The so-called “Atlantic overturning current”, which also includes the Gulf Stream, ensures mild temperatures in Europe. But researchers are now observing: The current is on the verge of collapse – thanks to climate change. The consequences for Europe would be enormous.
According to current research, ocean currents in the Atlantic may have lost so much of their stability that this system could collapse. This is the result of a study in the specialist journal “Nature Climate Change”, which the Potsdam Institute for Climate Impact Research (PIK) involved in it reported on Thursday. Warnings are given of the consequences for weather systems worldwide.
The study deals with the Atlantic Meridional Overturning Circulation (AMOC), which also includes the Gulf Stream. “AMOC transports warm water masses from the tropics on the sea surface to the north and cold water on the sea floor to the south, which accounts for the relatively mild temperatures in Europe is of great importance ”, explained the PIK.
“Approaching a critical threshold” “The AMOC is one of the most important circulation systems on our planet”, explained the author of the study, Niklas Boers from the Potsdam Institute for Climate Impact Research, the Free University Berlin and of Exeter University. He pointed out that in the history of the earth AMOC had already assumed an alternative, much weaker state in addition to the current strong state. “In principle, abrupt transitions” are also possible between these two states.
According to the study, the current system is currently “as weak as never before in the past thousand years”. According to Boers, it has so far been unclear whether this is only associated with a change in the mean state of circulation or an actual loss of dynamic stability. “The difference is crucial,” emphasized Boers, because a reduction in dynamic stability would mean that “a transition to the weak mode of circulation could probably be irreversible in practice”.
According to Boers, several pieces of evidence indicate that the weakening “probably means the approach of a critical threshold beyond which the circulatory system could collapse”.
Researchers surprised by the rapid change Reference is made in the study to additional factors that would be added to the direct effects of warming the Atlantic on its circulation. This includes the inflow of fresh water from the melting of the Greenland ice sheet, from melting sea ice, from increasing rainfall and from water from rivers. Freshwater reduces the tendency of water in the North Atlantic to sink from the surface to greater depths, which is one of the drivers of the upheaval.
“I did not expect that the additional amounts of freshwater that flowed into the ocean over the last century would already provoke such a response from the AMOC,” said Boers. Therefore, existing models “urgently need to be brought into line with the observations available” in order to “assess how far the AMOC is actually still from the critical threshold value”. Even if the respective importance of the various factors still needs to be investigated, they are in any case “related to man-made climate change”.