NC Media Watch

A quest for reason and accuracy in letters to the editor, guest editorials and other issues of interest to the citizens of Western Nevada County.

Thursday, November 11, 2004

CLIMATE CHANGE UPDATE III
John Ray, a retired Australian university teacher writes about glacial cycles.
NATURAL CLIMATE CYCLES

New data from Patagonia:

In our many reviews of recently-published studies that reveal the existence of a widespread millennial-scale oscillation of climate, we routinely draw attention to evidence for the worldwide occurrence of the Little Ice Age, Medieval Warm Period, Dark Ages Cold Period, Roman Warm Period, etc. We here continue in this vein in reviewing a study that identifies all of the above climatic intervals -- plus others -- in the Patagonian ice fields of South America.

Glasser et al. (2004) describe a large body of evidence related to glacier fluctuations in the two major ice fields of Patagonia: the Hielo Patagonico Norte (47o00'S, 73o39'W) and the Hielo Patagonico Sur (between 48o50'S and 51o30'S). This evidence indicates that the most recent glacial advances in Patagonia occurred during the Little Ice Age, out of which serious cold spell the earth has been gradually emerging for the past two centuries, causing many glaciers to retreat. Prior to the Little Ice Age, however, there was an interval of higher temperatures known as the Medieval Warm Period, when glaciers also decreased in size and extent; and this warm interlude was in turn preceded by a still earlier era of pronounced glacial activity that is designated the Dark Ages Cold Period, which was also preceded by a period of higher temperatures and retreating glaciers that is denoted the Roman Warm Period.

Prior to the Roman Warm Period, Glasser et al.'s presentation of the pertinent evidence suggests there was another period of significant glacial advance that also lasted several hundred years, which was preceded by a several-century interval when glaciers once again lost ground, which was preceded by yet another multi-century period of glacial advance, which was preceded by yet another long interval of glacier retrenchment, which was preceded by still another full cycle of such temperature-related glacial activity, which at this point brings us all the way back to sometime between 6000 and 5000 14C years before the present (BP).

Glasser et al. additionally cite the works of a number of other scientists that reveal a similar pattern of cyclical glacial activity over the preceding millennia in several other locations. Immediately to the east of the Hielo Patagonico Sur in the Rio Guanaco region of the Precordillera, for example, they report that Wenzens (1999) detected five distinct periods of glacial advancement: "4500-4200, 3600-3300, 2300-2000, 1300-1000 14C years BP and AD 1600-1850."
It would appear the recent multi-decade warming cycle started about 1850. No wonder the glaciers are shrinking.
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