Mysterious Climate Cycle

Potsdam, 20 May 2003

During the last Ice Age, which ended ten thousand years ago, over twenty abrupt and dramatic warmings have occurred. These so-called Dansgaard-Oeschger-events show a striking and puzzling regularity, as climatologist Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research (PIK) in Germany shows in a new study published this week in Geophysical Research Letters.

Dansgaard-Oeschger-(or DO-)events are the perhaps most dramatic climate shifts known: starting from frosty Ice Age conditions, they involve sudden warmings of up to ten degrees Centigrade within a decade or two. The anomalous warmth then typically lasted for several centuries. The leading theory to explain these warmings involves a northward push of warm Atlantic waters towards the Arctic, into the Greenland and Norwegian Seas (see press releases of 5 January 2001 and 18 January 2002). But the ultimate trigger of such changes in ocean currents remains unknown.

In a new study of Greenland ice core data, Rahmstorf has now unvailed an intriguing clue: the warm events appear to be paced by an extremely regular cycle of 1,470 years duration. This cycle does not trigger a DO event each time; in 23 investigated cycles only 13 events were triggered. The existence of such a cycle had been noticed before, yet the high regularity revealed by the new analysis came as a surprise. The length of the cycle is maintained constant within a few percent of 1,470 years over a time interval of at least 35,000 years.

Such regularity points strongly to an extraterrestrial origin of this cycle - perhaps an orbital cycle. "No oscillation within the Earth system could be so regular," says Rahmstorf. "Even the known solar cycles show greater variations in their periods."

The hunt is now on to find an orbital cycle with a period of 1,470 years, since such a cycle is so far not known.

The Potsdam Institute for Climate Impact Research (PIK) was founded in 1992 and employs 121 scientists. Its research on climate change, climate impacts and sustainable development is of international renown. PIK is a member of the Leibniz Association.


Prof. Dr. Stefan Rahmstorf,, Tel. +49/331/288-2688

Press office:
Anja Wirsing,, Tel. +49/331/288-2507

Original article:

Rahmstorf, Stefan 2003: Timing of abrupt climate change: A precise clock. Geophysical Research Letters, Vol. 30, No. 10.

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