Sunday, June 17, 2012

5265.txt

cc: "Gabi Hegerl" <hegerlatXYZxyze.edu>, <peter.stottatXYZxyzoffice.gov.uk>, "myles" <m.allen1atXYZxyzsics.ox.ac.uk>, "Tim Barnett" <tbarnett-ulatXYZxyzd.edu>, "Nathan Gillett" <n.gillettatXYZxyz.ac.uk>, "Phil Jones" <p.jonesatXYZxyz.ac.uk>, "David Karoly" <dkarolyatXYZxyzsby.metr.ou.edu>, "Jesse Kenyon" <kenyonatXYZxyze.edu>, "Reto Knutti" <knuttiatXYZxyzmate.unibe.ch>, "Tom Knutson" <Tom.KnutsonatXYZxyza.gov>, "Toru Nozawa" <nozawa@nies.go.jp>, "Doug Nychka" <nychka@cgd.ucar.edu>, "Claudia Tebaldi" <tebaldi@rap.ucar.edu>, "Ben Santer" <santer1atXYZxyzl.gov>, "Richard Smith" <rlsatXYZxyzil.unc.edu>, "Daithi Stone" <stonedatXYZxyz.ox.ac.uk>, "Michael Wehner" <MFWehneratXYZxyz.gov>, "Xuebin Zhang" <Xuebin.ZhangatXYZxyzgc.ca>, "francis" <francis.zwiersatXYZxyzgc.ca>, "Hans von Storch" <hvonstorchatXYZxyz.de>
date: Mon, 21 May 2007 22:16:00 +0200
from: "Knutti Reto" <reto.knuttiatXYZxyz.ethz.ch>
subject: RE: 5AR runs next iteration- reply by 26th
to: "Karl Taylor" <taylor13atXYZxyzl.gov>

Dear Karl, dear all,

I agree with you, to estimate the carbon cycle feedback, there should be no other forcings. However, from talking to Jerry it is my understanding that the simulations proposed in the EOS article prescribe CO2 with the intention to derive allowable emissions for that CO2 path. Those allowable emissions should then be given to WGIII to calculate the cost and possible ways to follow such an emission pathway. This however is not meaningful with scenarios without non CO2 forcing. The allowable emissions will already be off today.

So to me, it is not clear whether two sets are needed. An idealized set with CO2 only to estimate the carbon cycle feedback, and a set with all forcings and a plausible CO2 scenario for which the allowed emissions can be given to WGIII.

Another question: so far, the only simulations proposed are coupled carbon cycle and high resolution short term. Are there any plans to do 1%/yr, 2xCO2, A1B/B1/A2? Not that we would learn much more in terms of climate, but to be able to compare the new and old generation of models, some of those seem crucial. One question that always comes up in every IPCC report is why are the new projections lower or higher than the old ones. Having at least one common scenario is key to answer that.

Regarding ensembles, my opinion is that if there are several scenarios (like B1, A1B and A2 in AR4), it would be better to have many members for one and only one or two for the other scenarios, such that there is at least one scenario where many members are available for those who need them. The conclusions from other scenarios are mostly the same anyway.

In addition, it would be nice if a minimum number of ensemble members could be done by each group. In many statistical exercises, the number of ensemble members must be the same for each model (signal to noise), which resulted in people often using only one member per model because a few models provided only one. I don't know whether that's feasible though.

Reto


----------------------------------------------
Reto Knutti
Institute for Atmospheric and Climate Science
Swiss Federal Institute of Technology
Universit�tstrasse 16 (CHN N 12.1)
CH-8092 Z�rich, Switzerland
reto.knuttiatXYZxyz.ethz.ch
http://www.iac.ethz.ch/people/knuttir
Phone: +41 44 632 35 40
Fax: +41 44 633 10 58
----------------------------------------------

> -----Original Message-----
> From: Karl Taylor [mailto:taylor13@llnl.gov]
> Sent: Montag, 21. Mai 2007 21:21
> To: Knutti Reto
> Cc: Gabi Hegerl; peter.stott@metoffice.gov.uk; myles; Tim Barnett;
> Nathan Gillett; Phil Jones; David Karoly; Jesse Kenyon; Reto Knutti;
> Tom Knutson; Toru Nozawa; Doug Nychka; Claudia Tebaldi; Ben Santer;
> Richard Smith; Daithi Stone; Michael Wehner; Xuebin Zhang; francis;
> Hans von Storch
> Subject: Re: 5AR runs next iteration- reply by 26th
>
> Hi all,
>
> Concerning Reto's point about trying to estimate the carbon cycle
> feedbacks in the absence of climate change: this indeed is not possible
> if you have "other" forcings. I have been thinking about several
> related issues concerning the experiment design and which scenarios
> should be run, and I think feedback analysis in general will need to be
> done with idealized experiments (like 1%/yr expts.), not with either
> historically realistic or reasonably realistic scenarios runs (for the
> future). More on this after I have a chance to write my thoughts down.
>
> cheers,
> Karl
>
>
> Knutti Reto wrote:
> > Hi Gabi,
> >
> > Even if the 20th century trends are not explicitly used in tuning,
> model developers will remember how the previous model versions compared
> to observed trends. Also, they will look at climate sensitivity and
> TCR, which is related to the observed trends. So I think it's hard to
> argue that the observed trends should not be used.
> >
> > May I suggest a slight rewording of the following sentence...
> > "Reto points out that there is a problem with 20th century forcing
> for the runs with carbon cycle that makes the use of non-CO2 forcing
> problematic, but essential for getting the 20th century right. EMIC
> tests might help."
> >
> > into...
> > Reto points out there is a problem with the non CO2 forcing in the
> runs with interactive carbon cycle. Non CO2 must be included in order
> to provide meaningful projections and to be able to compare the 20th
> century model results to observations. However, the idea of estimating
> the carbon cycle feedbacks based on comparing a coupled carbon cycle
> simulation with a carbon cycle under constant climate assumes no other
> forcings. EMICs with coupled carbon cycle (as already used in AR4) may
> help with tests on how to deal with the non CO2 forcing.
> >
> > Apart from that, I think your document gets the main points.
> >
> > Regards from Zurich,
> >
> > Reto
> >
> >
> > ----------------------------------------------
> > Reto Knutti
> > Institute for Atmospheric and Climate Science
> > Swiss Federal Institute of Technology
> > Universit�tstrasse 16 (CHN N 12.1)
> > CH-8092 Z�rich, Switzerland
> > reto.knuttiatXYZxyz.ethz.ch
> > http://www.iac.ethz.ch/people/knuttir
> > Phone: +41 44 632 35 40
> > Fax: +41 44 633 10 58
> > ----------------------------------------------
> >
> >> -----Original Message-----
> >> From: Gabi Hegerl [mailto:hegerl@duke.edu]
> >> Sent: Freitag, 18. Mai 2007 23:26
> >> To: Karl Taylor
> >> Cc: peter.stott@metoffice.gov.uk; myles; Tim Barnett; Nathan
> Gillett;
> >> Phil Jones; David Karoly; Jesse Kenyon; Reto Knutti; Tom Knutson;
> Toru
> >> Nozawa; Doug Nychka; Claudia Tebaldi; Ben Santer; Richard Smith;
> Daithi
> >> Stone; Michael Wehner; Xuebin Zhang; francis; Hans von Storch
> >> Subject: Re: 5AR runs next iteration- reply by 26th
> >>
> >> Hi all,
> >>
> >> I see this. On the other hand, when some republicans did a grilling
> >> about attribution in some house subcommittee,
> >> I was very happy to be able to resort to Tim's argument that the
> model
> >> runs were older than the heat uptake data
> >> and therefore, there was no secret tuning in the 2001 ocean
> attribution
> >> results..
> >>
> >> So using the 20th c for tuning is just doing what some people have
> long
> >> suspected us of doing...
> >> and what the nonpublished diagram from NCAR showing correlation
> between
> >> aerosol forcing and
> >> sensitivity also suggested.
> >> Slippery slope... I suspect Karl is right and our clout is not
> enough
> >> to
> >> prevent the modellers from doing this
> >> if they can. We do loose the ability, though, to use the tuning
> >> variable
> >> for attribution studies.
> >>
> >> Should we ask to admit in their submission what variables were
> >> considered when tuning, and if any climate
> >> change data were considered and at what temporal and spatial
> >> representation (global mean trend?),
> >> and advise that we will not be able to use those models for any
> future
> >> attribution diagrams? That would at least lay it in the open...
> >>
> >> Gabi
> >>
> >> Karl Taylor wrote:
> >>
> >>> Hi Peter and all,
> >>>
> >>> There will clearly be different perspectives on this. A model
> >>> developer will want to make use of all available observational
> >>> information to help decide whether his model is realistic or not.
> >>>
> >>> We can envision two candidate models that appear equivalent in most
> >>> respects, but one fails to produce ENSO's. The developer would
> >> choose
> >>> the one that simulated ENSO.
> >>>
> >>> Likewise, suppose two candidate models were identical in most
> >>> respects, but one could accurately simulate the climate of the 20th
> >>> century (when all forcings were included), whereas the second had a
> >>> very low global sensitivity and produced too little warming. The
> >>> developer would again want to choose the model that reproduced the
> >>> observed trends. In fact this model would probably produce a
> better
> >>> estimate when forced by future emissions scenarios too (because,
> >>> presumably, its sensitivity is closer to the truth).
> >>>
> >>> It would be hard to argue that information about 20th century
> trends
> >>> shouldn't be used in model development.
> >>>
> >>> I agree that this may rule out attribution studies (following the
> >>> established approaches), but wouldn't we have to argue that
> >>> attribution studies are more important that model projections to
> >>> convince the groups not to consider trends in the model development
> >>> cycle?
> >>>
> >>> cheers,
> >>> Karl
> >>>
> >>>
> >>> peter.stottatXYZxyzoffice.gov.uk wrote:
> >>>
> >>>> Hello everybody,
> >>>>
> >>>> We're having a lively debate in the Hadley Centre about whether
> >> climate
> >>>> change experiments should be run as part of the model development
> >>>> process, ie whether model developers should test their model
> against
> >>>> climate change as they are developing their model. I think it
> might
> >> be
> >>>> worthwhile us developing and expressing a view on this as we don't
> >> want
> >>>> to risk getting into a position where attribution results in AR5
> are
> >>>> undermined by the development and model tuning procedure adopted
> by
> >>>> modelling centres.
> >>>>
> >>>> Also I don't think you quite captured the point that another
> reason
> >> for
> >>>> separating out the ghg response from the response to other
> forcings
> >> is
> >>>> to aid understanding, as we are finding out in trying to
> understand
> >> the
> >>>> precipitation response. I think that requesting ALL, GHG, and NAT
> >>>> ensembles would be the basic set.
> >>>>
> >>>> Best wishes,
> >>>> Peter
> >>>>
> >>>> On Fri, 2007-05-18 at 10:33 -0400, Gabi Hegerl wrote:
> >>>>
> >>>>> 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
> >>>>>
> >>>>> Gabi
> >>>>>
> >> --
> >> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >> 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: hegerl@duke.edu,
> >> http://www.env.duke.edu/faculty/bios/hegerl.html
> >>
> >

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