cc: Ronald Stouffer date: Fri, 19 Sep 2008 04:01:15 -0700 from: Karl Taylor subject: Proposed experiment design for CMIP5 (revised) to: bryant.mcavaney@lmd.jussieu.fr, Curtis Covey , Jerry Meehl , "Mitchell, John FB (Chief Scientist)" , mlatif@ifm-geomar.de, Tom.Delworth@noaa.gov, Andreas Hense , Asgeir Sorteberg , Erich Roeckner , Evgeny Volodin , "Gary L. Russell" , Gavin Schmidt , GFDL.Climate.Model.Info@noaa.gov, Greg Flato , Helge Drange , Jason Lowe , Jean-Francois Royer , Jean-Louis Dufresne , Jozef Syktus , Julia Slingo , Kimoto Masahide , Peter Gent , Qingquan Li , Seita Emori , Seung-Ki Min , Shan Sun , Shoji Kusunoki , Shuting Yang , Silvio Gualdi , Stephanie Legutke , Tongwen Wu , Tony Hirst , Toru Nozawa , Wilhelm May , Won-Tae Kwon , Ying Xu , Yong Luo , Yongqiang Yu , Kamal Puri , Tim Stockdale , Gabi Hegerl , James Murphy , Marco Giorgetta , George Boer , Myles Allen , claudia tebaldi , Ben Santer , Tim Barnett , Nathan Gillett , Phil Jones , David Karoly , Dáithí Stone , "Stott, Peter" , Francis Zwiers , Toru Nozawa , Ken Sperber , Dave Bader , Mike MacCracken , boyle5@llnl.gov, Stephen Klein , "A. Pier Siebesma" , William Rossow , Chris Bretherton , George Tselioudis , Mark Webb , Sandrine Bony , James Hack , Martin Miller , Ken Kunkel , Christian Jakob , Kathy Hibbard , "Eyring, Veronika" , pasb@dsm-mail.saclay.cea.fr, giorgi@ictp.trieste.it, c.lequere@uea.ac.uk, naki@eeg.tuwien.ac.at, stephen.griffies@noaa.gov, Peter Cox , Pierre Friedlingstein , Olivier Boucher , Bala Govindasamy , Jonathan Gregory , Chris Jones , "Jones, Gareth S" , David Lobell , peter gleckler , Cath Senior , Keith Williams , "stephen e. schwartz" , David Easterling , Inez Fung , Duane Waliser , William Collins , Ken Caldeira , Dave Randall , Joyce Penner , Anna Pirani , Bjorn Stevens , "V. Ramaswamy" , Susan.Solomon@noaa.gov, Bin Wang , Tianjun Zhou , Thomas Stocker Content-Type: text/plain; charset=windows-1252; format=flowed X-MIME-Autoconverted: from 8bit to quoted-printable by ueamailgate01.uea.ac.uk id m8JB2EeK011729 Dear all, As you know, the experiment design for CMIP5 has been under review. Thanks to those of you who have commented on the draft of July 21?, 2008. In response to input from individuals and groups, I have modified the document except when a suggestion seemed controversial or had previously been ruled out by consensus. The revised experiment design summary is attached (Taylor_CMIP5_expts7.pdf), and below is a brief summary of the major changes made and the major issues raised in response to the earlier draft. These issues will need to be discussed at the WGCM meeting next week. I apologize for not having time to revise the document earlier. I also have failed to fully synthesize a clear consensus for the experiment design. After the WGCM addresses the major outstanding issues, I will revise the document once more and try to incorporate any input I have already received that is consistent with the agreed upon design. I have attached three other documents prepared by interested groups: 1. A document (OzoneDatabase_InputCMIP5_V2.pdf) from SPARC CCMVal describing their plan to “provide stratospheric ozone boundary conditions suitable for long-term global climate model simulations such as the … CMIP5 experiments 1.2 and 2.1-2.4.” 2. A summary (comments_IDAG.pdf) from the “International Detection & Attribution Group,” providing a perspective on a possible shift of priorities for some of the CMIP5 experiments, and contributing text that provides further motivation for performing the detection and attribution experiments summarized in Table 6. 3. A letter (CFMIP2_WGCM_Sept2008_summary.pdf) from the CFMIP coordination committee (with the endorsement of WGNE and of the GEWEX Scientific Steering Group) suggesting that the CMIP5 experiment design should include a few additional (short) experiments and output useful for diagnosing cloud responses in models. Important changes made to the CMIP5 experiment design document include the following: 1. The document now reflects the view that the near-term and long-term experiments are equally important, but modeling groups are not required to contribute results for both types of simulations. In the earlier draft, the fact that none of the near-term experiments were designated as mandatory made it appear that those experiments were not of as much interest. 2. Several changes were made to Table 2, which summarizes the future projection runs with prescribed concentrations of long-lived greenhouse gases according to various representative concentration pathways (RCP’s), including the following: - the priorities of RCP2.7 and RCP4.5 were switched, with RCP4.5 now considered mandatory (but not RCP2.7). This change was made because RCP4.5 will be imposed in expt. 3.3, the emission-driven coupled carbon climate model run (instead of RCP8.5, which was so designated in the previous draft). RCP4.5 will now also be specified in the near-term experiments. - likewise, the highest priority for extending an RCP run beyond the 21^st century has been switched to the RCP4.5 simulation. - The first priority for each RCP will be to simulate through the end of the 21^st century, rather than to year 2150 as previously specified. 3. The possibility that the WGCM will decide that the analysis of carbon climate feedbacks should be done for a realistic RCP, rather than for the idealized 1%/yr CO2 increase, was allowed for by including expt. 3.4. In this case expts. 4.2a,b would be eliminated. 4. The priority of one run of Expt. 4.2 has been downgraded to “very high”, and Expt. 4.3c, which would have allowed us to analyze “fast” responses of the carbon cycle to changes in atmospheric concentrations, was eliminated. 5. Following the advice of the detection and attribution community, the priority of expt. 6.2 has been increased to “very high” and the simulation has been switched to GHG-only from anthro-only. The highest priority ensemble simulation (expt. 6.4) has been switched to natural-only from GHG-only. 6. Sections 7 and 8 were switched, so now all the long-term expts. are described before the near-term experiments. 7. Section 9 (additional remarks) was eliminated. There are a number of issues that must be resolved. Issues: 1. Should additional experiments be performed that aim to isolate in each model the effects of aerosols. In particular should special diagnostic runs be performed to calculate aerosol forcing, just as special CO2-only runs are a part of the experiment design? 2. Should the strength of carbon/climate feedbacks be evaluated in the historical and RCP4.5 simulations or in the idealized 1%/yr simulation? 3. Should the priority of the detection and attribution experiments be higher? 4. Should the CFMIP recommendation, which calls for some additional experiments to be performed that would improve understanding of the range of cloud feedbacks in models, be accepted? It can be argued that the consequences of uncertainty in cloud feedbacks are at least as important as the consequences of uncertainty in carbon/climate feedbacks, which receive considerable attention under the current experiment design. 5. Is it important to isolate the impact of land use changes on historical and future climate change? The current experiment design will not provide this information. 6. The ending date for the historical runs and the start date for future runs need to be agreed upon. It has been proposed to extend the historical runs to very near present (say 2009), but start the projection runs earlier (say 2005). Whatever is decided, the historical concentrations (or emissions) should smoothly transition into the future. 7. Is it absolutely necessary for models with a carbon cycle component to run two control simulations, one with prescribed pre-industrial concentrations and one fully coupled and free to evolve? I hope those of you who will be at the WGCM meeting next week will have a moment to think about these issues, and I look forward to the discussion. With best regards, Karl Karl E. Taylor PCMDI Attachment Converted: "c:\eudora\attach\Taylor_CMIP5_expts7.pdf" Attachment Converted: "c:\eudora\attach\OzoneDatabase_InputCMIP5_V2.pdf" Attachment Converted: "c:\eudora\attach\CFMIP2_WGCM_Sept2008_summary.pdf" Attachment Converted: "c:\eudora\attach\comments_IDAG.pdf" Attachment Converted: "c:\eudora\attach\preWGCM_letter.pdf"