from: "Wahl, Eugene R" <wahleatXYZxyzred.edu>
subject: RE: confidential
to: "Keith Briffa" <k.briffaatXYZxyz.ac.uk>
Thanks to you Keith, for all the huge volume of work you have done/are doing on this -- even before it became a special target for review.
I'll be happy to look over the materials.
Dr. Eugene R. Wahl
Asst. Professor of Environmental Studies
1 Saxon Drive
Alfred, NY 14802
From: Keith Briffa [mailto:k.briffaatXYZxyz.ac.uk]
Sent: Mon 7/24/2006 2:40 PM
To: Wahl, Eugene R
Subject: RE: confidential
Will pass all comments to you before they are fixed in stone- nothing
from review article will be mentioned.
Really grateful to you - thanks
At 05:08 22/07/2006, you wrote:
>Glad to help. (!)
>If I could get a chance to look over the sections of my text you
>would post to the comments before you do, I would appreciate it. If
>this is a burden/problem let me know and we'll work it out.
>If it is anything from the Wahl-Ammann paper, of course that is fine
>to use at once since it is publicly available. There will only be
>exceedingly minor/few changes in the galleys, including a footnote
>pointing to the extended RE benchmarking analysis contained in the
>Ammann-Wahl review article.
>What I am concerned about for the time being is that nothing in the
>review article shows up anywhere. It is just going in, and
>confidentiality is important. The only exception to this are the
>points I make in my blue comments in the big review file on page
>104, concerning the MM way of benchmarking the RE statistic. Those
>comments are fine to repeat at this point. [Please excuse my
>hesitance in this way.]
>Actually, all the other blue comments I made in the big review file
>are also fine to use at once.
>Again, if this request is in any way a problem, let me know and
>we'll figure out something.
>Dr. Eugene R. Wahl
>Asst. Professor of Environmental Studies
>From: Keith Briffa [mailto:k.briffaatXYZxyz.ac.uk]
>Sent: Fri 7/21/2006 2:00 PM
>To: Wahl, Eugene R
>Subject: RE: confidential
>your comments have been really useful and reassuring that I am not
>doing MM a disservice. I will use some sections of your text in my
>comments that will be eventually archived so hope this is ok with
>you. I will keep the section in the chapter very brief - but will
>cite all the papers to avoid claims of bias. I really would like to
>discuss the whole issue of the reconstruction differences at a later
>, less stressful time. I completely accept the arguments about the
>limitation in the r2 and the value of capturing longer-term variance
>. I think I will have to stop now as the temp and humidity are killing here.
>Thanks a lot again
>At 18:39 21/07/2006, you wrote:
> >Hi Keith:
> >I'm sorry that there is a bit to digest...although I know it is just
> >a result of the nature of things.
> >By the way, copied below is a synopsis that I sent this morning to a
> >person in DC who is working on all this with regard to the House of
> >Representative hearings. Evidently, there is to be at least one
> >more hearing next week, and Mike Mann will go. The person I sent
> >this to is trying to understand the importance of the proxy PC
> >issues --especially how, no matter what way the PC extraction is
> >done, the reconstructions converge if the structures actually
> >present in the data are not tossed out by truncating the number
> >retained PCs at a too low level. What I've copied is this
> >synopsis. I think it is straightforward -- maybe a bit dense, but
> >at least brief.
> >Also, let me know if I can help on the issue of RE vs r^2. I could
> >write a few brief sentences as something for you to look at if you
> >would like. Wahl-Ammann show very clearly that there is objectively
> >demonstrated skill at the low-frequency level of the verification
> >period mean for all the MBH segments, although the earlier MBH
> >segments do have really low r^2 values (indicating very little skill
> >at the interannual level). Our argument that to throw out the
> >reconstruction completely based on the fastest varying frequency,
> >when it has objectively demonstrable meaning at lower frequencies,
> >is to me quite reasonable. That it is some how entirely ad hoc, as
> >McIntyre claims in one (more?) of his comments, is neither logical
> >nor factual in my perspective. The idea of frequency dependent
> >skill/non-skill is not new to the literature, and the independent
> >re-reviewer that Steve Schneider had look over Wahl-Ammann said s/he
> >had experienced this issue in his/her work. G.
> >****************************** COPIED TEXT ******************************
> >What it boils down to in the end is as follows:
> >1) The different reference periods used to calculate proxy PCs from
> >N. America (calibration only for MBH, full period for MM) only have
> >the effect of re-arranging how the hockey stick shape appears across
> >the rank ordering of PCs. In MBH it is concentrated in PC1. In the
> >full-period method, it is spread over PCs 1 and 2. If one adds PCs
> >1 and 2 (either arithmetically or as vectors) from either
> >convention, you get an essentially IDENTICAL time series, only the
> >amplitudes are a bit different. [Note that the input data were
> >centered AND standardized before being put into the PC calculation
> >algorithm. This is important, as shown below.]
> > WHEN ACTUALLY USED IN THE RECONSTRUCTION, THE DIFFERENCE
> > IS MINISCULE -- MBH is colder over 1400-1449 by 0.05 degrees!
> >2) IF the data are centered but NOT standardized and are input into
> >in a PCA algorithm using the variance-covariance matrix and not the
> >correlation matrix (the way MM did it), then the hockey stick shape
> >shows up in PC4. MM in fact reported this first in their 2005
> >Energy and Environment article. In effect, the first two PCs are
> >ARE ACTING TO DO THE STANDARDIZING OF THE DATA not done as a
> >pre-processing step. [When the correlation matrix is used instead
> >in the PCA algorithm, then the standardization is in effect done by
> >the algorithm, because all the correlations are "standardized" by
> >construction--they all range between 0 and 1.]
> > When 4 PCs from this calculation method are used rather
> > than 2 PCs calculated as above, then the RECONSTRUCTION CONVERGES
> > TO THE SAME AS ABOVE.
> >3) Thus, all the different "flavors" for PC extraction have
> >essentially no effect on reconstruction when one does the exercise
> >of adding PCs sequentially from 2 to 5 for any flavor. In the case
> >of (1), the reconstructions converge by the second PC. In the case
> >of (2), they converge by PC4. They don't change with higher order
> PCs added.
> > THIS SHOULD BE EXPECTED FROM FIRST PRINCIPLES. That is,
> > the same underlying information is there in all cases, it is only
> > how the structures present in these data are spread across the rank
> > order of PCs, as explained. The simple exercise of taking the
> > reconstructions to convergence across the number of PCs used shows
> > this clearly.
> >4) In fact, MM essentially say all this in the 2005 EE
> >article--INCLUDING ABOUT THE RECONSTRUCTION RESULTS -- but they
> >strongly claim that the movement of the hockey stick shape to the
> >4th PC shows it is not a leading pattern of variance as MBH claim,
> >and thus should not be used. This might be logical if their
> >analysis was an apples-apples comparison, but it is not, due to the
> >PCA method they use and applying it on NON-standardized data.
> > THESE TWO DIFFERENCES (which one can only fully get
> > from their actual code, not in the articles published) DRIVE THEIR
> > ENTIRE ARGUMENT ON THIS PARTICULAR ISSUE. What they do not say is
> > that convergence to something like the MBH result is expectable,
> > and indeed MUST happen given the data used, because the hockey
> > stick shape is actually IN the data, it is NOT an artifact of PC
> > calculation procedure.
> >5) FINALLY, note that all of this rests on the foundation that
> >keeping the bristlecone pine records in the data is appropriate,
> >which Caspar and I find can be reasonable presumption. If one
> >believes that the bristlecone data should be removed, then the
> >1400-1449 reconstruction does not pass verification testing with the
> >RE statistic, and the MBH reconstruction should commence from 1450 on out.
> >Although there are a number of reasons to keep the bristlecone data
> >in, maybe the most compelling reason they are a NON-ISSUE is that,
> >over the common period of overlap (1450-1980), the reconstruction
> >based on using them from 1400-1980 is very close to the
> >reconstruction based on omitting them from 1450-1980. Since the
> >issues about the bristlecone response to climate are primarily about
> >1850 onwards, especially 1900 onwards [KEITH -- PLEASE LET ME KNOW
> >IF I AM NOT ACCURATE IN THIS], there is no reason to expect that
> >their behavior during 1400-1449 is in any way anomalous to their
> >behavior from 1450-1850. Thus, THERE IS NO REASON TO THINK THAT THE
> >BRISTLECONES ARE SOMEHOW MAKING THE 1400-1449 SEGMENT OF THE MBH
> >RECONSTRUCTION BE INAPPROPRIATELY SKEWED.
> >****************************** END OF COPIED TEXT *******************
> >Peace, Gene
> >Dr. Eugene R. Wahl
> >Asst. Professor of Environmental Studies
> >Alfred University
> >1 Saxon Drive
> >Alfred, NY 14802
> >From: Keith Briffa [mailto:k.briffaatXYZxyz.ac.uk]
> >Sent: Fri 7/21/2006 4:51 AM
> >To: Wahl, Eugene R
> >Subject: RE: confidential
> >thanks a lot for this - I need to digest and I will come back to you.
> >thanks again
>Professor Keith Briffa,
>Climatic Research Unit
>University of East Anglia
>Norwich, NR4 7TJ, U.K.
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.