date: Mon, 5 Mar 2001 13:51:29 -0800
from: Chick Keller <ckeller@igpp.ucsd.edu>
subject: Quick question
to: k.briffa@uea.ac.uk

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Keith,

	I'm reading reprints Phil Jones sent me.  One of them by you, 
"Trees Tell of past climates: but are they speaking less clearly 
today?, Phil. Trans. R. Soc. Lond. 1998, 65-73.

Two things--you argue persuasively that "standardization" problems 
severely degrade our ability to infer low freq. trends from tree 
rings (even with improvements such as RCS and even though density 
seems less affected than TRW.  But you conclude, it doesn't matter, 
we can rely on the tree rings anyway??  At least that's how the 
article comes across.  Do you base this on comparisons with other 
proxy data?

Second, to show how new I am to all this, I can't follow the 
reasoning about Possible long-term anthropogenic changes in tree 
growth.

Figure 6 compares instrumental data (1880-1990+),  with Proxy density 
and width curves in which the proxy temperatures diverge (go lower) 
from the instrumental curve after 1960.  You go on to say that this 
might be due to increased growth due to CO2 or some combinations of 
factors (similarly on p. 101, Briffa, Annual climate variability in 
Holocene, Quaternary Sci Rev, 19 (2000).

But I'm now in the dark because figure 6 seems to show that the 
effect has tree rings being narrower for a given temp after 1960 
(because the temperature from these curves isn't increasing as much 
as the instrumental record), but Fig 7 seems to show them wider???? 
then figure 8 seems to be showing them stable or getting smaller 
after 1950.  (although you don't define BAI I inferred it to be area 
increments at the base of the tree due to tree ring growth (using 
area to minimize ring width dependence on diameter).

Now if increased CO2 and other fertilizers are at work, ring width 
should increase, but I can't make Figure 6 work then. Also despite 
the increases shown in Fig 7 and 8, they seem to have no effect in 
Fig 6 prior to 1960???

Sorry to be so opaque.

Regards,

Chick




Charles. "Chick" F. Keller,
IGPP.SIO.UCSD - Attn: Chick Keller
9500 Gilman Drive
La Jolla, CA 92093-0225
(858) 822-1510  office
(858) 456-9002  home
Is the noticeable increase in surfers off Scripps Beach a possible
indication of global warming? 
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