From: Keith Briffa <k.briffa@uea.ac.uk>
To: Martin Juckes <m.n.juckes@rl.ac.uk>
Subject: Re: Mitrie: Bristlecones
Date: Thu Nov 16 17:21:25 2006

   Martin
   This last point is likely true  (though CO2 began to rise earlier than the 1960s and the
   authors of the original paper believed that the  high elevation (and concomitant low CO2
   partial pressure) may have amplified the response to small concentration changes. There is
   also the possibility that a synergistic increase in water-use (and possibly nitrogen use)
   efficiency could have contributed .
   However,  I agree that the rapid growth increase is most likely a result of a change in the
   proportion of net photosynthetic production potential (ie needle mass) relative to the area
   of living cambium that could occur as a tree shifts from "normal" to strip bark form .If
   this changes suddenly , as growth occurs only along a small strip rather than around the
   whole circumference (I know this is oversimplified) then you could easily get this apparent
   change in growth rate . BUT , if this is seen synchronously in many trees it would be hard
   to believe that this was the cause. To look at this would require a detail examination of
   all the data (in relation to the precise sample geometry) . Changing precipitation trends ,
   such as occurred pre- and post the mid 1970s will also  confuse things .
   Thanks Jan and Rob also for this discussion.
   At 17:14 16/11/2006, Keith Briffa wrote:

     To: Martin Juckes <m.n.juckes@rl.ac.uk>
     From: Keith Briffa <k.briffa@uea.ac.uk>
     Subject: Re: Mitrie: Bristlecones
     In-Reply-To: <200611161642.00377.m.n.juckes@rl.ac.uk>
     References: <21885F5ACD984446A17A573C47C6D846250054@exchng2.physics.ox.ac.uk>
     <p06210202c1821017d50b@[10.15.4.248]> <003701c7098e$b8b4c850$9d07d781@geos.ed.ac.uk>
     <200611161642.00377.m.n.juckes@rl.ac.uk>
     This last point is likely true  (though CO2 began to rise earlier than the 1960s and the
     authors of the original paper believed that the  high elevation (and concomitant low CO2
     partial pressure) may have amplified the response to small concentration changes. There
     is also the - and I agree that the rapid growth increase is most likely a result of the
     proportion of net photosynthetic production potential (ie needle mass) relative to the
     area of living cambium .If this changes suddenly , as growth occurs only along a small
     strip rather than around the whole circumference (I know this is oversimplified) then
     you could easily get this apparent change in growth rate . To look at this would require
     a detail examination of all the data (in relation to the precise sample geometry) .
     However, changing precipitation trends pre- and post the mid 1970s will also  confuse
     things .At 16:41 16/11/2006, you wrote:

     Thanks for all those comments.
     I'm trying to avoid omitting data on the basis of cicrumstantial evidence,
     even when it is presented enthusiastically. The Bunn et al. study is
     interesting (attached) because they show estimated dates of the onset of
     strip-bark growth. It looks to me as though the growth anomaly of the
     strip-bark trees relative to the others is more to do with this change than
     anything else. The onset of a positive growth anomaly in the 1850s is
     certainly too early to be associated with CO2 increases.
     cheers,
     Martin
     On Thursday 16 November 2006 14:51, Rob Wilson wrote:
     > Re: Mitrie: BristleconesDear All,
     > For the D'Arrigo et al. 2006 paper, I did indeed consider using the
     Bristlecone pine data.
     > However, due to the issues raised by Macintyre and others, we felt that it
     would be unwise to use these data, especially as our data-set was biased more
     to higher latitudes.
     >
     > However, I did look at the data. I do not like ignoring potential data-sets.
     >
     > Of the BP data that I managed to get my hands on, I identified a
     significant, but relatively weak, correlation with local gridded mean summer
     temperatures for three sites. These three sites are: Hermit Hill (N = 38;
     1048-1983) and Windy Ridge (N = 29; 1050-1985) from Colorado and Sheep
     Mountain (N = 71; 0 - 1990) from California.
     >
     > The attached figure compares the RCS chronology using these data (very
     similar to the STD version in actual fact) with the North American RCS
     composite series used in D'Arrigo et al. (2006). Both series have been
     normalised to the 1200-1750 period to highlight any potential differences in
     the 20th century.
     >
     > There is generally fairly good coherence between the two series between 1100
     and the 1900. I personally do not think we have enough sites prior to 1400,
     so the lack of coherence prior to 1100 might just reflect regional
     differences and not enough series to derive a meaningful mean function.
     Although correlation with gridded temperatures are relatively low (~0.40),
     the coherence with the NA composite would seem to suggest that temperature is
     the dominant signal over the last 900 years or so.
     >
     > In the 20th century, the BP index values are clearly UNDER the NA mean. I
     would interpret this as suggesting that there does not appear to be any CO2
     influence in the BP data. This of course assumes that there is no
     fertilisation effect in the rest of the NA data.
     >
     > There is also the Salzer BP based temperature reconstruction:
     > [1]http://www.ncdc.noaa.gov/paleo/pubs/salzer2005/salzer2005.html
     >
     > again this does not correlate particular well with gridded temperatures - in
     fact it is driven more by trends, but there are some similarities with my BP
     chronology and NA series.
     >
     > I hope this helps the discussion
     > best regards
     > Rob
     >
     >   ----- Original Message -----
     >   From: Jan Esper
     >   To: Keith Briffa ; Martin Juckes ; Myles Allen
     >   Cc: anders@misu.su.se ; Eduardo.Zorita@gkss.de ; hegerl@duke.edu ;
     weber@knmi.nl ; t.osborn@uea.ac.uk ; Wilson Rob
     >   Sent: Thursday, November 16, 2006 1:36 PM
     >   Subject: Re: Mitrie: Bristlecones
     >
     >
     >   ...no, no, not a lot to add from my side. This is much more than I could
     have said. Except, I once looked at strip bark growth trees in Central Asia,
     and at least there the cause for this growth form was clear to me (Esper
     2000, The Holocene):
     >
     >
     >   "Strip-bark growth forms (Ferguson, 1968; Fritts, 1969; Graybill and Idso,
     1993; Kelly et al., 1992; Wright and Mooney, 1965) also appear in older
     Juniper trees. This condition develops as the cambium is damaged locally and
     will no longer be overgrown. Mechanical damage by rockfall seems to be the
     principle stimulus for cambial dieback and unilateral growth. In extreme
     cases only a narrow strip on the stem is still active, creating these
     eccentric growth forms."
     >
     >
     >   I didn't visit the Bristlecone sites yet, but the mechanism might be the
     same (some physical damage).
     >
     >
     >   I believe that over time the crown and root system are reduced, but not at
     the same rate than the reduction in circumference covered by the cambium.
     This would be the key for strip bark tree rings being wider than "normal"
     rings.
     >
     >
     >   I am not very convinced that there are long-term fertilization effects by
     CO2 (but have of course no proof for this). As far as I know, (most) results
     from free air CO2 enrichment experiments suggest that there is no long-term
     effect.
     >
     >
     >   I Cc Rob Wilson to the mail, as he might have looked at Bristlecone data
     recently. Pehaps he wants to add something.
     >
     >
     >   Best --je
     >
     >
     >   At 11:57 Uhr +0000 16.11.2006, Keith Briffa wrote:
     >     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 [[2]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
     >
     >     [3]http://www.cru.uea.ac.uk/cru/people/briffa/
     >
     >
     >
     >
     > --
     > PD Dr. Jan Esper
     >   Swiss Federal Research Institute WSL
     >   Zuercherstrasse 111, 8903 Birmensdorf, Switzerland
     >   Voice: +41-44-739 2510
     >   Fax:   +41-44-739 2515
     >   [4]http://www.wsl.ch/staff/jan.esper

     --
     Professor Keith Briffa,
     Climatic Research Unit
     University of East Anglia
     Norwich, NR4 7TJ, U.K.

     Phone: +44-1603-593909
     Fax: +44-1603-507784
     [5]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
   [6]http://www.cru.uea.ac.uk/cru/people/briffa/

References

   1. http://www.ncdc.noaa.gov/paleo/pubs/salzer2005/salzer2005.html
   2. mailto:m.n.juckes@rl.ac.uk
   3. http://www.cru.uea.ac.uk/cru/people/briffa/
   4. http://www.wsl.ch/staff/jan.esper
   5. http://www.cru.uea.ac.uk/cru/people/briffa/
   6. http://www.cru.uea.ac.uk/cru/people/briffa/

