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Little Ice Age (Regional - South America: Peru) -- Summary
That the North Atlantic Ocean and surrounding lands have experienced a millennial-scale oscillation of climate from time immemorial, extending through glacial and interglacial periods alike, is a well-established fact, as is evidenced by the findings of Bond et al. (1997), Oppo et al. (1998), Raymo et al. (1998), Bianchi and McCave (1999), McManus et al. (1999), Keigwin and Boyle (2000), Bond et al. (2001), McDermott et al. (2001), Andersson et al. (2003) and Dokken et al. (2003); and the incredible regularity of this oscillation between warmer and cooler states literally cries out for an extraterrestrial explanation, which further suggests that the cyclic phenomenon in question should be evident around the planet generally, for an other-worldly forcing factor, such as cyclical variations in solar activity, would have to be manifest on a much broader geographic scale than just the North Atlantic Ocean and its immediate environs. And so it is, with one of the more engaging examples of the recurrent climatic oscillation coming from a study of the in-filled basin of the ancient Incas' sacred lake of Marcacocha, which is located high in the Central Andean region of Peru some 45 km northwest of the legendary city of Cuzco.

Different aspects of this intriguing study are described by Chepstow-Lusty et al. (1998, 2003) and Chepstow-Lusty and Winfield (2000), who in 1993 measured and analyzed various indicators of past climatic conditions in a highly-organic sediment core extracted from the center of the in-filled Marcacocha basin. Centered on approximately 1000 years ago, they identified what Chepstow-Lusty and Winfield describe as "the warm global climatic interval frequently referred to as the Medieval Warm Epoch," which arid interval in this particular part of South America may have played a significant role in the collapse of the Tiwanaku civilization further south, where a contemporaneous prolonged drought occurred in and around the area of Lake Titicaca (Binford et al., 1997; Abbott et al., 1997).

Near the start of this extended dry period, which had gradually established itself between about AD 700 and 1000, Chepstow-Lusty and Winfield report that "temperatures were beginning to increase after a sustained cold period that had precluded agricultural activity at these altitudes." This earlier colder and wetter interval was coeval with the Dark Ages Cold Period of the North Atlantic region, which in the Peruvian Andes had held sway for a good portion of the millennium preceding AD 1000, as revealed by a series of climatic records developed from sediment cores extracted from yet other lakes in the Central Peruvian Andes (Hansen et al., 1994) and by proxy evidence of concomitant Peruvian glacial expansion (Wright, 1984; Seltzer and Hastorf, 1990).

Preceding the Dark Ages Cold Period in both parts of the world was what in the North Atlantic region is called the Roman Warm Period. This well-defined climatic epoch is strikingly evident in the pollen records of Chepstow-Lusty et al. (2003), straddling the BC/AD calendar break with one to two hundred years of relative warmth and significant aridity located on either side of it.

Returning to the Medieval Warm Period and preceding towards the present, the data of Chepstow-Lusty et al. (2003) reveal the occurrence of the Little Ice Age, which in the Central Peruvian Andes was characterized by relative coolness and wetness. These characteristics of that climatic interval are also evident in ice cores retrieved from the Quelccaya ice cap in southern Peru, the summit of which extends 5670 meters above mean sea level (Thompson et al., 1986, 1988). And finally, both the Quelccaya ice core data and the Marcacocha pollen data reveal the transition to the drier Modern Warm Period, which has developed over the past 100-plus years.

Also working in Peru, Goodman et al. (2001) analyzed soil properties of several glacial moraines located in the Cordillera Vilcanota and Quelccaya Ice Cap regions, where they found that "the most extensive advance during the late Holocene in southern Peru occurred during the Little Ice Age," which was dated to around 400 years before present in the Cordillera Vilcanota and 300 years before present in the vicinity of the Quelccaya Ice Cap.

Three years later, Georges (2004) constructed a 20th-century history of glacial fluctuations in the Cordillera Blanca of Peru (7730'W, 9S), which is the largest glaciated area located within the earth's tropics. This work revealed that "the beginning of the century was characterized by a glacier recession of unknown extent, followed by a marked readvance in the 1920s that nearly reached the Little Ice Age maximum." Then came the 1930s-1940s shrinkage of the glacial mass that was, in his words, "very strong," after which there was a period of quiescence that was followed by an "intermediate retreat from the mid-1970s until the end of the century." And in comparing the two periods of glacial wasting, Georges says that "the intensity of the 1930s-1940s retreat was more pronounced than that of the one at the end of the century." In fact, his graph of the ice area lost in both time periods suggests that the rate of wastage in the 1930s-1940s was twice as great as that of last two decades of the 20th century.

In conclusion, we note that the extensive climatic correspondences that have been shown to exist between South American countries such as Peru and various parts of the Northern Hemisphere are not coincidental; they reveal the existence of a significant millennial-scale oscillation of climate that is global in scope and, hence, driven by a regularly-varying extraterrestrial forcing factor. Although one can argue about the identity of that forcing factor and the means by which it exerts its influence, one thing is clear: it is not the atmosphere's CO2 concentration, which has only varied in phase with the climatic oscillation over the Little Ice Age-to-Modern Warm Period transition and has exhibited no millennial-scale cyclicity over the entire rest of the record. This being the case, it should be clear to most rational people that the climatic amelioration of the past century or more has had absolutely nothing to do with the concomitant rise in the air's CO2 content, but absolutely everything to do with the influential extraterrestrial forcing factor that has governed the millennial-scale oscillation of earth's climate as far back in time as we have been able to detect it.

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Last updated 10 February 2010