date: Fri, 25 May 2007 13:22:30 -0400
from: Tom Knutson <Tom.KnutsonatXYZxyza.gov>
subject: Re: 5AR runs next iteration- reply by 26th
Hi Tim et al,
I had a quick response from my perspective at GFDL on Tim's comments
earlier on the tuning vs good luck of modeling groups.
> the actual forcing data is a must. right now we have some
> famous models that all agree surprisely well with 20th obs, but
> whose forcing is really
> different. clearly, some tuning or very good luck involved. I doubt
> the modeling world will be able to get away with this much
> longer....so let's preempt any potential problems.
At GFDL, we were generally aware, during the coupled model development
process, of the model's equilibrium climate sensitivity to CO2 doubling.
I have a plot on my door showing values of 2.6 to 4.6 at various
stages of development. However this was not used as means of tuning
the model or in choosing a model. Also we did not run more
than historical scenarios with
more than one model and then choose between them. In fact we ran
historical scenarios with our two pre-tuned models (tuned on their
performance at simulating present day climate) and reported on
Although our "All forcing" model agrees pretty well with obs over the
20th century (Knutson et al. J. CLimate, 2006), we did not include
any indirect aerosol forcing, as that
part of the model is still under development. Some estimates are that
this "missing forcing" is quite substantial, so when it is
included in future experiments, we may well obtain worse agreement than
shown in our current All-Forcing runs.
-- Tom Knutson
Tim Barnett wrote:
> hi gabi.....some suggestions in haste
> for the oceans...daily averaged near surface (10m?) wind stress 1950 on
> (at least). also daily averaged heat budget components at the ocean
> surface. stuff like this for baroclinic components of change. i assume
> sea ice is a given. hi freq data to look at storm track changes.
> over land....add daily snow cover and major river flows into the oceans if
> the models have them. add soil moisture, probably monthly. with will
> have lots to do with hydrological cycle. start from 1950 at least
> global...let's see those clouds. they are supposed to be 'the' key
> climate variable, models do them poorly and we have new satellite data
> sets to see just how poorly or how well.
> runs....beyond D&A...yes i agree we need a whole set of runs with
> different future GHG forcings. since the memory is in the ocean and that
> partially determines the response time (what's in the pipeline) we need
> emission reduction scenarios to see what track we are on as we begin to
> reduce co2. e.g. how much do we need to reduce emissions to ensure Lake
> Mead does not go dry? in the future there will be lots of stress on 'what
> do we have to do NOT to exceed some threshold"
> yes continuous runs 1900-2100.
> the actual forcing data is a must. right now we have some famous models
> that all agree surprisely well with 20th obs, but whose forcing is really
> different. clearly, some tuning or very good luck involved. I doubt the
> modeling world will be able to get away with this much longer....so let's
> preempt any potential problems.
>> Hi all.
>> From your comments, I assembled a word file with our suggestions on the
>> 5AR run
>> proposal, but I am not sure
>> I caught it all completely. Also, I had a chat with Jerry yesterday, and
>> he said getting
>> suggestions of what should be stored will be useful at this point.
>> My plan is to communicate this with Jerry when we are done with it, and
>> then propose
>> it at the WGCM meeting.
>> I drew a strawman list of what I could think of in 3 minutes, and am
>> asking you to
>> add to it. Its all in track changes, so dont hesitate to go wild (but
>> please keep in mind that
>> we need to restrict data requests to something you think you will work
>> with in the next
>> years, since it is a fair amount of effort from the modelling centres to
>> haul the data over
>> etc, and the more we request, the more likely it is that only few
>> ensemble members etc
>> get sent...)
>> Karl, I am cc;ing you since your perspective would be useful
>> Gabriele Hegerl
>> Division of Earth and Ocean Sciences,
>> Nicholas School for the Environment and Earth Sciences,
>> Box 90227
>> Duke University, Durham NC 27708
>> Ph: 919 684 6167, fax 684 5833
>> email: hegerlatXYZxyze.edu, http://www.env.duke.edu/faculty/bios/hegerl.html
Geophysical Fluid Dynamics Lab /NOAA | phone: +1-609-452-6509
P.O. Box 308 | fax: +1-609-987-5063
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Princeton, New Jersey 08542 U.S.A. | http://www.gfdl.noaa.gov/~tk