cc: Edward Cook <drdendro@ldeo.columbia.edu>
date: Wed, 1 Oct 2008 09:48:31 -0400
from: Edward Cook <drdendro@ldeo.columbia.edu>
subject: Re: recognize this?!
to: Keith Briffa <k.briffa@uea.ac.uk>, Tim Osborn <t.osborn@uea.ac.uk>

   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
   well.

   Cheers,

   Ed
   ==================================
   Dr. Edward R. Cook
   Doherty Senior Scholar and
   Director, Tree-Ring Laboratory
   Lamont-Doherty Earth Observatory
   Palisades, New York 10964  USA
   Email: [1]drdendro@ldeo.columbia.edu
   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 7.1.0.9

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

     To: Keith Briffa <[2]k.briffa@uea.ac.uk>

     From: Tim Osborn <[3]t.osborn@uea.ac.uk>

     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]t.osborn@uea.ac.uk

     phone:    +44 1603 592089

     fax:      +44 1603 507784

     web:      [5]http://www.cru.uea.ac.uk/~timo/

     sunclock: [6]http://www.cru.uea.ac.uk/~timo/sunclock.htm

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

