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Earth's Geomagnetic Field Intensity and Global Climate Change
Gallet, Y. and Genevey A. 2007. The Mayans: Climate determinism or geomagnetic determinism? EOS, Transactions, American Geophysical Union 88: 129-130.

What was done
The authors documented what they call a "good temporal coincidence" between "periods of geomagnetic field intensity increases and cooling events," as measured in western Europe, where cooling events were "marked by glacier advances on land and increases in ice-rafted debris in [North Atlantic] deep-sea sediments."

What was learned
Gallet and Genevey's analyses revealed "a succession of three cooling periods in western Europe during the first millennium AD," the ages of which, in their words, were "remarkably coincident with those of the main discontinuities in the history of Maya civilization," building upon the earlier similar work of Gallet et al. (2005), who found a "good temporal coincidence in western Europe between cooling events recovered from successive advances of Swiss glaciers over the past 3000 years and periods of rapid increases in geomagnetic field intensity," the latter of which were "nearly coeval with abrupt changes, or hairpin turns, in magnetic field direction," which phenomena they refer to as archeomagnetic jerks.

What it means
In attempting to make some sense out of these several observations, Gallet and Genevey conclude that "the most plausible mechanism linking geomagnetic field and climate remains a geomagnetic impact on could cover," whereby "variations in morphology of the earth's magnetic field could have modulated the cosmic ray flux interacting with the atmosphere, modifying the nucleation rate of clouds and thus the albedo and earth surface temperatures (Gallet et al., 2005; Courtillot et al., 2007)."

These observations clearly suggest a global impact on climate, which is further suggested by the close relationship that has been found to exist between "cooling periods in the North Atlantic and aridity episodes in the Middle East," as well as by the similar relationship demonstrated by Gallet and Genevey to have prevailed between periods of aridity over the Yucatan Peninsula and well-documented times of crisis in Mayan civilization.

Courtillot, V., Gallet, Y., Le Mouel, J.-L., Fluteau, F. and Genevey, A. 2007. Are there connections between the Earth's magnetic field and climate? Earth and Planetary Science Letters 253: 328-339.

Gallet Y., Genevey, A. and Fluteau, F. 2005. Does Earth's magnetic field secular variation control centennial climate change? Earth and Planetary Science Letters 236: 339-347.

Reviewed 4 April 2007