A possible relationship between major changes in global ice volume, geomagnetic variations, and short-term climate cooling has been investigated through a study of climate and geomagnetic records of the past 400,000 yr. Calculations suggest that redistribution of the Earth's water mass can cause rotational instabilities that lead to magnetic excursions; these magnetic variations in turn may lead to rapid coolings through several proposed mechanisms. Such double coincidences of magnetic excursions and sudden cooling and glacial advance at times of major ice-volume changes have occurred at about 13,500, 30,000, 110,000, and 180,000 B.P. The last four and possibly five times of maximum eccentricity of the Earth's orbit were closely followed by magnetic excursions; catastrophic cooling and rapid ice buildup accompanied several of these excursions. Thus, Milankovitch cycle parameters may lead to glaciation through both insolation changes and geomagnetic effects on climate.

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