cc: wg1-ar4-ch06@joss.ucar.edu 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 >plenary) >- 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 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/ _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://www.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06