In geology the effects to be explained have almost all occurred already, whereas in these other sciences effects actually taking place have to be explained.
James Croll was a 19th-century Scottish scientist who developed a theory of climate variability 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, the son of David Croll, mason, and his wife Janet Geddes. NO1733. He was largely self-educated. At 16 he became an apprentice wheelwright at Collace near Wolfhill, and then because of health problems a tea merchant in Elgin, Moray. In 1848 he married Isabella Macdonald, daughter of John Macdonald and Annabella Sime, of Forres.
Twenty questions, eight minutes on the clock, and a percentile measured against everyone who has taken it. No sign-up.
Take the IQ test →In the 1850s he managed a temperance hotel in Blairgowrie, and was then an insurance agent in Glasgow, Edinburgh and Leicester. In 1859, he became a janitor at the museum of the Andersonian University in Glasgow. He was able to use the university library to get access to books, and taught himself physics and astronomy to develop his ideas.
From 1864, Croll corresponded with Sir Charles Lyell, on links between ice ages and variations in the Earth's orbit. He theorized that changes in the earth's orbit could cause the Gulf stream to be diverted, bringing less heat to the Arctic. More ice would then lead to more sunlight being reflected, causing a feedback loop. His ideas were published in the Philosophical Magazine in 1864, attributed to "James Croll, Anderson's University". This led to a position in the Edinburgh office of the Geological Survey of Scotland, as keeper of maps and correspondence, where the director, Sir Archibald Geikie, encouraged his research. He published a number of books and papers which "were at the forefront of contemporary science", including Climate and Time, in Their Geological Relations in 1875. He corresponded with Charles Darwin on erosion by rivers.
In 1876, he was elected Fellow of the Royal Society, and awarded an honorary degree by the University of St Andrews. He retired in 1880 because of ill health, and died on 15 December 1890 at 5 Pitcullen Crescent, Perth, Scotland. He was buried in a family grave in Cargill, Perthshire.
Theory of ice ages
Croll was the leading proponent of an astronomical-based theory of climate change in the nineteenth century. Using formulae for orbital variations developed by Urbain Le Verrier 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. Croll further argued that the accumulation of snow would change the pattern of trade winds, leading to the deflection of warming currents like the Gulf Stream, and finally a self-sustaining ice age. He suggested that when orbital eccentricity is high winters will tend to be colder when the 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.
Croll's theory predicted multiple ice ages, asynchronous in northern and southern hemispheres, and that the last ice ages 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 if glaciation was synchronous between the hemispheres, though the limited evidence more pointed towards synchronicity than not. More crucially, estimates of the recession rate of the Niagara 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 discredited. However, the basic idea of orbitally-forced insolation variations influencing terrestrial temperatures – now known generally as Milankovitch cycles – 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
- 1889: Stellar Evolution and Its Relations to Geological Time
- 1896: posthumous publication of Autobiographical Sketch of James Croll, With Memoir of His Life and Work, edited by J. C. Irons
Top questions
Who was James Croll?
James Croll was a Scottish scientist and Fellow of the Royal Society who developed a theory of climate variability based on changes in the Earth's orbit. Born in 1821 near Wolfhill in Perthshire, he was largely self-educated and rose from apprentice wheelwright and hotel manager to a post at the Geological Survey of Scotland.
What was James Croll's theory of ice ages?
Croll argued that changes in the Earth's orbit drive climate cycles. Decreases in winter sunlight would favour snow accumulation, and he coupled this to a positive ice-albedo feedback that amplifies the change, with snow shifting trade winds and deflecting warming currents such as the Gulf Stream. His theory is now known as the Astronomical Theory of Climate Change.
What is ice-albedo feedback?
Ice-albedo feedback is a loop in which more ice reflects more sunlight, which brings more cooling and more ice. Croll devised the concept and, for the first time, coupled a positive ice-albedo feedback to orbital variations, so that small changes in sunlight could be amplified into a self-sustaining ice age.
Was James Croll right about ice ages?
Only in part. Croll's theory was widely discussed but generally discredited by the end of the 19th century, partly because estimates of Niagara Falls recession ruled out its predicted timing of the last ice age for those who accepted the measurements. His basic idea of orbitally forced sunlight variations, developed by Milutin Milankovitch, triumphed in modified form in 1976.
How did James Croll teach himself science?
Croll was largely self-educated. After working as an apprentice wheelwright, a tea merchant, a hotel manager and an insurance agent, he became a janitor at the museum of the Andersonian University in Glasgow in 1859. He used the university library to teach himself physics and astronomy and to develop his ideas.
What is Croll's book Climate and Time?
Climate and Time, in Their Geological Relations, published in 1875, was one of a number of books and papers by Croll that were at the forefront of contemporary science. He published it during his time at the Geological Survey of Scotland in Edinburgh, where director Sir Archibald Geikie encouraged his research.
What honours did James Croll receive?
In 1876 Croll was elected a Fellow of the Royal Society and awarded an honorary degree by the University of St Andrews. He retired in 1880. The highest award of the Quaternary Research Association is the James Croll Medal, and some scholars call the orbital cycles the Croll-Milankovitch Cycles.
