Never before in over 1000 years the Atlantic Meridional Overturning Circulation (AMOC), also known as Gulf Stream System, has been as weak as in the last decades.
Never before in over 1000 years the Atlantic Meridional Overturning Circulation (AMOC), also known as Gulf Stream System, has been as weak as in the last decades. This is the result of a new study by scientists from Ireland, Britain and Germany. The researchers compiled so-called proxy data – taken mainly from natural archives like ocean sediments or ice cores – reaching back many hundreds of years to reconstruct the flow history of the AMOC. They found consistent evidence that its slowdown in the 20th century is unprecedented in the past millennium – it is likely linked to human-caused climate change. The giant ocean circulation is relevant for weather patterns in Europe and regional sea-levels in the US; its slowdown is also associated with an observed ‘cold blob’ in the northern Atlantic.
“The Gulf Stream System works like a giant conveyor belt, carrying warm surface water from the equator up north, and sending cold, low-salinity deep water back down south. It moves nearly 20 million cubic meters of water per second, almost a hundred times the Amazon flow,” explains Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research PIK, initiator of the study published in Nature Geoscience. Previous studies by Rahmstorf and colleagues showed a slowdown of the ocean current of about 15 percent since the mid-20th century, linking this to human-caused global warming, but a robust picture about its long-term development has up to now been missing: This is what the researchers provide with their review of results of proxy data studies.
“For the first time, we have combined a range of previous studies and found they provide a consistent picture of the AMOC evolution over the past 1600 years,” says Rahmstorf. “The study results suggest that it has been relatively stable until the late 19th century. With the end of the little ice age in about 1850, the ocean currents began to decline, with a second, more drastic decline following since the mid-20th century.” Already the 2019 special report on the oceans of the Intergovernmental Panel on Climate Change (IPCC) concluded with medium confidence ‘that the Atlantic Meridional Overturning Circulation (AMOC) has weakened relative to 1850–1900.’ “The new study provides further independent evidence for this conclusion and puts it into a longer-term paleoclimatic context,” Rahmstorf adds.
Read More: Potsdam Institute for Climate Impact Research
