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Published Online June 22, 2006
Science DOI: 10.1126/science.1125249

Reports

Submitted on January 23, 2006
Accepted on June 9, 2006

Early Pleistocene Glacial Cycles and the Integrated Summer Insolation Forcing

Peter Huybers 1*

1 Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA.

* To whom correspondence should be addressed.
Peter Huybers , E-mail: phuybers{at}fas.harvard.edu

Long-term variations in Northern Hemisphere summer insolation are generally thought to control glaciation. But while the intensity of summer insolation is primarily controlled by 20 kyr cycles in the precession of the equinoxes, early Pleistocene glacial cycles occur at 40 kyr intervals, matching the period of changes in Earth's obliquity. The resolution of this 40 kyr problem is that glaciers are sensitive to insolation integrated over the duration of the summer. The integrated summer insolation is primarily controlled by obliquity and not precession because, by Kepler's second law, the duration of the summer is inversely proportional to Earth's distance from the sun.


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Science. ISSN 0036-8075 (print), 1095-9203 (online)