In Defense of the Astronomical Theory of Glaciation

Abstract

Milankovitch (1920, 1930, 1938) presented the hypothesis that the oscillations in climate which characterize the last million or so years of earth history were caused by variations in summer insolation in the Northern Hemisphere resulting from the earth’s precession and variations in its tilt. Curves for the tilt variation (period ~40,000 yr) and for the precessional variation (period ~22,000 yr) are reproduced in Fig. 1. From these Milankovitch constructed a composite radiation curve for various latitudes. His high latitude curves (which are dominated by the tilt effect) are widely quoted. The character of the curves depends strongly on the relative weighting of the two effects [Broecker (1966), see Fig. 2]. For example, considering the last 150,000 yr as the precessional component is increased, the prominent warm peak at 40,000 yr disappears and a new warm peak appears at 106,000 yr. Most geophysicists and meteorologists have failed to give this hypothesis serious consideration because they feel that the insolation changes are too small to have a significant effect on world climate.

Lamont Geological Observatory Contribution No. 1124.