Overview - The "Hockey Stick" and Historic Climate Change

But alas, MM’s analysis also fell to inadequate data processing methods. The one common thread running through all skeptic criticisms of the hockey stick is that MBH98 did not “sand the paleoclimate block” fine enough to prove that 20th century temperatures were unprecedented. But this claim has little meaning unless we clarify what is meant by “fine enough” and “unprecedented”. It is not enough to show that some historical dataset (or time series) has uncertainties—all do. We must show that its uncertainties are large enough to invalidate the underlying trend that has been ascribed to it. To date, no skeptic criticism of the hockey stick has done this. Virtually all have been generalized accusations of “uncertainty” and/or “variability” in the proxy datasets—nothing specific enough or demonstrably large enough to invalidate the Mann et al results.

In this case MM used a different set of components that they felt did not over-represent the tree ring data but failed to recognize that changing the components used changes the number required for an accurate answer (smaller, or differently shaped bricks will change the number of bricks needed for a foundation, and how they should be placed). They did their reconstruction using the same number of components that Mann et al used, but it has since been shown that their method requires more components to be reliable. When this problem is corrected their analysis does not significantly differ from that of MBH98. A statistically significant hockey stick shape emphasizing 20th century warming is inherent in the resulting time series.

Furthermore, other paleoclimate studies that used more complete datasets and different methodologies altogether (for instance, Moberg et al, 2005 and Rutherford et al, 2005). These analyses are not subject to the criticisms of MM05 yet yield results similar to those of MBH98. In June of 2006 the National Academy of Sciences published the results of its investigation of MBH98 and the hockey stick. They concluded that while there were certain problems with the MBH98 treatment of tree ring proxies, their analysis had been adequately complete given the data available at the time, and the resulting errors did not significantly alter the study’s conclusions. Despite this affirmation, many skeptics decided that the NAS study “vindicated” their complaints about MBH98… simply because it acknowledged the presence of some errors. Once again, a touting of “errors” and “uncertainties” without consideration of their impact (one is reminded of the methods of fundamentalist creationists and their claims of alleged “problems” with evolution—problems that somehow never end up being quantified or even clarified adequately!).

Finally, even if we were to concede to MM that 20th century warming was not “unprecedented” in the last 600-1000 years, this is still a far cry from proving that it is commonplace and not due to anthropogenic activity. At best, on the few occasions that climate skeptics have gotten specific on this point they’ve managed to come up with no more than one or two instances during the last 1000 or more years when they believe temperatures were higher. This does not relegate the last century to business-as-usual that we needn’t worry about. It may be that the guy up the block from me ended up with a broken basement window during a storm 10 years ago. It doesn’t follow from this that I shouldn’t be concerned about my house being broken into if I awake tonight at 3 AM to the sound of my ground floor windows shattering!

In the end, skeptic criticisms of the hockey stick are no different than their treatment of so many other climate change datasets. Highly generalized accusations of alleged problems and/or uncertainties for which defensible specifics are never provided. It comes as little surprise that the large majority of climate scientists today recognize that 20th century temperatures are in fact disturbingly unusual, and a direct consequence of human caused activity.