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We will start with the quote from Ian Jolliffe, and work backwards to unpack.
“I am by no means a climate change denier. My strong [impression] is that the evidence rests on much much more than the hockey stick. It therefore seems crazy that the MBH hockey stick has been given such prominence and that a group of influential climate scientists have doggedly defended a piece of dubious statistics.”
- Ian Jolliffe"
I am surprised to hear, today, that considered authoritative option thinks that the "hockey stick" is bad statistics, and that people who believe in global warming should admit this error, strive to be more rigorous, and move on with the other overwhelming facts of global warming.
I will modify my view.
Lets now work backward.
Ian Jolliffe's comment to Tamino: "http://tamino.wordpress.com/2008/08/10/open-thread-5-2/#comment-21873"
Tamino blogs at "http://tamino.wordpress.com/"
Jolliffe requests an apology from Tamino, because he feels words were placed into his mouth, to give full liberty to any use of the statistical technique of "decentred PCA" when a different origin is considered to be meaningful, even though he did no such thing. "Decentred PCA" is the technique that Mann used to bring the hockey stick into clearly resolved existence.
A reasonable starting place, from a moderately skeptical point of view, for information on Michael E. Mann's "Hockey stick": "http://en.wikipedia.org/wiki/Hockey_stick_controversy"
Tamino apologized (also at "http://tamino.wordpress.com/2008/08/10/open-thread-5-2/#comment-21873"), re-iterated that "It also seems to me (and I'm by no means the only one) that the origin in the analysis of MBH98 is meaningful" and ended by emphasizing a part Jolliffe's reply - "... the evidence rests on much much more than the hockey stick. It therefore seems crazy that the MBH hockey stick has been given such prominence ..." - which can be interpreted as back-tracking.
This has allowed some merchants of obscurantism to make hay: "http://climateaudit.org/2008/09/08/ian-jolliffe-comments-at-tamino/".
The above applies only to the original Mann hockey stick, for an overview of the evidence from all available sources of evidence of possible climate disruption see: