Wednesday, December 21, 2011

1156988605.txt

From: Eystein Jansen <Eystein.Jansen@geo.uib.no>
To: Keith Briffa <k.briffa@uea.ac.uk>
Subject: Fwd: Chpt 6 - last 1000 yrs
Date: Wed, 30 Aug 2006 21:43:25 +0200
Cc: Jonathan Overpeck <jto@u.arizona.edu>

Hi Keith,

John should have the latest versions of the comments file and the chapter text, i.e. the
ones that went out for LA review this summer. I believe he is after some more specific
answers in the comments and not so much changes to the text, and has selected the
bristlecone issue, the divergency issue and the verification and robustness issues. If you
are unsure what comments or tetx he refers to, I think the best thing is for to ask John
for the specific comments he thinks are not adequate, or the specific lines of text which
he suggests changed. It seems he needs some reassurance rather than you writing much new in
terms of comments and text, so the best would be to talk to him and ask what he needs you
to do to the documents.

Best wishes,

Eystein

Envelope-to: Eystein.Jansen@geo.uib.no
Date: Wed, 30 Aug 2006 15:31:12 +0100
To: Eystein Jansen <Eystein.Jansen@geo.uib.no>

From: Keith Briffa <k.briffa@uea.ac.uk>
Subject: Fwd: Chpt 6 - last 1000 yrs
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Eystein
John sent these remarks - have not talked with him yet - but not sure what is now
required
Keith

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Subject: Chpt 6 - last 1000 yrs
Date: Wed, 16 Aug 2006 16:14:52 +0100
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From: "Mitchell, John FB \(Chief Scientist\)" <john.f.mitchell@metoffice.gov.uk>
To: "Keith Briffa" <k.briffa@uea.ac.uk>
Cc: "Mitchell, John FB \(Chief Scientist\)" <john.f.mitchell@metoffice.gov.uk>
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Hi Keith
I have tried to cindense what I think the main issues for the and what the response is
below. The weakest area seems to be statistical significance and by implication the
likely/ very likely statements. I can't think of any easy solution - in the TAR for
detection and attribution we used 95% limits on stats tests and them downrated them to
allow for other uncertainties.
I am interested in your comments
John
Issues
1. Reliance on Bristlecone pine -
Response - the issues are in calibration period- they agree with other indicators for
the rest of the record
2. Centring of principle components leads to "hockeysticks"-
Response - this makes only a small difference when standardised data used.
Comment - Would be useful to know which reconstructions do and donot make this
assumption- this could strengthen the response
3. The divergence issue-
Response - it is only apparent in high latitudes, and only with some trees.
Comment- Do we know what happens if we eliminate those records with a divergence
problem. The wider issue is whether or not it is reasonable to extend the
reconstructions outside the calibration range.
4. There are different ways of verifying reconstructions and assigning significance
levels( calibration period or seprate verifying period, different statistics)
Response ?
Comment- it is difficult in the text to gauge how well reconstructions are validated -
eg using the calibration period to estimate errors as opposed to an independent period
clearly makes a difference. This is important where "likely", "very likely"are used-
based on what statistics? I think this is the area where I think the current response is
weakest
5. Robustness- Burger and Cubasch show a wide range of results using different
assumptions-
Response ?
Mann makes a reasoned defence- there are other checks and tests which would rule out
many of the arbitrary assumptions explored by Cubasch and Burger, but this is not clear
in the response to M&M etc

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

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

--

______________________________________________________________
Eystein Jansen
Professor/Director
Bjerknes Centre for Climate Research and
Dep. of Earth Science, Univ. of Bergen
All�gaten 55
N-5007 Bergen
NORWAY
e-mail: eystein.jansen@geo.uib.no
Phone: +47-55-583491 - Home: +47-55-910661
Fax: +47-55-584330

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