Tuesday, December 20, 2011

1141250377.txt

From: Tim Osborn <t.osborn@uea.ac.uk>
To: Stefan Rahmstorf <rahmstorf@ozean-klima.de>, Fortunat Joos <joos@climate.unibe.ch>
Subject: Re: latest draft of 2000-year section text
Date: Wed, 01 Mar 2006 16:59:37 +0000
Cc: Jonathan Overpeck <jto@u.arizona.edu>,Keith Briffa <k.briffa@uea.ac.uk>, cddhr@giss.nasa.gov,Eystein Jansen <eystein.jansen@geo.uib.no>

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Hi again Stefan,

At 14:55 01/03/2006, Stefan Rahmstorf wrote:
What about saying something along the lines:

>"At present, the extent of any such bias in specific reconstructions
>is uncertain, although probably not as large as suggested by Von
>Storch et al. (2004), whose work was affected by a calibration error
>(Wahl, Ritson and Amman, 2006)."

This sounds good and Keith is currently working your suggested
wording into the paragraph in question.

>p.s. Tim: Are you convinced the more recent papers by the VS group
>use the correct calibration? In those curves that are intended to
>show the pseudoproxies perform poorly even when calibrated
>correctly, as long as you add a lot more noise, I wonder why the
>pseudoproxies perform poorly even within the calibration interval,
>where they now should be calibrated to properly reproduce the 20th C
>warming trend, and they don't?

I am not certain, of course. And yes, there is a link between the
degree to which the trend over the calibration period is captured and
the amplitude of long-term fluctuations in the reconstruction. That
many of Burger's multitude of methods do not obtain the full warming
trend, while Mann et al. do, is certainly a concern here. But it is
also true (and I have myself analysed this one year before von Storch
et al. was published - if only I'd realised the implications I could
have had another Science paper! :-)) that correct implementation of a
regression method, keeping the trend in, can still lead to a massive
underestimation of that trend. So there's still more work to be done
on this topic!

Cheers

Tim


Dr Timothy J Osborn
Climatic Research Unit
School of Environmental Sciences, University of East Anglia
Norwich NR4 7TJ, UK

e-mail: t.osborn@uea.ac.uk
phone: +44 1603 592089
fax: +44 1603 507784
web: http://www.cru.uea.ac.uk/~timo/
sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm

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