The Azimuth Project
Younger Dryas

Idea

The Younger Dryas is a cold period in Europe that lasted roughly from 10,800 BC to 9,500 BC. As a fascinating and somewhat disturbing example of abrupt climate change, it is of great interest to scientists interested in global warming.


Greenland temperatures over the last 18,000 years

Temperatures had been rising since the end of the last glacial period, around 18,000 BC — but around 10,800 BC, in a matter of decades (or perhaps less) the temperature in Europe dropped about 7 °C. Ice cores from Greenland show an even larger drop: about 15 °C. In England it got so cold that glaciers started forming. In the Netherlands, in winter, temperatures regularly fell below -20 °C. Throughout much of Europe trees retreated, replaced by alpine landscapes, and tundra.

The climate was affected as far as Syria, where drought punished the ancient settlement of Abu Hurerya. But the Younger Dryas does not seem to have been a world-wide event (though this has been heavily debated).

This cold spell lasted for about 1300 years. And then, just as suddenly as it began, it ended! Around 9,500 BC, the temperature in Europe bounced back. Ice cores from Greenland show a warming of +10°C within a timescale of just a few years!

The most popular theory of the Younger Dryas is that a huge lake in North America formed by glacial meltwater, Lake Agassiz, burst its bank, and in a massive torrent lasting for years, the water from this lake rushed out to the Labrador Sea. By floating atop the denser salt water, this fresh water blocked a major current that flows in the Atlantic: the Atlantic Meridional Overturning Circulation. This current brings warm water north and helps keep northern Europe warm. So, northern Europe was plunged into a deep freeze.

References

The temperature chart at the top of the page is based on Greenland ice cores. It is taken from:

  • Richard B. Alley, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and our Future, Princeton U. Press, Princeton, 2002.

This paper gives evidence for an abrupt 10-degree warming at the end of the Younger Dryas:

category: climate