Thursday, May 10, 2012


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:
>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


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

phone: +44 1603 592089
fax: +44 1603 507784

**Norwich -- City for Science:
**Hosting the BA Festival 2-9 September 2006


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