cc: Tim Osborn <t.osbornatXYZxyz.ac.uk>, Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Eystein Jansen <eystein.jansenatXYZxyz.uib.no>
date: Tue, 18 Jul 2006 16:20:16 +0200
from: Fortunat Joos <joosatXYZxyzmate.unibe.ch>
subject: Re: new fig 6.14
to: Keith Briffa <k.briffaatXYZxyz.ac.uk>
My concerns comes from the following. I am not convinced that one gets
the same response when forcing a model with smoothed volcanic forcing
instead with the spikes. I suspect that the ocean will gain more heat in
the later case due to the longer time to respond to the forcing.
However, this remains to be tested, but nobody has done this as far as I
know. In other words, postprocessing the output of a model forced with
high resolution data does not necessarily give the same results as
forcing the model with smoothed input. There is a chance to get
different results. That is why I prefer to show the real forcing, i.e.
the volcanic spikes. As long as nobody has done such tests run I would
prefer to be scientifically on the save side with the figure. Sorry, but
this is my modellers view on this.
Forcings do not need to be on the same scale here. We know that
temporarily volcanic forcing, albeit negative, is much larger than
anthropogenic forcing. Why should we hide this well-know fact? Sceptics
my call on this. Readers of our chapter are hopefully able to interpret
The TS-team (in this case neither me nor Peck) asked us to show the
A point of the figure is to show the implication of low solar forcing
(WLS versus Bard) that is why I prefer to blow the solar panel somewhat
up. We have varied solar forcing between the different runs. Of course
the point about the natural forcing only simulation not able to get the
20th century warming is very important. Indeed, I believe that this
important conclusion is underscoored if we make it very clear that we
have varied solar forcing over a wide range (by a factor of 3).
It would also be nice to show the 11-yr solar cycle that is in the data
(sun spots, but also 14C).
As far as normalisation of the forcing is concerned. I have no strong
opinion. There is a consistency issue with chapter 2 where radiative
forcing is always defined relative to 1750 (1750==0). This point may
especially be important for the TS. There is also the issue about
agreement over recent decades. This is why I slightly prefer to
normalize the forcing to be zero around 1750.
The sulfur figure will show volcanic spikes. We have agreed in Bergen
that we add a sentence to the caption to point out that sulfate
deposition may strongly vary regionally.
I think we have with fig 13 and 14 now the opportunity to convey to the
readers the same information in two different ways. Perhaps, we should
not miss this opportunity. In any case, we will find a solution and then
Keith Briffa wrote:
> Fortunat et al
> My opinions were consistent with Tim's expression - we discussed his
> response. The importance of consistency between different modelling
> Figures ( time response of filters and in the absolute magnitude of
> forcing scale) are the most important aspects. To start showing
> apparently different volcanic spikes (in the sulphate and EMIC Figure )
> will lead to confusion also. Ultimately we should remember that the
> point of this Figure is to show that you can not get simulated
> temperatures to match observations without anthropogenic forcing - not
> to show proportional responses to different solar or volcanic events.
> At 13:45 18/07/2006, Fortunat Joos wrote:
>> 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.
>>> 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
>>>> 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
>>>> 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
>>>> With best wishes,
>>>> 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
>>>>> 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
>>>>> (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.
>>> Dr Timothy J Osborn, Academic Fellow
>>> Climatic Research Unit
>>> School of Environmental Sciences, University of East Anglia
>>> Norwich NR4 7TJ, UK
>>> e-mail: t.osbornatXYZxyz.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/
> Professor Keith Briffa,
> Climatic Research Unit
> University of East Anglia
> Norwich, NR4 7TJ, U.K.
> Phone: +44-1603-593909
> Fax: +44-1603-507784
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