Another serious issue to be considered relates to the fact that the PC1 time series in the Mann et al. analysis was adjusted to reduce the positive slope in the last 150 years (on the assumption - following an earlier paper by Lamarche et al. - that this incressing growth was evidence of carbon dioxide fertilization) , by differencing the data from another record produced by other workers in northern Alaska and Canada (which incidentally was standardised in a totally different way). This last adjustment obviously will have a large influence on the quantification of the link between these Western US trees and N.Hemisphere temperatures. At this point , it is fair to say that this adjustment was arbitrary and the link between Bristlecone pine growth and CO2 is , at the very least, arguable...Keith [Briffa]
At 15:01 15/11/2006, Martin Juckes wrote:
Hi, Concerning Bristlecones, I had a sympathetic reply from Prof. North, but he deferred to the person who wrote the relevant paragraph in the NAS report (Franco Biondi) who is firmly of the view that strip-bark bristlecones should not be used. I've read a few of the articles cited to back up this statement and I am surprised by the extreme weakness of the evidence. There is one study of 27 strip-bark pines which shows that they clearly developed anomalous growth around 1850. Attributing this to CO2 is odd, to say the least. I'm writing a brief review of the literature which I'll send round in a few days time.