cc: "Pittock,Barrie" , nleary@earth.usgcrp.gov, "Pittock,Barrie" , lindam@ucar.edu, "Jones, Roger" , m.hulme@uea.ac.uk, djgriggs@meto.gov.uk, meehl@ncar.ucar.edu, "Whetton, Peter" , tkarl@ncdc.noaa.gov, m.manning@niwa.cri.nz date: Mon, 23 Oct 2000 10:37:12 -0700 (PDT) from: Stephen H Schneider subject: RE: Table 3-10: a third version and some other considerations to: Timothy Carter Hello all--very constructive exchange. I agree with Barrie that downgrading a star maybe a better reading of the literature--but since I've only read half of it I don't have a strong opinion. I do think two stars would be wrong because that implies we have a great deal of information--thus confidence--that the event is pretty unlikely. Tim, you are indeed right that medium confidence means indifference to more or less since 50% is the random event. THis is why both in umpteen e-mail reviews of SPMs and TS (as well as in the guidance paper) I have tried--mostly in vain--to get people to make positive assertions without qualifiers like could. Then medium confidence has much more meaning. For instance, your table goes at least half way--you do specify the year and rough climate scenario. The best thing would be to make a real estimate of what might happen then--like the 10% ncrease in hurricane intensity--or give a range, say, temperature will increase by 2-4 deg C. Then a medium confidence is a pretty affirmative statement of what we think we know. Medium confidence is true, virtually by definition, when we restrict ourselves to predicting just dierction of change and haven't much extra info to push it up or down. Nevertheless, it does make sense to keep it here, since the WG 2 assignment is for consequences, and if it is consequential to have an event that we deem equally likely to happen and it matters, then so be it--this is represented by your last table with the impacted sectors explicit. Of course, it would be more controvrsial and take a sub group months to craft a real range of projections for 2100 for a given scenario, but then the confidence scale would be more meaningful. But at this stage just stay with what most of us seem to be able to live with--directions of change--and thus we'll have medium confidence almost by definition for those categories where the state of the science doesn't push our confidence in the projection much higher or lower--and that is, as I said, non-trivial information for policymakers who otherwise would be clueless whether such events were expected. Cheers, Steve PS Just got Roger Jones good comments and I agree that we sometimes confuse confidence in events with confidence levels in the state of the science--shouldn't give low confidence on the occurence of an event when we mean specualtive science and we don't really know the likelihood of the event very well. I'm not sure how to deal with this operationally for the Table at this stage, other than to add a phrase to this effect in the already long list of footnotes at the bottom for those entries for which this porblem fits. On Mon, 23 Oct 2000, Timothy Carter wrote: > Dear Barrie et al., > > A few responses/queries to Barrie's helpful comments before Australia logs > out for the day: > > >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. > > [TC] I think we have some of the latter information in the caption and > footnotes. I agree that changes to the text will be needed. > > Am I right in interpreting the views I have heard so far as arguing for > retaining this Table (simplified version) in the SPM? > > >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. > > [TC] Are you (Barrie) suggesting that this should come in the caption or > the text? > > >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). > > [TC] I agree that 4 stars is too high. > > This was a response to the WG I table entry "some models", meaning that all > models analysed showed this, that theoretical studies show such a change, > but that "few current models are configured in such a way to reasonably > represent such changes". > > However, Easterling et al. have possible (= 3 stars), and I would suggest > downgrading to 3 stars rather than 2, for consistency with Easterling et al. > > Caveat re. changes in regional TC frequencies is still footnoted, but I > think we should keep 3 stars for the global changes as the Table entry. > > > > >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). > > [TC] This is given a "likely" label by Easterling et al., who also note "no > direct model analyses, but these changes are physically plausible on the > basis of other simulated model changes", which explains the footnote (c). > > Furthermore, in the footnote to the WG I SPM table, it states: "recent > trends for conditions to become more El Nino-like in the tropical Pacific > are projected to continue in many models, although confidence in such > projections is tempered by some shortcomings in how well El Nino is > simulated in global climate models" > > I'm open to dropping the footnote, if you feel that is appropriate. I > suppose we could downgrade this to 3 stars from 4 stars - any other opinions? > > > > >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. > > [TC] Agreed, I think we should reinstate the references we had in an > earlier version of Table 3-10 on hail and lightning. > > Final comment: I want to have a sense that we are all on the same > wavelength concerning the meaning of the 3 stars (medium confidence) > category. This is defined as 33-67% likelihood. Am I right in thinking > that, baldly expressed, it implies an equal likelihood that something may > or may not happen. Some WG I authors thought that the term medium > confidence conveyed the idea that "though we don't have high confidence in > something happening, we do have medium confidence, implying that though we > may harbour some doubts, we still think on balance, that it will happen" > > Sorry to hark back to endless prior discussions, but better here than in > Plenary! > > Regards, > > Tim > > > ************************************************ > > Dr. Timothy Carter > Finnish Environment Institute > Box 140, Kesäkatu 6, FIN-00251 Helsinki, FINLAND > > Tel: +358-9-40300-315; GSM +358-40-740-5403 > Fax: +358-9-40300-390 > Email: tim.carter@vyh.fi > > ************************************************ > > ------ Stephen H. Schneider Dept. of Biological Sciences Stanford University Stanford, CA 94305-5020 U.S.A. Tel: (650)725-9978 Fax: (650)725-4387 shs@leland.stanford.edu