cc: Bette Otto-Bliesner , Keith Briffa ,Jonathan Overpeck date: Tue, 04 Jul 2006 10:21:33 +0100 from: Tim Osborn subject: Re: hockey stick to: Stefan Rahmstorf At 18:46 03/07/2006, you wrote: >To the hockey game experts - you might have seen my exchange with >von Storch in Science this week, and be interested in my comments to >their Response available here: http://www.pik-potsdam.de/~stefan/vscomment.html > >Cheers, Stefan Thanks for the email, Stefan. You make some interesting points and it's another useful opportunity to highlight the error in the von Storch et al. implementation of the MBH method. I think, however, that in places you are confusing (or at least not properly distinguishing) the issues of bias and of random error. They really need to be considered independently. The main thrust of your letter appears to be that the size of the bias indicated by von Storch et al. for the HadCM3 simulation is no larger than the random uncertainty error published by MBH. But this bias (if it exists at all) is present *as well as* the random uncertainty error. So, regardless of whether any bias is larger or smaller than the published random error, if the bias exists it will affect both the reconstruction central value and the reconstruction uncertainty range. Please don't take this email to mean that I agree with all of von Storch et al.'s reply, and disagree with all of your points, because I don't. I just think that the issue of whether different error components are smaller or larger than each other is a red herring... ideally we should not ignore any error components. In practise we can ignore any components that are shown to be always negligible. The calibration bias has been shown to be negligible in some situations and for some methods; we need to do more work to find those methods for which the bias can be shown to be negligible in all reasonable situations, or if this is not easily possible, then we would have to accept that bias might exist and then quantify its likely magnitude. Best wishes Tim Dr Timothy J Osborn, Academic Fellow 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 **Norwich -- City for Science: **Hosting the BA Festival 2-9 September 2006