Variations in the Earth's Orbit: Pacemaker of the Ice Ages

Abstract

1) Three indices of global climate have been monitored in the record of the past 450,000 years in Southern Hemisphere ocean-floor sediments. 2) Over the frequency range 10(-4) to 10(-5) cycle per year, climatic variance of these records is concentrated in three discrete spectral peaks at periods of 23,000, 42,000, and approximately 100,000 years. These peaks correspond to the dominant periods of the earth's solar orbit, and contain respectively about 10, 25, and 50 percent of the climatic variance. 3) The 42,000-year climatic component has the same period as variations in the obliquity of the earth's axis and retains a constant phase relationship with it. 4) The 23,000-year portion of the variance displays the same periods (about 23,000 and 19,000 years) as the quasi-periodic precession index. 5) The dominant, 100,000-year climatic [See table in the PDF file] component has an average period close to, and is in phase with, orbital eccentricity. Unlike the correlations between climate and the higher-frequency orbital variations (which can be explained on the assumption that the climate system responds linearly to orbital forcing), an explanation of the correlation between climate and eccentricity probably requires an assumption of nonlinearity. 6) It is concluded that changes in the earth's orbital geometry are the fundamental cause of the succession of Quaternary ice ages. 7) A model of future climate based on the observed orbital-climate relationships, but ignoring anthropogenic effects, predicts that the long-term trend over the next sevem thousand years is toward extensive Northern Hemisphere glaciation.

Orbital forcing in Pliocene–Pleistocene Mediterranean lacustrine deposits: dominant expression of eccentricity versus precession

“…During the Pleistocene, eccentricity maxima corresponded to warm periods (interglacials), while glacial periods occurred during eccentricity minima (Hays et al, 1976). In the early Pliocene, however, there was no eccentricity-related glacial-interglacial climatic regime.…”

“…In summary, the cycles in Megalopolis look very similar to those in Lupoaia and they are dominated by the same astronomical period and moreover have the same phase relationship. Contrary to Lupoaia, which was deposited during a warm (early Pliocene) period, Megalopolis was deposited during the middle Pleistocene ice age regime, when 100 kyr (eccentricity) became the dominant astronomical (quasi-) period controlling glacial cyclicity (Hays et al, 1976;Imbrie et al, 1984).…”

The role of orbital forcing, carbon dioxide and regolith in 100 kyr glacial cycles

“…One of the major challenges to the classical Milankovitch theory is the presence of 100 kyr cycles that dominate global ice volume and climate variability over the past million years (Hays et al, 1976;Imbrie et al, 1993;Paillard, 2001). This periodicity is practically absent in the principal "Milankovitch forcing" -variations of summer insolation…”

The middle Pleistocene transition: characteristics, mechanisms, and implications for long-term changes in atmospheric pCO2

“…Introduction N.J. Shackleton's fundamental contributions to our understanding of climate variability at orbital timescales (10 4 -10 5 yr) continue to define the field today. Hays et al (1976) first established that the timing of variations in the Earth's orbit around the Sun corresponded to variations in Earth's climate over the last 430,000 years, providing strong support for the Milankovitch hypothesis for the cause of the ice ages. They also concluded that while climate responded linearly to precession (23 kyr) and obliquity (41 kyr), the dominant response over this interval has been to the small eccentricity forcing at 100 kyr, requiring some nonlinear amplification of the forcing.…”