Section 1.5 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.)


 5. What is the evidence that the amplitude of warming during the Medieval Warm Period (MWP) is not underestimated by tree ring evidence?

6 Responses to “Section 1.5 Response”

  1. Jimchip Says:

    0906042912 (Sept, 1998) also discuss MWP and LIA:

    “a number of us have been saying for years ( especially Ray and Malcolm) that the LIA and MWE were not that global and not that different from today’s temperatures. Mike’s paper in Nature reiterates this. Keith and I have been thinking of writing a forum piece for The Holocene addressing in somewhat provocative terms what paleoclimatologists should be doing with regard the detection issue and to some extent with respect to science in general – should be continue using terms like LIA and MWE for example… I know proxies tell us about other aspects of the climate as well, but a clear, unambiguous temperature signal is what is needed.” For example, Brian’s Jasper recon >has a sample depth of ca 28 trees in the last century, but drops off to ca. >5 in the 12th century and 1 (?) in the 11th century. The “quality” of the >recon must degrade too?? In contrast, some non-dendro reconstructions may >not verify as well as dendro vs the instrumental record, but they might not >degrade with time either since the sample density doesn’t change with time. >Thus, could it be that at some point back in time, the dendro records >degrade to the same quality (or worse) than other proxies??? > >5) Talking specifically about Jasper, it is interesting that the 20th >century is as warm or warmer than everything in the last 1000 years EXCEPT >before ca. 1110 AD. Since the sample depth before this time is 5 or less, >how much faith should we put in those warmer than modern temps??”

    0933716462 Aug 3, 1999 (Mann to Tom Pedersen) is a response to a post by Doug Hoyt based on an email from Pedersen to Ray Bradley:

    “Amongst other things Hoyt has taken the Mann reconstruction and >reconstructed it by “removing the effect on tree ring thickness that >results from CO2 fertilization” (paraphrased). You will see the figure on >his site. He concludes that there is no significant warming in the last >half of this century relative to the last millenium. Do you know this guy? >Are you familiar with his reconstruction of your reconstruction? Didn’t >Keith Briffa correct his tree-ring reconstructions for CO2 fertilization? >[Keith: any comments?]. Steve and I would be most interested to hear your >collective comments…”

    0938018124 22 Sep 1999 (see also related in 1.2) 9/22/1999 Jones to Mann, Briffa, Folland, Tom Karl is also quoted:

    “We both mentioned the lack of evidence >>> for global scale change related to the MWE and LIA, but all the later >>> Japanese speakers kept saying the same old things. >>> >>> As for the TAR Chap 2 it seems somewhat arbitrary divison to exclude >>> the >>> tree-ring only reconstructions. Keith’s reconstruction is of a different >>> character to other tree-ring work as it is as ‘hemispheric in scale’ as >>> possible so is unlike any other tree-ring related work that is reported >>> upon. >>> If we go as is suggested then there would be two diagrams – one simpler >>> one with just Mann et al and Jones et al and in another section Briffa et >>> al. This might make it somewhat awkward for the reader trying to put them >>> into context.

    1018539404 12 April 2002 Cook to Mann and Hughes: see also 3.2 A very long chain mail and a reading of the whole text will give a summary as of 12 April 2002.

    “First of all, ECS acknowledged up front the declining available data prior to 1200 and its possible effect on interpreting an MWP in the mean record. ECS also showed bootstrap confidence intervals for the mean of the RCS chronologies and showed where the chronologies drop out. Even allowing for the reduction in the number of represented sites before 1400 (ECS Fig. 2d), and the reduction in overall sample size (ECS Fig. 2b), there is still some evidence for significantly above average growth during two intervals that can be plausibly assigned to the MWP. Of course we would like to have had all 14 series cover the past 1000-1200 years. This doesn’t mean that we can’t usefully examine the data in the more weakly replicated intervals. In any case, the replication in the MWP of the ECS chronology is at least as good as in other published tree-ring estimates of large-scale temperatures (e.g., NH extra-tropical) covering the past 1000+ years. It also includes more long tree-ring records from the NH temperate latitudes than ever before. So to state that “this is a perilous basis for an estimate of temperature on such a large geographic scale” is disingenuous, especially when it is unclear how many millennia-long series are contributing the majority of the temperature information in the Mann/Bradley/Hughes (MBH) reconstruction prior to AD 1400. Let’s be balanced here.”

    1018647333 12 Apr 2002 (Hughes quoted):

    “Dear Ed and Mike and others, All of our attempts, so far, to estimate hemisphere-scale temperatures for the period around 1000 years ago are based on far fewer data than any of us would like. None of the datasets used so far has anything like the geographical distribution that experience with recent centuries indicates we need, and no-one has yet found a convincing way of validating the lower-frequency components of them against independent data. As Ed wrote, in the tree-ring records that form the backbone of most of the published estimates, the problem of poor replication near the beginnings of records is particularly acute, and ubiquitous. I would suggest that this problem probably cuts in closer to 1600 than 1400 in the several published series. Therefore, I accept that everything we are doing is preliminary, and should be treated with considerable caution.

    Therefore, I would guess that you would apply the word “perilous” to everyones’ large-scale NH reconstructions covering the past 500-1000 years including those that you have been involved in. Why the sudden increase in caution now? It sounds very self-serving to me for you to call ECS “perilous” and not describe every other large-scale reconstruction in that way as well…there is a discussion of the problems arising from applying RCS when pith age is not known, “In the ring-width data, the final standardization curve probably slightly underestimates the width of young trees and could therefore impart a small positive bias to the standardized ring-width indices for young rings in a number of series. However, this effect will be insignificant when the biased indices are realigned according to calendar growth years and averaged with many other series.” The problem here is that this latter condition is not met (in my view), and the “small positive bias” that may be retained could turn out to be important to the most controversial conclusion of ECS (the Medieval question)…Are the MBH estimates of MWP warmth also similarly biased?… Even so, ECS gives prominence (second sentence of the abstract, for example) to the reconstruction in that very period, and makes a comparison with the magnitude of 20th-century warming. All the methods, and their realizations so far, have significant problems. In our letter Mike and I) we draw attention to a specific problem with this implementation of RCS that has a special bearing on the reconstruction of a period to which ECS have drawn attention. Hence the strong note of caution about the ECS conclusion on the comparison between the 10th/11th and late 20th centuries…There is obviously a lot more we can debate about here. I will simply stop here by saying that I stand by the results shown in ECS and will say so in my reply to your letter, pointing out that the use of the word “perilous” could be just as easily be applied to MBH.”

    1090610951 Jul 23, 2004 (Jones to Larson regardinging Legates’ critique):

    “Phil Jones has made a valid point in that some of the articles cited in my critique do not ‘directly’ address problems with Mann and Jones (MJ) but rather, address problems with earlier works by Mann, Bradley, and Hughes (MBH) and other colleagues. Fair enough – I have changed the critique to reflect that fact. The revised version has been posted since July 19 at: [1] However, I still contend that most of my original arguments – namely, the problems with the shaft, blade, and sheath – apply equally to Mann and Jones as well as the other Mann et al. manifestations of the ‘hockey stick’. MJ incorporate data from a number of the same sources as those used by MBH; for example, Mann’s unpublished PC1 from the western North American tree-ring data, Cook’s Tasmanian tree rings, Thompson’s Quelccaya and Dunde ice core oxygen isotope records (the latter embedded in Yang’s Chinese composite), and Fisher’s stacked Greenland ice core oxygen isotope record. Calibration and verification of MJ includes the flawed MBH curve. Thus, any errors in MBH effectively undermine the calibration-verification results of MJ, leaving this study unsupported and any problems with the underlying common proxies identified in critiques of MBH will also result in identical problems in MJ. My criticism regarding the blade is that 0.6 deg C warming for the last century is noted by the IPCC whereas MJ (and other M et al representations) have up to 0.95 deg C warming in their observed record. See MJ’s figure 2 where for the global and NH reconstruction, their estimates for 2000 exceed +0.4 and +0.5 (nearly +0.6), respectively. MJ’s NH curve is included in the attached graph. Thus, I stand by my criticism of MJ on this point, which is more egregious in MJ than other M et al representations.”

    1104893567 4 Jan 2005 (Overpeck to Briffa): see also 1.3, 3.3

    “pp. 8-18: The biggest problem with what appears here is in the handling of the greater variability found in some reconstructions, and the whole discussion of the ‘hockey stick’. The tone is defensive, and worse, it both minimizes and avoids the problems. We should clearly say (e.g., page 12 middle paragraph) that there are substantial uncertainties that remain concerning the degree of variability – warming prior to 12K BP, and cooling during the LIA, due primarily to the use of paleo-indicators of uncertain applicability, and the lack of global (especially tropical) data. Attempting to avoid such statements will just cause more problems.

    1132094873 Nov 15, 2005 (Briffa to Mann, McIntyre quoted regarding poster at CCSP):

    More on Hockey Sticks: The Case of Jones et al. [1998]
    Stephen McIntyre,
    Multiproxy studies purporting to show 20th century uniqueness have been applied by policymakers, but they have received remarkably little independent critical analysis. Jones et al. [1998] is a prominent multi-proxy study used by IPCC [2001] and others to affirm the hockey stick shaped temperature reconstruction of Mann et al. [1998]. However, the reconstruction of Jones et al. [1998] is based on only 3-4 proxies in the controversial Medieval Warm Period, including non-arms-length studies by Briffa et al. [1992] and Briffa et al [1995]. We show that the Polar Urals data set in Briffa et al [1992] fails to meet a variety of quality control standards, both in replication and crossdating. The conclusion of Briffa et al. [1995] that 1032 was the “coldest year” of the millennium proves to be based on inadequate replication of only 3 tree ring cores, of which at least 2 are almost certainly incorrectly crossdated. We show that an ad hoc adjustment to the Tornetrask data set in Briffa et al [1992] cannot be justified. The individual and combined impact of defects in the Polar Urals data set and Tornetrask adjustments on the reconstruction of Jones et al [1998] is substantial and can be seen
    to have the effect of modifying what would otherwise indicate pronounced Medieval Warm Period in the proxy reconstruction. Inhomogeneity problems in the Polar Urals and Tornetrask data sets, pertaining to altitude, minimum girth bias and pith centering bias will also be discussed”

  2. jimchip Says:

    The most remarkable impression is surely the tremendous lack of consistency of proxies in any given year. You see this used to argue that the MWP was regional or occurred in different places at different times, but surely it is just as remarkable to see the lack of consistency in 20th century proxies, especially since they have already undergone a cherrypicking process even to be in the table. There are very few years in which the average of the proxies can be said to be inconsistent with a mean of 0. The blue lines show a 95% confidence interval. There are 990 years here -so there are actually fewer cyan values outside the confidence intervals than one would expect from random numbers with a mean of 0 – this is without even bringing autocorrelation into the equation.

  3. jimchip Says:

    See also wrt to data:
    From: Hans von Storch
    To: Keith Briffa

    If you actually look at the medieval proxy index of the “other” studies (Briffa 2000, Crowley and Lowery 2000, Esper et al 2002, Moberg et al 2005), the medieval proxy index is usually just a razor’s edge less than modern proxy index – just enough that the study can proclaim with relief that the modern values exceed all values in the past millennium. However, there’s a lot of data handling that is a lot like accounting and there are decisions that are like accounting decisions. If the profit is very slim, wise investors know that there were might have been some decisions where choices were made to get the accounts into the black, which might equally have gone the other way

  4. jimchip Says:


    >Mike , I agree very much with the above sentiment. My concern was motivated
    >by the possibility of expressing an impression of more concensus than might
    >actually exist . I suppose the earlier talk implying that we should not
    >’muddy the waters’ by including contradictory evidence worried me . IPCC is
    >supposed to represent concensus but also areas of uncertainty in the
    >evidence. Of course where there are good reasons for the differences in
    >series ( such as different seasonal responses or geographic bias) it is
    >equally important not to overstress the discrepancies or suggest
    >contradiction where it does not exist.

    >>So, if we show Keith’s series in this plot, we have to comment that
    >>”something else” is responsible for the discrepancies in this case. Perhaps
    >>Keith can
    >>help us out a bit by explaining the processing that went into the series
    >>and the potential factors that might lead to it being “warmer” than the
    >>et al and Mann et al series?? We would need to put in a few words in this
    >>regard. Otherwise, the skeptics have an field day casting
    >>doubt on our ability to understand the factors that influence these
    >>and, thus, can undermine faith in the paleoestimates.

    From: “Michael E. Mann”
    To: Keith Briffa , “Folland, Chris” , ‘Phil Jones’

    Subject: RE: IPCC revisions
    Date: Thu, 23 Sep 1999 13:47:22 -0400

  5. jimchip Says:

    0952106664.txt Also applies to 3.2

    1. I’ve shown that the borehole data in Europe agree well with the long
    instrumental data in both the UK and Europe. The biggest differences/problems
    seem to come with the North American borehole data, which show the 16/17/18th
    data much cooler than the European/Asian/African data in the 16/17th century.
    I’m still reminded by the potential effects of land-use changes, principally
    in the eastern US, which could be making your North American series too
    cool. I realise you’ve taken great care with the selection, but this is
    a nagging doubt and will be picked up by the few skeptics trying to divide
    us all about the course of change over the last millennium. Is it possible
    to subdivide the North American borehole data into regions where we can
    be confident of no land-use changes (possibly and thinking aloud say Canada
    and the western US and Alaska) ? The aim of this (possibly joint work) is
    to try and reconcile the low- and high-freq proxies. Tom Crowley has a
    series for the NH where he’s combined about 20 series (a few of which are
    in Mike’s and the series we’ve produced here but he has over half the series
    from less-well resolved proxies – shallow marine and lake sediments) and
    he gets something very similar to Mike and CRU.

    2. As all our (Mike, Tom and CRU) all show that the first few centuries of
    the millennium were cooler than the 20th century, we will come in for some
    flak from the skeptics saying we’re wrong because everyone knows it was
    warmer in the Medieval period. We can show why we believe we are correct
    with independent data from glacial advances and even slower responding
    proxies, however, what are the chances of putting together a group of
    a very few borhole series that are deep enough to get the last 1000 years.
    Basically trying to head off criticisms of the IPCC chapter, but good
    science in that we will be rewriting people’s perceived wisdom about
    the course of temperature change over the past millennium. It is important
    as studies of the millennium will help to show that the levels of natural
    variability from models are reasonable. Tom has run his EBM with current
    best estimates of past forcing (Be-10 as a proxy for solar output and Alan
    Robock’s ice core volcanic index) and this produces a series similar
    to all series of the last 1000 years.

    The above is just ideas of how we, as a group, could/should try and reduce
    criticisms etc over the next year or so. Nothing is sacred. Your North
    American borehole series could be correct as it is annual and most of the
    high-freq proxy series respond mainly to summer variations. Is yours really
    annual when there is a marked seasonal snow cover season ?


    From: Phil Jones

    To: Shaopeng Huang ,
    Subject: Nature paper and beyond
    Date: Fri, 03 Mar 2000 13:04:24 +0000

  6. Jimchip Says:

    1065636937.txt 1.6 also. MWP, LIA Mann to Wigley EOS, S&B so Section 5 also.

    From: “Michael E. Mann”
    To: Tom Wigley
    Subject: Re: Fwd: EOS: Soon et al reply
    Date: Wed, 08 Oct 2003 14:15:37 -0400
    Cc: Caspar Ammann ,, Keith Briffa ,,,,,, Scott Rutherford , Kevin Trenberth , Tom Wigley ,,

    Thanks Tom,
    In fact, I’m almost done with a brief (<750 word) response that addresses all of these
    issues, and I'll be looking forward to comments on this. Hope to send it out later today,
    At 12:05 PM 10/8/2003 -0600, Tom Wigley wrote:

    I agree with Kevin that any response should be brief.
    On the second page of their comment, SBL quote some of the caveat statements in their
    earlier papers. The irony is that they do not heed their own caveats. If taken
    literally, all these proxy data problems would mean that one can draw no conclusions
    about the existence or otherwise of the MWE or LIA as global phenomena. This is what we
    say (I hope — at least I have said this in the paper cited below) — but our over-bold
    skeptics say that these anomalous intervals *did* exist. You can't have it both ways —
    and basically what BS are doing is a confidence trick.
    What is still needed here is an analysis of the BS method to show that it could be used
    to prove anything they wanted.
    I am still concerned about 'our' dependence on treerings. Are our results really
    dependent on one region pre 1400 as SNL state? Is the problem of nonclimate obfuscating
    factors in the 20th century enough to screw up calibrations on moderate to long
    timescales? If not, we need to state and document this clearly. Does this problem apply
    to both widths and densities? Are the borehole data largely garbage? I recall a paper of
    Mike's on this issue that I refereed last year — and there was something in GRL (I
    think) very recently pointing out some serious potential problems.
    Finally, did we really say what SBL claim we did in their p. 1 point (2)? Surely the
    primary motive for all of this paleo work is that it DOES have a bearing on
    human-induced climate effects?
    Michael E. Mann wrote:

    Thanks Kevin,
    I agree w/ your take on this. We need to come up with a short, but powerful rebuttal.
    According to Judy Jacobs, we're only allowed 750 words, so we will need to be even more
    sparing and precise in our words that in the original Eos piece. By the way, we have 3
    weeks to submit (i.e., our response is due October 27).
    We need to focus on the key new claims, while simply dismissing, by reference to earlier
    writings, the recycled ones. The Kalnay et al paper seems to be the new darling of the
    contrarians, and you're precise wording on this will be very helpful. Phil, Tim and
    others should be able to put to rest, in one or two sentences, the myths about urban
    heat bias on the CRU record. A few words from Malcolm and Keith on the biological tree
    growth effects would help too. The comments on the various paleo figures are confusing
    and inconsistent, but from what I can tell, just plain wrong. I'll draft some words on
    I'll just continue to assimilate info and suggestions from everyone over the next week
    or so, and then try to put this in the form a rough draft rebuttal to send out.
    Thanks for your quick reply. Looking forward to hearing back from others,
    At 09:16 AM 10/6/2003 -0600, Kevin Trenberth wrote:

    Hi Mike et al
    Firstly, you should know that comments by myself and the group at NCDC (Vose et al) on
    the Kalnay and Cai Nature paper were accepted (after a rebuttal and review process), and
    then fine tuned. But it is a slow process and Kalnay and Cai have yet to finalize their
    rebuttal. I am attaching FYI the "final" version of my comment. NCDC deals with the
    problems with the records.
    My reaction to the reply is as follows:
    The first page deals with comments on proxy records and their problems. I think we
    should agree that there are issues with proxy records, they are not the same as
    instrumental records (which have their own problems), but they are all we have.
    However, some are better than others (e.g. borehole) and annual or better resolution is
    highly desirable in particular to make sure that anomalies are synchronous. The records
    are not really the issue here, it is there use (and abuse).
    There are several charges about only US or Northern Europe that can be quickly dealt
    with. However the main points are on p 2.
    We know from the observational record that global or hemispheric means are typically
    small residuals of large anomalies of opposite signs so that large warm spots occur
    simultaneously with large cold regions (witness last winter).
    This fact means that we need high temporal resolution (annual or better) AND an ability
    to compute hemispheric averages based on a network. The Soon and Baliunas approach
    fails dismally on both of these critical points.
    BS point out that Fig 2 of Mann and Jones show some temperatures as high as those in the
    20th C. (They are wrong, do they mean Fig 2 of
    M03?) You can counter that by looking at China where this is far from true.
    I would be inclined to respond with a fairly short minimalist but powerful rebuttal,
    focussing mostly on the shortcomings of BS and not defending the M03 and other records.
    It should point out (again) that their methodolgy is fundamentally flawed and their
    conclusions are demonstrably wrong. For this, the shorter the better.
    Michael E. Mann wrote:

    Dear Colleagues,
    Sorry to have to bother you all with this– I know how busy our schedules are, and this
    comes at an unfortunately busy time for many of us I would guss. But I think we *do*
    have to respond, and I'm hoping that the response can be, again, something we all sign
    our names to.
    I've asked Ellen for further guidance on the length limits of our response, and the due
    date for our response. The criticisms are remarkably weak, and easy to reply to in my
    view. S&B have thus unwittingly, in my view, provided us with a further opportunity to
    expose the most egregious of the myths perpetuated by the contrarians (S&B have managed
    to cram them all in there) in the format of a response to their comment.
    THeir comment includes a statement about how the article is all based on Mann et al
    [1999] which is pretty silly given what is stated in the article, and what is shown in
    Figure 1. It would be appropriate to begin our response by pointing out this obvious
    straw man.
    Then there is some nonsense about the satellite record and urban heat islands that Phil,
    Kevin, and Tom W might in particular want to speak to. And Malcolm and Keith might like
    to speak to the comments on the supposed problems due to non-biological tree growth
    effects (which even if they were correctly described, which they aren't, have little
    relevance to several of the reconstructions shown, and all of the model simulation
    results shown). There is one paragraph about Mann and Jones [2003] which is right from
    the Idsos' "Co2 science" website, and Phil and I and Tim Osborn and others have already
    spoken too. I will draft a short comment on that.
    I'd like to solicit individual comments, sentences or paragraphs, etc. from each of you
    on the various points raised, and begin to assimilate this into a "response". I'll let
    you know as soon as I learn from Ellen how much space we have to work with.
    Sorry for the annoyance. I look forward to any contributions you can each provide
    towards a collective response.

    Date: Sun, 05 Oct 2003 08:23:03 -0400
    To: Caspar Ammann ,
    , Keith Briffa
    , Tom Crowley, “Malcolm Hughes”
    , Tim Osborn
    , Jonathan Overpeck
    , Scott Rutherford
    , Kevin Trenberth
    , Tom Wigley

    From: “Michael E. Mann”
    Subject: Fwd: EOS: Soon et al reply

    Date: Sat, 04 Oct 2003 12:33:04 -0400
    From: Ellen Mosley-Thompson
    Subject: EOS: Soon et al reply

    To: “Michael E. Mann”
    Cc: ,

    X-Mailer: QUALCOMM Windows Eudora Version
    Dear Dr. Mann (and co-authors of the Forum piece that appeared in EOS),
    Dr. Willie Soon and his co-authors have submitted a reply to your Forum piece that I
    have accepted. Let me outline below the official AGU procedure for replies so that you
    know the options available. I have sent these same instructions to Dr. Soon.
    As you wrote the original piece you now have the opportunity to see their comment
    (attached) on your Forum piece. You may decide whether or not to send a reply. If you
    choose not to reply – their reply will be published alone.
    Should you decide to reply then your response will be published along with their comment
    on your paper. One little twist is that if you submit a reply, they are allowed to see
    the reply, but they can’t comment on it. They have two options: they can let both
    their and your comments go forward and be published together or (after viewing your
    reply) they also have the option of withdrawing their comment. In the latter case, then
    neither their comment or your reply to the comment will be published. Yes this is a
    little contorted, but these are the instructions that I received from Judy Jacobs at
    I have attached the pdf of their comment. Please let me know within the next week
    whether you and your colleagues plan to prepare a reply. If so, then you would have
    several weeks to do this.
    I have copied Lee Zirkel and Judy Jacobs of AGU as this paper is out of the ordinary and
    I want to be sure that I am handling all this correctly.
    I look forward to hearing from you regarding your decision on a reply.
    Best regards,
    Ellen Mosley-Thompson
    EOS, Editor
    cc: Judy Jacobs and Lee Zirkel

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