date: Fri, 23 Mar 2001 16:09:16 +0200 from: Timothy Carter subject: Re: ATEAM scenario text to: Tim Mitchell , m.hulme@uea.ac.uk Tim and Mike, I have revised the scenarios document, taking on board all of our correspondence so far. I have taken some minor liberties with Tim M's notation and made a few assumptions of my own worth noting: (a) For the full 200 year "natural variability" time series, we would append an adjusted AOGCM control run output (as suggested by Tim M) for 2001-2100 to the observed time series (1901-2000), rather than to the detrended observed series as suggested. In this way, we would assume alternative natural variability series following the historical trend. The rationale here is that the present-day vegetation is adapted to the historical climate, not to a detrended climate. The future development in vegetation attributable to natural variability can then be compared directly to that attributable to a perturbed climate, for which our scenarios do assume the historical climate. (b) I have kept the number of scenarios open for the time being, referring to 1-5 scenarios per ATEAM scenario family. Tim M suggested using 5 patterns for one of the central scenarios, but we might consider using these for the lower and upper extreme scenarios. We can decide this later. (c) Perhaps we should consider using only 5 or less ensembles per GCM for the natural variability, but for 2-3 GCMs. These could be hand-picked to give the maximum multi-decadal variability. (d) I am still concerned that if we are constructing full time series, that the impact modellers will need Tmax and Tmin, and will not wish to adjust the Tmean data set themselves. Of course, we could always supply a program to convert the DTR and Tmean times series into Tmax and Tmin. There may be some other things, but I don't recall them right now. See what you think. Best regards, Tim Attachment Converted: "c:\eudora\attach\clscen02.doc" ************************************************ Dr. Timothy Carter Finnish Environment Institute Box 140, Kesäkatu 6, FIN-00251 Helsinki, FINLAND Tel: +358-9-40300-315; GSM +358-40-740-5403 Fax: +358-9-40300-390 Email: tim.carter@vyh.fi ************************************************