Corrections to the Mann et al (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series


The well-known study
  • Mann, M.E., Bradley, R.S. & Hughes, M.K. (1998) Global-Scale Temperature Patterns and Climate Forcing Over the Past Six Centuries, Nature, 392, 779-787, 1998.

    is one of the most influential scientific papers of the past 10 years. It introduced the “multiproxy” method to the study of past climates, and produced what was purported to be a 600-year history of the average temperature of the Northern Hemisphere. It is the basis for the claim by Environment Canada (and many other governmental agencies) that the Earth is “warmer” now than it has been for 600 years. A companion paper published a year later in Geophysical Research Letters extended the 600-year series back to 1000 and spliced a surface temperature record to 1998, producing the famous hockey stick graph of the NH climate.

    This graph figures prominently in the Third Assessment Report of the Intergovernmental Panel on Climate Change and has been reproduced many times. It was the basis for the claim in pamphlets mailed by the Government of Canada to Canadians in 2002 that said “The 20th Century was the warmest globally for the past 1,000 years.” The pamphlets were sent to generate support for ratifying and implementing the Kyoto Protocol in Canada.

    In 2003, Steven McIntyre, a Toronto business man who specialized in mathematics at university, got interested in the process by which IPCC Reports were being put together and used for driving major policy decisions. Long experience in the mining industry, including close observation of the delinquent accounting that led to the Bre-X scandal, gave him a good nose for promotions based on unaudited claims. It also taught him that when big investments are at stake, due diligence requires relentless testing and independent verification of the data by all parties at every stage. Also, attention must be paid to potential conflicts of interest—for instance the author of a project feasibility study should not also be a major shareholder in the project. These are rigorous requirements in the private sector, yet in the case of the IPCC, chapter authors routinely promote their own research. This makes it even more important that there be external auditing of the reports’ foundation.

    The Mann hockey stick curve was given central prominence in the 2001 IPCC Report. The IPCC claims it has a rigorous review process. If this is true, the Mann, Bradley and Hughes paper should have no problem passing a detailed audit. Since governments around the world (including here in Canada) are making some very expensive policy decisions based on uncritical acceptance of the IPCC Report, an independent review seemed in order, and indeed should be a mere formality.

    Mr. McIntyre obtained the underlying data set from Professor Michael Mann of the University of Virginia. Based on some apparent difficulties experienced by Mann's associates in supplying the data set, he surmised that it was possible that no one had ever previously requested the data set and that it would be a worthwhile endeavour to try to replicate the famous graph.

    In the summer of 2003 he contacted Ross McKitrick, an Associate Professor of Economics at the University of Guelph and coauthor of Taken By Storm: the Troubled Science, Policy and Politics of Global Warming, to discuss his findings to that point. They joined forces to write up the results and publish them. Their paper has been published in the British journal Energy and Environment.

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