Sao Carlos (SP)
The ocean water circulation system that maintains much of the stability of the global climate is becoming increasingly vulnerable. And it risks being “shut down” if Earth’s temperature continues to rise, a study signed by Dutch scientists warns.
The study, published recently in the journal Science Advances, does not give dates for the collapse, but estimates what signs might be present and indicate a “tipping point” in current ocean currents.
A change of this magnitude would have serious impacts on various regions and ecosystems. The consequences of the phenomenon predicted by the Utrecht University team include a sudden drop in the average temperature in Europe, with a drop 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 like London or Paris being transported to the Arctic.
At the same time, the transformation would also have an impact on the tropics, with the possibility of a “switch” between the current wet and dry seasons in the Amazon these would occur at opposite times of the year. Such a profound and rapid environmental change on a scale of decades would pose an enormous challenge to the region's biodiversity, which would find it difficult to adapt.
The work, coordinated by René van Westen of the Dutch University's Institute of Marine and Atmospheric Research, combined current data on melting glaciers around the world with a sophisticated computer simulation of Earth's climate over time. The aim 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, which grossed more than half a billion dollars.
In the plot, a large portion of the Northern Hemisphere, including the city of New York, where some of the plot's characters are located, is frozen in an instant thanks to a series of superstorms.
It's worth noting that even the most catastrophic version of the process would never have anything close to immediate impact in the real world: the change would take decades, which would already be extremely rapid from the perspective of Earth's climate system.
Several other researchers have already expressed concerns about what will happen to Amoc, whose current presence and intensity are largely responsible, among other things, for Western Europe's relatively mild climate.
To function, Amoc relies on the balance between temperature and salinity of the water masses circulating through the ocean. In general, warmer, less dense water like air tends to rise, while colder, denser water sinks.
The salinity of the water also influences the density, which increases with saltier water and decreases with less salty water.
This variation in seawater conditions, which also depends on the temperature of the atmosphere, ultimately leads to a large water cycle in the Atlantic Ocean that transports hot water north and cold water south.
The problem is that due to the climate crisis caused by human activity, the Atlantic is increasingly being supplied with additional fresh water, mainly from the melting of glaciers like those in Greenland. And since the balance of salinity is one of the crucial factors for the functioning of Amoc, it is tempting to imagine that blood circulation could be impaired or even “turned off” by this phenomenon.
This is what computer analysis by scientists at Utrecht University has shown: a collapse is indeed possible, and there are worrying signs that we are approaching the tipping point.
In addition, the team found that measurements of water conditions at 34 degrees south latitude about the same level as Buenos Aires could be a good indication of how close we are to this closure.
“At this location, measurements help to measure how much fresh water enters the Atlantic Ocean and to what extent it destabilizes Amoc,” explained René van Westen 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 continues to flow in its current state. If it is exceeded, we have a sign that an abrupt collapse of Amoc will soon occur,” he concludes.
The only way to address the risk, as with many other dimensions of the climate crisis, is to significantly reduce emissions of gases that cause global warming.