Saturday, March 31, 2012

3035.txt

cc: barrie.pittock@dar.csiro.au, peter.whetton@dar.csiro.au, m.hulmeatXYZxyz.ac.uk
date: Thu, 24 Jun 1999 16:18:18 +0300
from: Timothy Carter <tim.carteratXYZxyz.fi>
subject: SRES and stabilisation scenarios for GCM runs
to: martin.dixatXYZxyz.csiro.au

Dear Dr. Dix,

Barrie Pittock has passed on a query about priorities concerning SRES and
stabilisation scenario runs:

***********

"....3. I should clarify responsibilities at CAR for the new SRES runs with
the CSIRO GCM. Martin Dix here is the key person, and is already in
negotiation with Joyce Penner to get sulfate forcing scenarios based on
the SRES scenarios. Would you please clarify with Martin exactly which
SRES and stabilisation scenarios should have priority in any runs done
here, and faciliate this as far as possible. Martin is ready to start
the runs as soon as the necessary input data is available. We are really
very keen to do this, partly because I have such strong reservations
about linear scaling without aerosol effects. ..."

************

I have to say that I don't know of any IPCC "policy" on this. On SRES, I
only know that some modelling groups are proceeding with a subset of the 4
SRES marker scenario forcings. For details of these, you really have to
consult the modelling groups themselves. Any co-ordination should really
come from among these groups.

>From the impacts perspective, clearly we are happy to obtain runs for as
many SRES storylines as possible. However, we do appreciate that the
climatic outcomes of some runs might be very similar: e.g. an A1 forcing
versus a B2 forcing (at least this may be the case for GHG forcing, though
estimates of the global sulphate loading by 2050s for A1 are almost twice
that for B2). It would certainly be useful to have a grasp of the range of
climatic outcomes from the different SRES forcings (implying the use of A2
and B1 - the two SRES "extremes"). Perhaps this is where some co-ordination
between different GCM groups would be useful, as time is limited for TAR.

In any case, there is little that the impacts community can do with these
outputs for TAR except for a few "fast track" impact assessments with
"ready" models. Rather, these simulations can contribute to WG I Chapters 9
(global model projections), 10 (regional projections) and 13 (climate
scenarios), allowing a GCM-based interpretation of the SRES scenarios, GCM
intercomparisons, and comparison with linear scaling methods based on
previous 1% forced GCM simulations in conjunction with simple global
models. These comparisons will also feature in Chapter 3 of WG II on
scenarios for impact assessment.

On stabilisation, the time horizons are even more tight as the emissions
scenarios are not even finalised yet! I only know what I learnt at the
Copenhagen (WG III) meeting on that theme, following discussions between
Morita, Mitchell, Hulme and myself for the IPCC Task Group on Scenarios
(summarised in the note I sent to Barrie). A recommendation of that note is
that IPCC should provide some guidance about what would be preferred from
the climate modellers, but I really don't know how this will be taken
forward. In the absence of guidance, you might contact John Mitchell
(jfbmitchell@meto.gov.uk) to find out his views. He is in the same quandary
as you are. I think there is some discrepancy between what the energy
modellers are producing (CO2 stabilisation scenarios) and what the UNFCCC
people are asking for (CO2-equivalent stabilisation). If you are
considering CO2 and other gases separately in your GCM, then this
distinction is probably important. Also, from the impacts point of view
(i.e. CO2 concentration and socio-economic storyline), a stabilised 550
ppmv (or any other CO2 level) world by 2100 may be quite different from an
equivalent-550 ppmv world over the same time frame.

I am copying this to Mike Hulme, so that he can communicate the concerns of
your group (and I suspect others) to the Scenarios Task Group about how to
handle these new forcing scenarios.

I'm sorry if I appear to be passing the buck, but I don't have a mandate to
advise you on which runs to conduct - I can only suggest that you
co-ordinate your activities with other modelling groups who are in a
similar position, so that the most productive use is made of research and
CPU time.

Best wishes,

Yours sincerely,

Tim Carter


************************************************

Dr. Timothy Carter
Finnish Environment Institute
Box 140, Kes�katu 6, FIN-00251 Helsinki, FINLAND

Tel: +358-9-40300-315
Fax: +358-9-40300-390
Email: tim.carteratXYZxyz.fi

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