cc: Mike Wallace , Phil Jones date: Thu, 11 Dec 2008 09:00:32 -0700 from: David Thompson subject: Re: A new paper on 20th century global-mean temperature variability to: Kevin Trenberth Kevin, I agree. The signal of other aerosols is presumably isolated in the residuals (ie, perhaps as the cool-down in the 70s). We should clarify that in the text. -Dave On Dec 11, 2008, at 8:56 AM, Kevin Trenberth wrote: David I forgot to include one other aspect you may want to consider also: and that is the role of aerosol forcing. You do include the volcanic aerosol, and find a nice cleaner relationship, and so it implies that changes in other aerosol may also have a signal that is not accounted for. Kevin David Thompson wrote: Kevin, Thanks much for the helpful comments (and so quick!). Your points about the figures are well taken. I admit noting 'ticks at xx' is a little lazy, and that the reader would appreciate specific units on the axes. And I'll think about the precipitation relationships. I'm not sure I've ever seen a map of grid point precipitation regressed on global-mean temperatures (with ENSO removed), but it would be interesting if it turns out useful. Either way, I'll be sure to mention the work. Thanks, Dave On Dec 10, 2008, at 11:11 AM, Kevin Trenberth wrote: David This looks like a very valuable contribution. I have a few suggestions. Firstly you may find the following two publications of interest Trenberth, K. E., and D. J. Shea, 2005: Relationships between precipitation and surface temperature. Geophys. Res. Lett., 32, L14703, doi:10.1029/2005GL022760.[[1]Paper (.pdf)] Trenberth, K. E., and A. Dai, 2007: Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering. Geophys. Res. Lett., 34, L15702, doi:10.1029/2007GL030524. [2][PDF] The first paper notes that there are strong relationships between precipitation and surface temperature that vary with latitude and season. Over land there is a strong negative correlation in summer extratropical continents and year round in tropics so that conditions are either hot and dry or cool and wet. So this relates to wetter conditions also being cloudier and changing SH and LH surface fluxes, etc. In winter at high lats the correlation is positive which is Clausius Clapeyron: warm and moist advection and ability of air to hold moisture. Over oceans there are also some interesting relations, some governed by ENSO: high SSTs go with rain. Anyway you mention natural variability and the SLP field but some of this may be through the precip relation, not just flow of air from land to ocean to land etc. You may want to at least mention this and the assoc mechanisms, and it may we a way to further reduce the "noise"? The second paper may be of interest wrt the volcanic eruption effects and the radiative forcing, and again the huge effect on rain and runoff. Although not speculated on in the paper, we show that after Pinatubo there is a decrease in land precip. We think this comes about in two stages. 1) the land cools more than ocean and the precip moves off shore, but at this stage there is no global decease in precip; then 2) there is a decease in evaporation and thus in global precip. For your study, this has two implications. 1) Part of the mechanism for influencing temperatures also comes through the precip link noted in paper (1) above. (2) In your Fig 7 you have the effects stratified by total, land and ocean, and it would be of interest to also see land minus ocean, and see whether the response is indeed quicker over land. Eyeballing it, it seems so. Now a few other comments on the paper. These are offered in the hope that it will help give the paper the impact it deserves. 1) The figures could use some work. Actually a lot of work. a) I urge you to add the zero line on all the time series. This helps also to see whether the time series does have low frequency components. b) I urge you to add some labels on the y axis. At least 0 and plus and minus 0.1C. (c) This sort of thing could easily be done in Illustrator. If you don't use Illustrator for your figures, I strongly recommend it and can talk to you about it. You can input ps files and generate eps, with nice labels and all sorts of touch ups, control of line widths and dot-dash types etc. You can control the white space and layout nicely also. In Illustrator you can also "save for microsoft" and it generates png files that are ideal in size for word documents or powerpoint, and so the size of the files is much reduced (e.g. from what you have). d) Fig. 2 is hard to see the white lines. (e) Fig 13 needs units on x axis: months? 2) The natural variability can, of course, also be affected by climate change and warming. A central question is how ENSO changes with climate change, for instance. You method is good but you should acknowledge (more) that the "natural variability" may also contain some climate change signals. 3) The difference in the effective heat capacity may also reflect the tropics (ENSO) vs global nature for volcanoes? You may want to speculate about the implications of these figures for changes in solar forcing and especially the 111 year sun spot cycle. 4) Alan Robock and Caspar Amann have a new volcanic forcing time series, pub in press in JGR I believe. Hope these help Kevin David Thompson wrote: Dear Kevin, Ben, Tom, Hope all is well. Mike Wallace, Phil Jones, John Kennedy (Met Office) and myself are about to submit a paper on the time-history of 20th century global-mean temperatures. The study is a follow-on to our study last summer which documented the discontinuity in SSTs in ~1945. Anyway, the paper is being passed around the authors for one last look, and we thought you might appreciate the chance to comment on the manuscript before it's submitted. I understand everyone is busy, especially at this time of year. And it's likely one or more of you will get the paper to review. But if you're interested and have any general comments, we'd appreciate your thoughts. Our rough plan is to submit within the first couple weeks after the New Year. The paper is attached as a doc file. And the figures are online at: [3]www.atmos.colostate.edu/~davet/outgoing/Figures_JClimate_Dec9.pdf Since it's at the (near-final) draft stage, please treat the work as confidential for now (ie please don't distribute the text or figures). Thanks, Dave = _______________________________________________________________________________ -------------------------------------------------------------------- -------------------------------------------------------------------- David W. J. Thompson [4]www.atmos.colostate.edu/~davet Dept of Atmospheric Science Colorado State University Fort Collins, CO 80523 USA Phone: 970-491-3338 Fax: 970-491-8449 = -- **************** Kevin E. Trenberth e-mail: [5]trenbert@ucar.edu Climate Analysis Section, [6]www.cgd.ucar.edu/cas/trenbert.html NCAR P. O. Box 3000, (303) 497 1318 Boulder, CO 80307 (303) 497 1333 (fax) Street address: 1850 Table Mesa Drive, Boulder, CO 80305 -------------------------------------------------------------------- -------------------------------------------------------------------- David W. J. Thompson [7]www.atmos.colostate.edu/~davet Dept of Atmospheric Science Colorado State University Fort Collins, CO 80523 USA Phone: 970-491-3338 Fax: 970-491-8449 -- **************** Kevin E. Trenberth e-mail: [8]trenbert@ucar.edu Climate Analysis Section, [9]www.cgd.ucar.edu/cas/trenbert.html NCAR P. O. Box 3000, (303) 497 1318 Boulder, CO 80307 (303) 497 1333 (fax) Street address: 1850 Table Mesa Drive, Boulder, CO 80305 -------------------------------------------------------------------- -------------------------------------------------------------------- David W. J. Thompson www.atmos.colostate.edu/~davet Dept of Atmospheric Science Colorado State University Fort Collins, CO 80523 USA Phone: 970-491-3338 Fax: 970-491-8449