From	Jonathan T. Overpeck	Date	Tue, 28 Feb 2006 11:21:28 -0700
To	Tim Osborn
CC	Keith Briffa, Stefan Rahmstorf, cddhr@giss.nasa.gov, Fortunat Joos, Eystein Jansen
Subject	Re: latest draft of 2000-year section text
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 Mail and Fedex Address: Institute for the Study of Planet Earth 715 N. Park Ave. 2nd Floor University of Arizona Tucson, AZ 85721 direct tel: +1 520 622-9065 fax: +1 520 792-8795 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/