date: Sat, 22 Jul 2006 00:08:05 -0400
from: "Wahl, Eugene R" <wahleatXYZxyzred.edu>
subject: RE: confidential
to: "Keith Briffa" <k.briffaatXYZxyz.ac.uk>
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:email@example.com]
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:
>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 *******************
>Dr. Eugene R. Wahl
>Asst. Professor of Environmental Studies
>1 Saxon Drive
>Alfred, NY 14802
>From: Keith Briffa [mailto:firstname.lastname@example.org]
>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.
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.