- James Croll
Infobox Person
name = James Croll
caption =
birth_date = birth date|1821|1|2
birth_place =
death_date = death date and age|1890|12|15|1821|1|2
death_place =
other_names =
nationality = Scottish
known_for =
occupation =Scientist
spouse = Isabella Macdonald (1848-1890)James Croll (
2 January 1821 –15 December 1890 ) was a 19th century Scottishscientist who developed a theory ofclimate change based on changes in the earth's orbit.Life
James Croll was born in 1821 on the farm of Little Whitefield, near Wolfhill in
Perthshire ,Scotland (NO1733). He was largely self-educated, teaching himselfphysics andastronomy . At 16 he became an apprenticewheelwright at Collace near Wolfhill, and then because of health problems a tea merchant in Elgin,Moray . He married Isabella Macdonald in 1848.In the 1850s he managed a temperance hotel in Blairgowrie, and was then an insurance agent in
Glasgow ,Edinburgh andLeicester . In 1859 he became a caretaker in the museum at theAndersonian College and Museum , Glasgow, so as to have access to books to allow him to develop his ideas.From 1864, Croll corresponded with Sir
Charles Lyell [cite web
url=http://www.nahste.ac.uk/pers/c/GB_0237_NAHSTE_P0321/
title=Index of some of Croll's correspondence
publisher=NAHSTE
accessdate=2006-07-30] , on links between ice ages and variations in the earth's orbit. This led to a position in theEdinburgh office of the Geological Survey of Scotland, as keeper of maps and correspondence, where the director, SirArchibald Geikie , encouraged his research. He published a number of books and papers which "were at the forefront of contemporary science" [cite web
url=http://web.archive.org/web/20041011190311/http://www.scoti.org.uk/local_heroes.htm
title=Croll: a forgotten hero of Perth
author=Prof David Crichton
publisher=(Copy at web.archive.org)
accessdate=2004-10-11] , including "Climate and Time, in Their Geological Relations" in 1875. He corresponded withCharles Darwin onerosion by rivers.In 1876, he was elected Fellow of the
Royal Society , and awarded an honorary degree by theUniversity of St Andrews . He retired in 1880 because of ill health, and died in 1890.Theory of ice ages
Using formulae for orbital variations developed by
Leverrier (which had led to the discovery of Neptune), Croll developed a theory of the effects of variations of the earth's 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 age s occur on 22,000 year cycles in each hemisphere, and alternate between southern and northern hemispheres, lasting approximately 10,000 years each.Croll's theory predicted multiple ice ages, asynchronous in northern and southern hemispheres, and that the last
ice age s should have ended 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 ifglaciation was synchronous between the hemispheres, though the limited evidence more pointed towards synchronicity than not. More crucially, estimates of the recession rate of theNiagara 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.Croll's work was widely discussed, but by the end of the 19th century, his theory was generally disbelieved. However, the basic idea of orbitally-forced insolation variations influencing terrestrial temperatures was further developed by
Milutin Milankovitch and eventually, in modified form, triumphed in 1976.Works
* 1857: "The Philosophy of Theism"
* 1875: "Climate and Time, in Their Geological Relations"
* 1885: "Climate and Cosmology"
* 1896: posthumous publication of "Autobiographical Sketch of James Croll, With Memoir of His Life and Work", edited by J. C. IronsNotes
References
* Imbrie and Imbrie, "Ice ages - solving the mystery", Harvard University Press, 1979. [http://www.amazon.co.uk/Ice-Ages-Solving-Mystery-Imbrie/dp/0674440757/ref=sr_1_1?ie=UTF8&s=books&qid=1221930736&sr=1-1]
* Gribbin & Gribbin, "Ice Age", Allen Lane, 2001. [http://www.amazon.co.uk/Ice-Age-John-Gribbin/dp/0713996129/ref=sr_1_1?ie=UTF8&s=books&qid=1221930658&sr=1-1]ee also
*
Milankovitch cycles External links
* [http://www.geo.ed.ac.uk/scotgaz/people/famousfirst1577.html James Croll - unsung scientist]
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