Collapse of Atlantic currents is an imminent risk – 02/16/2024 – Environment

The ocean water circulation system that helps maintain much of the stability of the global climate is becoming increasingly vulnerable. And it runs the risk of being “switched off” if the Earth’s temperature continues to rise, warns a study signed by Dutch scientists.

The research, recently published in the specialized journal Science Advances, does not point out dates for the collapse, but estimates which signs could be present and could indicate a “turning point” in current marine currents.

A change on this scale would have severe effects on different regions and ecosystems. Among the consequences of the phenomenon predicted by the Utrecht University team are sudden drops in Europe’s average temperature, with a decrease of more than 1°C per decade.

In some cities in the northwest of the continent, the cooling could ultimately be between 5°C and 15°C less. In other words, it would be as if London or Paris were transported to the Arctic.

At the same time, the transformation would also have effects on the tropics, with the possibility of a “switch” between the current wet and dry seasons in the Amazon — they would start to occur at reversed times of the year. Such a profound and rapid environmental change, on a scale of decades, would be a tremendous challenge for the region’s biodiversity, which would have great difficulty adapting to it.

The work, coordinated by René van Westen, from the Institute for Marine and Atmospheric Research at the Dutch university, combined current data on the melting of glaciers around the world with a sophisticated computer simulation of the Earth’s climate over time. The objective was to simulate future scenarios for the phenomenon known by the English acronym Amoc (“inverted Atlantic meridional circulation”).

The effects of an Amoc shutdown were even dramatized in the 2004 disaster film “The Day After Tomorrow”, starring Dennis Quaid and Jake Gyllenhaal, with a box office of more than half a billion dollars.

In the plot, a large part of the Northern Hemisphere, including the city of New York, where some of the plot’s characters are located, becomes frozen from one moment to the next thanks to a series of superstorms.

It is worth saying that even the most catastrophic version of the process in the real world would never have almost instantaneous effects: the change would take decades, which would already be extremely fast from the point of view of the Earth’s climate system.

Several other researchers have already expressed concern about what will happen to Amoc, whose current presence and intensity are largely responsible for the relatively mild climate in Western Europe, among other things.

To function, Amoc depends on the balance between the temperature and salinity of the water masses that circulate through the ocean. In general, as with air, warmer, less dense water tends to rise, while cold, denser water sinks.

The salt content of the water also influences the density, which increases if the water is saltier and decreases if it is less salty.

This variation in seawater conditions, which also depends on the temperature of the atmosphere, ends up producing a large water circuit in the Atlantic Ocean, carrying hot water towards the north and cold water towards the south.

The problem is that, with the climate crisis caused by human action, the Atlantic has increasingly received an extra supply of fresh water, coming mainly from the melting of glaciers, such as those in Greenland. And, as salinity balance is one of the crucial factors for the functioning of Amoc, it is natural to imagine that circulation could be affected or even “turned off” by this phenomenon.

That’s what computer analysis conducted by scientists at Utrecht University showed — collapse is indeed a possibility, and there are worrying signs that we are approaching the tipping point.

Furthermore, the team identified that measurements of water conditions carried out at 34 degrees South latitude — about the height of Buenos Aires — could be a good indication of how close we are to this shutdown.

“At this location, measurements help measure how much fresh water is entering the Atlantic Ocean and to what extent it is destabilizing Amoc,” René van Westen explained to Sheet.

“Based on the results of our climate model, there is a critical value for freshwater transport at this latitude. As long as this value is not exceeded, Amoc will still continue to flow in its current state. If it is crossed, we have an indication that an abrupt collapse of Amoc will soon follow”, he concludes.

The only way to face the risk, as with many other dimensions of the climate crisis, is to significantly reduce emissions of gases that cause global warming.