Friday, December 02, 2011

1997: Briffa points out issues with trying to use trees as thermometers; he also says "There are people in this field whose motives or at least methods I have always regarded with suspicion"

ClimateGate FOIA grepper - Email 1438

The real problem arises when there is bias in the samples at a particular time that is not related to a climate shift - i.e. if one cohort all derive from an elevation that is significantly different from the mean, or perhaps all from a more boggy site so that growth was suppressed overall by this fact alone, then this bias will be imparted to the final chronology.

This, I believe, may be a common problem in long, poorly replicated sub-fossil derived chronologies, especially where the tree age is relatively short. ...There are people in this field whose motives or at least methods I have always regarded with suspicion. You two, however, are motivated only by genuine scientific goals....

You specifically asked for my comments, so here they are. I think (as does Fritz) that you have been able to locate 'extreme' sites where greater recent ring-width increases occur than are apparent in many other northern or high altitude sites. Which of the sites is 'typical' and 'of what' are the most pertinent questions. It is possible that your sites are the 'odd' ones because they reflect extreme sensitivity to recent warming or even perhaps to some change in another growth limiting factor, e.g. Nitrate input. However, where I think you and Fritz have possibly gone wrong is in adopting too rigid interpretations of what your data, or Fritz's data, say about global change questions.... What the subject in general does not need is sweeping statements, oversimplifying and partly misrepresenting each other's positions.

Hat tip: AJ

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