James Croll: a scientist ahead of his time

Abstract

James Croll (1821-1890) was a Scottish scientist who made major, although still largely unrecognised, contributions to the theory of the effects of variations in the Earth's orbit on the global climate. He was the first to identify the importance of positive feedbacks in the climate system, especially the ice-albedo feedback, and he placed the astrochronological method on a sound footing. Croll's theory was the first to predict multiple ice ages. However, it was unable to place the end of the most recent glaciation more recently than 80,000 years ago, and as evidence accumulated throughout the 19th century for a much more recent date than this Croll's theory fell into neglect. We argue that this was particularly unfortunate since several of his key ideas were forgotten, and that this has delayed the development of the orbital theory of paleoclimate.

Paradigms, projections and people

“…The Croll/Milankovitch theory highlighted triggers and timing, but left major, unresolved questions about mechanisms. The external forcing involved in the orbital variations was much smaller than the dramatic climatic responses appeared to require, exactly as Croll had emphasised (Bol'shakov et al, 2012) in his masterly exposition of the crucial role of positive feedbacks in the climate system. As in the case of Plate Tectonics, much of the related science went on as before but with an over-riding obligation to consider, eventually, the way in which the data gathered and episodes characterised by terrestrial, stratigraphic studies, pollen analysis and the like might fit within the MIS scheme.…”

Comment on “Quaternary glaciations: from observations to theories” by D. Paillard [Quat. Sci. Rev. 107 (2015), 11–24]

“…The main one is the consideration of precession variations of insolation modulated by eccentricity as the major factor which determines the fluctuations in global climate (see Bol'shakov et al, 2012). Paillard (2015:16) pointed out the shortcomings of Croll: "In particular, once again, the expectations from Croll are entirely reversed: if ice ages are indeed linked to eccentricity changes, they are associated with low values, not high ones."…”

A link between global climate variability in the Pleistocene and variations in the Earth’s orbital parameters

“…In their paleoclimate modeling and interpreta tions, the Milankovitch's followers use more discrete insolation curves, i.e., monthly (June or July) or even daily summer solstice insolation and local insolation at 65° N. However, it was shown (Bol'shakov, 2003b(Bol'shakov, , 2012Bol'shakov and Kapitsa, 2011) that Milanko vitch's insolation curve, and more discrete insolation curves commonly used by the Milankovitch's follow ers, could not be applied, in principle, to paleoclimate modeling and interpretations. This became increas ingly apparent as many researchers came to realize the paramount importance of feedback processes in the transformation of orbital insolation forcing into global climate change.…”

“…It is important to note that variations in insolation driven by variations in these orbital parameters have different structures (Bol'shakov, 2003b(Bol'shakov, , 2012. The precession cycle gov erns the seasonal insolation contrasts in each hemi sphere.…”

“…In other words, changes in the total annual insolation for all latitudes should be taken into account. This idea was put forth a century and a half ago by the British astronomer J. Herschel and the German naturalist A. von Hum boldt (Croll, 1875;Imbrie, J. and Imbrie, K.P., 1988;Bol'shakov, 2003b;Bol'shakov et al, 2012). However, the problem of accounting for total insolation is that changes in the global annual insolation due to preces sion and obliquity are virtually null.…”