Sunday, December 11, 2011


From: Keith Briffa <>
To: Edward Cook <>
Subject: Re: Review- confidential
Date: Tue Apr 29 13:55:38 2003

Thanks Ed
Can I just say that I am not in the MBH camp - if that be characterized by an unshakable
"belief" one way or the other , regarding the absolute magnitude of the global MWP. I
certainly believe the " medieval" period was warmer than the 18th century - the equivalence
of the warmth in the post 1900 period, and the post 1980s ,compared to the circa Medieval
times is very much still an area for much better resolution. I think that the geographic /
seasonal biases and dating/response time issues still cloud the picture of when and how
warm the Medieval period was . On present evidence , even with such uncertainties I would
still come out favouring the "likely unprecedented recent warmth" opinion - but our
motivation is to further explore the degree of certainty in this belief - based on the
realistic interpretation of available data. Point re Jan well taken and I will inform him
At 07:59 AM 4/29/03 -0400, you wrote:

Hi Keith,
I will start out by sending you the chronologies that I sent Bradley, i.e. all but
Mongolia. If you can talk Gordon out of the latter, you'll be the first from outside
this lab. The chronologies are in tabbed column format and Tucson index format. The
latter have sample size included. It doesn't take a rocket scientist (or even Bradley
after I warned him about small sample size problems) to realize that some of the
chronologies are down to only 1 series in their earliest parts. Perhaps I should have
truncated them before using them, but I just took what Jan gave me and worked with the
chronologies as best I could. My suspicion is that most of the pre-1200 divergence is
due to low replication and a reduced number of available chronologies. I should also say
that the column data have had their means normalized to approximately 1.0, which is not
the case for the chronologies straight out of ARSTAN. That is because the site-level
RCS-detrended data were simply averaged to produce these chronologies, without concern
for their long-term means. Hence the "RAW" tag at the end of each line of indices.
Bradley still regards the MWP as "mysterious" and "very incoherent" (his latest
pronouncement to me) based on the available data. Of course he and other members of the
MBH camp have a fundamental dislike for the very concept of the MWP, so I tend to view
their evaluations as starting out from a somewhat biased perspective, i.e. the cup is
not only "half-empty"; it is demonstrably "broken". I come more from the "cup half-full"
camp when it comes to the MWP, maybe yes, maybe no, but it is too early to say what it
is. Being a natural skeptic, I guess you might lean more towards the MBH camp, which is
fine as long as one is honest and open about evaluating the evidence (I have my doubts
about the MBH camp). We can always politely(?) disagree given the same admittedly
equivocal evidence.
I should say that Jan should at least be made aware of this reanalysis of his data.
Admittedly, all of the Schweingruber data are in the public domain I believe, so that
should not be an issue with those data. I just don't want to get into an open critique
of the Esper data because it would just add fuel to the MBH attack squad. They tend to
work in their own somewhat agenda-filled ways. We should also work on this stuff on our
own, but I do not think that we have an agenda per se, other than trying to objectively
understand what is going on.

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
simply 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.
At 10:01 AM 4/28/03 -0400, you wrote:

Hi Keith,
Here is the new Esper plot with three different forms of regionalization: linear vs.
nonlinear (as in the original paper), north vs. south as defined in the legend, and east
vs. west (i.e. eastern hemisphere vs. western hemisphere). All of the series have been
smoothed with a 50-yr spline after first averaging the annual values. The number of
cores/chronologies are given in the legend in parentheses. Not surprisingly, the north
and south chronologies deviate most in the post-1950 period. Before 1950 and back to
about 1200 the series are remarkably similar (to me anyway). Prior to 1200 there is more
chaos, perhaps because the number of chronologies have declined along with the
within-chronology replication. However, there is still some evidence for spatially
coherent above-average growth. I showed this plot at the Duke meeting. Karl Taylor
actually told me that he thought it looked fairly convincing, i.e. that the
low-frequency structure in the Esper series was not an artefact of the RCS method.

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909
Fax: +44-1603-507784


Dr. Edward R. Cook
Doherty Senior Scholar and
Director, Tree-Ring Laboratory
Lamont-Doherty Earth Observatory
Palisades, New York 10964 USA
Phone: 845-365-8618
Fax: 845-365-8152

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909
Fax: +44-1603-507784



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