cc: "Keith Briffa" <k.briffaatXYZxyz.ac.uk>, "Myles Allen" <allenatXYZxyz.ox.ac.uk>, "Jan Esper" <esperatXYZxyz.ch>, email@example.com, Eduardo.Zorita@gkss.de, firstname.lastname@example.org, email@example.com, t.osbornatXYZxyz.ac.uk
date: Thu, 16 Nov 2006 16:41:57 +0000
from: Martin Juckes <m.n.juckesatXYZxyzac.uk>
subject: Re: Mitrie: Bristlecones
to: "Rob Wilson" <rob.wilsonatXYZxyzac.uk>
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.
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:
> 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
> ----- Original Message -----
> From: Jan Esper
> To: Keith Briffa ; Martin Juckes ; Myles Allen
> Cc: andersatXYZxyzu.su.se ; Eduardo.ZoritaatXYZxyzs.de ; hegerlatXYZxyze.edu ;
weberatXYZxyzi.nl ; t.osbornatXYZxyz.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"
> 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
> 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
> 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
> 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?
> At 15:01 15/11/2006, Martin Juckes wrote:
> Concerning Bristlecones, I had a sympathetic reply from Prof. North,
> deferred to the person who wrote the relevant paragraph in the NAS
> (Franco Biondi) who is firmly of the view that strip-bark bristlecones
> not be used. I've read a few of the articles cited to back up this
> and I am surprised by the extreme weakness of the evidence. There is
> study of 27 strip-bark pines which shows that they clearly developed
> anomalous growth around 1850. Attributing this to CO2 is odd, to say
> least. I'm writing a brief review of the literature which I'll send
> a few days time.
> On Sunday 12 November 2006 22:21, Myles Allen wrote:
> > Although it probably doesn't feel like it, it seems to me you're
> > rather well...
> > -----Original Message-----
> > From: Martin Juckes [mailto:firstname.lastname@example.org]
> > Sent: 10 November 2006 15:24
> > To: email@example.com; Eduardo.Zorita@gkss.de; firstname.lastname@example.org;
> > email@example.com; firstname.lastname@example.org; Myles Allen; email@example.com;
> > t.osbornatXYZxyz.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
> > really
> > meant "don't use bristlecones", as he is quoted by McIntyre. I
> > it
> > would be incorrect to select sites on the basis of what the data
> > the
> > sites looks like, and this makes up a substantial part of the
> > in
> > Graybill and Idso (1993).
> > Does anyone know where I can get hold of the categorisation of the
> > Mountain trees used by Graybill and Idso (ca534.rwl from the WDC for
> > paleoclimatology I think) into "strip-bark" and "full-bark"? I've
> > 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,
> > Ecological Modelling). This appears to be a source of considerable
> > confusion
> > among the climate sceptics. The shifted series fits nicely with the
> > that
> > the Medieval Warm Period was warmer than the 20th century, so there
> > widespread perception that it is being ignored to fudge the results.
> > Apart from a couple of oversights in the documentation of the data
> > McIntyre hasn't come up with much yet. I need to read up a bit more
> > the
> > different Tornetraesk/Fennoscandia series. There was an interesting
> > discussion on "cherrypicking", with contributors suggesting that
> > the
> > effect of removing each proxy series in turn was "cherrypicking" and
> > that
> > selecting series based on subjective analysis of what the series
> > like
> > would be much better!
> > I've had a comment from the editor saying that responses to
> > comments are optional, especially if the comments are not relevant
> > 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
> PD Dr. Jan Esper
> Swiss Federal Research Institute WSL
> Zuercherstrasse 111, 8903 Birmensdorf, Switzerland
> Voice: +41-44-739 2510
> Fax: +41-44-739 2515
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