Two UK scientists have developed a simple rule that can predict the end of ice ages and the beginning of the warmer interglacial periods over the past million years.
The rule doesn't rely on knowing climate or atmospheric data, but instead uses a simple measure of the sun's radiation in summer at a latitude of 65° north, around the north of Sweden, and the time since the end of the last ice age.
The pacing of the expansion and contraction of Northern Hemisphere ice sheets is driven by small changes in the Earth's orbit and the tilt of the Earth on its axis. Between 2.6 million and 1 million years ago, these changes led to the onset of interglacial periods about every 41,000 years.
However, over the past 1 million years, interglacials have occurred less frequently, approximately every 100,000 years. Although previous models have been able to reproduce this pattern, many require knowledge of numerous inputs, such as carbon dioxide concentrations, and none has been able to fully account for the pattern and timing of interglacials over the past million years.
Chronis Tzedakis developed a statistical model that uses only the mean daily exposure to solar radiation in the summer half of the year at 65° N latitude and the time since the previous deglaciation to accurately predict each complete deglaciation of the past million years.
Stephen Meyers confirmed a theory that the Earth's orbital variations are chaotic, suggesting that the timing of interglacials prior to about 50 million years ago is probably unpredictable, unless firm chronological tie-points can be found.
Studying an ancient geological formation in present-day Colorado, the he found such a tie-point and conclude that a shift in the interactions between the orbits of the Earth and Mars occurred 85–87 million years ago. This finding could help to constrain reconstructions of the link between climate and astronomical factors throughout the Earth's distant past.