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 date: Mon, 21 May 2007 12:20:45 -0700 from: Karl Taylor subject: Re: 5AR runs next iteration- reply by 26th to: Knutti Reto 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 > Universitätstrasse 16 (CHN N 12.1) > CH-8092 Zürich, Switzerland > reto.knutti@env.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.stott@metoffice.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 >> >