cc: plattner@climate.unibe.ch, Tim Osborn , Jonathan Overpeck , Anders Levermann , Eva Bauer , Eystein Jansen , Keith Briffa , oyvind.paasche@bjerknes.uib.no date: Wed, 15 Feb 2006 12:47:25 +0100 from: Stefan Rahmstorf subject: Re: Fwd: Re: Millennium Simulations to: Fortunat Joos 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 ºC 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: rahmstorf@ozean-klima.de (My former addresses @pik-potsdam.de are read by my assistant Brigitta.) Stefan Rahmstorf www.ozean-klima.de www.realclimate.org