Scientists have been discussing for a long time whether the Gulf Stream could ever collapse. Researchers are skeptical – but there is still no all-clear.
To anticipate: the Gulf Stream itself is not in danger of collapsing. Because it is mostly driven by winds. “As long as the earth rotates, there will also be the Gulf Stream,” says Niklas Boers. He is a physicist and researches ocean currents at the Potsdam Institute for Climate Impact Research and the Technical University of Munich.
However, the Gulf Stream is part of a larger current, the Atlantic overturning circulation. The current, known as AMOC (Atlantic Meridional Overturning Circulation) for short, transports water masses through the Atlantic. Another part of it, namely the North Atlantic Current, functions as Europe’s hot water heater, which the Gulf Stream is always mistaken to be. If this stream dried up, temperatures could change dramatically, not only in Europe. And there could also be more extreme weather events.
Graphical representation of the global current system: it connects four oceans and combines them into one great cycle.
The climate would change significantly
However, the images of eternal winter in Europe, also used by Hollywood, would probably not be entirely correct. If the Atlantic overturning current collapsed, the consequences for us in Central Europe would probably not be particularly great. The temperatures would probably only change by a few degrees. In northern Europe, however, it could be significantly colder.
In addition, the climate would also change significantly in other parts of the world. For example, the tropical rain zone would shift south. The Sahel zone would become even drier. Farther south it would rain a lot more.
AMOC as an important engine
In addition, the AMOC is part of an even larger flow system. The so-called global conveyor belt transports nutrients from the depths of the ocean to the surface and oxygen to the deep sea. It is the only way for animals at depth to be supplied with oxygen. Because deep down in the sea there is not enough light for plants to carry out photosynthesis there.
The Atlantic overturning circulation is the main engine of this conveyor belt. If the current were to collapse here, it would have major consequences for animals in all parts of the ocean.
Study provokes clear criticism
If and when the Atlantic overturning circulation will really collapse is not yet clear. A recent one in the magazine Study published in “Nature Communications”. had forecast an imminent collapse. According to the authors, this could already happen in 2025.
However, there was clear criticism of the study. “In detail, the statistical analysis itself is correct, but very simplifying assumptions are made regarding the mechanistic description of the meridional overturning circulation in the Atlantic itself,” says Niklas Boers, for example, to the Science Media Center.
The oceanographer Johanna Baehr from the University of Hamburg is also critical: “Personally, I am surprised at the far-reaching conclusions that can be drawn from the purely mathematical analysis for realistically expected developments in the North Atlantic circulation.” These conclusions could not be reached in this way.
A vicious circle threatens
Nevertheless, there is no all-clear. In its most recent report, the Intergovernmental Panel on Climate Change predicted with high probability that the current in the Atlantic will not collapse completely before the end of the century. At the same time, there are signs that it is currently weakening. And even a collapse at the end of the century would have serious consequences.
The fact that it could come to this at all is due to the melting sea ice. Because if ice melts, the water off Greenland, for example, is no longer dense enough to then cool down and sink, taking oxygen and CO2 with it. This in turn would lead to a vicious circle. Because so far, a considerable part of the CO2 we produce has been transported underground in this way. If this mechanism fails or its function is reduced, less CO2 will be stored and climate change will accelerate.
Others too ocean circulation in danger
At the same time, another phenomenon is puzzling researchers. In the Antarctic winter, the extent of the ice is just as small as it has ever been at this time of year. The reasons are still unclear.
Even in summer, the ice in Antarctica is melting faster than before. One in May in the journal Study published in “Nature”. has calculated that this will reduce ocean currents around Antarctica by 40 percent by 2050.
This ocean current is also part of the global conveyor belt. Stephen Rintoul from the Australian Scientific and Industrial Research Agency CSIRO is one of the authors of the study. He says: “Both Antarctica and Greenland have lost ice. In both ice sheets, the ice is melting. Most of the time we think of this as contributing to sea level rise. But what this study shows is that it has another effect , namely the slowing down of these ocean currents.”