Volume 16, Number 7: 13 February 2013
Following the end of the earth's most recent ice age, the planet entered into an interglacial period of time known as the Holocene, the warmest portion of which - the Holocene Climatic Optimum - prevailed from about 9,000 to 5,000 years B.P. Thereafter, the earth began to cool again; and glaciers began to reform and grow, as the planet experienced the Neoglacial period of "renewed glaciation." And it is this period of time on which Munroe et al. (2012) focus their attention in a recently published study of the glaciers of Montana's Glacier National Park (GNP), where there has been a reduction in the area of glaciers in excess of 36% since approximately 1850 (Key et al., 2002), about which they write that "such dramatic glacier retreat is frequently highlighted as a signal of global warming (e.g. Apenzeller, 2007)," but while noting that "in reality very little is known about fluctuations of glaciers in GNP before the Little Ice Age."
In a study designed to provide more information regarding this important topic, the seven U.S. scientists developed what they describe as "the first detailed Neoglacial chronology for Glacier National Park." This they did via analyses of "sedimentary properties sensitive to the extent and activity of upstream glacier ice, including: water, organic matter, carbonate, and biogenic silica content; bulk density; mass accumulation rate; phosphorus fractionation; magnetic susceptibility; L*a*b* color values; and grain size distributions."
So what did they discover? First of all, Munroe et al. say that all but one of the records they developed contain evidence for glacier advances during the last millennium, corresponding with the Little Ice Age," which latter period they describe as "the most extensive event" of the entire Neoglacial, and which they further note is "strongly expressed globally," citing Davis et al. (2009). But even more impressive is their finding that the Little Ice Age maximum advance was the most recent in a series of advance/retreat cycles during the past several millennia, and that retreat from the Little Ice Age maximum "was the most dramatic episode of ice retreat in at least the last 1000 years."
So what was responsible for both the birth and demise of the very coldest interval of the entire Neoglacial period? Climate alarmists like to think that the Little Ice Age's demise was brought about by CO2-induced global warming. But if that were the case, one has to ask: what brought the planet into the Little Ice Age? Munroe et al. adhere to the theory that both the birth and the death of the Little Ice Age were promoted by one and the same phenomenon: solar irradiance variability. This idea has been described by Denton and Karlen (1973) and Koch et al. (2007); and Munroe et al. say that it has been "solidified by identification of a link between ice-rafted debris (IRD) in the North Atlantic, and solar irradiance as tracked by the production of atmospheric cosmogenic nuclides (Bond et al., 2001)." And they add that "the IRD variability features a quasi-periodic cycle of ~1500 years, and has been connected to glacier fluctuations in Europe (Holzhauser et al., 2005; Matthews et al., 2005; Nussbaumer et al., 2011)," which also helps to explain the occurrence of the Medieval Warm Period that preceded the Little Ice Age, the prior Dark Ages Cold Period, the still earlier Roman Warm Period, and so forth, over which oscillating global temperature history the air's CO2 content has varied hardly at all, and nothing like what has occurred since the inception of the Industrial Revolution, from the start of which the atmosphere's CO2 content has risen by some 40%, while global air temperature is no higher now than it was during the peak warmth of the Medieval and Roman Warm Periods.
Clearly, atmospheric CO2 variability has had but a miniscule impact on earth's temperature throughout the entire Holocene; and it is having next to no impact on it now.
Sherwood, Keith and Craig Idso
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Key, C.H., Fagre, D.B. and Menicke, R.R. 2002. Glacier retreat in Glacier National Park, Montana. In: Krimmel, R.M. (Ed.). Glaciers of the Western United States. U.S. Geological Survey, Reston, Virginia, USA, pp. J329-J381.
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Munroe, J.S., Crocker, T.A., Giesche, A.M., Rahlson, L.E., Duran, L.T., Bigl, M.F. and Laabs, B.J.C. 2012. A lacustrine-based Neoglacial record for Glacier National Park, Montana, USA. Quaternary Science Reviews 53: 39-54.
Nussbaumer, S.U., Steinhilber, F., Trachsel, M., Breitenmoser, P., Beer, J., Blass, A., Grosjean, M., Hafner, A., Holzhauser, H. and Wanner H. 2011. Alpine climate during the Holocene: a comparison between records of glaciers, lake sediments and solar activity. Journal of Quaternary Science 26: 703-713.