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Swiss Alps Glacier Lengths During the Holocene
Hormes, A., Beer, J. and Schluchter, C. 2006. A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss Alps. Geografiska Annaler Series A 88: 281-294.

What was done
The authors determined radiocarbon dates of 71 samples of wood and peat found in the basal shear planes and proglacial outwashes of eight mid-latitude glaciers in the Central Swiss Alps; and by virtue of the dates clustering within discrete time intervals, they were able to specify periods during which the glaciers' leading edges were less extended than they were during the 1990s.

What was learned
Hormes et al. determined that "the glaciers investigated were less extensive than during the 1990s, with a shorter length during several defined periods." These periods were: 10,110-9550, 9210-7980, 7450-6500, 6370-5950, 5860-3360, 2940-2620 and 2500-1170 years before present. They also report that "some of these periods with reduced glacier lengths are also documented on Svalbard in the Arctic, the Subantarctic Kerguelen islands in the Indian Ocean, and in Scandinavia." In addition, they state that "the defined radiocarbon-dated periods with less extensive glaciers coincide well with periods of reduced 14C production, pointing to the sun's role in glacier variation processes."

What it means
Contrary to the strident claim of Hansen et al. (2006) that probably the planet as a whole" is approximately as warm now as at the Holocene maximum," the findings of Hormes et al. suggest that for huge periods of the Holocene this statement was likely far from the truth, not only for the Central Swiss Alps, but also for the other parts of the planet where similar Holocene contractions of glacier lengths have been observed. In addition, there is reason to believe that much of the world's superior warmth during those many earlier periods (when the atmosphere's CO2 concentration was only about two-thirds of what it is today) was orchestrated by variations in the activity of the sun, which further suggests there is no compelling reason to believe that the much lesser warmth of today must be due to the atmosphere's elevated CO2 concentration, as it has been significantly warmer than it is currently many times throughout the Holocene when there has been much less CO2 in the air than there is today.

Hansen, J., Sato, M., Ruedy, R., Lo, K., Lea, D.W. and Medina-Elizade, M. 2006. Global temperature change. Proceedings of the National Academy of Sciences USA 103: 14,288-14,293.

Reviewed 12 December 2007