Variations in the Earth’s Orbit: Pacemaker of the Ice Ages
J. D. Hays, John Imbrie, N. J. Shackleton. 1976. Variations in the Earth’s Orbit: Pacemaker of the Ice Ages. Science, New Series, Vol. 194, No. 4270, (Dec. 10, 1976), pp. 1121-1132.
Note: this classic, seminal paper changed the science of paleoclimatology. It is one of the most important papers ever written in any scientific discipline.
Full text [here]
Selected excerpts:
Introduction
For more than a century the cause of fluctuations in the Pleistocene ice sheets has remained an intriguing and unsolved scientific mystery. Interest in this problem has generated a number of possible explanations (1, 2). One group of theories invokes factors external to the climate system, including variations in the output of the sun, or the amount of solar energy reaching the earth caused by changing concentrations of interstellar dust (3); the seasonal and latitudinal distribution of incoming radiation caused by changes in the earth’s orbital geometry (4); the volcanic dust content of the atmosphere (5); and the earth’s magnetic field (6). Other theories are based on internal elements of the system believed to have response times sufficiently long to yield fluctuations in the range 104 to 106 years. Such features include the growth and decay of ice sheets (7), the surging of the Antarctic ice sheet (8); the ice cover of the Arctic Ocean (9); the distribution of carbon dioxide between atmosphere and ocean (10); and the deep circulation of the ocean (11). Additionally, it has been argued that as an almost intransitive system, climate could alternate between different states on an appropriate time scale without the intervention of any external stimulus or internal time constant (12).
Among these ideas, only the orbital hypothesis has been formulated so as to predict the frequencies of major Pleistocene glacial fluctuations. Thus it is the only explanation that can be tested geologically by determining what these frequencies are. Our main purpose here is to make such a test. Previous work has provided strong suggestive evidence that orbital changes induced climatic change (13-20). However, two primary obstacles have led to continuing controversy. The first is the uncertainty in identifying which aspects of the radiation budget are critical to climatic change. Depending on the latitude and season considered most significant, grossly different climatic records can be predicted from the same astronomical data. Milankovitch (4) followed Koppen and Wegener’s (21) view that the distribution of summer insolation (solar radiation received at the top of the atmosphere) at 65N should be critical to the growth and decay of ice sheets. Hence the curve of summer insolation at this latitude has been taken by many as a prediction of the world climate curve. Kukla (19) has pointed out weaknesses in Koppen and Wegener’s proposal and has suggested that the critical time may be September and October in both hemispheres. However, several other curves have been supported by plausible arguments. As a result, dates estimated for the last interglacial on the basis of these curves have ranged from 80,000 to 180,000 years ago (22).
