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Persistent Millennial-Scale Climate Oscillations of the Past Million-Plus Years
Raymo, M.E., Ganley, K., Carter, S., Oppo, D.W. and McManus, J.  1998.  Millennial-scale climate instability during the early Pleistocene epoch.  Nature 392: 699-702.

What was done
The authors studied various physical and chemical characteristics of an ocean sediment core obtained from a water depth of nearly 2,000 meters at a site south of Iceland.

What was learned
It was found that millennial-scale oscillations in climate were occurring well over one million years ago in a region of the North Atlantic that has been shown to strongly influence circum-Atlantic, and possibly global, climate.  These oscillations appeared to be similar in character and timing to the Dansgaard-Oeschger cycles of the most recent glacial epoch.

What it means
Because the climate of the early Pleistocene was too warm to support the growth and development of large 100,000-year ice sheets characteristic of the late Pleistocene, and because similar millennial-scale climate oscillations are evident in both time periods, the authors conclude that millennial-scale climate oscillations "may be a pervasive and long-term characteristic of Earth's climate, rather than just a feature of the strong glacial-interglacial cycles of the past 800,000 years."  Consequently, since neither the glacial nor the independent millennial-scale climate oscillations of the past million-plus years have been attributed to variations in atmospheric CO2 concentration, and since the air's CO2 content has varied significantly over this time period, there would appear to be little reason to attribute the observed warming of the past century or so to the concurrent increase in the atmosphere's CO2 concentration or to expect that any further rise in the air's CO2 content would trigger any significant warming in the future.

Reviewed 1 January 1999