In the latest Analog, Richard A. Lovett reviewed a book by William F. Ruddiman with an intriguing hypothesis. Ruddiman thinks that early in our history, e.g. the last twelve thousand years, human activity has prevented an ice age that would otherwise have happened. The book is an expansion of Ruddiman’s paper in Climatic Change, 61(3), December 2003, pp. 261-93.
Twelve thousand years ago was the beginning of agriculture, and the beginning of widespread land clearing. Ruddiman’s hypothesis takes into account three variations in the Earth’s orbit: a 41,000-year cycle in the tilt of the earth’s axis; a 26,000-year cycle caused by the earth’s precession around the sun; and a 100,000-year variation in the eccentricity of the earth’s orbit.
I won’t go into details here, but ice cores goning back as far as 400,000 years seem t support the hypothesis. Do grab the April/07 Analog and read the article for yourself, dig up your dog-eared March/05 Scientific American, or look for Plows, Plagues & Petroleum.
William F. Ruddiman is a retired professor from the University of Virginia.
