Sunday, May 6, 2012

3853.txt

cc: plattner@climate.unibe.ch, Tim Osborn <t.osbornatXYZxyz.ac.uk>, Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Anders Levermann <levermannatXYZxyz-potsdam.de>, Eva Bauer <eva.baueratXYZxyz-potsdam.de>, Eystein Jansen <eystein.jansenatXYZxyz.uib.no>, Keith Briffa <k.briffaatXYZxyz.ac.uk>, oyvind.paascheatXYZxyzrknes.uib.no
date: Wed, 15 Feb 2006 12:47:25 +0100
from: Stefan Rahmstorf <rahmstorfatXYZxyzan-klima.de>
subject: Re: Fwd: Re: Millennium Simulations
to: Fortunat Joos <joosatXYZxyzmate.unibe.ch>

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Hi all,

as you may remember from Christchurch, I've been uneasy with this
normalisation as well, for similar reasons as Kaspar and Fortunat. I did
then accept it mainly as a way to show the Von Storch correction from
Tim's paper more easily. However, now I have looked at it again and have
second thoughts. It would be wrong to have such a crucial figure of the
report compromised by one flawed model run - Von Storch et al. simply
made a serious mistake initialising their run in medieval times with
modern high CO2 values, causing a lasting downward drift of ~0.5 �C over
the millennium. That's simply not good scientific practice to have done
it this way.

One option would be to simply leave out this run, stating in the text
that we don't show it as it is affected by a major drift problem, citing
Tim's paper. By the time the report appears, this will be generally
accepted in the community, not just because of Tim's paper.

It would be good to see the alternative - I think for the other models,
it would actually look no worse than the present figure, and it would
avoid all those question about the different normalisation.

I tend to disagree with point (d) of Fortunat: for the runs with only
natural forcings, it would seem more logical to me if they are identical
with the full forcing runs in the preindustrial era, and then branch off
later (perhaps as dotted lines - but same colour as full forcing for
each model). We could say in the caption that the dotted lines are not
normalised in mid-20th C because they don't attempt to simulate 20th C
climate properly, they are just shown for comparison.

Regards, Stefan

--
To reach me directly please use: rahmstorfatXYZxyzan-klima.de
(My former addresses @pik-potsdam.de are read by my assistant Brigitta.)

Stefan Rahmstorf
www.ozean-klima.de
www.realclimate.org

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