cc: Tim Osborn <t.osborn@uea.ac.uk>
date: Thu Oct  2 15:58:11 2008
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Re: recognize this?!
to: Edward Cook <drdendro@ldeo.columbia.edu>

   Dear Ed
   Thanks for these comments - and while I agree with them , I do not necessarily concur on
   the "fashionable" opinion these days that IPCC has made a mistake in stressing the
   temperature issue and the rank magnitudes  of late Holocene warm periods. It is undeniable
   that hydroclimatic variability , past and future, is of enormous scientific and societal
   importance. However, the IPCC must follow the published literature and  to a large extent
   the assessment must maintain a reasonable degree of continuity. Just as it is vital to
   understand spatial variability  and mechanisms concerning temperature (and precipitation)
   changes, the extent of published knowledge has not, as yet, supported a strong emphasis on
   these topics. The focus on the MWP was perhaps to some degree a response to the
   misinformation peddled by certain climate warming sceptics, but I believe it was justified
   to devote the amount of limited space allotted to this section to the area of large-scale
   temperature reconstructions, especially considering the extent of the recent literature and
   the attacks on the TAR hockey stick. I hope we did a reasonable job in assessing the
   evidence honestly. I am in no doubt that  future IPCC reports will reflect a growing body
   of evidence for the existence of large natural variability in moisture conditions and ,
   hopefully, the dynamic mechanisms whereby temperature and moisture have varied over space
   in recent millennia. In our defence I would also say that the AR4 clearly pointed to the
   importance of the issue of natural drought occurence and cited the best relevant work
   demonstrating this -  ie your own.
   My beef with Esper is not because his conclusion is wrong - merely that his piece wrongly
   impugns the IPCC. Through a subtle combination of selective focus, blatant
   misrepresentation of the text, and a complete failure to acknowledge the circumspect
   language and explicit caveats therein, he builds a straw man and succeeds in publishing a
   trivial, unoriginal idea.
   cheers
   Keith
       At 14:48 01/10/2008, you wrote:

     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>

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

   Phone: +44-1603-593909
   Fax: +44-1603-507784
   [8]http://www.cru.uea.ac.uk/cru/people/briffa/

