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Solar Influence on Temperature (South America) -- Summary
Climate alarmists frequently claim that earth's climate is becoming more variable and extreme as a result of CO2 induced global warming. With respect to temperature, we have shown elsewhere on our website that its modern frequency and severity fall well within the range of natural variability (see Natural Variability of Climate and Temperature Trends in our Subject Index). In the present review, we examine the issue of attribution, specifically investigating the natural role or influence of the sun on temperature in South America.

We begin with the study of Nordemann et al. (2005), who examined tree rings from species sensitive to fluctuations in temperature and precipitation throughout the southern region of Brazil and Chile, along with sunspot data, via harmonic spectral and wavelet analysis in an effort to obtain a greater understanding of the effects of solar activity, climate and geophysical phenomena on the continent of South America, where the time interval covered by the tree-ring samples from Brazil was 200 years and that from Chile was 2500 years. Results of the spectral analysis revealed periodicities in the tree rings that corresponded well with the DeVries-Suess (~200 yr), Gleissberg (~80 yr), Hale (~22 yr), and Schwabe (~11 yr) solar activity cycles; while wavelet cross spectrum analysis of the sunspot number and tree-ring growth data revealed a clear relation between the tree-ring and solar series.

Next, utilizing a lichenometric method for dating glacial moraines, the Bolivian and French research team of Rabatel et al. (2005) developed what they call "the first detailed chronology of glacier fluctuations in a tropical area during the Little Ice Age," focusing on fluctuations of the Charquini glaciers of the Cordillera Real in Bolivia, where they studied a set of ten moraines that extended below the present glacier termini. Based on the chronology, the researchers determined that the maximum glacier extension in Bolivia "occurred in the second half of the 17th century, as observed in many mountain areas of the Andes and the Northern Hemisphere [our italics]." In addition, they found that "this expansion has been of a comparable magnitude to that observed in the Northern Hemisphere, with the equilibrium line altitude depressed by 100-200 m during the glacier maximum." What is more, they state that "the synchronization of glacier expansion with the Maunder and Dalton minima supports the idea that solar activity could have cooled enough the tropical atmosphere to provoke this evolution."

As for the magnitude and source of the cooling in the Bolivian Andes during the Little Ice Age, three years later Rabatal et al. (2008) estimated it to have been 1.1 to 1.2C below that of the present, while once again noting that at that time there was a "striking coincidence between the glacier expansion in this region of the tropics and the decrease in solar irradiance: the so-called 'Maunder minimum' (AD 1645-1715) during which irradiance might have decreased by around 0.24% (Lean and Rind, 1998) and could have resulted in an atmospheric cooling of 1C worldwide (Rind et al., 2004)."

Further south, Glasser et al. (2004) analyzed 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). That evidence indicated that the most recent glacial advances in Patagonia also 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.

Working on a bog, as opposed to a glacier, Chambers et al. (2007) presented new proxy climate data they obtained from the Valle de Andorra northeast of Ushuaia, Tierra del Fuego, Argentina, which data, they emphasize, are "directly comparable" with similar proxy climate data obtained in numerous studies conducted in European bogs, "as they were produced using identical laboratory methods [our italics]." This latter point is very important because Chambers et al. say their new South American data show there was "a major climate perturbation at the same time as in northwest Europe," which they describe as "an abrupt climate cooling" that occurred approximately 2800 years ago, and that "its timing, nature and apparent global synchronicity lend support to the notion of solar forcing [our italics] of past climate change, amplified by oceanic circulation."

The five European researchers further state that their finding that "rapid, high-magnitude climate changes might be produced within the Holocene by an inferred decline in solar activity (van Geel et al., 1998, 2000, 2003; Bond et al., 2001; Blaauw et al., 2004; Renssen et al., 2006) has implications for rapid, high-magnitude climate changes of the opposite direction -- climatic warmings, possibly related to increases in solar activity." In this regard, they further note that "for the past 100 years any solar influence would for the most part have been in the opposite direction (i.e., to help generate a global climate warming) to that inferred for c. 2800-2710 cal. BP." And they conclude that this observation "has implications for interpreting the relative contribution of climate drivers of recent 'global warming'," implying that a solar-induced, rather than a CO2-induced, climate driver may have been the primary cause of 20th-century global warming.

Lastly, we cite the study of Polissar et al. (2006), who working with data derived from sediment records of two Venezuelan watersheds, along with ancillary data obtained from other studies that had been conducted in the same general region, developed continuous decadal-scale histories of glacier activity and moisture balance in a 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 (Canada, Spain, United States, Venezuela) team of scientists write that "comparison of the Little Ice Age history of glacier activity with reconstructions of solar and volcanic forcing suggest 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 1.4C 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 climate alarmists have had difficulty accepting. Hopefully, this paper and the others we have reviewed in this and other sections in our Subject Index (see Solar Influence) will help them "see the light" on this subject a little clearer.

References
Blaauw, M., van Geel, B. and van der Plicht, J. 2004. Solar forcing of climate change during the mid-Holocene: indications from raised bogs in The Netherlands. The Holocene 14: 35-44.

Bond, G., Kromer, B., Beer, J., Muscheler, R., Evans, M.N., Showers, W., Hoffmann, S., Lotti-Bond, R., Hajdas, I. and Bonani, G. 2001. Persistent solar influence on North Atlantic climate during the Holocene. Science 294: 2130-2136.

Chambers, F.M., Mauquoy, D., Brain, S.A., Blaauw, M. and Daniell, J.R.G. 2007. Globally synchronous climate change 2800 years ago: Proxy data from peat in South America. Earth and Planetary Science Letters 253: 439-444.

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.

Lean, J. and Rind, D. 1998. Climate forcing by changing solar radiation. Journal of Climate 11: 3069-3094.

Nordemann, D.J.R., Rigozo, N.R. and de Faria, H.H. 2005. Solar activity and El-Nio signals observed in Brazil and Chile tree ring records. Advances in Space Research 35: 891-896.

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.

Rabatel, A., Francou, B., Jomelli, V., Naveau, P. and Grancher, D. 2008. A chronology of the Little Ice Age in the tropical Andes of Bolivia (16S) and its implications for climate reconstruction. Quaternary Research 70: 198-212.

Rabatel, A., Jomelli, V., Naveau, P., Francou, B. and Grancher, D. 2005. Dating of Little Ice Age glacier fluctuations in the tropical Andes: Charquini glaciers, Bolivia, 16S. Comptes Rendus Geoscience 337: 1311-1322.

Renssen, H., Goosse, H. and Muscheler, R. 2006. Coupled climate model simulation of Holocene cooling events: solar forcing triggers oceanic feedback. Climate Past Discuss. 2: 209-232.

Rind, D., Shindell, D., Perlwitz, J., Lerner, J., Lonergan, P., Lean, J. and McLinden, C. 2004. The relative importance of solar and anthropogenic forcing of climate change between the Maunder minimum and the present. Journal of Climate 17: 906-929.

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 BP and global evidence for solar forcing: a hypothesis. The Holocene 10: 659-664.

Van Geel, B., van der Plicht, J., Kilian, M.R., Klaver, E.R., Kouwenberg, J.H.M., Renssen, H., Reynaud-Farrera, I. and Waterbolk, H.T. 1998. The sharp rise of δ14C ca. 800 cal BC: possible causes, related climatic teleconnections and the impact on human environments. Radiocarbon 40: 535-550.

Van Geel, B., van der Plicht, J. and Renssen, H. 2003. Major δ14C excursions during the Late Glacial and early Holocene: changes in ocean ventilation or solar forcing of climate change? Quaternary International 105: 71-76.

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.

Last updated 22 April 2009