James Croll

James Croll (2 January 1821 – 15 December 1890) was a Scottish physical scientist who was the leading proponent of an astronomical theory of climate change in the 19th century. The son of a stonemason and crofter from Cargill in Scotland, he started work as a millwright, but became caretaker at Anderson's College, Glasgow, in 1859. He was later appointed resident geologist in the Edinburgh office of the Geological Survey, where he remained until he retired in 1880. Croll, who was effectively self-taught, is best known for his work on the astronomical theory of the ice ages, but he also made major contributions on the glacial geology of Scotland, on the mechanisms that drive ocean circulation and the impact of that circulation on climate, tidal theory and the rotation of the Earth.

His insights into the interplay between astronomical and geological factors – into cosmic physics and climate dynamics -- were extremely influential. In 1875 Croll published his major book Climate and Time which had a profound influence on geologists around the world. Charles Lyell, the leading geologist of the time, revised his Principles of Geology in response to Croll’s theory. His view was notably followed by James Geikie in The Great Ice Age (1874–84),

In 1864, Croll published an article entitled On the Physical Cause of the Change of Climate During Geological Epochs, where he proposed that periodic variations in the earth’s orbit around the sun accounted for the periodic variations in climate evidenced by geological evidence of ice ages , and alternating cold and warm periods in each hemisphere (i.e. that ice ages in the Northern Hemisphere coincided with interglacials in the Southern Hemisphere). He proposed that feedback mechanisms, including the radiative effects of the ice fields, enhanced formation of cloud and fog, changes in sea level, and the mixing and redirection of warm and cold ocean currents enhanced the climatic changes initiated by the orbital changes. Because of uncertainties in the timing of ice ages, and because Croll’s theory predicted glaciation in only one hemisphere at a time, his theory was disregarded at first. Nevertheless, Croll's work attracted much attention, not least because Croll had worked with none of the advantages of a scientific training, and he was awarded the Wollaston Medal of the Geological Society of England in 1872.

Croll's other works included The Philosophy of Theism (1857), Climate and Cosmology (1885) and The Philosophic Basis of Evolution (1890). In 1876, Croll was elected as a Fellow of the Royal Society and was awarded an honorary doctorate from the University of St Andrews. His 1889 book Stellar Evolution and Its Relations to Geological Time contains "the first modern attempt to explain the chemical composition of the stars"