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A 400-Year Temperature History Derived from Glacial Data
Volume 8, Number 11: 16 March 2005

According to the author of this intriguing paper (Oerlemans, 2005), "a temperature history for different parts of the world [was] constructed from 169 glacier length records."  This is a well-crafted statement; for being based on glacial data only, there is no guarantee that the result applies to the globe as a whole, as glaciers are found over only a tiny portion of it.  We also note that the new temperature history is but a first-order approximation of reality, for glaciers are very individualistic entities that are hard to fit into a single mold, and many assumptions had to be made, and short-cuts taken, in the process of translating temporal changes in glacier length data into temperature data.  All things considered, however, Oerlemans likely did about as good a job in this regard as could reasonably be expected.

So, to get right to the heart of the subject, what do Oerlemans' findings suggest about the hockeystick temperature histories of Mann and company (Mann et al., 1998, 1999; Mann and Jones, 2003)?

First of all, because the new temperature history only spans a four-century period of time (1600-2000), it cannot tell us anything definitive about the most contentious aspect of the hockeystick temperature history, i.e., its failure to provide any indication whatsoever of the existence of the Medieval Warm Period, which has been detected in many dozens of research papers we have reviewed on our website that were published subsequent to the hockeystick's creation, as well as many dozens of papers that preceded it and were either knowingly ignored or dismissed out-of-hand by Mann et al.

With respect to the Little Ice Age, however, which also is nowhere to be seen in the Mann et al. hockeystick representations of earth's climatic history, the new glacial temperature record does tell us something important.  It indicates that the Little Ice Age was a very real phenomenon, and that it was reasonably globally-synchronous, with 96 of the records upon which it is based coming from the European Alps, 27 from Northwest America, nine from Central Asia, eight from Scandinavia, eight from the Caucasus, six from Patagonia, five from Tropical Africa, four from Iceland, three from Svalbard, two from Irian Jaya, two from New Zealand, one from South Greenland, and one from Jan Mayen.  What is more, the fact that the hockeystick temperature history totally misses the Little Ice Age makes it just that much easier to understand how it also could totally miss the Medieval Warm Period.  So perhaps the glacial-based temperature record does imply something about this aspect of the hockeystick temperature record after all.

Another important observation of Oerlemans is that the glacial-based dataset "suggests that the Little Ice Age was at its maximum around 1800 rather than at the end of the 19th century as seen in some other temperature proxies (Mann and Jones, 2003)."  In fact, whereas the warming that led to the development of the Modern Warm Period begins about 1855 in the glacial-based record, the Mann et al. record does not show it starting until 1910!

The biggest question of all, however, is what happened over the final two decades of the 20th century.  Mann et al. terminated their largely tree-ring-based reconstruction and continued their history with the instrumental temperature record.  This tactic enabled them to utilize temperatures that may well have been significantly inflated by urban heat island effects, and it allowed them to ignore tree-ring-based temperature reconstructions that did not indicate nearly as much warming as the instrumental record did over this period.  So what does the glacial-based temperature history reveal?

Unfortunately, the number of glaciers with records extending all the way to the year 2000 is but a small fraction of the number that provided data over the bulk of the 20th century; and Oerlemans thus terminated his temperature history at about 1990.  However, if one looks at the stacked records of all glacier length data that do extend to the end of the 20th century, which Oerlemans presents in his Figure 2B, one sees that for both the plots of all glaciers and Alps excluded, mean glacial retreat ceases and is actually replaced by glacial advance over the last few years of the 1990s, so that mean glacial length ends up at a value that is equivalent to what it was between about 1975 and 1985, where glaciers exhibited little to no trend for about ten years; and over that period of time (1975-1985), the mean temperature of Orelemans' glacial-based reconstruction was actually less than what it was in 1940!

Clearly, it is tremendously important that the missing glacier lengths for this period of time, as well as for the first few years of the new millennium, be acquired as soon as is humanly possible; for much is riding on what they have to tell us.  From what we have seen so far, it looks like it will be a strong confirmation of what the IPCC and its climate-alarmist friends simply refuse to acknowledge, i.e., that the hockeystick is not only broken, it is shattered.

Sherwood, Keith and Craig Idso

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1998.  Global-scale temperature patterns and climate forcing over the past six centuries.  Nature 392: 779-787.

Mann, M.E., Bradley, R.S. and Hughes, M.K.  1999.  Northern Hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations.  Geophysical Research Letters 26: 759-762.

Mann, M.E. and Jones, P.D.  2003.  Global surface temperatures over the past two millennia.  Geophysical Research Letters 30: 10.1029/2003GL017814.

Oerlemans, J.  2005.  Extracting a climate signal from 169 glacier records.  Sciencexpress / / 03 March 2005.