Wednesday, December 28, 2011


From: Mike MacCracken <>
To: Jason Lowe <>, Jerry Meehl <>
Subject: Re: Proposed experiment design for CMIP5
Date: Wed, 30 Jul 2008 11:25:01 -0400
Cc: "Cox, Peter" <>, Karl Taylor <>, <>, Curtis Covey <>, "Mitchell, John FB (Chief Scientist)" <>, <>, <>, Andreas Hense <>, Asgeir Sorteberg <>, Erich Roeckner <>, Evgeny Volodin <>, "Gary L. Russell" <>, Gavin Schmidt <>, <>, Greg Flato <>, Helge Drange <>, 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 <>, D�ith� Stone <>, "Stott, Peter" <>, Francis Zwiers <>, Ken Sperber <>, Dave Bader <>, <>, 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" <>, <>, <>, <>, <>, <>, 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 <>, Ronald Stouffer <>

Dear Jason and Jerry (and Karl and Ron)--One of my suggestions on an
earlier round was such a simulation--to determine how models might do and
compare with a declining concentration (optimistic as such a scenario might
be). The one you are doing would seem to have an overshoot on the forcing,
but probably not (or not much) on the global average temperature due to lag
effects in the system. It seems to me it would be worthwhile figuring out
such a run that also got the temperature decreasing, so maybe returned to
below the equivalent concentration we have now (so below something like 375
ppm when counting aerosol effects). In that such scenarios would likely lead
to sharp cuts in CO2 emissions, they would also presumably lead to sharp
reductions in the SO2/SO4 offset, we are really already at about 450 ppm CO2
equivalent for GHGs alone--and so to really get cooling started, the run
would likely have to go back to 350 ppm or below--so basically to the level
Jim Hansen has been arguing is required to get back near 1990s climatic

I would also note that the CO2 equivalence calculations are being done using
the 100-year GWPs. While there is not much difference for N2O and most
halocarbons, the 20-year GWP for methane is about 3 times the 100-year value
and so over the near-term methane changes (from stringent methane control,
or additional release from thawing tundra) could have a very large effect on
the short-term forcing and so on temperature change over the next several
decades, so when the peak occurs and how one comes back thereafter. While
CO2 control may well take time, methane control is very cost effective and
should be being pushed very hard as a strategy (along with soot and air
pollutants contributing to tropospheric ozone--a point made several years
ago by Jim Hansen). In any case, it seems to me it is not implausible to
imagine that we could get to conditions where radiative forcing is coming
down, and that type of run needs to be explored--so having some sort of
standard run that groups could try if they have resources would make good

Mike MacCracken

On 7/29/08 4:48 PM, "Jason Lowe" <> wrote:

> Hi Peter,
> I seem to be the only person not in Snowmass!
> In addition to the Japanese proof of concept the EU Ensembles project
> is also running a model intercomparison with a low end scenario that
> peaks at a little over 500ppm CO2eq before declining to an eventual
> 450ppm. Emissions will be diagnosed and, hopefully, many of
> the groups with C-C cycle feedback will also diagnose the feedback!
> It will be interesting to see the spread.
> Regards,
> Jason
> On Tue, 2008-07-29 at 11:48 -0600, Jerry Meehl wrote:
>> Hi Peter,
>> How long will you be in Snowmass? I get there tomorrow late afternoon
>> and will be there for the sessions Thursday and Friday. Ron and I were
>> planning on re-visiting the experimental design more then, and if you
>> could join in that would be great.
>> Regarding your point in favor of using the RCPs for carbon cycle
>> feedback, I think Ron and I arrived at this conclusion independently
>> while we both attended a US-Japan workshop in Colorado a few weeks ago.
>> The Japanese have performed a proof-of-concept experiment using two
>> idealized mitigation scenarios and basically computed numbers for the
>> Aspen experiments you originally proposed in 2006. There were two key
>> additional points that we noted--one was that they started from a
>> pre-industrial control run so they had 20th and 21st century in the
>> "climate-carbon feedback" contrasted to "no-climate carbon feedback"
>> allowable emissions plots. Second, they had some kind of 20th century
>> "observations" of carbon emissions they plotted on their allowable
>> emissions graphs to show that their model with carbon-climate feedback
>> actually tracked those observations for 20th century. Since there are
>> so few observations to compare carbon cycle feedback to, this seemed
>> like a fairly compelling reason to use RCPs, which is what you also note
>> below.
>> I think Karl and Ron had lumped the carbon cycle feedback experiments in
>> the 1% runs both because this had come up as a possibility in the
>> post-Aspen WGCM meeting in Victoria in 2006, and because it could
>> possibly present a more pleasing context to evaluate all feedbacks,
>> carbon cycle and all others. However, on further review, in addition to
>> the points you raised, deriving allowable emissions from RCPs allows a
>> check to what the IAMs used for emissions in the first place (and used
>> to derive concentrations used in the ESMs). Also, it seems to me that
>> carbon cycle feedback falls into a new category of feedback that we in
>> the AOGCM world are not used to evaluating. We must depend on the
>> advice from you and others in that community. Though it's tempting to
>> think that everything can be boiled out of 1% runs, I think those are
>> most useful for feedbacks basically "managed" by the atmosphere (like
>> clouds, water vapor, etc.). The original Aspen concept for carbon cycle
>> feedback always depended on using actual mitigation scenarios, and I
>> think we're coming around again to agreeing on that.
>> Another point is that the cloud feedback community will make a proposal
>> to WGCM to enlarge the idealized 1% feedback experiment list, so that
>> makes separating out the carbon cycle feedback experiments in a separate
>> category using RCPs more compelling.
>> Hopefully we can discuss this more Thursday.
>> Jerry
>> Cox, Peter wrote:
>>> Dear Karl and Ron
>>> Thanks for this very thorough document.
>>> Generally speaking I think we should be focusing much more on realistic
>>> policy relevant scenarios rather than 1% per year type experiments. There
>>> are two reasons for this:
>>> 1) Most now consider a ("business as usual") 1% per year scenario not to
>>> represent a viable future. So detailed information on these scenarios is
>>> less and less relevant to people outside of the GCM modeling community.
>>> 2) More realistic scenarios allow us to utilize observations to validate
>>> models/reduce uncertainties in a way that idealized scenarios do not.
>>> So I am in favour of diagnosing feedbacks in the more policy-relevant RCP
>>> scenarios wherever possible. I say this even though Ron, who is sitting
>>> beside me here now in Snowmass, has told me that this makes identifying
>>> model differences more difficult. Ron also tells me that this is a fight not
>>> worth fighting, but I can't resist commenting anyway..:-)
>>> More usefully I would like to respond to your PS. regarding the diagnosis of
>>> carbon cycle feedbacks. I strongly believe these should be diagnosed
>>> relative to the RCP scenarios. Carbon cycle feedbacks cannot easily be
>>> reduced to an equilibrium response plus a timescale. Carbon uptake
>>> essentially relies on disequilibrium and is therefore dependent on scenario,
>>> so I don't think it is very helpful to define c cycle feedback relative to
>>> idealised 1% per year runs. There are also the potential for significant
>>> "cold-start" problems with the carbon cycle (as land and ocean uptake are
>>> both highly dependent on history). So I vote for diagnosing carbon cycle
>>> feedbacks (at least) relative to the RCP scenarios.
>>> All the best
>>> Peter
>>> Prof Peter Cox,
>>> Met Office Chair in Climate System Dynamics,
>>> Room 336, Harrison Building,
>>> School of Engineering, Computing and Mathematics,
>>> University of Exeter,
>>> Exeter,
>>> EX4 4QF,
>>> Email:,
>>> Tel (univ): 01392 269220,
>>> Tel (mob) : 07827 412572
>>> -----Original Message-----
>>> From: Karl Taylor []
>>> Sent: Tue 22-Jul-08 09:25 AM
>>> To:; Curtis Covey; Jerry Meehl; Mitchell,
>>> John FB (Chief Scientist);;;
>>> Andreas Hense; Asgeir Sorteberg; Erich Roeckner; Evgeny Volodin; Gary L.
>>> Russell; Gavin Schmidt;; 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;
>>> D�ith� Stone; Stott, Peter; Francis Zwiers; Toru Nozawa; Ken Sperber; Dave
>>> Bader; Mike MacCracken;; 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;
>>;; Cox, Peter; 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
>>> Cc: Ronald Stouffer
>>> Subject: Proposed experiment design for CMIP5
>>> Dear all,
>>> As most of you know, plans are well underway for a coordinated set of
>>> climate model experiments, which will constitute the Fifth phase of
>>> CMIP. Attached is a description of the proposed experiments. As
>>> members of the CMIP panel, which was established by the WCRP's Working
>>> Group on Coupled Modelling (WGCM) to help coordinate this activity, we
>>> are seeking your comments. Considerable thought and input from a wide
>>> community of scientists have already contributed to the CMIP5 design,
>>> and therefore major changes are not envisioned. Competing interests and
>>> various tradeoffs have been carefully considered before coming up with
>>> the proposed suite of experiments. Please keep in mind that modeling
>>> groups have limited resources and the experiment must represent a
>>> compromise among various priorities. We will not be able to please everyone.
>>> The CMIP panel must present a final design plan for CMIP5 to the WGCM at
>>> its annual meeting in September, just two months from now. Given this
>>> tight deadline (which cannot slip if the CMIP5 results are to be
>>> available in time for the IPCC's Fifth Assessment Report). For this
>>> reason, we ask that you send us ( and
>>> any comments and suggestions you have by
>>> September 1, 2008.
>>> Feel free to pass this document on to anyone you think will have an
>>> interest in it. We invite comments from scientists associated with all
>>> aspects of the climate change issue, spanning the three IPCC working groups.
>>> With best regards,
>>> Karl Taylor (PCMDI) and Ron Stouffer (Chair, CMIP panel).
>>> P.S. Please note that there are remaining details yet to be worked out.
>>> In particular it has been suggested that experiments 4.2 a&b described
>>> in the document should be performed in conjunction with the so-called
>>> RCP-driven experiments given in Table 2 rather than with the idealized
>>> (1% CO2 increase per year) experiments of Table 4. Experiments 4.2
>>> allow us to separate out the climate-carbon cycle feedback. The original
>>> proposal was in fact to do this separation for the RCP runs, but several
>>> scientists offered compelling arguments for switching this diagnostic
>>> analysis to the 1% runs. Some of the reasons for making this change
>>> from the original proposal can be found in section 9. Still, there are
>>> some scientists who continue to express a preference for the original
>>> design. Please let us know what you think about this.

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