date: Fri, 11 May 2001 14:10:15 +0100 (GMT Daylight Time)
from: Julie Burgess <J.Burgess@uea.ac.uk>
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/

