The hockey stick: a retrospective - Climate Change: The Facts - page 151

• The CE scores range from near zero to negative, which tells us that Mann's results
were junk.
Another exercise in obfuscation concerned the reliance on bristlecones. The NAS report
said the following:
Suchtrees[bristlecones]aresensitivetohigheratmosphericCO2concentrations…possiblybecauseofgreaterwater-use
efficiency … or different carbon partitioning among tree parts … While 'strip-bark' samples should be avoided for
temperaturereconstructions,attentionshouldalsobepaidtotheconfoundingeffectsofanthropogenicnitrogendeposition
… For periods prior to the 16th century, the Mann … reconstruction that uses this particular principal component
analysis technique is strongly dependent on data from the Great Basin region in the western United States. Such issues of
robustness need to be taken into account in estimates of statistical uncertainties. 19
Stripping away the bark, here is what this means:
• Bristlecone records are sensitive to a variety of environmental conditions other
than temperature and should be avoided for climate reconstructions;
• Mann's results strongly depend on the bristlecone records; and
• His results are therefore not robust, an important point over and above the lack of
statistical significance.
The NAS report also made a few other points, buried in elliptical prose or scattered around
the report where the press would be sure of never finding them (not that they looked).
Putting them together, they upheld all the claims in our submission:
McIntyre and McKitrick 20 demonstrated that under some conditions, the leading principal component can exhibit a
spurious trend-like appearance, which could then lead to a spurious trend in the proxy-based reconstruction … 21 As part
of their statistical methods, Mann et al. used a type of principal component analysis that tends to bias the shape of the
reconstructions. 22
The report even included its own graphical replication of the artificial hockey stick effect
from feeding red noise into Mann's algorithm, and noted that the usual RE significance
benchmark 'is not appropriate' 23 and that 'uncertainties of the published reconstructions
have been underestimated'. 24
The censored folder
Mann also published an online review article in 2000 that assured readers in categorical
terms that their results were 'robust' to non-climatic bias in tree ring data 25 and even to
the complete removal of tree rings from their data set, though they illustrated that point
only for the post1760 interval. 26 In the course of our analysis, McIntyre found some