There has been some recent chatline discussion on whether the MBH98 bristlecone pine series were “adjusted” for non-climatic factors. A number of posters seem to think that they were so “adjusted. For example, Tom Rees said on http://www.davidappell.com:
on Monday, January 31st, Tom Rees said
Me again… James: Mann et al 1999 seem to be very clear. They’re not sure what causes the surge in the Bristlecone pines, so they play safe and remove it. So it’s not in the ‘Hockey stick’ at all…
To the extent that one can ever be certain about MBH98 methods, I am completely confident that the “adjustment” discussed in MBH99 was not implemented in MBH98. The archived MBH98 PC series can be replicated almost exactly and do not show any such “adjustment”; an email to Natuurwetenschap by Mann states that the sensitivity on bristlecones was done after MBH98.
This does not totally end the story. Curiously, the archived version of the North American PC1 at NOAA for MBH99 is not the “adjusted” version, but the unadjusted version from the BACKTO_1000 directory. In most walks of life, there would be some check that they did not forget to do the adjustment in their downstream calculations, but I am unaware of any such checks, and, the unavailability of source code or supporting calculations makes direct verification impossible.
Secondly, one of the representations of MBH98 was that the proxies were all linearly related to climatic factors. The discussion of MBH99 states quite clearly that non-climatic factors affect bristlecone pine growth and adjustments are required. (I disagree with the MBH99 adjustment, but will return to that with a full description of the procedure on another occasion in the near future.) If so, then this clearly imposes an obligation on MBH to have promptly notified Nature of the fact that some of the MBH98 proxies did not meet the criteria set out and to publish a Corrigendum, demonstrating the effect on MBH98 calculations.
Shouldn’t MBH “adjust” the bristlecone pines before they do their PC calculations for the 15th century network? Shouldn’t they have done this a long time ago? The bristlecones have already been demoted to the PC4 using correct PC calculations? If they are “adjusted” according to MBH99 methods, do they fall still further? Is there any change to their “significance”? Inquiring minds want to know.
I didn’t mention this issue in my first remarks on the current efforts to salvage MBH98, but it seems it might be an important issue and that MBH have little more homework to do.