Harsh Climate Change Once Fell Swiftly

Aug. 1, 2008 -- It's one of the most dramatic examples of climate change in Earth's history, and scientists now say it happened almost entirely in one year's time.

Thirteen thousands years ago, Europe was much like it is today -- cool but temperate, with great forests carpeting the land. Ice sheets still nibbled at Finland and Sweden, but for much of the continent the last Ice Age was a distant memory.

Suddenly, the climate went haywire. Warm Gulf Stream currents that brought heat from the equator up toward the pole began to fail. Temperatures plummeted 3 to 4 degrees Celsius, and stayed that way for a millennium.

Now scientists believe they've pinpointed the exact time the northern hemisphere was plunged back into a deep freeze. Examining sediments preserved at the bottom of a remote lake in western Germany, they found that what's known as the Younger Dryas cold period took just a year to sweep across the continent, starting in the autumn, 12,679 years ago.

Led by Achim Brauer of the German Research Center for Geosciences in Potsdam, Germany, the team believes such a quick, profound change in climate could only have been brought about by a shift in winds across the northern hemisphere.

Today prevailing winds in the northern hemisphere above the tropics tend to blow from the southwest to the northeast. Air that flows over Texas soon crosses the Atlantic and winds up over Norway.

As it travels the air passes over the Gulf Stream, a warm ribbon of water pouring northward from the tropics. The balmy air brings heat to Europe, which otherwise would be chilly.