cc: Jonathan Overpeck , Keith Briffa , Eystein Jansen date: Tue, 18 Jul 2006 14:45:32 +0200 from: Fortunat Joos subject: Re: new fig 6.14 to: Tim Osborn Dear Tim, Sorry, that was a very careless and a totally inappropriate choice of words. I seriously apologize. Of course smoothing is not dishonest (I do it also all the time). To the contrary, I very much apreciate all your hard work to do these figures. I know that it is very time consuming from own experience ... (that is perhaps why I did not reflect on my wording when writing the e-mail). What I wanted to say is that if one has the opportunity to show directly what forcing was used by the model than I very much prefer to do so. I hope there remains no misunderstanding. I realize now that I should have used more modest wording at various places. Let us see what Eystein, Peck and Keith are thinking about it. With best wishes, Fortunat Tim Osborn wrote: > Hi all, > > thanks for the responses, Peck and Fortunat. > > I drafted the new figure 6.14 following as closely as possible the > approach used for the original forcing/simulation figure (now 6.13). > This is why I smoothed all series and used a common anomalisation period > for all curves across all panels. It can greatly help to interpret why > the simulated temperature responds in the way it does, because the zero > (or "normal" level) is comparable across plots and because the strengths > of different forcings can be compared *on the same timescale* as the > simulated temperatures are shown. And, for 6.13, with so many different > forcings and models shown, it would have been impossible to use > unsmoothed series without making the individual curves indistinguishable > (or indeed fitting them into such a compact figure). > > Now that the EMIC panels are separate from the original 6.13, we do have > the opportunity to make different presentational choices. But I think, > nevertheless, that some of the reasons for (i) proportional scaling, > (ii) common anomalisation period; and (iii) smoothing to achieve > presentation on comparable time scales, that held for 6.13 probably also > hold in 6.14. > > However, I also appreciate the points raised by Fortunat, specifically > that (i) it is nice to be able to compare the magnitude of the 11-yr > solar cycles with the magnitude of the low-frequency solar variations; > and (ii) that using a modern reference period removes the interpretation > that we don't even know the forcing today. > > So we have various advantages and disadvantages of different > presentational choices, and no set of choices will satisfy all these > competing demands. > > One thing that I am particularly perturbed about is Fortunat's > implication that to show smoothed forcings would be scientifically > dishonest. I disagree (and I was also upset by your choice of > wording). If it were dishonest to show smoothed data, then presumably > the same holds for 6.13 (but its impossible to distinguish all the > different volcanic forcings if shown unsmoothed), but also to every > other graphic... should I be showing the EMIC simulated temperatures > without smoothing too, so you can see the individual yearly responses to > the volcanic spikes? But annual means are formed from the temperatures > simulated on the model timesteps, so we still wouldn't be showing > results that had not been post-processed. Most climate models, even > GCMs, respond in a quasi-linear way, such that the smoothed response to > unsmooth forcing is very similar to the response to smooth forcing. So > if we are interested in the temperature response on time scales of 30 > years and longer, it seems entirely appropriate (and better for > interpretation/comparison of forcings) to show the forcings on this time > scale too, because the forcing variations on those time scales are the > ones that are driving the temperature response (even though the forcing > may be intermittent like volcanoes or have 11-yr cycles like solar). > > The choice of smoothing / no smoothing is not, therefore, anything to do > with honesty/dishonesty, but is purely a presentational choice that can > made accordingly to what the purpose of the figure is. Here our purpose > seems to be long-term climate changes, rather than response to > individual volcanoes or to the 11-yr solar cycle. > > So the position is: > > (1) smoothing or no smoothing: there are arguments for both choices, > though clearly I prefer smoothing and Fortunat prefers no smoothing. I > could make a figure which kept the smooth lines but put the raw annual > histogram volcanic spikes underneath in pale grey, as Peck requested > anyway (and possibly put the 11-yr solar cycles in pale brown underneath > the smoothed brown solar series). This would be a compromise but the > main problem is that the scale of the largest volcanic spikes would far > exceed the scale I am using to show the smoothed series (so the panel is > not large enough to do this)! > > (2) pre-industrial or present-day anomalisation reference period: again > there are arguments for both choices. Whatever we choose, I firmly > believe it should be the same for *all* curves in this figure (which can > make a dramatic difference). > > (3) exaggeration of solar scale or proportional vertical scales: this is > the one that I have the firmest opinion about. I see no reason to > exaggerate the scale of the solar forcings relative to volcanic or > anthropogenic forcings. The difference between the forcings looks clear > enough in the version of the figure that I made. Exaggerating it will > wrongly make the Bard 2.5% case look (at first glance) bigger than the > anthropogenic forcing, and make it look more important than volcanic > forcing. > > I'll hold off from making any more versions till decisions are made on > these issues. > > Cheers > > Tim > > At 09:01 18/07/2006, Fortunat Joos wrote: > >> Hi Tim and co, >> >> Thanks for the figure. I like the figure showing the model results and >> the general outline/graphic style. >> >> However, I am concerned about what is shown in the forcing figure. >> >> 1) Volcanic panel: I strongly believe that we should show what was >> used by the model and not some 40 year smoothed curves for volcanic >> forcing or any other forcing. So please use the original data file. >> Scientific honesty demands to show what was used and not something >> post-processed. >> >> 2) solar panel: >> 2a) We must show the Wang-Lean-Shirley data on the original resolution >> as used to drive the models. In this way, we also illustrate the >> magnitude of the 11-yr annual cycle in comparison with the background >> trend. The record being flat, apart from the 11-yr cycle, during the >> last decades is a reality. >> 2b) Do not apply any smooting to the Bard data. Just use them as they >> are and how they were published by Bard and used in the model. >> 2c) It is fine to supress the Bard 0.08 case after 1610 (not done in >> my figure version) >> 2d) the emphasis of the figure is on the solar forcing differences. >> So, please show solar somewhat overproportional in comparison to >> volcanic and other forcings. >> >> 3) other forcings: again no smoothing needed here. It would be hard to >> defend a double smoothing. >> >> 4)- normalisation of solar forcing to some period mean. If the >> different solar forcings disagree for today as in your option, we may >> send the signal that we do not even know solar forcing today. >> Thus, I slightly prefer to have the same mean forcing values for all >> solar records during the last few decades as shown in the attached >> version. However, I also can see some arguments for other normalisations. >> >> To illustrate points 1 to 4, I have prepared and attached a version of >> the forcing panel. >> >> other points >> >> - Your choice of colors is fine >> - time range 1000-2000 AD is fine >> - suggest to remove the text from the y-labels except the units W/m2. >> >> Sorry for this additional comments coming a bit late. However, I did >> not realise that you planned to smoothed the model input data in any way. >> >> With best wishes, >> >> Fortunat >> >> Tim Osborn wrote: >> >>> Hi Peck, Eystein and Fortunat, >>> I've drafted two versions of the new fig 6.14, comprising a new panel >>> showing the forcing used in the EMIC runs, plus the old fig 6.13e >>> panel showing the EMIC simulated NH temperatures. Keith has seen >>> them already. >>> First you should know what I did, so that you (especially Fortunat) >>> can check that what I did was appropriate: >>> (1) For the volcanic forcing, I simply took the volcanic RF forcing >>> from Fortunat's file and applied the 30-year smoothing before >>> plotting it. >>> (2) For the solar forcing there are 2 curves. For the first, I took >>> the Bard 0.25% column from Fortunat's RF file. For the second, I >>> took the Bard 0.08% column from Fortunat's RF file from 1001 to 1609, >>> and then appended the WLS RF forcing from 1610 to 1998. Then I >>> smoothed the combined record. NOTE that for the Bard0.25%, the line >>> is flat from 1961 onwards which probably isn't realistic, even though >>> that is what was used in the model runs. >>> (3) For the "all other forcings" there are 2 curves. For the first, >>> I took the CO2 concentrations provided by Fortunat, then used the >>> "standard" IPCC formula from the TAR (in fact the first of the three >>> options for CO2 in IPCC TAR Table 6.2) to convert this to a radiative >>> forcing. I then added this to the non-CO2 radiative forcings data >>> from Fortunat's file, to get the total radiative forcing. For the >>> second, I replaced all values after 1765 with the 1765 value (for the >>> natural forcings case). Then I smoothed the combined record (as in >>> fig 6.13c, I only applied a 10-year smoothing when plotting the "all >>> other forcings", because it is fairly smooth anyway and using a high >>> smoothing results in lower final values when there is a strong trend >>> at the end of a time series). >>> Now, some comments on the figures themselves (please print them and >>> refer to them when reading this): >>> (1) File 'chap6_f6.14_option1.pdf' is strongly preferred by Keith and >>> me. This shows the three forcing components separately, which helps >>> with understanding the individual causes of specific warming and >>> cooling periods. I have managed to reduce the size of this >>> considerably, compared to the equivalent panel in fig 6.13, because >>> with only a few series on it I could squeeze them together more and >>> also reduce the range of the vertical axes. >>> (2) Although we don't prefer it, I have also made >>> 'chap6_f6.14_option2.pdf' which is even smaller by only showing the >>> sum of all the forcings in the top panel. >>> Which version do you prefer? Please let me know so I can make final >>> changes only to the preferred version. >>> Some more comments: >>> (1) Fig 6.14b was originally Fig 6.13e. When it was part of that >>> figure, the colour bar showing the shades of grey used to depict the >>> overlapping ranges of the published temperature reconstructions was >>> only on Fig 6.13d. Do you think I should now also add it to the EMIC >>> panel (6.14b), now that it is in a separate figure? It will be a bit >>> of a squeeze because of the legend that is already in 6.14b. >>> (2) Another carry over from when 6.14b was part of 6.13, is that the >>> time range of all panels had to match (900-2010). Now that the EMICs >>> are in a separate figure, I could start them in year 1000, which is >>> when the forcing and simulations begin. Unless you want 6.13 and >>> 6.14 to remain comparable? Again please comment/decide. >>> (3) I wasn't sure what colours to use for the forcing series. In >>> option 1, the volcanic and other forcings apply to all runs, so I >>> chose black (with thick/thin used to distinguish the "all" forcings >>> from the "natural-only" forcings (basically the thin flat line in >>> "all other forcings). The cyan-green-blue runs used strong solar >>> forcing, so I used blue for that forcing. The red-orange-brown runs >>> used weak solar forcing, so I used brown for that forcing. Sound ok? >>> Sorry for the long email, but I wanted to get everything explained to >>> avoid too many iterations. >>> Please let me know your decisions/comments on these questions, or on >>> any other aspects of the new figure. >>> Cheers >>> Tim > > > > > Dr Timothy J Osborn, Academic Fellow > Climatic Research Unit > School of Environmental Sciences, University of East Anglia > Norwich NR4 7TJ, UK > > e-mail: t.osborn@uea.ac.uk > phone: +44 1603 592089 > fax: +44 1603 507784 > web: http://www.cru.uea.ac.uk/~timo/ > sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm > > **Norwich -- City for Science: > **Hosting the BA Festival 2-9 September 2006 > -- Climate and Environmental Physics, Physics Institute, University of Bern Sidlerstr. 5, CH-3012 Bern Phone: ++41(0)31 631 44 61 Fax: ++41(0)31 631 87 42 Internet: http://www.climate.unibe.ch/~joos/