Harrison and Winchester (2000) used dendrochronology, lichenometry and aerial photography to date 19th- and 20th-century fluctuations of the Arco, Colonia and Arenales glaciers on the eastern side of the Hielo Patagonico Norte in southern Chile. This work revealed that these glaciers, plus four others on the western side of the ice field, began to retreat, in the words of the two researchers, "from their Little Ice Age maximum positions" somewhere between 1850 and 1880, well before the air's CO2 content began to rise at a significant rate. They also note that the trend continued "through the first half of the 20th century with various still-stands and oscillations between 1925 and 1960 ... with retreat increasing since the 1960s," just as has been observed at many sites in the Northern Hemisphere. Consequently, it is becoming ever more clear that even as far away from the lands that surround the North Atlantic Ocean as southern Chile, the Little Ice Age is evident in a variety of proxy climate records.

Still, however, the question remains: what caused the global warming that led to the Little Ice Age's demise throughout the world?

The likely answer to this question is provided by Glasser et al. (2004), who describe a large body of evidence related to glacier fluctuations in the two major ice fields of Patagonia: the Hielo Patagonico Norte and the Hielo Patagonico Sur. 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 century and a half, causing many glaciers to retreat. Prior to the Little Ice Age, however, their data indicate 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 brings us all the way back to sometime between 6000 and 5000 ¹⁴C years before present (BP).

Glasser et al. additionally cited 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 constitute "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," and they say that this observation was what "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)," to which we would also add the findings of Kaser and Georges (1997) for the Peruvian Cordillera Blanca and Francou et al. (2003) for the Bolivian Cordillera Real. 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)," all of which evidence points to the operation of a globally-distributed forcing factor such as that provided by cyclically-varying solar activity.

In light of this significant body of evidence, and Glasser et al.'s analysis of it, it would appear that the history of glacial activity they describe suggests the existence of a millennial-scale oscillation of climate that operates on a broad scale that may, in fact, include the entire earth. Viewed in this light, the current recession of many of earth's glaciers is seen to be but the most recent and still-ongoing phase of a naturally-recurring phenomenon that has been "doing its thing," over and over, without any help from variable atmospheric CO2 concentrations, throughout the entire last half of the Holocene.

But the story continues.

Based on various types of evidence collected by many investigators over the years, Georges (2004) constructed a 20th-century history of glacial fluctuations in the Cordillera Blanca of Peru, which is the largest glaciated area within the tropics. This history reveals, in Georges words, 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 "very strong" 1930s-1940s glacial mass shrinkage, 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."

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, which provides absolutely no support for the climate-alarmist claim that earth warmed at a rate, and to a level, that was unprecedented over the past millennium or more during the latter time period.

It is also interesting to note that Georges is quite at ease talking about the Little Ice Age south of the equator in Peru, which is a very long way from the lands that border the North Atlantic Ocean, which is the only region on earth where the world's climate alarmists willingly admit the existence of this chilly era of the planet's climatic history. What is perhaps even more interesting, however, is the fact that the glacial extensions of the Cordillera Blanca in the late 1920s were almost equivalent to those experienced there during the depths of the Little Ice Age, which is generally recognized as being the coldest period of the current interglacial, which suggests it is not at all strange that there should be a sizable warming of that part of the planet subsequent to its achieving a level of cold that was unprecedented over the past several millennia.

Moving south again, Koch and Kilian (2005) mapped and dated, by dendrochronological means, a number of moraine systems of Glaciar Lengua and neighboring glaciers of Gran Campo Nevado in the southernmost Andes of Chile, after which they compared their results with those of researchers who studied the subject in other parts of South America. According to their findings, in the Patagonian Andes "the culmination of the Little Ice Age glacier advances occurred between AD 1600 and 1700 (e.g., Mercer, 1970; Rothlisberger, 1986; Aniya, 1996)," but that "various glaciers at Hielo Patagonico Norte and Hielo Patagonico Sur also formed prominent moraines around 1870 and 1880 (Warren and Sugden, 1993; Winchester et al., 2001; Luckman and Villalba, 2001)." In addition, they note that their study "further supports this scenario," and that from their observations at Glaciar Lengua and neighboring glaciers at Gran Campo Nevado, it would appear that "the 'Little Ice Age' advance was possibly the most extensive one during the Holocene for this ice cap," which harmonizes with its being the coldest period of the past several millennia.

Last of all, and working with biogenic silica, magnetic susceptibility, total organic carbon (TOC), total nitrogen (TN), δ¹³CTOC, δ¹⁵NTN and C/N ratios derived from the sediment records of two Venezuelan watersheds, which they obtained from cores retrieved from Lakes Mucubaji and Blanca, together with ancillary data obtained from other studies that had been conducted in the same general region, Polissar et al. (2006) developed continuous decadal-scale histories of glacier activity and moisture balance in that part of the tropical Andes (the Cordillera de Merida) over the past millennium and a half, from which they were able to deduce contemporary histories of regional temperature and precipitation. So what did they learn?

The international team of scientists - representing Canada, Spain, the United States and Venezuela - write that "comparison of the Little Ice Age history of glacier activity with reconstructions of solar and volcanic forcing suggests that solar variability is the primary underlying cause of the glacier fluctuations," because (1) "the peaks and troughs in the susceptibility records match fluctuations of solar irradiance reconstructed from ¹⁰Be and δ¹⁴C measurements," (2) "spectral analysis shows significant peaks at 227 and 125 years in both the irradiance and magnetic susceptibility records, closely matching the de Vreis and Gleissberg oscillations identified from solar irradiance reconstructions," and (3) "solar and volcanic forcing are uncorrelated between AD 1520 and 1650, and the magnetic susceptibility record follows the solar-irradiance reconstruction during this interval." In addition, they write that "four glacial advances occurred between AD 1250 and 1810, coincident with solar-activity minima," and that "temperature declines of -3.2 ± 1.4°C and precipitation increases of ~20% are required to produce the observed glacial responses."

In discussing their findings, Polissar et al. say their results "suggest considerable [our italics] sensitivity of tropical climate to small [our italics] changes in radiative forcing from solar irradiance variability," which is something many people have had difficulty accepting in prior years. Hopefully, this paper will help them "see the light" a little clearer with respect to this subject. Not to be purveyors of too much good news, however, the six scientists say their findings imply "even greater probable responses to future anthropogenic forcing," and that "profound climatic impacts can be predicted for tropical montane regions."

With respect to these latter ominous remarks, we note that whereas Polissar et al.'s linking of significant climate changes with solar radiation variability is a factual finding of their work, their latter statements with respect to hypothesized CO2-induced increases in down-welling thermal radiation are but speculations that need not follow from what they learned; for the two types of radiative forcing operate quite differently from each other, and there are many contemporaneous biological consequences of atmospheric CO2 enrichment that may produce powerful cooling effects on earth's climate. Hence, there is no guarantee there will be any net impetus for warming as the atmosphere's CO2 content continues to rise.

Another point worth noting in this regard is Polissar et al.'s acknowledgement that "during most of the past 10,000 years, glaciers were absent from all but the highest peaks in the Cordillera de Merida," which indicates that warmer-than-present temperatures are the norm for this part of the planet, and that any significant warming that might yet occur in this region (as well as most of the rest of the world) would only mark a return to more typical Holocene (or current interglacial) temperatures, which have themselves been significantly lower than those of all four prior interglacials. What is more, atmospheric CO2 concentrations were much lower during all of those much warmer periods, providing further evidence that it is the sun that likely rules the world's climate, and not CO2.

References
Aniya, M. 1996. Holocene variations of Ameghino Glacier, southern Patagonia. The Holocene 6: 247-252.

Francou, B., Vuille, M., Wagnon, P., Mendoza, J. and Sicart, J.E. 2003. Tropical climate change recorded by a glacier in the central Andes during the last decades of the 20th century: Chacaltaya, Bolivia, 16°S. Journal of Geophysical Research 108: 10.1029/2002JD002473.

Georges, C. 2004. 20th-century glacier fluctuations in the tropical Cordillera Blanca, Peru. Arctic, Antarctic, and Alpine Research 35: 100-107.

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 (29°S), northern Chile. The Holocene 8: 473-479.

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

Harrison, S. and Winchester, V. 2000. Nineteenth- and twentieth-century glacier fluctuations and climatic implications in the Arco and Colonia Valleys, Hielo Patagonico Norte, Chile. Arctic, Antarctic, and Alpine Research 32: 55-63.

Kaser, G. and Georges, C. 1997. Changes in the equilibrium line altitude in the tropical Cordillera Blanca (Peru) between 1930 and 1950 and their spatial variations. Annals of Glaciology 24: 344-349.

Koch, J. and Kilian, R. 2005. "Little Ice Age" glacier fluctuations, Gran Campo Nevado, southernmost Chile. The Holocene 15: 20-28.

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.

Luckman, B.H. and Villalba, R. 2001. Assessing the synchroneity of glacier fluctuations in the western Cordillera of the Americas during the last millennium. In: Markgraf, V. (Ed.), Interhemispheric Climate Linkages. Academic Press, New York, NY, USA, pp. 119-140.

Mercer, J.H. 1970. Variations of some Patagonian glaciers since the Late-Glacial: II. American Journal of Science 269: 1-25.

Polissar, P.J., Abbott, M.B., Wolfe, A.P., Bezada, M., Rull, V. and Bradley, R.S. 2006. Solar modulation of Little Ice Age climate in the tropical Andes. Proceedings of the National Academy of Sciences USA 103: 8937-8942.

Rothlisberger, F. 1986. 10 000 Jahre Gletschergeschichte der Erde. Verlag Sauerlander, Aarau.

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.

Warren, C.R. and Sugden, D.E. 1993. The Patagonian icefields: a glaciological review. Arctic and Alpine Research 25: 316-331.

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.

Winchester, V., Harrison, S. and Warren, C.R. 2001. Recent retreat Glacier Nef, Chilean Patagonia, dated by lichenometry and dendrochronology. Arctic, Antarctic and Alpine Research 33: 266-273.