date: Fri, 11 May 2001 14:10:15 +0100 (GMT Daylight Time) from: Julie Burgess subject: 'Malcolm is quite right ...' to: k.briffa@uea.ac.uk Keith, please read the email carefully. There is one word missing which I couldn't read and I may have misread/misinterpreted other bits. Thanks, Julie 11 May 2001 Keith, Malcolm is quite right that you have seriously misinterpreted the climate response change described in our (1998) *Nature* paper. Actually, I do not think that you can use the "destruction of archives" line in forest-related research too, but to a limited extent. Destruction of old growth forests in some areas of eastern Siberia and even the United States do constitute a loss of palaeoarchives *but these* (plus, of course, the widespread destruction of tropical forests (and teak), as stated by Malcolm). This, though, is *nothing* to do with what Malcolm calls the "Briffa effect", which cannot be interpreted in any way as impugning the value of trees as palaeoarchives. Rather it refers to a subtle decadal-scale *trend* divergence between one tree-ring variable (Tree-Ring Density) and one temperature window (April-Sept. mean). It does not affect many other growth variables (e.g. Basal area increment, which shows a very different history) and is not ubiquitous even in density data. All high-latitude trees were, and *still* are, valuable indicators of temperature variability. The interpretation of the climate 'signal' is difficult in recent decades because of (I believe) non-climate changes. Unlike Malcolm, I have always realised the inherent danger in assuming a time-invariant response between some (albeit optimal and objectively-defined) temperature variable and any tree-ring (or other) climate proxy. There is a lot of work showing the time-dependent changes in empirically-calibrated associations between proxies and climate data. However, the effect we describe is ostensibly a 'new' and likely unprecedented change. I *do not* believe it is adequately explained by the snow-lie change - but this story belongs on another forum. There is probably some justification for flagging the problem of interpretational bias in proxies as introduced by anthropogenic __?__ but Malcolm is dead right that the way the piece reads now, over dramatises and misleads the reader by implying trees are now no good. I have suggested a minor rephrasing to set the record straight - but if you require the dramatic - I suggest you remove the tree reference altogether. Cheers, Keith ******************************************************** Julie Burgess Climatic Research Unit University of East Anglia Norwich NR4 7TJ Tel. +44 (0)1603 592722 Fax. +44 (0) 1603 507784 CRU web site: http://www.cru.uea.ac.uk/