From: Jonathan Overpeck <jto@u.arizona.edu>
To: Tim Osborn <t.osborn@uea.ac.uk>
Subject: Re: latest draft of 2000-year section text
Date: Tue, 28 Feb 2006 11:21:28 -0700
Cc: Keith Briffa <k.briffa@uea.ac.uk>, rahmstorf@ozean-klima.de, cddhr@giss.nasa.gov, joos <joos@climate.unibe.ch>, Eystein Jansen <eystein.jansen@geo.uib.no>

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Hi Tim, Keith and Stefan - We certainly can't get into the details of 
the debate, both for space reasons, and because K & T have gotten us 
away from the more "defensive" impression our FOD gave reviewers and 
others. Although I share Stefan's concern that we almost have to 
hammer the misinformation to death, I think we'll be ok dealing with 
it succinctly, and focusing on the bigger picture - Mann et al., and 
all the controversy is history - we know much more now, and it makes 
for stronger statements. Keith and Tim have done a nice job balancing 
all this, and we have to hope that all the Mann et al controversy 
will start sounding as dated as it is. I know I make that point 
pretty clearly when I talk to the media.

BUT, I leave it to Keith and Tim to tweak the discussion to reflect 
Stafan's concern as appropriate.

thanks, Peck

>Hi Stefan,
>
>our (Keith and mine) understanding of this issue is that Burger et 
>al. (2006, Tellus, already published and therefore citable) already 
>point out the von Storch et al. (2004) mistake in implementing the 
>Mann et al. (1998) method.  But we haven't stated this (or cited the 
>Science in press comment) because Burger et al. also demonstrate 
>that when they implement the method without the detrending step 
>(i.e., following the Mann et al. approach more accurately than von 
>Storch et al. did) then the bias is still there, though of smaller 
>magnitude than von Storch et al. (2004) suggested.  Given that we 
>already say that the extent of any bias is uncertain, it does not 
>seem necessary to go into the details any further by discussing the 
>implementation by von Storch et al. of the Mann et al. method.
>
>Finally, I think (though here it is less clear from their paper and 
>I am relying on my recollection of talking to Gerd Burger) that 
>Burger et al. also show that the amount of noise von Storch et al. 
>added to create the pseudo-proxies yields a pseudo-reconstruction 
>that has much better verification skill than obtained by Mann et al. 
>(1998) for their real reconstruction.  If they increase the noise 
>added (deteriorating the "skill" of the pseudo-proxies) until they 
>get similar verification statistics as Mann et al. report, then the 
>size of the bias gets bigger.  In fact, the bias they obtain with 
>the higher noise but "correct" no-detrending method is actually very 
>similar to the bias von Storch et al. reported with lower noise but 
>incorrect detrending method!  So where does that leave us?  I don't 
>think there's room to put all this in.  Of course the magnitude of 
>the bias cannot be determined from any pseudo-proxy simulation 
>anyway, and will be different for different models.
>
>We'd be interested to know if your (or others on the cc list) 
>interpretation of Burger et al. (2006) is significantly different to 
>this.
>
>Cheers
>
>Tim
>
>At 16:42 28/02/2006, Stefan Rahmstorf wrote:
>>Hi Keith and others,
>>
>>attached is the draft Keith sent on 21 Feb of the 2000-year 
>>section, with comments and edits (grey) from me.
>>
>>I note that Von Storch et al. 2004 is cited without it being 
>>mentioned that they did not implement the Mann et al. method 
>>correctly - by detrending before calibration, the performance of 
>>the method was greatly degraded in their model. I guess you left 
>>this out because the comment to Science showing this is still in 
>>press? Will it be added once this has been published? I think it is 
>>a major point, as it was such a high-profile paper - Von Storch's 
>>contention that the "hockey stick" is "nonsense" (cited in the US 
>>Senate) is based on a mistake.
>>
>>Cheers, Stefan
>>
>>--
>>To reach me directly please use: rahmstorf@ozean-klima.de
>>(My former addresses @pik-potsdam.de are read by my assistant Brigitta.)
>>
>>Stefan Rahmstorf
>>www.ozean-klima.de
>>www.realclimate.org
>>
>>
>
>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


-- 
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences

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