James Croll

Born on the farm of Little Whitefield, near Wolfhill (Perth and Kinross), James Croll was largely self-educated. He became an apprentice wheelwright, but gave that up due to ill-health. Then variously a tea merchant, a manager of a temperence hotel in Blairgowrie and an insurance agent in Edinburgh and Glasgow. He was appointed as a janitor in the museum at Anderson's Institution, Glasgow, in 1859.

Croll corresponded with Sir Charles Lyell [1], on links between ice ages and variations in the earth's orbit.

Using formulae for orbital variations developed by Leverrier (whish had lead to the discovery of Neptune), Croll developed a theory of the effects of variations of the earths orbit on climate cycles. His idea was that decreases in winter sunlight would favour snow accumulation, and for the first time coupled this to the idea of a positive ice-albedo feedback to amplify the solar variations. He suggested that when orbital eccentricity is high, then winters will tend to be colder when earth is farther from the sun in that season and hence, that during periods of high orbital eccentricity, ice ages occur on 22,000 year cycles in each hemisphere, and alternate between southern and northern hemispheres, lasting approximately 10,000 years each. This is wrong, but that was not known then.

Crolls theory predicted multiple ice ages, asynchronous in northern and southern hemispheres, and that the last ice ages should have occurred about 80,000 years ago. Evidence was just then emerging of multiple ice ages, and geologists were interested in a theory to explain this. Geologists were not then able to date sediments accurately enough to determine if glaciation was synchronous between the hemispheres, though the limited evidence more pointed towards synchonicity than not. More crucially, estimates of the recession rate of the Niagra falls indicated that the last ice age ended 6,000 to 35,000 years ago - a large range, but enough to rule out Croll's theory, to those who accepted the measurements.

By the end of the 19th century, Crolls theory was widely disbelieved. However, the basic idea of orbitally-forced insolation variations influencing terrestrial temperatures was further developed by Milutin Milankovitch and eventually, in modified form, triumphant in 1976.

1. 1821: Born
2. 1848: Married Isabella Macdonald
3. 1867-80; Clerical post with the Geological Survey of Scotland, Edinburgh, as keeper of the maps and correspondence.
4. 1875: publ: Climate and Time, in their Geological Relations
5. 1885: publ: Climate and Cosmology
6. 1876: elected Fellow of the Royal Society; awarded an honorary degree by the University of St. Andrews.
7. 1890: Death

External links

1. http://www.geo.ed.ac.uk/scotgaz/people/famousfirst1577.html - "James Croll - unsung scientist"
2. http://www.nahste.ac.uk/pers/c/GB_0237_NAHSTE_P0321/ - index of some of Croll's correspondence
3. http://www.scoti.org.uk/local_heroes.htm - "Croll: a forgotten hero of Perth"

Reference

Imbrie and Imbrie, "Ice ages - solving the mystery", Harvard University Press, 1979.