Monday, May 21, 2012

4507.txt

date: Wed, 7 Nov 2007 16:03:07 -0800 (PST)
from: "David M. Ritson" <dmratXYZxyzc.stanford.edu>
subject: Re: RCS paleo reconstructions
to: Keith Briffa <k.briffaatXYZxyz.ac.uk>

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Dear Keith,

Many thanks for your reply. No need to feel apologetic.

Whenever you have time I would really like to get your current take on RCS,
certainly not an easy problem

Cheers

Dave


On Wed, 7 Nov 2007, Keith Briffa wrote:

> Dave
> I am sorry for not getting back to you - it was merely pressure of work . I
> am finally getting a few days free in the next fortnight as several of us
> from here are visiting Ed Cook in Lamont. I will have time to get down some
> response to you and also send a ( likely still be unfinished) draft paper on
> the RCS methodology written for a book Malcolm Hughes is Editing. I am really
> sorry but both Tim and I have been heavily inconvenienced this term by having
> to take on the convenership and teaching etc on our Masters course as the
> previous organiser left unexpectedly. On my part , this has left me behind on
> a number of reviewing and other outstanding jobs. The time in the States will
> give us time to take stock. Believe me that none of us here think the RCS is
> a panacea but in certain situations it offers the prospect of recovering
> tree-growth forcing information on time scales from one to several centuries
> . It is the medium-frequency biasing effects that I believe can lead to the
> biggest problems (particularly art the recent end of chronologies) as we try
> to calibrate the data . However it is also true that in many applications
> there is a severe limitation in the basis for comparing 20th century and
> earlier ( say medieval ) growth rates. Please give me a couple of weeks when
> I would really appreciate the opportunity to discuss the problems and issues
> of explicit chronology and calibration uncertainty that arise.
> Even now , I must go off to listen to student seminars!
> best wishes
> Keith
>
> At 22:43 06/11/2007, you wrote:
>
>> Dear Keith and Tim,
>>
>> I wrote in the summer relative to the statement that underpins mmuch of the
>> discussions on the merits of RCS versus conventional standardizations of
>> paleo climate reconstructions of Cook et al 1995 that `" ,,, the
>> cross-dated annual changes in ring-width between trees due to
>> climate are forced out of alignment and effectively averaged out in the
>> creation of the mean regional curve." This is commonly taken to imply that
>> RCS methods largely circumvent the segment-length curse. At the time I
>> believed that, in most instances,
>> the systematics inherent in the actual data, such as the fractions of
>> juvenile and mature trees in the sites invalidated the cancellations
>> implied
>> in the Cook et al. paragraph. There are cancellations, but in most
>> instances insufficient to better eliminate the segment curse. This appears
>> to be well known, by the professional dendrochronologist community. What is
>> disconcerting is that I find no clarifications or follow-up of the above
>> Cook statement either in the IPCC AR4 nor in the generally available
>> climate
>> change literature. If indeed such clarifications are missing then I think
>> it
>> is incumbent that you guys ensure that they are understood throughout the
>> climate community.
>>
>> My own take on the current situation is that the only hard statements that
>> can be trusted should be based on `bounds'. Juvenile growth for the first
>> century or so, is likely to be variable and probably juvenile data should
>> be ignored.
>> Subsequent to this an `upper' bound is provided by assuming that ring
>> width
>> growth is independent of tree age. More speculatively a lower bound is
>> provided by assuming ring-area growth constancy. However nobody provides
>> such bounds.
>>
>> Tim gave me some interim answers to the above, but promised me that Keith
>> would provide a more definitive summary of RCS status after the summer. I
>> certainly would appreciate your considered views as to the absolute
>> precision and trustworthiness of past millenial temperature
>> reconstructions. Obviously the North NAS committee had similar reservations
>> .
>>
>> Cheers
>>
>> Dave Ritson
>>
>
> --
> Professor Keith Briffa,
> Climatic Research Unit
> University of East Anglia
> Norwich, NR4 7TJ, U.K.
>
> Phone: +44-1603-593909
> Fax: +44-1603-507784
>
> http://www.cru.uea.ac.uk/cru/people/briffa/
>
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