Steve McIntyre finds yet another instance where Mann applies his special “secret hot sauce” to data, selling the sizzle, rather than the steak. It is another familiar tale of data holdback, gatekeeping, obfuscation, and cherry picking by The Team. One wonders just how long the rest of science will stand idly by.
From Climate Audit:
Mann et al 2008
Fisher 2002 (Holocene) carried out a principal component analysis on a wide variety of proxies for the 210 year period from 1761-1970 when the proxies were all available. Fisher created an archive of these proxies for the period 1761-1970, one of which was Law Dome (LAWA210.ANT). This was obviously only a fraction of the available data but was the portion used in his analysis.
Even though Mann had a current and much longer version of the Law Dome O18 series that he/Jones had obtained from van Ommen, Mann et al 2008 substituted the truncated version used in the Fisher principal components analysis. The difference in the two versions is shown below.
Figure 3. Law Dome versions. red- 2003 version; blue – Mann et al 2008 version ( truncation of 1997 version to 1761-1970).
It would take a while to calculate the effect of Mann’s use of an obsolete and truncated version of the Law Dome series on his SH reconstruction, but no one should assume that it didn’t and doesn’t “matter”. My guess is that this decision had a material impact.
Full story here