The July 1 issue of Nature magazine contains a correction by Michael Mann, Raymond Bradley, and Malcolm Hughes (MBH) of mistakes in their 1998 Nature article that purported to give an accurate reconstruction of global temperatures over the past six centuries (the initial source for the hockey stick graph). The brief notice does not contain the corrections beyond an uninformative list of data errors, but refers readers to www.nature.com/nature, where one can eventually also find changes to the studys methodology (referred to as “an expanded description of the methodological details”).
This highly unusual admission comes as the result of an article by Stephen McIntyre and Ross McKitrick, associate professor of economics at the University of Guelph, that exposed serious errors in data and methodology. The editors of Nature agreed and required Mann et al. to fix their mistakes.
“Corrigendum: Global-scale temperature patterns and climate forcing over the past six centuries” ends with an extraordinary statement: “None of these errors affect our previously published results.” McIntyre and McKitrick dispute this statement: “We have done the calculations and can assert categorically that the claim is false. We have made a journal submission to this effect and will explain the matter fully when that paper is published.”
It is also important to realize that this correction was not published as an Addendum, which, according to Natures published policy, is the case when “Authors inadvertently omitted significant information available to them at the time” but which does “not contradict the original publication,” as would surely be the case if MBH are correct in their assertion. Corrigenda are only published, “If the scientific accuracy or reproducibility of the original paper is compromised.”
Up until this climbdown, Mann, an assistant professor of environmental sciences at the University of Virginia, had ferociously defended his hockey-stick papers and had launched several ad hominem attacks on McIntyre and McKitrick. The corrigendum listed five references, but not the paper by McIntyre and McKitrick (“Corrections to the Mann et al (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series,” Energy and Environment 14(6)) that first drew attention to his mistakes.
The hockey-stick purports to show that the global mean temperature was relatively constant through the first nine hundred years of the past millennium and then rose sharply in the twentieth century. It was featured as proof of global warming in the U. N. Intergovernmental Panel on Climate Change’s Third Assessment Report. A number of papers have been published that challenge either the hockey sticks reconstruction of past temperatures (e.g., Esper et al., Science, 2002) or Manns handling of data in general (e.g. Chapman et al, Geophysical Research Letters, 2004).
Mann had to publish another correction to his published work in June in the Journal of Geophysical Results, following complaints from other paleoclimatologists that his methodology in another paper did not show as big a warming trend from the end of the Little Ice Age as is necessary. In other words, Mann underestimated how cold the Little Ice Age was.
The full debate over the “hockey stick” controversy can be followed at Ross McKitricks web site at http://www.uoguelph.ca/~rmckitri/ research/trc.html.