Posted by: climatewonk | December 2, 2009

Climate Gate Post 2 — The Hockey Stick

Our last episode ended with a retired minerals consultant/consultant to big oil and his sidekick, economics professor and fellow at the right-wing think tank The Fraser Institute, getting all hot under the collar about a graph adapted from an article by Mann, Bradley and Hughes (1998) used in the TAR: the infamous “Hockey Stick”:

They lamented the absence of the medieval warm period. To them, it contradicted an older less precise (by a long shot) graphic used in the First IPCC Assessment report.

In 2003, McIntyre and McKittrick published an article that challenged the methods and findings of the MBH(* paper used in the TAR.

From the paper:

The particular “hockey stick” shape derived in the MBH98 proxy construction – a temperature index that decreases slightly between the early 15th century and early 20th century and then increases dramatically up to 1980 — is primarily an artefact of poor data handling, obsolete data and incorrect calculation of principal components.

Note that the article was not published in a peer-reviewed journal listed in the JCR – Journal Citation Reports.

In response, Mann, Bradley and Hughes published a corrigendum in Nature, a very well-recognized science journal.

Next is M&M’s response, published in GRL, “Hockey Sticks, Principal Components and Spurious Significance” in which they critique the use of Principal Components Analysis.

From the article:

“Through Monte Carlo analysis, we show that MBH98 benchmarks for significance of the Reduction of Error (RE) statistic are substantially under-stated and, using a range of cross-validation statistics, we show that the MBH98 15th century reconstruction lacks statistical significance.”

So, we see some back and forth between Mann et. al and others in the climate science community and M&M over the use of certain statistical analysis, PC, to analyze paleoclimate data. Not only did they reject the use of PC analysis, but also the use of a specific set of paleoclimate data, Bristlecone Pines.

More on that in another post.


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