Monday, June 11, 2012


cc: Edward Cook <>
date: Wed, 1 Oct 2008 09:48:31 -0400
from: Edward Cook <>
subject: Re: recognize this?!
to: Keith Briffa <>, Tim Osborn <>

Hi Keith and Tim,

I have quickly read through the Esper paper and have the following comments to make. First,
I hadn't seen it before, so it is all new to me. It is certainly true that Jan did not do a
proper job citing Briffa et al. (1992). That was a clear mistake, especially given that
Douglass (1929) was cited for crossdating. I also note that Jan did not cite Osborn et al.
(1997) on adjusting the variance in series for sample size changes. That too was an clear
oversight given that Frank et al. (2007) was cited. Hopefully, neither was done
intentionally. I tend to give people the benefit of a doubt on that unless it is a chronic
problem in their publications. The latter issue of variance adjustment is also relevant to
the discussion concerning spatial homogeneity or lack thereof. Am I correct in assuming
that some form of variance adjustment was made to the series used in the AR4 report? I
haven't read the report closely enough to recall if that was done. If it was done, that
would tend to force the data towards an appearance of greater homogeneity, I would guess,
hence the relative stability of the bootstrap intervals, etc.. In any case, I do tend to
agree with Jan that nothing very definitive can be said about the spatial homogeneity of
the putative MWP until we get more records to look at that truly express temperature and
not something else.

The whole issue of whether or not the MWP was more spatially heterogeneous or not is a huge
"red herring" in my opinion anyway. A growing body of evidence clearly shows that
hydroclimatic variability during the putative MWP (more appropriately and inclusively
called the "Medieval Climate Anomaly" or MCA period) was more regionally extreme (mainly in
terms of the frequency and duration of megadroughts) than anything we have seen in the 20th
century, except perhaps for the Sahel. So in certain ways the MCA period may have been more
climatically extreme than in modern times. The problem is that we have been too fixated on
temperature, especially hemispheric and global average temperature, and IPCC is enormously
guilty of that. So the fact that evidence for "warming" in tree-ring records during the
putative MWP is not as strong and spatially homogeneous as one would like might simply be
due to the fact that it was bloody dry too in certain regions, with more spatial
variability imposed on growth due to regional drought variability even if it were truly as
warm as today. The Calvin cycle and evapotranspiration demand surely prevail here:
warm-dry means less tree growth and a reduced expression of what the true warmth was during
the MWP.

That is my take on the Esper and Frank paper, with obvious editorial comments included as


Dr. Edward R. Cook
Doherty Senior Scholar and
Director, Tree-Ring Laboratory
Lamont-Doherty Earth Observatory
Palisades, New York 10964 USA
Email: [1]
Phone: 845-365-8618
Fax: 845-365-8152
On Sep 29, 2008, at 11:06 AM, Keith Briffa wrote:

X-Mailer: QUALCOMM Windows Eudora Version

Date: Mon, 29 Sep 2008 09:50:59 +0100

To: Keith Briffa <[2]>

From: Tim Osborn <[3]>

Subject: recognize this?!

Dr Timothy J Osborn, Academic Fellow

Climatic Research Unit

School of Environmental Sciences

University of East Anglia

Norwich NR4 7TJ, UK

e-mail: [4]

phone: +44 1603 592089

fax: +44 1603 507784

web: [5]

sunclock: [6]

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.
Phone: +44-1603-593909
Fax: +44-1603-507784
[7] <esper frank IPCC on MWP hetero 2008.pdf>

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