Monday, June 11, 2012


cc:,, Rob Swart <>,, Tsuneyuki MORITA <>,
date: Tue, 04 Sep 2001 17:44:30 -0400
from: Steve Smith <>
subject: Re: TGCIA scenario recommendations
to: Rob Swart <>,

I had just one point to make regarding this discussion:

>science-policy interface. If science cannot demonstrate that it makes a
>difference in terms of avoided climate change and impacts if GHG
>concentrations are stabilised, why bother? Currently a Danish guy, Bj�rn

There is an important point that was missed here.

Its that "science" can't demonstrate these differences, but that
**GCM's** can't demonstrate these differences.

As Tom noted, doing impact analysis on multiple GCM runs of the type
you propose (i.e., baseline cases vs different policy cases) does not
make much sense. I certainly would council any impact analyst not to
waste their time doing such a thing since, as Tom noted, unless you
can first demonstrate that the climate change patterns (not just
magnitude) differ significantly (in at statistical sense) between the
base case and policy case runs, there's not point in doing a complex

If someone did want to look at this issue, one approach would be to
compare the base case with a 'synthetic" model run, derived from a
combination of the GCM run and simple model results (perhaps with
artificial noise added to derive statistical results). Such an
analysis might be quite valuable. But doing an analysis using only a
handful of GCM runs would not provide any scientifically useful
results that I can see.



>Lomborg, is making the headlines again (Guardian, New York Times,
>Economist), TV programmes, etc.) telling the public (and policymakers) not
>only that there aren;'t any environmental problems, but also, even if
>climate change may be real, it does not make any sense at all to do
>something about it, since efforts to control GHG emissions are expensive
>and the mitigation would not make any difference at all anyway in terms of
>avoiding negative consequences. Very popular message. Now clearly,
>scientists should clearly explain what they can say about this issue. My
>expectation would indeed be that comparing climate changes resulting from
>reference cases and from stabilization cases would not be distinguishable
>until well into the 2nd half of the century (like in the GRL paper), but if
>this is so, so be it. 2050 seems a lot closer now in 2001 (2050 is THIS
>century and our childrens' lifetime) than it was in 1999 (when 2050 was
>something of the next century and some abstract next generations). It is a
>matter of communication skills to get the message across about the long
>timescales and inertia of the systems involved, and the difficulty of
>identifying the climate change signal in the noise of natural variability.
>I would be curious what your opinion is about the UK work of Nigel Arnell,
>Martin Parry, John Mitchell and others, analysing the (significant) avoided
>impacts of 550 stabilisation from an IS98a reference. Another strategy of
>concerned scientists may be not to do these analyses at all in order to
>avoid a possible result that the differences between reference and
>stabilisation can not be demonstrated in a scientifically credible and
>unambiguous way and hence climate policy action may be obstructed. To me,
>this does not seem to be the honest way to go.
>I am not sure what this all implies for the planned recommended
>stabilization runs. Your points about the climate sensitivity and non-CO2
>gases are well taken. I am not sure the sulfur emissions in the proposed
>post-SRES scenarios would make a lot of difference, since already in the
>SRES base cases sulfur emissions are pretty low, and these would only be
>slightly different (usually lower) in the stabilisation cases. You suggest
>"carefully constructed idealized scenarios". Do you mean carefully
>constructed from the climate system point of view in order to get
>"distinguishable results", or carefully constructed from the socio-economic
>point of view so as to analyse real-world consistent and plausible futures
>(the latter is what Morita's exercise tried to achieve)? My answer would
>be: both.
>I'd like to reflect a little bit more on this and since I am a scenario
>expert rather than a climate expert, await reactions from people more
>expert in the area of climate modelling, like Sarah, Mike and Tim, and
>Martin himself as chair of the TGCIA.
>Thanks again,
> Tom Wigley
> <wigley@ucar. To: Rob Swart
> edu> cc:,
>Tsuneyuki MORITA <>, steve smith
> 25-08-01 <>, (bcc: Rob
> 01:47 Subject: Re: TGCIA
>scenario recommendations
> Please
> respond to
> wigley
>Rob and others,
>The key thing with doing stabilization runs with AOGCMs is (as Rob says)
>that the different cases "would have to be distinguishable from one
>another". This is the crux of the problem (in fact, it is a non-trivial
>problem even to define what is meant by "distinguishable from one
>A few years ago we decided to try to do some matched no-climate-policy
>and (550ppm) stabilization runs where the two scenarios had some
>semblance of realism. (It turns out that the only similar work is that
>done by the Hadley Ctr, but the scenarios they used are highly
>idealized.) Our runs were also idealized in that we only changed CO2 --
>in the best scientific tradition of changing only one thing at a time to
>assess sensitivities. The first results of our exercise (using CSM) are
>in Dai et al., J. Climate 14, 485-519, 2000. A number of things were
>clear from this. First, one cannot tell much from single realizations of
>the two cases -- ensemble runs are essential. Second, as we already knew
>from running simple models, the no-policy and stabilization runs diverge
>only slowly. Even after 50 years, the two are only just distinguishable
>at the global-mean level; so, clearly,differences at the regional level
>(especially for precipitation) would not be detectible above the noise
>of natural variability.
>So our next step was to do ensembles of 5, this time using PCM instead
>of CSM (this paper is in press in BAMS -- for a pdf preprint, look at
> Even then, for ensemble means, the
>separation between the no-policy and stabilization cases is slow. So I
>devised an extended no-policy case out to 2200 (50 years beyond where
>the CO2 level stabilizes in the stabilization run), and we extended some
>of the runs out to 2200. This work is in press in GRL (and downloadable
>from the above site). Additional important results come from these
>experiments. One important result is that, even for precipitation, the
>*patterns* of change are not detectibly different between the no-policy
>and stabilization runs. A second important result is that, for most of
>the world the intra-ensemble differences are similar to or greater than
>the underlying signals of change. Distinguishing the no-policy and
>stabilization runs therefore presents a much greater challenge than any
>of you probably realize.
>There are two issues to keep in mind, however. The first is that PCM and
>CSM have quite low climate sensitivities. So, will things be different
>if one used a more sensitive model? I suspect not in any major way. The
>reason is because inter-annual variability tends to be higher in more
>sensitive models, so the signal-to-noise ratio may not change much. This
>also applies to the intra-ensemble noise, since the root cause of these
>intra-ensemble differences is the internal variability of the model.
>The second issue is that we have only changed CO2 in our experiments. We
>know that attempts to stabilize CO2 via emissions reductions also affect
>SO2 emissions -- so perhaps the no-policy and stabilization cases might
>be more distinguishable if one accounted for these concomitant SO2
>effects? I have addressed this issue at the global-mean level in a paper
>on stabilization that I will attach to this email. (A more extensive
>analysis is in another paper, with Steve Smith as my co-author, that I
>am not ready to share with anyone just yet.) My judgment, as someone
>with quite a lot of experience in this area, is that having full spatial
>details will not make the problem any easier; since, as the spatial
>scale is reduced so the noise increases.
>My recommendation from all this is that, first, you read the attached
>paper (and I would welcome feedback on this) and the three
>above-mentioned Dai et al. paper. Then, you might want to re-consider
>what your strategy should be. In my view, I do not think we as a
>community are at the stage where we can blindly develop paired no-policy
>and stabilization scenarios and simply feed them into AOGCMs to see the
>consequences. I believe that carefully constructed idealized scenarios
>(perhaps based on what Morita is doing) will provide much more useful
>information. You are already probably well aware of the need to do
>ensemble runs, and I don't need to remind you how computationally
>expensive this can be.
>I hope these comments, and the papers, are useful. I'm sorry that it is
>impossible for me to come to the Barbados meeting, but I am willing to
>help in any way that I can.
>Best wishes (and good luck), Tom.
>Rob Swart wrote:
> >
> > Dear Sarah, Tom, Tsuneyuki, Martin, Mike and Tim,
> >
> > Back from holidays I found your email exchange. Let me first apologize
> > I did not inform Sarah about this TGCIA action. I remembered from the
> > IPCC-TGCIA meeting ? apparently wrongly - that Mike and/or Tim would
> > Sarah, as they would be in touch with her anyway (I did not even have
> > Sarah's email address at the time). Let me also reiterate the reason for
> > Tsuneyuki's invited proposal. In order to have comparable GCM results
> > available and impact studies based on these results at the time of the
> > Fourth Assessment Report, and taking into account that GCM teams are
> > unlikely to perform dozens of runs, the IPCC-TGCIA (chaired by Martin)
> > intends to recommend a limited set of both baseline and stabilization
> > scenarios for such runs. In this way, impact modellers in the coming
> > could base their analysis on different runs from different GCMs for the
> > same socio-economic scenario(s). Evidently, teams are free to run
> > scenario they think interesting, but comparability would be preferable,
> > many teams have proven responsive to IPCC-TGCIA recommendations in the
> > as I understand it.
> >
> > The TGCIA has reached agreement on which 4 of the 40 SRES baseline
> > scenarios would be most interesting (see meeting report: 4 scenarios
> > A2, B1 and B2) for 3 time periods 2020s, 2050s and 2080s). The next
> > question was: since a (maybe "the") core policy question is what the
> > benefits (or avoided impacts) would be of stabilizing GHG concentrations
> > various levels, and since impact analysis should be based directly on GCM
> > results rather than on results from simple climate models/IA models, it
> > would be useful to also recommend a limited set of stabilization cases.
> > make this a sensible effort, all the cases would have to be
> > from one another from a GCM viewpoint. This may allow for combining
> > scenarios which may be very different socio-economically, but would give
> > very similar climate results for this century, such as the B1 and 550,
> > the 650 and B2 cases. The stabilization cases would be selected from the
> > following table, of which the cells contain available (post-SRES)
> > runs:
> > |-------------+-------------+-------------+-------------+-------------|
> > | |450 ppm |550 ppm |650 ppm |750 ppm |
> > |-------------+-------------+-------------+-------------+-------------|
> > |A1T | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> > |A1B | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> > |A1FI | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> > |A2 | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> > |B1 | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> > |B2 | | | | |
> > |-------------+-------------+-------------+-------------+-------------|
> >
> > It was suggested to select 2-4 cases from the more than 70 scenarios runs
> > in the post-SRES programme co-ordinated by Tsuneyuki. Tom, it may well be
> > that your "post-WRE" work serves the same purpose, but the rationale for
> > selecting post-SRES cases would be: consistency with the SRES narratives
> > and numbers of the IPCC, and the much-acclaimed multi-model
> > of the (post-)SRES work. To downsize the 70-odd cases to 2-4 cases and
> > burden Sarah too much, it was suggested to have one model (MAGICC) run a
> > subset of some 10-15 cases which seemed to make sense. Please also note
> > that not all 70-odd cases are useable, either because they do not have
> > relevant GHG gases, or there have been questions about the
> > consistency/quality of their assumptions, e.g. a correct simulation of
> > SRES base case by teams participating in post-SRES but not in SRES
> > Tsuneyuki?). More importantly, Tsuneyuki used his intimate knowledge of
> > cases and their distribution over base cases and stabilization levels to
> > recommend 13 cases. This selection was discussed with me and Naki during
> > brief meeting in Washington in June and seemed to be a very appropriate
> > one.
> >
> > I noted the remark by Sarah that mean climate change results would be
> > rather be model-independent (for a given climate sensitivity), while
> > Tsuneyuki notes the large differences in the post-SRES work. These
> > differences may not have to do with different approaches with respect to
> > the carbon cycle or radiative forcing calculations, but rather with the
> > freedom modellers had (or rather: took) in selecting the time path
> > 2100) towards stabilization/time horizon, and the changes in emissions of
> > non-CO2 GHG in the stabilization analyses which focused primarily on CO2
> > stabilization. This would need to be clarified in detail for the runs to
> > selected, and I suggest that only those runs are further used for which
> > authors provide sufficient information on these issues.
> >
> > Concluding, I would like to ask Sarah, if she would be willing to take
> > material provided by Tsuneyuki and perform the required calculations for
> > the 13 cases (radiative forcing, global mean temperature and sea level
> > rise, right, Mike/Tim?) within the next 1-2 months. The results would be
> > discussed electronically in a small group (the addressees of this
> > in October/November and a preliminary proposal based on these discussions
> > would be the input for a discussion on this issue during the next TGCIA
> > meeting in Barbados, in November. Tom's recent work may be useful for
> > discussion as well, and I wonder if the mentioned (draft) papers could be
> > distributed to this group or even the full TGCIA.
> >
> > Kind regards,
> >
> > Rob
> >
> > Dr. Rob Swart
> > Head, Technical Support Unit
> > Intergovernmental Panel on Climate Change Working Group III: Mitigation
> > P.O. Box 1
> > 3720 BA Bilthoven
> > Netherlands
> > tel. 31-30-2743026
> > fax. 31-30-2744464
> > email:
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