Section 1.1 Response

The terms of reference are as follows:

1.1 Examine the hacked e-mail exchanges, other relevant e-mail exchanges and any other information held at CRU to determine whether there is any evidence of the manipulation or suppression of data which is at odds with acceptable scientific practice and may therefore call into question any of the research outcomes.


1. The allegation of ignoring potential problems in deducing palaeotemperatures from tree ring data that might undermine the validity of the so-called “hockey-stick” curve. In the late 20th century, the correlation between the tree ring record and instrumental record of temperature change diverges from that for the earlier period. The cause of this divergence does not appear to be understood. If the method used to deduce temperatures from tree ring proxy metrics for the earlier tree ring record is applied to the late 20th century tree ring series, then declining temperatures would be deduced for the late 20th century. It is alleged that if the cause of divergence between the tree ring and instrumental temperature record is unknown, it may have existed in earlier periods.  Therefore if tree rings had similarly failed to reflect the warming of the early Middle Ages, they may significantly under- estimate the warming during the Medieval Warm Period, thus falsely enhancing the contrast between the recent warming and that earlier period.  (It is this contrast that has led to statements that the late 20th century warming is unprecedented during at least the last 1000 years.)


1 What method do you use to deduce palaeotemperatures from tree ring data?


11 Responses to “Section 1.1 Response”

  1. Jimchip Says:

    For background,
    088520855 provides an overview of the Jan., 1998 status of some of the science by prospective Ph.D student GERNER THOMSEN who will be working with Briffa and Schweingruber. 0908633388 (17 Oct 1998) Vaganov to Briffa, provides Tree-ring Widths (TRW) chronologies (Draft manuscript: VARIABILITY OF LARCH RADIAL GROWTH IN THE EAST OF TAYMIR AND PUTORAN FOR THE LAST 2000 YEARS) with references and discussion of some the species and locations, including a keywords list. etc.

    0924030302, 13 Apr 1999 (Mann to Briffa/Osborn) discusses NH vs. SH emphasis in datasets: “what we *DONT* take into account (though I challenge anyone to really ever be able to take this into account!) is the unknown potential bias due to degradation from diminishing quality of the underlying proxy data back in time…” and “It is not “a moot point” because the problem you point out has largely been shown to apply to tree ring density data (which you have largely been using), and much less so tree ring width data (which we are using)”.

    0938712073 30 Sep 1999 (Jim Parks to mail list):
    “Ouch, my hackles are rising so high, it hurts. (Just what exactly are hackles, anyway?). Yes, computer crossdating ring series with special problems is always dangerous. But this is where good old skeleton-plot dating with intensive and thorough visual examination of the WOOD becomes the way to go…I’ve worked with, rings piching in and out can be a problem. You can lose 50-100 rings that way, sometimes. However, a different radius of the sample may possess all those absent rings. It’s nice to have a cross-section of the subject tree, though I know this isn’t always possible…Traditional skeleton-plot croosdating — along with its concomitant intensive visual analysis — made it possible to sort though these problems…I myself was recently involved dating high-elevation bristlecone pine from northern Arizona, U.S.A. The multi-millenial length of the chronology — as well as the freedom from absent rings and the presence of frost-year marker rings — made computer crossdating advisable. Of course every significant computer dating correlation was thoroughly checked out on the WOOD, and if the visual characteristics of the tree rings themselves did not support the computer dating, we threw out the date — right out the window. Discarded computer dates collected on the parking lot beneath our offices and needed to be hauled off to the dump everyday.”

  2. Jimchip Says:

    1051638938 4/29/03 Cook qutoed in Briffa to Cook. A longer chain mail:

    thanks for this – and it is intriguing , not least because of the degree of coherence in these series between 1200 and 1900 – more than can be accounted for by either replication of data between the series (of which there is still some) or artifact of the standardisation method (with the use of RCS curves which are possibly inappropriate for all the data to which each is applied) . Having then got some not insubstantial
    confidence in the likelihood of a real temperature signal in this period – the question of why the extreme divergence in the series pre-1200 and post 1900? A real geographic difference in the forcing , replication and standardisation problems? – both are likely. We would like the raw cores for each site: the RCS indices upon which you base the
    chronologies ; the site chronologies (which I think you sent to Ray?). At first we will imply plot the site chronologies , correlate each with local climate and come back to you again. We will also plot each “set” of indices and compare site RCS curves and reconsider the validity of the classification into linear and non-linear growth patterns. I know you have done all this but we need to get a feel for these data and do
    some comparisons with my early produce ring-width RCS chronologies for ceratin sites and compare the TRW series with the same site MXD chronologies – all a bit suck and see at first. I am talking with Tim later today about the review idea and I will email/phone before 16.00 my time today.

    1141068509 27 Feb 2006 Rob Wilson to Osborn A longer technical email regarding reconstructions, Datset selction and D.Arrigo’s NAS appearance

  3. jimchip Says:

    Mann and Schmidt have a Hissy Fit

    based on a Daily Kos discussion of RegEM

    One can read the comments from realclimate (presumeably Mann) regarding claims of skill and robustness. pdfs of some Mann papers are still available, for example and

    Click to access RuthetalJClimate05.pdf

    “We wil discredit your main new point: You now ask for a study that compares the MBH98 and RegEM approaches. Why don’t you take another look at the Mann et al (2005)paper provided above, and actually read it. What does figure 2 show? Ah yes, a comparison of applications of RegEM and MBH98 approach to the same precise data set, showing the two methods give very nearly the same result, well within the mutual uncertainties.” with a reply

    I’m sorry, but I really can’t see how Figure 2 could prove that RegEM is superior to MBH98 – which was the outstanding issue, wasn’t it?

    An early reply in the same thread is the one referenced and compares MBH vs. RegEM

    “Which proxy study proves that RegEM is superior to EOF based approaches? Certainly not Schneider 2001 himself: “Hence, any claim that the regularized EM algorithm or any other technique for the imputation of missing values in climate data is “optimal” in some general sense would be unjustified. The performance of the regularized EM algorithm must be assessed in practice.” – I am unaware of such an assessment.”

  4. jimchip Says:

    See also wrt to NAS/NRC related to D’Arrigo

    D’Arrigo, Wilson and Jacoby [2006] represents state-of-the-art in dendrochronology and is hot off the press. It is unique among such studies in using a considerable amount of up-to-date data and is relatively candid about its results. I’ll try to discuss it in more detail. Here I want to pick up on one issue that featured strongly in my review of Osborn and Briffa – my inability to replicate the claimed correlation of bristlecones to gridcell temperature. Remarkably DWJ06 make the same point: thus we have the remarkable situation of two dendrochronological studies published in the same week, making completely opposite claims about the correlation of bristlecones and foxtails to gridcell temperature.

  5. Jimchip Says:

    Hockey Stick Studies

    Proxy data

    Station Data

    Econometrics: Grant Farnsworth, Econometrics in R, Econometrics has been far more attentive to autocorrelation issues than paleoclimate, but the data issues have a lot in common.

    Click to access Farnsworth-EconometricsInR.pdf

  6. Jimchip Says:

    Salzer 2005
    Reconstructed Temperature and Precipitation on a Millennial Timescale from Tree-Rings in the Southern Colorado Plateau, U.S.A.

    Emails wrt Salzer
    1163771694.txt <—This last, Mc, Wilson, D' Arrigo

    From: "Rob Wilson"
    To: “Martin Juckes”
    Subject: Re: Mitrie: Bristlecones
    Date: Fri, 17 Nov 2006 08:54:54 -0000
    Cc: “Keith Briffa” , “Myles Allen” , “Jan Esper” , , , , ,


    Morning Martin,

    It might be worth taking Keith’s advice and contacting Malcolm Hughes.

    I am not convinced that the Bunn study is fully relevant to addressing the use of BP data
    from Colorado and California as their study site is Montana. Malcolm gave a presentation
    earlier this year in Edinburgh which presented updated analyses on his BP work which played
    down the CO2 influence.



    —– Original Message —–

    From: [1]Martin Juckes

    To: [2]Rob Wilson

    Cc: [3]Keith Briffa ; [4]Myles Allen ; [5]Jan Esper ; [6] ;
    [7] ; [8] ; [9] ; [10]

    Sent: Thursday, November 16, 2006 4:41 PM

    Subject: Re: Mitrie: Bristlecones

    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:
    > [11]
    > 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: [12] ; [13] ; [14] ;
    [15] ; [16] ; 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
    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
    > (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
    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
    > > rather well…
    > >
    > > —–Original Message—–
    > > From: Martin Juckes []
    > > Sent: 10 November 2006 15:24
    > > To: [17]; [18]; [19];
    > > [20]; [21]; Myles Allen; [22];
    > > [23]
    > > 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
    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
    > >
    > > 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

    > PD Dr. Jan Esper
    > Swiss Federal Research Institute WSL

  7. Jimchip Says:

    Salzer et al 2009 – A First Look

    Salzer, Hughes et al (PNAS 2009) is in the news. It reports that “unprecedented” high-altitude bristlecone growth, citing increased growth at Sheep Mountain, Mount Washington and Pearl Peak, but especially Sheep Mountain. pdf PNAS SI Salzer SI

    CA readers are obviously familiar not just with bristlecones, but with Sheep Mountain. As pointed out in the MM articles, Sheep Mountain was the most important single series in the Mann PC1. Bristlecone chronologies had been introduced by Donald Graybill and arch-skeptic Sherwood Idso as supposed evidence of CO2 fertilization at high latitudes and IPCC 2AR in 1995 included a caveat.

    The paper:
    Matthew W. Salzera,1, Malcolm K. Hughesa, Andrew G. Bunnb, and Kurt F. Kipfmuellerc
    Recent unprecedented tree-ring growth in bristlecone
    pine at the highest elevations and possible causes

  8. Jimchip Says:

    1062527448.txt Mann’s reply to

    Technical discussion of his “white noise” approach [snark]

    From: “Michael E. Mann”
    To: Tim Osborn
    Subject: Re: reconstruction uncertainties
    Date: Tue, 02 Sep 2003 14:30:48 -0400
    Cc: Scott Rutherford ,

    Hi Tim
    Thanks for sending this. Unfortunately, I don’t really have the time look into any of this
    in detail, but let me offer the following additional explanation which will hopefully
    clarify the nature of any differences between our results. I fear that I may not have been
    clear enough in my previous explanation.
    The reason that our uncertainty estimates reduce little fwith increasing timescale for the
    earlier networks is that the effective degrees of freedom are diminished sharply by the
    redness of the calibration residuals for networks prior to AD 1600 and earlier. But unlike
    you, wee do not model the residuals as an AR process–this may the source of some of the
    Back to AD 1600 (and later networks), the calibration residuals pass for “white noise” ,
    and the estimates follow simply from the residual uncalibrated variance, and the reduction
    of variance upon averaging follows standard sqrt(N) statistics.
    Prior to that, the networks failed the test. So we decomposed the calibration residuals
    into a “low-frequency” band (all timescales longer than 40 years which are not
    distinguishable from secular timescales, since I had a roughly 80 years series and was
    evaluating the spectrum using a multiple-taper estimate with a spectral bandwidth of +/-2
    Rayleigh frequencies). We then estimated the enhancement of unresolved variance in the
    low-frequency band relative to the nominal white noise level. The enhancement was about a
    factor of 5-6 or so for the earlier networks, as I recall. To get the component of
    uncertainty for the low-frequency band alone (timescales longer than 40 years), I simply
    took that enhancement factor x the nominal unresolved calibration variance x the bandwidth
    of the “low-frequency” band (0.025 cycle/year). This yields a reduction in variance that is
    far less than the nominal “sqrt N” reduction applied to the individual annual
    uncertainties. Of course, one could calculate the equivalent N’ (effective temporal
    degrees of freedom) that this implies in a model of the residuals as AR(1) red noise, but
    we didn’t take this approach. We modeled it as a simple step-increase spectrum (w/ the
    boundary at f=0.025 cycle/yr). Modeling the residuals as red noise would, my guess is,
    generally yield the same result, but it might have the effect of dampening the estimated
    enhancement of unresolved variance at the longest timescales. In any case, it should yield
    similar, but it would be very surprising if identical(!), results, consistent w/ your
    My guess for the difference in the AD 1600 network is that, based on the spectrum test, we
    did not reject the white noise null hypothesis for the residuals. So there was no variance
    enhancement factor for that, or subsequent, networks. It would appear that your method
    argues for significant serial correlation in that case. Not sure why we come to different
    conclusions in this case (perhaps using different criteria for testing for the significance
    of redness in the spectrum/serial correlation), but that’s probably the reason…
    I hope that clarifies this. Please keep me in the loop on this. I’ve copied to Scott, who
    may have some additional insights here, since we’ve been dealing w/ these issues now in the
    RegEM estimates (Scott:did we ever reject the white noise null hypothesis in the residuals
    for any of our proxy-based NH reconstrucitions in the paper submited to J. Climate? I don’t
    At 04:33 PM 8/29/2003 +0100, you wrote:

    Hi Mike,
    after a few bits of holiday here and there, I’ve now had time to complete my (initial)
    approach to estimating reconstruction errors on your NH temperature reconstruction.
    This is all based on the calibration residuals that you kindly sent me a few weeks ago.
    My rationale for doing this was that I wanted uncertainty/error estimates that were
    dependent on the time scale being considered (e.g. a decadal mean, an annual mean, a
    30-year mean, etc.). I didn’t think you had published timescale-dependent errors, hence
    my attempt.
    A second reason is that I wanted to be able to model (i.e., stochastically generate)
    time series of the errors, with appropriate timescale characteristics. Again, I didn’t
    think that I could get this from your published results.
    The attached document summarises the progress I’ve made. There are a few questions I
    have, and I’m concerned that the reduction in uncertainty with increasing time scale is
    too great. Perhaps one should be ultra conservative and have no reduction with time
    scale? Yet surely there ought to be some cancelling of partly uncorrelated errors? The
    document is not meant to form part of any paper on this (I hope to use the errors in a
    paper, but the point of the paper is on trend detection, not estimating errors), it just
    seemed appropriate to write it up like this to inform you of what I’ve done so far.
    Any comments or criticisms will be very useful.

  9. Jimchip Says:

    Technical comment on scanners vs. microscopes for people who actually do experiments.

  10. Jimchip Says:

    How to account for and guarantee the quality of dendrochronological results
    by Torbjörn Axelson

    (Recommendation from Rob Wilson on the dednro listserve)

  11. Lin Memmer Says: gamestop

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