Huybers’ Comment and Our Reply

Comments&Replies McIntyre and McKitrick November 2005 Huybers’ and von Storch-Zorita Comments, and Our Replies The Comments and Replies are available at http://www.climateaudit.org/?p=413. Steve has posted extended discussions on the two comments, which are also linked from the above URL. This note is just a quick summary of the counterpoints. 1. Huybers Huybers makes two arguments. 1. Mann’s PC method is biased toward finding hockey sticks in a data set. We (M&M) illustrated the bias by comparing a principal component (PC) produced by Mann’s algorithm to that produced by a standard algorithm, which does an algebraic decomposition of the covariance matrix. However the underlying data should be transformed to have a standardized variance prior to taking a PC, which implies we should have used a PC based on the decomposition of the correlation matrix rather than the covariance matrix. The correlation PC—as computed by Huybers—looks much more like a hockey stick, indicating that the M&M comparison exaggerates the bias from the MBH method. 2. To compute a significance benchmark for the RE statistic, M&M used pseudo-“predicted values” generated by feeding red noise into the MBH98 algorithm. This is the correct procedure, however the MBH98 algorithm generates PCs with a much smaller variance than the temperature data it is being used to predict. So there ought to be a step in which the variance of the pseudo-predicted values is scaled up to ...