James Croll in Context

The Encounter between Climate Dynamics and Geology in the Second Half of the Nineteenth Century

Abstract

This paper provides historical context and illuminates the roots of the work of Milutin Milankovic’ by examining early contributions to climate dynamics by James Croll (1821-1890), the leading proponent of an astronomical theory of climate change in the nineteenth century. Inspired by Joseph Adhémar’s work, Révolutions de la mer (1842), and taking into account precession of the equinoxes, variations in the eccentricity of the orbit, and tilt of the axis, Croll proposed that the “true cosmical cause” of climate change “must be sought for in relations of our earth to the sun,” that “geological and cosmical phenomena are physically related by a bond of causation,” and that changes in the earth’s orbital elements, combined with physical feedbacks, were “sufficiently great to account for every extreme of climatic change evidenced by geology.”2 Although Croll’s theory of orbital elements has often been criticized as “wrong,” and characterized as a precursor of Milankovic’, there are far more interesting historical perspectives on his work. His fundamental insights into the interplay of astronomical and geological factors – into cosmic physics and climate dynamics -- were extremely influential, especially in the case of the leading geologist of his day, Charles Lyell, who revised his Principles of Geology in response to Croll’s theory. In order to examine the interplay of climate dynamics and “science dynamics” on centuries-to-decades time scales, the paper concludes with a comparison between the carbon dioxide theory and the astronomical theory of climate change, both of which experienced eclipse and reformulation before reemerging transformed in the twentieth century.