The Gulf Stream has never been so weak in the last thousand years. And it is a problem

The Gulf Stream has been slowing since the mid-nineteenth century and has never been, in the last millennium, as weak as it is today. Considering the flow rate of this current, which moves over 20 million cubic meters of water per second, one hundred times the flow rate of the Amazon, and its important function of redistribution of heat on our planet, moving hot water from the equator to the north. and colder, deeper water from north to south, the implications are serious: there could be a rise in sea level on the eastern shores of the United States and a multiplication of extreme climatic events in Europe. A study published in Nature Geoscience by researchers from the Potsdam Institute for Climate Impact Research and the Irish Climate Analysis Unit of Maynooth University.

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“The continuous measurements on the Gulf Stream only started in 2004, but in this study we were able to reconstruct the changes in the last millennium by crossing a whole series of data that the scientific community has only recently understood how to use” he explains to Green&Blue Levke Caesar, a Maynooth University researcher and co-author of the study. “Just to give an example: the size of the grains that are part of the sediments on the ocean floor gives us clues about the speed of the current in the various periods corresponding to the superimposed layers: if a” core “of sediments is extracted from the seabed, the presence of larger grains in a certain layer indicate that the current was faster at that time, because it could carry those too. “

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The slowdown of the Gulf Stream has a beginning: “Around the middle of the nineteenth century, and then there is an increase in the slowdown in the middle of the twentieth century. To get to the last decade, in which the minimum speed is reached. estimated in the last 1,000 / 1,600 years, “explains Caesar.

“The first slowdown, that around 1850, coincides with the end of the so-called” Little Ice Age “, a period in which Europe was particularly cold. One of the causes of this phenomenon could be in part the human activity of the industrial revolution , but there could also be natural causes linked to the increase in volcanic activity: this is still unclear. The impact of global warming from anthropogenic activities in the slowdown we see in the mid-twentieth century is much more likely. “

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The increase in the melting of Arctic ice and the warming of surface waters in the North slows down one of the “engines” of the Gulf Stream, namely the movement of cold and deep water towards the South. “The Current works like this: there is a mass of hot, salty water that arrives from the equator in the Nordic seas, where it cools, becomes denser and heavier and descends to the deeper layers. At that point, for the principle of conservation of mass, it must go somewhere: and back south, “explains Caesar. “Now: if water from dissolved glaciers and rain are added to this mechanism in the Nordic seas, surface water from the South becomes less dense and less heavy, which will go less rapidly towards the bottom. And the whole mechanism slows down” .

There are already some ideas on the effects. “Some climate models suggest that we may have more frequent and stronger winter storms in northwestern Europe,” says Caesar. “The models suggest that if global warming continues, the Gulf Stream could slow up to 45% by the year 2100. This slowdown causes less hot and less salty water to reach the North. And salt is useful for make the water that has to sink in the North to return to the South become denser – and heavier. If this mechanism becomes exasperated, a vicious circle can set up such that even stopping global warming, it will not be possible to prevent further slowing of the Current of the Gulf. And the climate would become increasingly unstable “.

The interview