Navy Bob urged me to get over to Climate Audit this morning. I’m glad he did. Steve McIntyre (who was a guest on CNN’s American Morning today, by the way — we’ll post the video later) walks through the CRU e-mails leading up to the IPCC’s Third Assessment Report.
Of interest is the concern expressed over not “diluting” the impact of the IPCC report by including the late-20th-century decline evidenced in Keith Briffa’s tree-ring proxy reconstruction — hoping instead to present “a nice tidy story” of unprecedented warming over the last millennium. IPCC lead authors Chris Folland from the Hadley Centre and Tom Karl (that’s Dr. Tom Karl to you) from the NOAA were not only included on the e-mails, it is Folland who writes:
But the current diagram with the tree ring only data [i.e. the Briffa reconstruction] somewhat contradicts the multiproxy curve and dilutes the message rather significantly… This is probably the most important issue to resolve in Chapter 2 at present.
The footprints in the powder suggest to McIntyre that all of this was discussed at the IPCC meeting in Tanzania on September 1-3, 1999. Note Mann’s e-mail of September 22:
So if Chris[Folland] and Tom [Karl] are ok with this, I would be happy to add Keith’s series. That having been said, it does raise a conundrum: We demonstrate … that the major discrepancies between Phil’s and our series can be explained in terms of spatial sampling/latitudinal emphasis … But …Keith’s series… differs in large part in exactly the opposite direction that Phil’s does from ours. This is the problem we all picked up on (everyone in the room at IPCC was in agreement that this was a problem and a potential distraction/detraction from the reasonably concensus viewpoint we’d like to show w/ the Jones et al and Mann et al series.
So in accordance with Folland’s wishes, and over the early concerns of Briffa, resolve it they did. A different version of Briffa’s reconstruction is sent around on October 5. On November 16 comes Jones’s “trick” — replacing the tree-ring data with temperature data after 1960, thus hiding the pesky decline. McIntyre offers this handy diagram comparing the two, with the tricked-out reconstruction dutifully truncated:
The tricked-out version presents no distracting/detracting problem for the Third Assessment report’s Figure 2.21 now: