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Millennial-Scale Oscillation of Climate Seen in History of Patagonian Glaciers
Volume 7, Number 44: 3 November 2004

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 (4700'S, 7339'W) and the Hielo Patagonico Sur (between 4850'S and 5130'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." With respect to the glacial advancements that occurred during the cold interval that preceded the Roman Warm Period, they say they are "part of a body of evidence for global climatic change around this time (e.g., Grosjean et al., 1998; Wasson and Claussen, 2002), which coincides with an abrupt decrease in solar activity," adding that this observation "led van Geel et al. (2000) to suggest that variations in solar irradiance are more important as a driving force in variations in climate than previously believed." Finally, with respect to the most recent recession of Hielo Patogonico Norte outlet glaciers from their late historic moraine limits at the end of the 19th century, Glasser et al. say that "a similar pattern can be observed in other parts of southern Chile (e.g., Kuylenstierna et al., 1996; Koch and Kilian, 2001)." Likewise, they note that "in areas peripheral to the North Atlantic and in central Asia the available evidence shows that glaciers underwent significant recession at this time (cf. Grove, 1988; Savoskul, 1997)," which again suggests the operation of a globally-distributed forcing factor such as cyclically-variable solar activity.

In concluding their study, Glasser et al. consider a number of "possible explanations for the patterns of observed glacier fluctuations." Since so many factors come into play in this regard, however, and since a good percentage of glaciers refuse to respond as their neighbors do, it is difficult to provide a "one size fits all" explanation for their behavior. Nevertheless, in as close as one can come to framing a general conclusion on this point, Glasser et al. state that "proxy climate data indicate that many of these broad regional trends can be explained by changes in precipitation and atmospheric temperature rather than systematic changes related to the internal characteristics of the ice fields."

In light of this body of evidence, and Glasser et al.'s analysis of it, it would appear that the history of glacial activity they describe does indeed suggest the existence of a millennial-scale oscillation of climate that operates on a broad scale ? perhaps, in fact, over all the earth. Viewed in this light, the current recession of many of earth's glaciers is seen to be but the most recent phase of a naturally-recurring phenomenon that has been "doing its thing," over and over, without any help from variable greenhouse gas concentrations, throughout the entire last half of the Holocene.

So what's new?

Nothing.

Sherwood, Keith and Craig Idso

References
Glasser, N.F., Harrison, S., Winchester, V. and Aniya, M. 2004. Late Pleistocene and Holocene palaeoclimate and glacier fluctuations in Patagonia. Global and Planetary Change 43: 79-101.

Grosjean, M., Geyh, M.A., Messerli, B., Schreier, H. and Veit, H. 1998. A late-Holocene (?2600 BP) glacial advance in the south-central Andes (29S), northern Chile. The Holocene 8: 473-479.

Grove, J.M. 1988. The Little Ice Age. Routledge, London, UK.

Koch, J. and Kilian, R. 2001. Dendroglaciological evidence of Little Ice Age glacier fluctuations at the Gran Campo Nevado, southernmost Chile. In: Kaennel Dobbertin, M. and Braker, O.U. (Eds.), International Conference on Tree Rings and People. Davos, Switzerland, p. 12.

Kuylenstierna, J.L., Rosqvist, G.C. and Holmlund, P. 1996. Late-Holocene glacier variations in the Cordillera Darwin, Tierra del Fuego, Chile. The Holocene 6: 353-358.

Savoskul, O.S. 1997. Modern and Little Ice Age glaciers in "humid" and "arid" areas of the Tien Shan, Central Asia: two different patterns of fluctuation. Annals of Glaciology 24: 142-147.

van Geel, B., Heusser, C.J., Renssen, H. and Schuurmans, C.J.E. 2000. Climatic change in Chile at around 2700 B.P. and global evidence for solar forcing: a hypothesis. The Holocene 10: 659-664.

Wasson, R.J. and Claussen, M. 2002. Earth systems models: a test using the mid-Holocene in the Southern Hemisphere. Quaternary Science Reviews 21: 819-824.

Wenzens, G. 1999. Fluctuations of outlet and valley glaciers in the southern Andes (Argentina) during the past 13,000 years. Quaternary Research 51: 238-247.