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METHANE HYDRATES IN QUATERNARY CLIMATE CHANGE: THE CLATHRATE GUN HYPOTHESIS James P. Kennett, Kevin G. Cannariato, Ingrid L. Hendy, and Richard J. Behl, 2003, 216 pp., $42.00, paperbound, American Geophysical Union, ISBN 0-87590-296-0
From time to time alternate interpretations are introduced that attempt to radically revise our basic conceptions of important issues. Such is the case with Methane Hydrates in Quaternary Climate Change: The Clathrate Gun Hypothesis. The authors try to explain the characteristic pattern of climate changes over the past 800,000 years (800 kyr) and, in the process, overturn many different interpretations in the fields of paleoclimatology, paleoceanography, marine and continental sedimentology, and paleoecology. There have been few climate-related books in recent times that are more all-inclusive and revolutionary.
Records of past climate changes during the glacial age (the Quaternary) indicate a "saw-tooth" pattern: rapid warming (in perhaps a few decades or less) initiated the cycle, followed by gradual cooling until the coldest point was reached; then rapid warming initiated a new cycle. The pattern was repeated at multiple time scales, from the 100-kyr cycles of glacial and interglacials to millennial cycles with cold stadials and warm interstadiale. The climate changes, even at the smaller time scales, appeared to be global in nature, although the evidence for that is somewhat sketchy. Determining why this pattern existed is a holy grail of paleoclimate research.
Accompanying the climate changes, as seen in ice-core data, were changes in the atmospheric concentration of various trace gases. Most climate studies emphasize carbon dioxide, which varied with the longest time-scale oscillations and some of the shorter-scale changes. But the focus of this book is the methane response, covarying with temperature, and presented here as arising from the instability of methane hydrates in continental shelf sediments.
Methane hydrates (also called clathrates) consist of biogenically produced methane from anaerobic microbes acting under anoxic reducing conditions (i.e., methane that is "frozen" into sediments). According to the authors' thesis, as the climate cooled, methane hydrates formed along the continental shelf/slope region, and as climate cooled further, more such sediments were generated. Specifically, the process the authors invoke involves the growth of ice on land altering...