date: Wed, 7 Nov 2007 16:03:07 -0800 (PST) from: "David M. Ritson" subject: Re: RCS paleo reconstructions to: Keith Briffa 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/ >