date: Fri, 23 Mar 2001 16:09:16 +0200
from: Timothy Carter <tim.carter@vyh.fi>
subject: Re: ATEAM scenario text
to: Tim Mitchell <t.mitchell@uea.ac.uk>, 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"


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Dr. Timothy Carter
Finnish Environment Institute
Box 140, Keskatu 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

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