cc: wg1-ar4-ch06@joss.ucar.edu date: Mon, 19 Dec 2005 01:47:16 +0100 from: Stefan Rahmstorf subject: [Wg1-ar4-ch06] the sports-implement-that-must-not-be-mentioned to: Jonathan Overpeck 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 _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://www.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06