From	Keith Briffa	Date	Tue Nov 21 09:51:52 2006
To	malcolm hughes
Subject	Fwd: Re: Mitrie: Bristlecones In confidence
Malcolm sorry , I should have cc'd this message sent to my coauthors some time ago(it pre-dates the message to you) , but I was sort of hoping this issue would recede . It would be useful to chat about this and other stuff if you are able to phone (afternoon my time preferably). Cheers Keith Date: Thu, 16 Nov 2006 11:57:09 +0000 To: Martin Juckes , "Myles Allen" From: Keith Briffa Subject: Re: Mitrie: Bristlecones Cc: anders@misu.su.se, Eduardo.Zorita@gkss.de, hegerl@duke.edu, esper@wsl.ch, weber@knmi.nl, t.osborn@uea.ac.uk Martin and all, I know Franco very well - but he has not worked extensively with the Bristlecones. I still believe that it would be wise to involve Malcolm Hughes in this discussion - though I recognise the point of view that says we might like to appear (and be) independent of the original Mann, Bradley and Hughes team to avoid the appearance of collusion. In my opinion (as someone how has worked with the Bristlecone data hardly at all!) there are undoubtedly problems in their use that go beyond the strip bark problem (that I will come back to later). The main one is an ambiguity in the nature and consistency of their sensitivity to temperature variations. It was widely believed some 2-3 decades ago, that high-elevation trees were PREDOMINANTLY responding to temperature and low elevation ones to available water supply (not always related in a simple way to measured precipitation) . However, response functions ( ie sets of regression coefficients on monthly mean temperature and precipitation data derived using principal components regression applied to the tree-ring data) have always shown quite weak and temporally unstable associations between chronology and climate variations (for the high-elevations trees at least). The trouble is that these results are dominated by inter-annual (ie high-frequency) variations and apparent instability in the relationships is exacerbated by the shortness of the instrumental records that restrict analyses to short periods, and the large separation of the climate station records from the sites of the trees. Limited comparisons between tree-ring density data (which seem to display less ambiguos responses) imply that there is a reasonable decadal time scale association and so indicate a real temperature signal , on this time scale .The bottom line though is that these trees likely represent a mixed temperature and moisture-supply response that might vary on longer timescales. The discussion is further complicated by the fact that the first PC of "Western US" trees used in the Mann et al. analyses is derived from a mixture of species (not just Bristlecones ) and they are quite varied in their characteristics , time span, and effective variance spectra . Many show low interannual variance and a long-term declining trend , up until about 1850 , when the Bristlecones (and others) show the remarkable increasing trend up until the end of the record. The earlier negative trend could be (partly or more significantly) a consequence of the LACK of detrending to allow for age effects in the measurements (ie standardisation) - the very early sections of relative high growth were removed in their analysis, but no explicit standardistion of the data was made to account for remaining slow width changes resulting from tree aging. This is also related to the "strip bark" problem , as these types of trees will have unpredictable trends as a consequence of aging and depending on the precise nature of each tree's structure . Another serious issue to be considered relates to the fact that the PC1 time series in the Mann et al. analysis was adjusted to reduce the positive slope in the last 150 years (on the assumption - following an earlier paper by Lamarche et al. - that this incressing growth was evidence of carbon dioxide fertilization) , by differencing the data from another record produced by other workers in northern Alaska and Canada (which incidentally was standardised in a totally different way). This last adjustment obviously will have a large influence on the quantification of the link between these Western US trees and N.Hemisphere temperatures. At this point , it is fair to say that this adjustment was arbitrary and the link between Bristlecone pine growth and CO2 is , at the very least, arguable. Note that at least one author (Lisa Gaumlich) has stated that the recent growth of these trees could be temperature driven and not evidence of CO2 fertilisation. The point of this message is to show that that this issue is complex , and I still believe the "Western US" series and its interpretation in terms of Hemispheric mean temperature is perhaps a "Pandora's box" that we might open at our peril! What does Jan say about this - he is very acquainted with these issues? cheers Keith At 15:01 15/11/2006, Martin Juckes wrote: Hi, Concerning Bristlecones, I had a sympathetic reply from Prof. North, but he deferred to the person who wrote the relevant paragraph in the NAS report (Franco Biondi) who is firmly of the view that strip-bark bristlecones should not be used. I've read a few of the articles cited to back up this statement and I am surprised by the extreme weakness of the evidence. There is one study of 27 strip-bark pines which shows that they clearly developed anomalous growth around 1850. Attributing this to CO2 is odd, to say the least. I'm writing a brief review of the literature which I'll send round in a few days time. cheers, Martin On Sunday 12 November 2006 22:21, Myles Allen wrote: > Although it probably doesn't feel like it, it seems to me you're doing > rather well... > > -----Original Message----- > From: Martin Juckes [[1]mailto:m.n.juckes@rl.ac.uk] > Sent: 10 November 2006 15:24 > To: anders@misu.su.se; Eduardo.Zorita@gkss.de; hegerl@duke.edu; > esper@wsl.ch; k.briffa@uea.ac.uk; Myles Allen; weber@knmi.nl; > t.osborn@uea.ac.uk > Subject: Mitrie > > Hello, > > well, I've had a few exchanges on climateaudit, and decided to leave > them to > it for a few days. > > I'm going to send an email to Prof. North of the NAS panel to ask if he > really > meant "don't use bristlecones", as he is quoted by McIntyre. I believe > it > would be incorrect to select sites on the basis of what the data from > the > sites looks like, and this makes up a substantial part of the argument > in > Graybill and Idso (1993). > > Does anyone know where I can get hold of the categorisation of the Sheep > > Mountain trees used by Graybill and Idso (ca534.rwl from the WDC for > paleoclimatology I think) into "strip-bark" and "full-bark"? I've sent > an > email to the WDC query address. > > I've also sent of for a publication which is cited by co2science as > using > Sargasso Sea data with the dating shifted by 50 years (Loehle, 2004, > Ecological Modelling). This appears to be a source of considerable > confusion > among the climate sceptics. The shifted series fits nicely with the idea > that > the Medieval Warm Period was warmer than the 20th century, so there is a > > widespread perception that it is being ignored to fudge the results. > > Apart from a couple of oversights in the documentation of the data files > > McIntyre hasn't come up with much yet. I need to read up a bit more on > the > different Tornetraesk/Fennoscandia series. There was an interesting > discussion on "cherrypicking", with contributors suggesting that testing > the > effect of removing each proxy series in turn was "cherrypicking" and > that > selecting series based on subjective analysis of what the series look > like > would be much better! > > I've had a comment from the editor saying that responses to non-refereee > > comments are optional, especially if the comments are not relevant to > the > paper. > > cheers, > Martin > > > -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [2]http://www.cru.uea.ac.uk/cru/people/briffa/ -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [3]http://www.cru.uea.ac.uk/cru/people/briffa/ References 1. mailto:m.n.juckes@rl.ac.uk 2. http://www.cru.uea.ac.uk/cru/people/briffa/ 3. http://www.cru.uea.ac.uk/cru/people/briffa/