date: Thu Sep 21 16:45:11 2006 from: Tim Osborn subject: Re: use of CLIMGEN for IPCC: before we meet to: "Rachel Warren" Rachel - we can talk some more when you come to see me, but Tom Wigley is not an author at any level, as far as I know, on any chapter in IPCC WG1 for the AR4. So his approval or disapproval may not be relevant (other than for scientific reasons of course!). In the way that you are using CLIMGEN, I think that there really only two things that need to be defended: (1) the GCM patterns that have been used; and (2) the pattern-scaling concept itself. The reason why I think these are the only two issues is that you could probably do the upscaling without using CLIMGEN at all, just by using these two things. Both issues are defensible in general. With specific reference to IPCC WG1, however, you should look to see what the draft says about regional climate change, and specifically whether pattern-scaling is criticised or supported or even mentioned. CLIMGEN is not reviewed or mentioned as far as I know, but provided the 2 concepts/issues mentioned above, then this is fine. The GCM runs from which the patterns are derived are not all very new; some of these runs are definitely still being used in AR4 WG1, but we can check if this applies to them all. All are at least TAR or later. Cheers Tim At 16:32 21/09/2006, you wrote: Dear Tim This is just to let you both know that I am using CLIMGEN to backwards-downscale (i.e. upscale) regional to global temperature for a key table in an IPCC WG2 chapter on climate impacts for ecosystems at different degrees of temperature rise using the range of GCMs in CLIMGEN. The method for uncertainty analysis for the upscaling was agreed with Martin Parry at the recent WG2 meeting I went to last week. I've already done a lot of calculations but I am going to do more following last week's decision, to include more uncertainty analysis for more of the entries in the table than I had previously done. I am wondering, however, whether WGI, given their recent tendency to object to anything that isn't in the WG1 report, may object to the use of CLIMGEN in this way. WG1 are currently opposing the use of anything in WG2/3 on climate science that isn't covered in their report, even if it's perfectly valid literature that they don't cover. However, CLIMGEN has the same methods as SCENGEN which was used in the TAR. I am wondering whether to talk to Tom Wigley about it - but given the SCENGEN/CLIMGEN tension that I think may have existed, this may make matters worse. Is CLIMGEN reviewed in IPCC WGI or not? Does Tom Wigley approve of CLIMGEN? If WG1 object to the use of CLIMGEN, because it is not SCENGEN or Tom Wigley's latest MAGICC-SCENGEN combination, they may argue to throw out the table, and I would lose all of my work on this subject and the chapter would be much the poorer - the review editor thinks that my table will get more attention than anything else in the chapter and some of it may end up in the SPM. Hence I cannot emphasise the importance of making sure that WG1 cannot complain about my using CLIMGEN to upscale! I'll be talking to you tomorrow to make sure that I fully understand exactly which GCM datasets are used in CLIMGEN so that I and the CLA and Martin Parry can defend how I have used it, and how it works, if the topic comes up in discussion at any time. Tim, I need to check whether you are using the same updated GCM patterns as the new version of SCENGEN (version 2.4 of 2003). The best thing would be to get Tom Wigley's approval of my using it, prior to any of the IPCC meetings ... Thanks Rachel Dr Rachel Warren Senior Research Fellow Tyndall Centre Zuckermann Institute University of East Anglia Norwich NR4 7TJ Telephone 01603 593912 Fax 01603 593901 E-mail r.warren@uea.ac.uk