OSLO A drastic cooling of the climate in western Europe happened exactly 12,679 years ago, apparently after a shift to icy winds over the Atlantic, scientists said on Friday, giving a hint of how abruptly the climate can change.
The study, of pollens, minerals and other matter deposited in annual layers at the bottom of Lake Meerfelder Maar in Germany, pinpointed an abrupt change in sediments consistent with a sudden chill over just one year.
"Our data indicate an abrupt increase in storminess during the autumn to spring seasons, occurring from one year to the next at 12,679 years before the present, broadly coincident with other changes in this region," they wrote in the journal Nature Geoscience.
Scientists have long known about the sharp chill towards the end of the last Ice Age, known as the Younger Dryas cooling. The study by researchers in Germany, Switzerland and the United States may help clear up the causes and exact duration.
"We suggest that this shift in wind strength represents an abrupt change in the North Atlantic westerlies towards a stronger and more zonal jet," they wrote.
The wind shift might in turn have been triggered by factors such as a slight southwards shift of sea ice in the North Atlantic caused by some other natural factors, they said.
Previously, scientists have speculated that the sudden cooling might have been caused by a meteorite that kicked up dust and dimmed sunlight.
Other theories have been a weakening of the warm Gulf Stream current, perhaps caused by a vast inflow to the Atlantic of fresh water from melting glaciers over North America or Europe.
The findings adds to evidence about conditions needed for abrupt climate shifts. Some modern scientists fear such wrenching changes may be caused by global warming widely blamed on human emissions of greenhouse gases from fossil fuels.
Some have suggested that a melting of Greenland ice, for instance, could lead to a flow of fresh water into the Atlantic that could also slow down the Gulf Stream current and bring an abrupt chill despite an overall warming trend.
(Editing by Giles Elgood)