Monday, June 11, 2012


date: Mon, 23 Oct 2000 13:12:45 +1100
from: "Pittock,Barrie" <>
subject: RE: Table 3-10: a third version and some other considerations
to: 'Timothy Carter' <>,,, "Pittock,Barrie" <>,, "Jones, Roger" <>,,,, "Whetton, Peter" <>,,,

Hi Tim et al.,

thanks for a job well done, if not yet finished! I agree with what Steve
and others have said, and applaud the efforts by Tim especially version 3 of
table 3-10.

I agree with the caption, but would like to see an explicit, up-front
statement of the need to provide appropriate risk assessment advice for
decisionmakers in WG2, as part of the text. This would also appear in the
SPM. I.e., we need to make clear why we consider possibilities which are not
in the high confidence categories, and which are not necessarily based on
AOGCMs at their coarse resolution, but also on high resolution limited area
models and on physical reasoning and observed correlations.

We should also consider wording that admits that there is a range of expert
opininon, and that the quantitative uncertainties given are therefore a
collective but not universally agreed view. I stand by to help with that
wording if you ask Tim.

At the risk of Tim tearing his hair I would also like to make a few detailed
comments on the entries.

Re TC "increased frequency", I know several vocal TC experts who argue
strongly that this is highly unlikely globally (see the two reviews by them
published in BAMS in recent years), and would therefore be happier to
downgrade the confidence for future increases to two stars. The footnote
should remain, as that is the main thing re TC frequencies (they will change
regionally in frequency, I think with high confidence).

Re a more El Nino-like mean state. I cannot understand why footnote c is
there. Practically all the evidence is from GCMs, and some is pretty
detailed analysis of frequency distributions of east-west temperature
contrasts in the simulations. One from our lab even looks at an ensemble of
runs (only three) and compares with observations, and suggests a reason for
a delay in appearance (Cai and Whetton, GRL 27, 2577-2580, Aug. 15, 2000).
However, I would also like to see the number of stars reduced to three as
the AOGCMs are not all that good and there is some disagreement (see the
latest PCMDI Report No. 61 "El Nino Southern Oscillation in coupled GCMs",
Sept. 2000 for a full account of the model shortcomings).

Both these suggested changes (TCs and ENSO) would be more in line with WG1
assessments I think, and not preclude WG2 considering the possible impacts
of the possible changes.

I do wonder if there should be more added in the text to justify our WG2
confidence levels, such as more references to the literature, especially to
some that may not have made it in WG1 (eg., how is hail and lightning dealt
with in WG1?). I have not yet read the WG1 SPM to see, nor of course the
latest changes to their chapters. But I leave that to Tim and others'
judgement as they are more involved more with WG1.

Thanks again, Tim. I will now go ahead and make minor changes to Ch.12 on
the basis that Table 3-10 will still support our chapter's treatment of
extreme events.



Dr A. Barrie Pittock
Post-Retirement Fellow*, Climate Impact Group
CSIRO Atmospheric Research, PMB 1, Aspendale 3195, Australia
Tel: +61 3 9239 4527, Fax: +61 3 9239 4688, email:

* This means I am working part-time, primarily on writing for the
Intergovernmental Panel on Climate Change. Please refer any matters re the
Climate Impact Group to Dr. Peter Whetton, Group Leader, at
<>, tel. +61 3 9239 4535.

"Far better an approximate answer to the right question which is often
vague, than an exact answer to the wrong question which can always be made
precise." J.W. Tukey as cited by R. Lewin, Science 221,636-639.

> -----Original Message-----
> From: Timothy Carter []
> Sent: Sunday, October 22, 2000 9:53 PM
> To:;;
> Subject: Table 3-10: a third version and some other considerations
> Dear extremes colleagues,
> Following Steve Schneider's rapid response yesterday, I have prepared a
> third version of Table 3-10 that is even closer to the original. In this
> case, I have merged old columns 1 and 2 (as in the WG I version and as
> Neil
> suggested earlier), and have modified the footnotes and caption, but
> retained all other features.
> In particular, note the part of the caption I have highlighted in bold
> (for
> your consideration), which attempts to explain why WG II has a
> quantitative
> scale and WG I does not (though the true reasons would require an academic
> thesis!). I am repeating the key sentence below and then note a possible
> alternative:
> In current version 3:
> "Entries in columns two and three are expressed in quantitative terms to
> assist policy interpretation, based on judgements by WG I and WG II
> authors."
> Another way of presenting these reasons might be to stress that this type
> of assessment is required by impact assessors in order to consider
> vulnerability in terms of risks of impact. This way, we would keep the
> reasoning "scientific", but from a WG II perspective, and would not need
> to appeal to "policy relevance".
> In view of the three versions you have been sent, in deciding on what
> course to take, I think we now have to consider seriously several points:
> (1) If we adopt version 2 (WG I-type descriptions), we are consistent with
> WG I, though the table contains additional information invented by us,
> using the same type of descriptive language as in the WG I Table. Here we
> would (a) still have to defend our subjective interpretation of WG I
> material for the categories not covered by WG I, (b) be inconsistent with
> chapters in WG II (unless they are able to change their wording, as
> Leonard
> Nurse indicated for small islands in his recent mail), and (c) go against
> the principle of providing "policy useful" information that Steve
> expressed
> (and see my alternatives above).
> (2) If we adopt versions 3 or 1 (likelihoods), we are taking a different
> course from WG I, and we are open to the charge of being inconsistent with
> WG I and providing additional information that does not appear (at least
> prominently) in WG I. We could be accused of over-representing our
> understanding and there will doubtless be an undercurrent of suspicion
> that
> WG II authors are not qualified to make such judgements on climatological
> matters. Are we prepared to defend ourselves against such (potential)
> charges?
> (3) If we use something like version 3 or version 1 (including
> likelihoods), we must consider how this should be reported in the SPM.
> This
> is what governments will comment on this time around (some, but I doubt
> many, may refer to the revised chapters). We can try to revise the
> simplified Table we have in the current draft SPM. Alternatively, we could
> finesse the problem of consistency by NOT including a table at all in the
> SPM, but rather use some appropriate (weasel?) wording to describe the
> changes in extremes expected, which represents a compromise between the WG
> I table and Table 3-10. Whatever the outcome, I need to draft some wording
> anyway that is consistent with the final Table 3-10 for the Chapter 3
> executive summary.
> Best regards,
> Tim
> <<t3-10v#3.doc>>

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