Tuesday, December 20, 2011


From: Jonathan Overpeck <jto@u.arizona.edu>
To: john mitchell <jfbmitchell@yahoo.co.uk>
Subject: Re: Review comments
Date: Wed, 21 Jun 2006 16:57:03 -0600
Cc: Eystein Jansen <eystein.jansen@geo.uib.no>, Jouzel@lsce.saclay.cea.fr, Keith Briffa <k.briffa@uea.ac.uk>, t.osborn@uea.ac.uk

Hi John - thanks. I'll cc to Keith and Tim too, and we'll be sure to discuss these in
Bergen. I'll be on my normal email to the extent we have time to be check email -
experience suggests it's tough. But... we'll try to keep an eye on email.

See you soon, best, peck

Hi Eystein, Jon,

I am in Geneva at the WMO EC meeting,so I have not had a lot of time to look at the SOD
comments. I can not get to Bergen before Tuesday. I had a quick look at the comments on
the hockey stick and include below the questions I think need to be addressed which I
hope will help the discussions. I do tbelieve we need a clear answer to the skeptics .
I have also copied these comments to Jean. Please let me know that you have received
this, and what email address I can contact you at in Bergen�.

With best wishes


1. There needs to be a clear statement of why the instrumental and proxy data are
shown on the same graph. The issue of why we dont show the proxy data for the last few
decades ( they dont show continued warming) but assume that they are valid for early
warm periods needs to be explained.

2 . There are number of methodological issues which need a clear response. There are two
aspects to this. First , in relation to the TAR and MBA which seems to be the obsession
of certain reviewers. Secondly (and this I believe this is the main priority for us) in
relation to conclusions we make in the chapter We should make it clear where our
comments apply to only MBH (if that is appropriate) , and where they apply to the
overall findings of the chapter. Our response should consider all the issues for both
MBH and the overall chapter conclusions

a. The role of bristlecone pine data

Is it reliable?

Is it necessary to include this data to arrive at the conclusion that recent
warmth is unprecedented?

b. Is the PCA approach robust? Are the results statistically significant? It
seems to me that in the case of MBH the answer in each is no. It is not clear how
robust and significant the more recent approaches are.

3. The chapter notes that new data has been included, but we dont say how much or
is this is substantial or minor. The impression I have that the amount added is minor,
but I cant tell.

4. The Esper et al and Moburg et al data both show increased variance, but the
temporal patterns are quite different. We need to say why the discrepancy does not
undermine our conclusions of greater cooling in the Little Ice Age.

5. I have not had time to check the original chapter, but the comments give the
impression that the recent 50 yr warming is unprecedented over the last 500years (seems
reasonable) and elsewhere over the last 1000years (less clear)

John FB Mitchell
13 De Vitre Green Wokingham
RG40 1SE
Tel 01189 782936


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Jonathan T. Overpeck
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