[dennisw]

[Steve Schulin]

Thanks for showing the Mann et al. hockey stick. McIntyre and McKitrick tried to get the Mann et al. method to show other than hockey stick, but it could not do so. Here's their Figure 2, which compares the effect of using conventional principal component analysis (top graph) versus using the Mann et al. method (bottom graph) in one experiment. The authors report that Mann et al. method produced the same distinctive hockey-stick-shaped graph for all ten experiments they performed.

Here are some other recent criticisms of the hockey stick which apply not just to Mann et al., but to other multiproxy studies too:

* In the body of the UN IPCC 2001 science working group assessment report, it was noted that if our best understanding of glacier retreat evidence is on track, the warming trend started earlier than depicted by the hockey stick. This would spread out the recent warming currently restricted to the 20th century part of the curve. Here's the frank statement in the body of the TAR: "...the timing of the onset of glacier retreat implies that a significant global warming is likely to have started not later than the mid-19th century. This conflicts with the Jones et al. (2001) global land instrumental temperature data (Figure 2.1), and the combined hemispheric and global land and marine data (Figure 2.7), where clear warming is not seen until the beginning of the 20th century. This conclusion also conflicts with some (but not all) of the palaeo-temperature reconstructions in Figure 2.21, Section 2.3 , where clear warming, e.g., in the Mann et al. (1999) Northern Hemisphere series, starts at about the same time as in the Jones et al. (2001) data. These discrepancies are currently unexplained."

* In his 2004 paper, Craig Loehle showed that the multiproxy method inherently tends to produce flatter shape due to smearing. Each proxy record has dating error. By combining the proxies, the multiproxy approach inherently tends to smear variability out of the record [Ref: Loehle. Using Historical Climate Data to Evaluate Climate Trends: Issues of Statistical Inference. Energy & Environment, 15(1):1-10, 2004]. This was a meaningful challenge to the flat shape of the curve, quite independent from the McIntyre and McKitrick point about the Mann et al. PCA technique.

* In their Science paper released this month, von Storch et al. showed that the multiproxy study error ranges do not include a significant uncertainty. This was a meaningful challenge to the gray area of the curve. [Ref: http://www.sciencemag.org/cgi/content/abstract/1096109v1 -- von Storch et al. Reconstructing Past Climate from Noisy Data. ScienceExpress, October 1, 2004]