Playing With a Broken Stick

I don't want to seem to be beating a dead horse, or rather a dead Unicorn, but I paid another visit to Greenie Watch and found a link to another article critical of the Michael Mann “hockey stick.”

In their two seminal papers, Mann and his colleagues purported to reconstruct Northern Hemisphere temperatures for the last thousand years. Since 1000, temperatures gradually decreased (the shaft of the hockey stick), only to increase sharply from 1900 onwards (the blade).The implication is obvious: Human interference caused this trend to change.

The subhead for the article, headlined “Breaking the hockey stick,” reads

The famous graph that supposedly shows that recent temperatures are the highest in a thousand years has now been shown by careful analysis to have been based on faulty data.

Read that again and remember that this graph is a critical component of The Assessment of the Intergovernmental Panel on Climate Change.

Read it again and remember that the IPCC report is the foundation for the Kyoto Protocol.

The National Post story is about further analysis of the research by Ross McKitrick and Stephen McIntyre. McKitrick and McIntyre's research focuses on statistical teqniuques.

They claim that Mann and his colleagues have misused an established statistical method -- principal component analysis (PCA) -- so that their calculations simply mined data for hockey-stick shaped series and that Mann's results are statistically meaningless.

The article recounts attempts by McKitrick and McIntyre to work with Mann that met with little success or outright resistence. One particular aspect of Mann's research that he was not willing to share, McKitrick and McIntyre stumbled across on an FTP site on which Mann had made source data available.

McIntyre and McKitrick requested original source code from Mann in order to fully reconcile their results. Mann refused. But McIntyre did make an interesting find at Mann's FTP site -- a Fortran program of about 500 lines for the calculation of tree-ring series, virtually the only source code on the entire site. They carefully studied the script and found a highly unusual procedure that had not been mentioned in the Nature article.

McIntyre says: “The effect is that tree-ring series with a hockey-stick shape no longer have a mean of zero and end up dominating the first principal [data] component; in effect, Mann's program mines for series with a hockey-stick shape.”
[...]
McIntyre and McKitrick decided to perform another check. Using computer simulations of so-called “red noise,” they generated networks of artificial tree-ring data over the period of 1400 to 1980. Red noise is commonly used in climatology and oceanography. McIntyre says: “If we used Mann's method on red noise, we consistently obtained hockey sticks with an inflection at the start of the 20th century. We have repeated the simulation thousands of times and in 99% of the cases, the result of the PCA was a hockey stick.”

This would seem to be a fairly clear cut case of manipulating the data to produce a desired conclusion. This faulty research is now a cornerstone of efforts to reshape the social, political, and economic structure of the industrial world. The hockey stick is broken, but the game will undoubtedly play on.

Posted by: Stephen Macklin at 03:47 PM | Comments (2) | Add Comment