cc: Tom Wigley , "Thomas.R.Karl" , John.Lanzante@noaa.gov, carl mears , "David C. Bader" , "'Dian J. Seidel'" , "'Francis W. Zwiers'" , Frank Wentz , Karl Taylor , Leopold Haimberger , Melissa Free , "Michael C. MacCracken" , "'Philip D. Jones'" , Sherwood Steven , Steve Klein , "Thorne, Peter" , Tim Osborn , Tom Wigley , myles , Bill Fulkerson date: Wed, 02 Jan 2008 13:54:59 -0700 from: Susan Solomon subject: Re: Douglass et al. paper to: santer1@llnl.gov Dear Ben, Thanks for your query. A number of the AR4 models have included ozone climatologies but only a partial description of the trends .e.g, some use Randel and Wu; CCSM used the one we developed with Jeff Kiehl. These had quite good ozone losses in the extratropics but do not include the observed losses below 20 km in the tropics. So they did not simulate the effect seen in Forster et al. The lower tropical ozone losses have long been viewed as 'possible but controversial' and hence left out of the earlier ozone trend climatologies. Better ozone measurements now make it much clearer to me that these tropical trends are real and should not be ignored. The most recent Randel and Wu paper includes it, but that is not what was used in the AR4 models. Of course, if you have extratropical ozone losses, that will have some effect on the global mean temperatures. But the tropical ozone effects can exert a huge influence on the global mean (e.g., tropics is about half the global area average; the Antarctic ozone hole, impressive as it is, and nicely included as it is in models, is a good deal less than 10% of the global area average). best Susan At 12:42 PM -0800 1/2/08, Ben Santer wrote: >Dear Susan, > >Many thanks for your email, which has stimulated >a lot of interesting discussion in our little >"focus group". I had a quick question. Your >email implies that none of the AR4 models >"prescribes an observed tropical ozone trend" in >the 20c3m simulations. Is this correct? About >half of the AR4 models prescribe stratospheric >ozone changes in their 20c3m runs (e.g., CCSM3, >PCM, GFDLCM2.0, GFDLCM2.1, GISS-EH and GISS-ER, >HadGEM1). In these simulations, are ozone trends >in the tropics set to zero? We will check this >in the next few days. I note that a number of >AR4 models also include some estimate of >observed changes in tropospheric ozone, obtained >with different chemical transport models. > >In both the 2005 Santer et al. Science paper and >Chapter 5 of the CCSP "Vertical Temperature >trends" report, we did attempt to partition the >model simulations into groups with and without >forcing by stratospheric ozone changes. For >example, in footnote #53 of CCSP Chapter 5 (page >110), we noted that: > >"Due to ozone-induced cooling of the lower >stratosphere, the model-average T2 trend is >slightly smaller (0.12 degrees C/decade) and >closer to the RSS result if it is estimated from >the subset of 20CEN runs that include >stratospheric ozone depletion. Subsetting in >this way has little impact on the model-average >T2LT and T*G trends." (T*G denotes a >layer-averaged (global-mean) tropospheric >temperature computed using the Fu et al. method) > >As we've pointed out in previous papers (most >recently in our water vapor D&A paper), one of >the problems with such subsetting exercises is >that they do not cleanly isolate the effect of >an individual forcing. > >Best regards and best wishes for 2008, > >Ben >Susan Solomon wrote: >>Dear All, >> >>Thanks very much for the helpful discussion on these issues. >> >>I write to make a point that may not be well >>recognized regarding the character of the >>temperature trends in the lowermost >>stratosphere/upper troposphere. I have already >>discussed this with Ben but want to share with >>others since I believe it is relevant to this >>controversy at least at some altitudes. The >>question I want to raise is not related to the >>very important dialogue on how to handle the >>errors and the statistics, but rather how to >>think about the models. >> >>The attached paper by Forster et al. appeared >>recently in GRL. It taught me something I >>didn't realize, namely that ozone losses and >>accompanying temperature trends at higher >>altitudes can strongly affect lower altitudes, >>through the influence of downwelling longwave. >>There is now much evidence that ozone has >>decreased significantly in the tropics near 70 >>mbar. What we show in the attached paper by >>Forster et al is that ozone depletion near 70 >>mbar affects temperatures not only at that >>level, but also down to lower altitudes. I >>think this is bound to be important to the >>tropical temperature trends at least in the >>100-50 mbar height range, possibly lower down >>as well, depending upon the degree to which >>there is a 'substratosphere' that is more >>radiatively influenced than the rest of the >>troposphere. Whether it can have an influence >>as low as 200 mbar - I don't know. But note >>that having an influence could mean reducing >>the warming there, not necessarily flipping it >>over to a net cooling. This 'long-distance' >>physics, whereby ozone depletion and associated >>cooling up high can affect the thermal >>structure lower down, is not a point I had >>understood despite many years of studying the >>problem so I thought it worthwhile to point it >>out to you here. It has often been said (I >>probably said it myself five years ago) that >>ozone losses and associated cooling can't >>happen or aren't important in this region - but >>that is wrong. >> >>Further, the fundamental point made in the >>paper of Thompson and Solomon a few years back >>remains worth noting, and is, I believe, now >>resolved in the more recent Forster et al >>paper: that the broad structure of the >>temperature trends, with quite large cooing in >>the lowermost stratosphere in the tropics, >>comparable to that seen at higher latitudes, is >>a feature NOT explained by e.g. CO2 cooling, >>but now can be explained by the observed ozone >>losses. Exactly how big the tropical cooling >>is, and exactly how low down it goes, remains >>open to quantitative question and improvement >>of radiosonde datasets. But I believe the >>fundamental point we made in 2005 remains true: >>the temperature trends in the lower >>stratosphere in the tropics are, even with >>corrections, quite comparable to that seen at >>other latitudes. >>We can now say it is surely linked to the >>now-well-observed trends in ozone there. >>The new paper further shows that you don't have >>to have ozone trends at 100 mbar to have a >>cooling there, due to down-welling longwave, >>possibly lower down still. Whether >>enhanced upwelling is a factor is a central >>question. >> >>No global general circulation model can >>possibly be expected to simulate this correctly >>unless it has interactive ozone, or prescribes >>an observed tropical ozone trend. The AR4 >>models did not include this, and any >>'discrepancies' are not relevant at all to the >>issue of the fidelity of those models for >>global warming. So in closing let me just >>say that just how low down this effect goes >>needs more study, but that it does happen and >>is relevant to the key problem of tropical >>temperature trends is one that I hope this >>email has clarified. >> >>Happy new year, >>Susan >> >> >>At 6:13 PM -0700 12/29/07, Tom Wigley wrote: >>>Tom, >>> >>>Yes -- I had this in an earlier version, but I did not want to >>>overwhelm people with the myriad errors in the D et al. paper. >>> >>>I liked the attached item -- also in an earlier version. >>> >>>Tom. >>> >>>+++++++++++++ >>> >>>Thomas.R.Karl wrote: >>> >>>>Tom, >>>> >>>>This is a very nice set of slides clearly >>>>showing the problem with the Douglass et al >>>>paper. One other aspect of this issue that >>>>John L has mentioned and we discussed when we >>>>were doing SAP 1.1 relates to difference >>>>series. I am not sure whether Ben was >>>>calculating the significance of the >>>>difference series between sets of >>>>observations and model simulations >>>>(annually). This would help offset the >>>>effects of El-Nino and Volcanoes on the >>>>trends. >>>> >>>>Tom K. >>>> >>>>Tom Wigley said the following on 12/29/2007 1:05 PM: >>>> >>>>>Dear all, >>>>> >>>>>I was recently at a meeting in Rome where Fred Singer was a participant. >>>>>He was not on the speaker list, but, in >>>>>advance of the meeting, I had thought >>>>>he might raise the issue of the Douglass et >>>>>al. paper. I therefore prepared the >>>>>attached power point -- modified slightly since returning from Rome. As it >>>>>happened, Singer did not raise the Douglass et al. issue, so I did not use >>>>>the ppt. Still, it may be useful for members >>>>>of this group so I am sending it >>>>>to you all. >>>>> >>>>>Please keep this in confidence. I do not >>>>>want it to get back to Singer or any >>>>>of the Douglass et al. co-authors -- at >>>>>least not at this stage while Ben is still >>>>>working on a paper to rebut the Douglass et al. claims. >>>>> >>>>>On slide 6 I have attributed the die tossing >>>>>argument to Carl Mears -- but, in >>>>>looking back at my emails I can't find the >>>>>original. If I've got this attribution >>>>>wrong, please let me know. >>>>> >>>>>Other comments are welcome. Mike MacCracken and Ben helped in putting >>>>>this together -- thanks to both. >>>>> >>>>>Tom. >>>>> >>>>>++++++++++++++++++++++++++++++++++++++++ >>>> >>>> >>>>-- >>>> >>>>*Dr. Thomas R. Karl, L.H.D.* >>>> >>>>*/Director/*// >>>> >>>>NOAA's National Climatic Data Center >>>> >>>>Veach-Baley Federal Building >>>> >>>>151 Patton Avenue >>>> >>>>Asheville, NC 28801-5001 >>>> >>>>Tel: (828) 271-4476 >>>> >>>>Fax: (828) 271-4246 >>>> >>>>Thomas.R.Karl@noaa.gov >>>> >>> >>> >>> >>>Attachment converted: Junior:Comment on Douglass.ppt (SLD3/«IC») (0022CEF5) > > >-- >---------------------------------------------------------------------------- >Benjamin D. Santer >Program for Climate Model Diagnosis and Intercomparison >Lawrence Livermore National Laboratory >P.O. Box 808, Mail Stop L-103 >Livermore, CA 94550, U.S.A. >Tel: (925) 422-2486 >FAX: (925) 422-7675 >email: santer1@llnl.gov >----------------------------------------------------------------------------