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North Atlantic Record of Cyclic Climate Change Replicated Near Cuzco, Peru
Volume 7, Number 7: 18 February 2004

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 (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; Dokken et al., 2003). The incredible regularity of this oscillation between relatively warmer and cooler states literally cries out for an extraterrestrial explanation, which further suggests that the cyclic phenomenon 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 forever-recurring climatic oscillation coming from a study of the in-filled basin of the ancient Inca's 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 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 in 1993. 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 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 that occurred over the past 100-plus years.

Extensive climatic correspondences such as these, occurring between widely separated Northern and Southern Hemispheric regions, 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 cyclicity at all over the entire rest of the record. This being the case, it should be clear to all 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.

Sherwood, Keith and Craig Idso

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