Climate Audit

An interesting take on the controversy from the leading Swiss newspaper.

The German version is online here. Here is my translation from the German, which tidies up the Google translation somewhat, but I’ve not tidied all the Germanicisms. I don’t vouch for the translation as I have limited German. But you’ll get the gist of it.

Controversy over famous climate curve
Doubt about the statistical relevance of the "hockey stick"

One of the most famous curves of climate research is the late 1990s temperature history of the Northern Hemisphere, published by American researchers Michael Mann, Raymond Bradley and Malcolm Hughes. It shows relatively stable average temperatures below today’s level in the last millennium, followed in the 20th Century by a rapid temperature rise. The graph, with a shape reminiscent of a hockey stick, was considered for a long time as the most accurate reconstruction obtained from climatic archives. Some see it also as basis for one of the conclusions of the Intergovernmental Panel on Climate CHANGE (IPCC), that the increase and level of temperatures toward the end of the 20th Century was unique within the last thousand years. Now however there is ever more doubt about this work.

One, who made these doubts public in recent months, is a Republican politician, Joe Barton, chairman of the House Committee for Energy and Commerce. He commenced an investigation in June, in order to evaluate the reliability of this work and the quality of IPCC publications. He also requested that the researchers disclose important experimental details. The criticisms rely on investigations of two Canadians, Stephen McIntyre and Ross McKitrick, which had already led in 2004 to a corrigendum of the original publication. At that time, Mann and his colleagues disclosed additional calculation steps not contained in the original publication and corrected errors in the listing of the archive actually used.[1 ] They wrote that these did not affect the results substantially.

McIntyre and McKitrick now claim to be able to show that Mann’s reconstructed temperature history in the 15th Century is not statistically meaningful. [2] Also the quality of climatic archives, which have, in their opinion, a dominant influence on the climatic reconstruction of that period, appears dubious to them. They maintain that the method used by Mann would produce a hockey stick even from random numbers. In a letter in reply, Mann argues vehemently against these criticisms. He accuses his critics of failing to carry out the reconstruction and statistical analysis correctly.

Other climatic researchers, such as, for instance, the renowned scientist, Hans von Storch of the GKSS Research Center in Geesthacht, Germany, consider the effect on the final results of the later published calculation steps to be negligible, especially if one considers the uncertainties in the climatic reconstructions presently under discussion. The research world must still face a further question: whether there is a connection between the prominent placing of this famous temperature reconstruction in the reports of the IPCC and the fact that Mann was one of the prominent authors of these reports. Mann answers this in the negative and refers to the large number of consultants involved. Von Storch however assumes a certain conflict of interest – for him, a reason to welcome at least this aspect of the investigation arranged by Barton.

Thorsten Bartels-Rausch

[ 1 ] Nature 430, 105 (2004); [ 2 ] Geophysical Research Letters 32, L03710 (2005).