cc: edwardcook <drdendro@ldeo.columbia.edu>, ralley@geosc.psu.edu
date: Sat, 11 Mar 2006 09:36:13 +0700
from: edwardcook <drdendro@ldeo.columbia.edu>
subject: Re: divergence problem, nrc committee
to: Keith Briffa <k.briffa@uea.ac.uk>, Jonathan Overpeck <jto@u.arizona.edu>, Richard Alley <ralley@essc.psu.edu>

   Hi Keith, Jonathan, and Richard,

   I heard about this controversy over some of Rosanne's presentation at the NRC Workshop just
   last night from Keith. It caught me by surprise I must admit. This is highly regrettable
   because it simply further obfuscates an already controversial and incompletely described
   topic: How do we reconstruct large-scale temperatures over the past 1000 years from
   (mostly) tree rings and what are the limitations?

   As you probably know, I was originally invited to give a talk on The Topic (a scientific
   version of the The Troubles in Northern Ireland) that Rosanne gave before the NRC panel.
   However, the NRC was not willing to fly me from Bangkok for the meeting in DC. At the time,
   I more or less said cest le vie and was even a bit relieved. In retrospect, I should have
   paid my own way there. This is not to say that Rosanne was necessarily wrong in what she
   presented. Rather, I would have emphasized things differently and put the divergence issue
   in its proper context as a far less significant part of my presentation on the The Topic,
   similar to what Keith has written here. I agree with Keith that it is honestly not the
   overriding issue with respect to The Topic, even if it is still not well understood. It is
   an interesting scientific problem for sure, but as Keith has indicated, it probably
   contributes relatively little to the NH temperature reconstructions made to
   date. But instead of enlightenment, we get obfuscation.

   The fact that the NRC panel has apparently come away with the notion that divergence places
   all of the NH temperature reconstructions in jeopardy is in my opinion just plain wrong. I
   have previously discussed the divergence issue in passing with Jeff Severinghaus, Conrad
   Hughen, and others (it was also brought up at the Mt Cook meeting, Richard), and have also
   touched on it in my QSR paper that reviewed the Esper et al. work and tried to clear up
   some of the misunderstanding and misinterpretation of that paper. (The QSR paper also
   sharpened the meaning of the Esper et al. work and corrected some sloppy wording on my part
   in the original paper.) There are many more far more important issues that the NRC panel
   could have latched on to, but divergence is not one of them. It is more of a red herring
   than anything else.

   I recommended that Keith give a talk to the NRC panel in my place because, in my
   estimation, he is the only other person in the world who can discuss in a totally objective
   way the hockystick and other reconstructions of past temperatures at the methodological
   level that is really at the heart of all the controversy, e.g. the hockeystick. So the NRC
   panel in my opinion probably has not received the level of information that it needs to
   make a truly informed recommendation. That is my opinion and is not intended to belittle
   Rosannes contribution. I simply would have emphasized things differently and made sure that
   the NRC panel didnt get side-tracked by the divergence issue vis-a-vis The Topic.

   So this whole mess looks like it could be a grossly unfair debacle for tree rings if the
   NRC panel mistakenly goes down the divergence path as the most important issue. That it is
   surely not! I honestly think the NRC should have commissioned a white paper by Keith and me
   (perhaps one or two others) on The Topic that would be sent out for extensive review to all
   NRC participants and others who are experts (and skeptics) in the field. The paper would be
   published in a form similar to invited papers in certain journals that include at the back
   of the  paper a series of detailed comments and rejoinders. This way, critics can't hide
   behind blogs, obscure journals, and complaints that they can't get their work published
   because of the biased peer review system. They would have to express their opinions and
   criticisms in an open form that is directly associated with the paper and published that
   way for all to see with our rejoinders. Unfortunately, this would be a very big job that
   would take a couple years to complete and publish. However, I dont know how else to deal
   with the information, misinformation, misunderstanding, and biased accusations that infuse
   the The Topic with such controversy. At the end of the day, some opinions will never
   change, but I do believe that a completely open evaluation is needed. The NRC has made a
   noble effort in this regard, but it appears to be inadequate and incomplete in my opinion.
   Since I was not there, I may be wrong on that account, but it doesn't sound that way to me.

   Cheers,

   Ed

    On Mar 11, 2006, at 1:06 AM, Keith Briffa wrote:

   Peck

   as promised, my brief response to Richard and yourself . I would appreciate it if you would
   forward to those you think relevant

   thanks

   -------------------------------------------------------------------------------------------
   -------------------------------------------------------------------------------------------
   Dear Richard, Peck and others

   First let me make it clear that as I did not attend the Committee meeting I am not able to
   comment specifically on the details of Rosanne DArrigos presentation, though I am aware of
   her papers with various co-authors related to an apparent divergence in the recent (circa
   post 1970 ) trends in tree-growth and temperature changes as recorded in instrumental data,
   at near tree-line sites in the Canadian Arctic. There are also other papers dealing with
   changing growth responses to climate in North American trees.

   I have co-authored a paper in Nature on the reduced response to warming as seen in
   tree-ring densitometric data at high-latitude sites around the Northern Hemisphere,
   increasingly apparent in the last 30 years or so.

   This subject is not directly addressed in the current SOD Chapter 6, though some generic
   reference of the possibility of recent environmental changes affecting proxies is made ,as
   Peck said in his earlier response.

   First, it is important to note that the phenomena is complicated because it is not clearly
   identifiable as a ubiquitous problem. Rather it is a mix of possible regionally distinct
   indications, a possible mix of phenomena that is almost certainly in part due to the
   methodological aspects of the way tree-ring series are produced. This applies to my own
   work, but also very likely to other work. The reason we did not discuss it in detail in our
   Chapter is that the evidence is at present, in part contradictory, and not well defined.
   Giving it too much space would be tantamount to building a straw man at this stage; one
   that would then necessitate complicated details and space to knock down.

   The implications at this stage for the hockey stick and other reconstructions, contrary to
   Richards conclusions, are not great. That is because virtually all long tree-ring
   reconstructions that contribute to the various reconstructions, are NOT affected by this.
   Most show good coherence with temperature at local levels in recent decades. This is not
   true for one series (based on the density data). As theses are our data, I am able to say
   that initial unpublished work will show that the problem can be mitigated with the use of
   new, and again unpublished, chronology construction methods.

   In the case of the work by Rosanne and colleagues, I offer my educated opinion that the
   phenomenon they describe is likely also, at least in part, a chronology construction issue.
   I am not saying that this is a full explanation, and certainly there is the possibility of
   increased moisture stress on these trees, but at present the issue is still being defined
   and explored. As the issue needs more work, this is only an opinion, and until there is
   peer-reviewed and published evidence as to the degree of methodological uncertainty , it is
   not appropriate to criticize this or other work . For my part, I have been very busy,
   lately with teaching and IPCC commitments, but we will do some work on this now, though
   again lack of funds to support a research assistant do not help.

   The matter is important but I do not believe that the facts yet support Rosannes
   contention, in her Global Biogeochemical Cycles paper (Vol. 18, GB3021,
   doi:10.1029/2004GB002249, 2004) that an optimum physiological threshold has been
   consistently exceeded at a site in the Yukon. This conclusion should certainly not be taken
   as indicating a widespread threshold exceedence.

   It was my call not to overplay the importance of the divergence issue, knowing the subtlety
   of the issues. We did always intend to have a brief section about the assumption of
   uniformitarianism in proxy interpretation , including mention of the possible direct carbon
   dioxide fertilization effect on tree growth (equally controversial), but it will conclude
   that here as well , there is no strong evidence of any major real-world effect. This and
   the divergence problem are not well defined, sufficiently studied,  or quantified to be
   worthy of too much concern at this point. The uncertainty estimates we calibrate when
   interpreting many tree-ring series will likely incorporate the possibility of some bias in
   our estimates of past warmth, but these are wide anyway. This does not mean that
   temperatures were necessarily at the upper extreme of the reconstruction uncertainty range,
   any more than they may have been at the bottom. The real problem is a lack of widespread
   (and non-terrestrial) proxies for defining the level of early warmth, and the vital need to
   up-date and study the responses of proxies in very recent times as is stated in our
   Chapter.

   We will mention the issues to which Richard refers in a future draft, but it is my opinion
   that this will not weaken our conclusions.

   best wishes

   Keith

   At 15:50 08/03/2006, Jonathan Overpeck wrote:

   Hi Richard - thanks for checking in. I got an email from Keith Briffa that indicates the
   situation isn't as bad as Rosanne might make it sound. Rather than dropping bombs (your
   language) I suggest we figure it out a bit more first. So, I'm going to cc this email to
   Keith and Eystein, and then forward Keith's email to you. Then, I'm hoping that Keith can
   help you and me figure this out before we potentially over react. As you say, it's clearly
   a concern that needs to be dealt with, but is it a bomb? I'm not yet convinced.

   Many thanks for your concern and willingness to check w/ me first.

   best, peck

   Peck--I almost sent this to Susan tonight, copied to you, but then thought I had better run
   it by you first, quickly.  I think that Susan has to be notified--I fear that the tree-ring
   reconstructions really are in bad shape, and that the IPCC and chapter 6 have a big problem
   coming up. I'll be in the office tomorrow if you want to call--814-863-1700--but I want to
   notify Susan soon.--Richard

   Greetings.  I was down and talked to the NRC "hockey stick" committee

   last week.  (Preparation for that is one of my excuses for slow performance during

   IPCC crunch time.  Also, please excuse my slang, but I will call the Mann reconstruction,
   and similar curves, the "hockey stick".) Based solely on what I heard there, I think it

   likely that the committee will end up casting grave doubts on the hockey stick, and on all
   of the reconstructions since.  In turn, this may raise issues for Chapter 6.

   Several points may arise, but Rosanne D'Arrigo's presentation and her very recent paper
   (co-authored by Rob Wilson and Gordon Jacoby, and attached, in case you're interested) are
   prominent.  She has led a wonderful piece of work, updating many of the tree-ring data
   series at least into the late 1990s, and using both traditional and improved paths for data
   reduction.

   In the abstract, they state

   "Although we conclude, as found elsewhere, that recent warming has been substantial
   relative to natural fluctuations of the past millennium, we also note that owing to the
   spatially heterogeneous nature of the MWP, and its different timing within different
   regions, present palaeoclimatic methodologies will likely "flatten out" estimates for this
   period relative to twentieth century warming, which expresses a more homogenous global
   "fingerprint".  Therefore we stress that presently available paleoclimatic reconstructions
   are inadequate for making specific inferences, at hemispheric scales, about MWP warmth
   relative to the present anthropogenic period and that such comparisons can only still be
   made at the local/regional scale."

   More striking to me, the recent updates show that the tree rings are no longer tracking the
   instrumental record.  "An apparent decrease in temperature sensitiviy for many northern
   sites... is evident in our reconstructions, with divergence from instrumental temperatures
   after ~1986... the divergence between the tree-ring and instrumental data results in
   weakening of calibration results and failed verification statistics".

   In her remarks to the committee (which was in open session, so these are public), she
   described their sampling near the northern limit of trees.  As I heard, they fly over long
   reaches of trees that, experience shows her, would have relatively weak correlation to
   temperature, to find the special grove of stressed, gnarly trees with high temperature
   sensitivity.  If the highly-temperature-sensitive region is so restricted, it seems
   reasonable to speculate that a given site might move from being in that region to being out
   of it with warming, and one might also speculate that a similar shift could have occurred
   across a previous warm interval.

   Regardless of the origin of this "divergence problem" of the tree-ring records diverging
   from the instrumental record over the most recent, large warming, the questions from the
   committee suggested to me that the members were highly focused on the divergence.
   (Roseanne

   seemed to downplay it as something that requires further study and could have many origins
   but is

   not highly damaging to the broader picture, but I believe based on their questions that at
   least some committee members were not convinced.) Between her overall assessment and the
   divergence problem, I doubt that the NRC panel can now return any strong endorsement of the
   hockey stick, or of any other reconstruction of the last millennium.  Although the
   reconstructions have been labeled as "multi-parameter", they have primarily been tree-ring
   based.

   It of course is possible that I'm completely confused, or that something new will come out.
   (There was in progress an Arctic-centered few-decadal reconstruction that used much broader
   indicators than tree rings, but I do not know the status--Peck?)

   Sorry to be dropping bombs.  I'm only dropping it on you two, and I will shut up unless
   asked to say something further, but I thought that this is potentially sufficiently large
   to merit a quick note.

   Best--Richard

   Attachment converted: Macintosh HD:2005JD006352.pdf (PDF /IC) (0011CBB8)

   --

   Jonathan T. Overpeck

   Director, Institute for the Study of Planet Earth

   Professor, Department of Geosciences

   Professor, Department of Atmospheric Sciences

   Mail and Fedex Address:

   Institute for the Study of Planet Earth

   715 N. Park Ave. 2nd Floor

   University of Arizona

   Tucson, AZ 85721

   direct tel: +1 520 622-9065

   fax: +1 520 792-8795

   [1]http://www.geo.arizona.edu/

   [2]http://www.ispe.arizona.edu/

   --

   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/

   ==================================

   Dr. Edward R. Cook

   Doherty Senior Scholar and

   Director, Tree-Ring Laboratory

   Lamont-Doherty Earth Observatory

   Palisades, New York 10964  USA

   Email:    [4]drdendro@ldeo.columbia.edu

   Phone:    845-365-8618

   Fax:    845-365-8152

   ==================================

