climate scientists from the University of New South Wales decided to improve their precision. In particular, they focused on the model’s ability to take into account the effects of the fresh water that is released into the oceans every year by the melting of Greenland’s glaciers, which, by diluting the salinity of the waters of the North Atlantic, directly affects the balance they keep the Amoc moving.
From their simulations, described in a study published in Nature Geoscience, it emerged that the slowdown in the current could already be underway, and that it would also proceed at a much higher rate than hypothesized by the IPCC: in the next 15 years it could reduce by a third, making the risk of it collapsing completely by the end of the century more real than ever.
“We have shown that in the last 70 years the ocean circulation has weakened due to the water coming from the melting of the glaciers of Greenland and the Arctic regions of Canada,” commented Gabriel Pontes, one of the two authors of the study, on the pages of New Scientist . “This will induce greater weakening faster than the IPCC predicts over the next few decades.”