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GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L03710, doi:10.1029/2004GL021750, 2005

Hockey sticks, principal components, and spurious significance

Stephen McIntyre

Northwest Exploration Co., Ltd., Toronto, Ontario, Canada


Ross McKitrick

Department of Economics, University of Guelph, Guelph, Ontario, Canada


Abstract

The “hockey stick” shaped temperature reconstruction of Mann et al. (1998, 1999) has been widely applied. However it has not been previously noted in print that, prior to their principal components (PCs) analysis on tree ring networks, they carried out an unusual data transformation which strongly affects the resulting PCs. Their method, when tested on persistent red noise, nearly always produces a hockey stick shaped first principal component (PC1) and overstates the first eigenvalue. In the controversial 15th century period, the MBH98 method effectively selects only one species (bristlecone pine) into the critical North American PC1, making it implausible to describe it as the “dominant pattern of variance”. Through Monte Carlo analysis, we show that MBH98 benchmarks for significance of the Reduction of Error (RE) statistic are substantially under-stated and, using a range of cross-validation statistics, we show that the MBH98 15th century reconstruction lacks statistical significance.

Received 14 October 2004; accepted 17 January 2005; published 12 February 2005.

Index Terms: 1620 Global Change: Climate dynamics (0429, 3309); 1694 Global Change: Instruments and techniques; 3344 Atmospheric Processes: Paleoclimatology (0473, 4900); 3337 Atmospheric Processes: Global climate models (1626, 4928); 9820 General or Miscellaneous: Techniques applicable in three or more fields.

Subscriber Access to Full Article (Nonsubscribers may purchase for $9.00, Includes print PDF, file size: 116569 bytes)

Citation: McIntyre, S., and R. McKitrick (2005), Hockey sticks, principal components, and spurious significance, Geophys. Res. Lett., 32, L03710, doi:10.1029/2004GL021750.