Steve McIntyre, Dec. 10 2009

Much recent attention has been paid to the email about the “trick” and the effort to “hide the decline”. Climate scientists have complained that this email has been taken “out of context”. In this case, I’m not sure that it’s in their interests that this email be placed in context because the context leads right back to a meeting of IPCC authors in Tanzania, raising serious questions about the role of IPCC itself in “hiding the decline” in the Briffa reconstruction.

Relevant Climategate correspondence in the period (September-October 1999) leading up to the trick email is incomplete, but, in context, is highly revealing. There was a meeting of IPCC lead authors between Sept 1-3, 1999 to consider the “zero-order draft” of the Third Assessment Report. The emails provide clear evidence that IPCC had already decided to include a proxy diagram reconstructing temperature for the past 1000 years and that a version of the proxy diagram was presented at the Tanzania meeting showing the late twentieth century decline. I now have a copy of the proxy diagram presented at this meeting (see below).

The emails show that the late 20th century decline in the Briffa reconstruction was perceived by IPCC as “diluting the message”, that “everyone in the room at IPCC” thought that the Briffa decline was a “problem” and a “potential distraction/detraction”, that this was then the “most important issue” in chapter 2 of the IPCC report and that there was “pressure” on Briffa and other authors to show a “nice tidy story” of “unprecedented warming in a thousand years or more”. [Update Dec 11 - see note at bottom on the chronology. Comments from readers have clarified that the issue at the Arusha meeting was that the Briffa reconstruction "diluted the message" more through its overall inconsistency as opposed to the decline, which was still relatively attenuated in the Arusha version. After the Arusha meeting, Briffa hastily re-calculated his reconstruction sending a new version to Mann on Oct 5, 1999 and it was this hastily re-done version that introduced the very severe decline that was hidden in the First Order Draft and Jones WMO Report]

The chronology in today’s posts show that the version of the Briffa reconstruction shown in the subsequent proxy diagram in the IPCC “First Order Draft” (October 27, 1999), presumably prepared under the direction of IPCC section author Mann, deleted the inconvenient portion (post-1960) of the Briffa reconstruction, together with other modifications that had the effect of not “diluting the message”.

Full story

Tags: Briffa, Climategate, Hide the Decline, IPCC, Mann

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