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Little Ice Age (Regional - South America: Chile) -- Summary
It has recently been noted by von Gunten et al. (2009) that "quantitative high-resolution global, hemispherical and regional climate reconstructions covering the last millennium are fundamental in placing modern climate warming into a long-term context," in order to "assess the sensitivity of the climate system to natural and anthropogenic forcings, and thus to reduce uncertainty about the magnitude and impact of future global climate change." In this regard, however, they note that for the entire Southern Hemisphere, "Mann and Jones (2003) considered only five data sets suitable for their work on surface temperature reconstructions for the past two millennia." What is more, they say that "only two of these data series are from South America," one of which is a tree-ring record "with unknown preservation of the low-frequency component of climate variability" and the other of which is a δ18O ice core record that they describe as "arguably putative at best" with respect to its temperature signal. Hence, it is important that more paleoclimate studies are conducted in South America; and in this summary we discuss the findings of several that have taken place in Chile, focusing on those that encompass the time period of the Little Ice Age.

Harrison and Winchester (2000) studied 19th- and 20th-century fluctuations of the Arco, Colonia and Arenales glaciers on the eastern side of the Hielo Patagonico Norte in the southern part of Chile. These glaciers, along with four others on the western side of the ice field, began to retreat from their Little Ice Age maximum positions somewhere between 1850 and 1880; and they continued to recede "through the first half of the 20th century with various still-stands and oscillations between 1925 and 1960," with the retreat increasing since the 1960s as the earth continued to rebound from the cooler temperatures of the Little Ice Age up to the end of the 1990s.

Two years later, Jenny et al. (2002) analyzed geochemical, sedimentological and diatom-assemblage data derived from sediment cores extracted from one of the largest natural lakes (Laguna Acuelo) in the central part of Chile, obtaining information about the hydrologic climate of that region over the past two millennia. From 200 BC, when their record commenced, until AD 200, conditions there were inferred to be primarily dry, during what is often referred to as the Roman Warm Period. Thereafter, from AD 200-700 (with a slight respite in the central hundred years of that period), there was a high frequency of flood events during what has come to be called the Dark Ages Cold Period. Then came a several-hundred-year period of less flooding that was coeval with the Medieval Warm Period. Last of all, there was another period of frequent flooding from 1300-1700, which picked up again about 1850 and which the researchers associated with the Little Ice Age.

About the same time, 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 (53S) 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. In doing so, they learned that, 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, "the 'Little Ice Age' advance was possibly the most extensive one during the Holocene for this ice cap."

Also publishing in the same year were Bertrand et al. (2005), who revealed yet another fingerprint of the Little Ice Age in Chile via their study of a six-century proxy precipitation record that they obtained from a sediment core retrieved from Lago Puyehue (40.70S, 72.45W). This work pointed to the presence of a wetter climate between AD 1490 and 1700, which was followed by drier conditions until about 1900. In addition, the wet and dry periods were found to correspond closely with other paleoclimate records of the region. The wetter period, for example, was said by the researchers to have been "strikingly consistent" with higher ice accumulation rates in the Quelccaya ice core of Peru (Thompson et al., 1985); and it corresponded with colder temperatures deduced from tree rings in Northern Patagonia (Luckman and Villalba, 2001), while the drier time period was similar to that reported by Lara and Villalba (1993). As for the significance of these results, Bertrand et al. note that the 1490-1700 wet period was "associated with the onset of the European Little Ice Age and interpreted as its local signature," which "supports the fact that the Little Ice Age was a global event, not only restricted to the Northern Hemisphere."

Two years later, Harrison et al. (2007) reconstructed the fluctuation histories of eleven outlet glaciers of the Hielo Patagonico Norte -- which caps the Andean Cordillera between 700 and 2500 meters above mean sea level and is 30-60 km wide, 120 km long, and centered at 4700'S, 7339'W -- based on information garnered from historical sources, aerial photographs, geomorphological mapping, lichenometry, dendrochronology and radiocarbon dating. This work revealed that glacial recession from maximal Little Ice Age positions, in the words of Harrison et al., "began in the early 1860s-1870s." And this recession, as they continue, "was largely synchronous on the western and eastern sides of the icefield," suggesting that "climate forcing over-rides second-order controls on glacier behavior such as the nature of the terminal environment or differences in glacier drainage basin area;" and they argue that "this icefield-wide glacier recession represents a response to post-Little Ice Age warming, and provides further evidence for the global extent and near synchronous termination of the Little Ice Age."

Contemporaneously, Araneda et al. (2007) utilized a large body of "colonial and republican (seventeenth, eighteenth and nineteenth centuries) bibliographic sources" -- which they describe as "reserved, 'first-hand,' original documents, including geographical and hydrographical records made by explorers visiting Laguna San Rafael," into which the San Rafael glacier (located at 4640'S, 7456'W) flows -- to "identify the historical movements of San Rafael glacier from the first Spanish exploration until the early twentieth century."

This exercise, according to Arenda et al., indicated that in 1675, when the records began, "temperate conditions, probably similar to those at present, prevailed," and that "the glacier was confined within its valley, not penetrating the Laguna." Thereafter, however, they write that "the glacier advanced noticeably during the nineteenth century and probably reached a maximum position for the 'Little Ice Age' around AD 1875," after which "the historical sources suggest a slight retreat in AD 1904 in relation to the conditions prevailing 29 years earlier."

As a result, the seven researchers concluded that "the historical data show that the eighteenth to nineteenth century cooling period at San Rafael glacier was within the temporal window of the European 'Little Ice Age'," and they say that this finding "provides independent, direct historical evidence for the occurrence of this event in southern Chile."

The following year, Rebolledo et al. (2008) analyzed changes in marine productivity and contemporaneous terrestrial input in a study of sediment cores retrieved from the Jacaf Channel (44S, 72W) of Chilean Northern Patagonia that contained data pertaining to the past 1800 years, using biogenic opal, siliceous microorganisms, alkenones, and organic (Corg content, molar C/N) and inorganic (Cinorg, Fe, Ti, Ca) elements as proxies for terrestrial input and/or carbonate productivity, after which they compared their findings with those of other researchers who had conducted similar paleoclimate studies in various parts of South America and Antarctica.

This work revealed, in the words of the seven scientists who conducted it, that "the downcore record clearly shows two productivity/climate modes." As they describe it, the first period -- prior to 900 cal yr BP and including the Medieval Warm Period -- was characterized by "decreased marine productivity and a reduced continental signal, pointing to diminished precipitation and runoff," while they report that the second period -- between 750 cal yr BP and the late 1800s, and including the Little Ice Age -- was characterized by "elevated productivity and an increased continental signal, suggesting higher precipitation and runoff." In addition, their data clearly showed that the Medieval Warm Period and Little Ice Age were "separated by a relatively abrupt transition of ~150 years." And in a subsequent study conducted at the same location, [not yet posted, so it needs a linkage] Sepulveda et al. (2009) also observed two different climatic regimes: "a relatively dry/warm period before 900 cal yr BP (higher runoff and average SST 1C warmer than present day) and a wet/cold period after 750 cal yr BP (higher runoff and average SST 1C colder than present day)," which they associated with the Medieval Warm Period and Little Ice Age, respectively.

In addition to providing another demonstration of the reality of both the Medieval Warm Period and Little Ice Age in earth's Southern Hemisphere -- where climate alarmists like to pretend they never occurred -- Rebolledo et al. state that the good correspondence between their record and "other paleoclimate studies carried out in South America and Antarctica demonstrates that the Chilean fjord area of Northern Patagonia is not just sensitive to local climatic variability but also to regional and possibly global variability." And Sepulveda et al. conclude that "the reasonably good correlation between [their] results (particularly SST) and other continental and marine archives from central-south Chile, Peru, and Antarctica ... confirms the occurrence of globally important climatic anomalies such as the Medieval Warm Period and the Little Ice Age." And, of course, their SST data indicate that the current level of warmth in that part of the world still has a long way to go before equaling the warmth experienced there a thousand and more years ago.

Last of all, we come to the study of von Gunten et al. (2009), who developed a continuous high-resolution (1-3 years sampling interval, 5-year filtered reconstruction) austral summer (December to February) temperature reconstruction based on chloropigments derived from algae and phototrophic bacteria found in sediment cores retrieved from Central Chile's Laguna Aculeo in 2005 that extended back in time to AD 850, which they describe as "the first quantitative temperature reconstruction for Central Chile for the last millennium." This work, in their words, provides "quantitative evidence for the presence of a Medieval Climate Anomaly (in this case, warm summers between AD 1150 and 1350; ΔT = +0.27 to +0.37C with respect to (wrt) twentieth century) and a very cool period synchronous to the 'Little Ice Age' starting with a sharp drop between AD 1350 and AD 1400 (-0.3C/10 years, decadal trend) followed by constantly cool (ΔT = -0.70 to -0.90C wrt twentieth century) summers until AD 1750."

Looking at the graph of their data, the peak warmth of the Medieval Climate Anomaly appears to be about 0.7C warmer than the last decade or so of the 20th century, but only about 0.25C warmer than the peak warmth of the 20th century, which occurred in the late 1940s for both their reconstructed temperatures and their instrumental data, which are essentially identical over most of the 1900s. In addition, they state that the "structure of variability" that is present in their data "is consistent in great detail with annually resolved tree-ring based warm-season temperature and river discharge reconstructions from northern Patagonia for the past 400 years, with qualitative climate reconstructions from Andean glacier fluctuations, and with hydrological changes in Patagonian lake sediment records."

The meticulous work of the five researchers clearly demonstrates the existence of both the Medieval Warm Period and Little Ice Age in the Southern Hemisphere, as well as the fact that the Medieval Warm Period was warmer (and for a lot longer period of time) than the Current Warm Period has been to date. And hearkening back to the comments of the Swiss, German and UK scientists that we cited in the introduction to this summary -- i.e., the fact that "quantitative high-resolution global, hemispherical and regional climate reconstructions covering the last millennium are fundamental in placing modern climate warming into a long-term context" -- we can now appreciate that there is nothing unusual, unnatural or unprecedented about the planet's current level of warmth or the rate at which it was achieved, which further suggests that there is no compelling need to invoke earth's current higher atmospheric CO2 concentration as the cause of these nondescript features of our current climate.

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

Araneda, A., Torrejon, F., Aguayo, M., Torres, L., Cruces, F., Cisternas, M. and Urrutia, R. 2007. Historical records of San Rafael glacier advances (North Patagonian Icefield): another clue to "Little Ice Age" timing in southern Chile? The Holocene 17: 987-998.

Bertrand, S., Bos, X., Castiaux, J., Charlet, F., Urrutia, R., Espinoza, C., Lepoint, G., Charlier, B. and Fagel, N. 2005. Temporal evolution of sediment supply in Lago Puyehue (Southern Chile) during the last 600 yr and its climatic significance. Quaternary Research 64: 163-175.

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.

Harrison, S., Winchester, V. and Glasser, N. 2007. The timing and nature of recession of outlet glaciers of Hielo Patagonico Norte, Chile, from their Neoglacial IV (Little Ice Age) maximum positions. Global and Planetary Change 59: 67-78.

Jenny, B., Valero-Garces, B.L., Urrutia, R., Kelts, K., Veit, H., Appleby, P.G. and Geyh M. 2002. Moisture changes and fluctuations of the Westerlies in Mediterranean Central Chile during the last 2000 years: The Laguna Aculeo record (3350'S). Quaternary International 87: 3-18.

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

Lara, A. and Villalba, R. 1993. A 3620-year temperature record from Fitzroya cupressoides tree rings in Southern South America. Science 260: 1104-1106.

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.

Mann, M.E. and Jones, P.D. 2003. Global surface temperatures over the past two millennia. Geophysical Research Letters 30: 1-4.

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

Rebolledo, L., Sepulveda, J., Lange, C.B., Pantoja, S., Bertrand, S., Hughen, K. and Figueroa, D. 2008. Late Holocene marine productivity changes in Northern Patagonia-Chile inferred from a multi-proxy analysis of Jacaf channel sediments. Estuarine, Coastal and Shelf Science 80: 314-322.

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

Sepulveda, J., Pantoja, S., Hughen, K.A., Bertrand, S., Figueroa, D., Leon, T., Drenzek, N.J. and Lange, C. 2009. Late Holocene sea-surface temperature and precipitation variability in northern Patagonia, Chile (Jacaf Fjord, 44S). Quaternary Research 72: 400-409.

Thompson, L.G., Mosley-Thompson, E., Bolzan, J.F. and Koci, B.R. 1985. A 1500-year record of tropical precipitation in ice cores from the Quelccaya ice cap, Peru. Science 229: 971-973.

Von Gunten, L., Grosjean, M., Rein, B., Urrutia, R. and Appleby, P. 2009. A quantitative high-resolution summer temperature reconstruction based on sedimentary pigments from Laguna Aculeo, central Chile, back to AD 850. The Holocene 19: 873-881.

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

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.

Last updated 10 March 2010