Paleo Home Research Data Education What's New Features Paleo Perspectives Site Map Mirror Sites National Climatic Data Center, Asheville, North Carolina navigation bar
Paleo Slide Set: The Ice Ages
Photograph of James Croll from J. C. Irons (1896)
Adhémar's theory was seriously flawed, but it nevertheless contained the seed of a theory developed in the 1860's and '70s by Scottish scientist James Croll, shown here. There were three major points to Croll's theory. First, Croll argued that while the total amount of insolation received at a given latitude did not vary from year to year, the amount received in a given season for a given latitude could vary significantly from year to year because of changes in the earth's orbit. Second, he claimed that these seasonal variations were caused by two orbital phenomena known as precession and eccentricity. He was also aware that the tilt of the earth's axis changed, but he was unable to include obliquity into his calculations because the mathematical relationship for this aspect of the Earth's orbit had yet to be developed. Finally, Croll suggested that while the initial climatic effect of changes in the earth's orbit might be rather small, but that these changes were amplified significantly by climatic feedback mechanisms in the earth's climate system. To better understand Croll's ideas, it is helpful to learn more about earth's orbit and how it changes through time.

Photo Credits:
Courtesy of John Imbrie
Department of Geological Sciences, Brown University
Click to View Larger Image
Click on above image to enlarge.

Download a zip file
of a full resolution TIF image

Back to Slide Sets.....

Contact Us
Last Modified: 12 October 2001

Paleoclimatology Program Home Page