Friday, March 30, 2012


date: Sun, 18 Dec 2005 21:51:10 -0700
from: Jonathan Overpeck <>
subject: [Wg1-ar4-ch06] Re: the
to: Stefan Rahmstorf <>

Hi Stefan and Chap 6 friends - normalizing to the 20th century was
the way we agreed to do it at the TS/SPM meeting, so thanks for your
independent endorsement. Even more thanks to Keith and Tim who need
to work on all these figs. Best, Peck

>Dear chapter 6 colleagues,
>I'd like to come back to a point Susan made in the plenary: the
>millennium reconstruction curves should be normalised for the 20th
>Century (or parts thereof, e.g. mid 20th Century). I strongly agree
>with Susan here, for the reasons below:
>- normal people (policy makers) think of climate change relative to
>recent experience, not in some abstract absolute terms
>- those data do in fact not give absolute temperatures, but those
>relative to the recent instrumental period - they are in fact
>normalised for this (a very valid point that Gabi made in the
>- the main conclusion we draw is that recent warmth is unprecedented
>- if you want to see this, you must show the curves relative to the
>recent times
>- it makes no sense if the proxy curves diverge strongly in the 20th
>Century, since this is only period where we really know what the
>climate was like.
>These arguments are slightly different for the model results, hence
>in the current draft, the proxy data are normalised for recent
>climate, and the model results for something else. For the models
>maybe we need to debate this - the main reason for doing it
>differently for the models seems to be to show the correction for
>the Von Storch result. When the AR4 comes out, this will be in the
>published literature, so no need to make our whole graph look
>different just to cater for one bad model run. I think the models
>would be better shown normalised the same way as the proxy data;
>this would also help avoid possible confusion. But I very strongly
>feel that the simplified joint plot shown in the plenary, with the
>envelopes of both models and proxies, definitely must be normalised
>for the 20th Century.
>Cheers, Stefan

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

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