UPDATE: Annan now suggests the IPCC “is in a bit of a pickle”, see below.
UPDATE2: Title has been changed to reflect Annan’s new essay, suggesting lying for political purposes inside the IPCC. Also added some updates about Aldrin et al and other notes for accuracy. See below.
Readers may recall there has been a bit of a hullabaloo at Andrew Revkin’s Dot Earth of the New York Times over the press release I first carried at WUWT, saying that I had “seized on it”.
Purveyors of climate doubt have seized on a news release from the Research Council of Norway with this provocative title: “Global warming less extreme than feared?”
I beg to differ with Andy’s characterization, as I simply repeated the press release verbatim without any embellishments. My only contribution was the title: Yet another study shows lower climate sensitivity. It turns out to the surprise of many that the subject of the press release was not peer reviewed, but based on previous cumulative work by the Norwegian Research Council. That revelation set Andy off again, in a good way with this: When Publicity Precedes Peer Review in Climate Science (Part One), and I followed up with this story demonstrating a lack of and a need for standards in climate science press releases by the worlds largest purveyor of Science PR, Eurekalert: Eurekalert’s lack of press release standards – a systemic problem with science and the media
It turns out that all of this discussion was tremendously fortuitous.
Surprisingly, although the press release was not about a new peer reviewed paper (Update: it appears to be a rehash and translation of a release about Aldrin et al from October), it has caused at least one scientist to consider it. Last night I was cc’d an exceptional email from Andrew Revkin forwarding an email (Update: Andy says of a comment from Dot Earth) quoting climate scientist James Annan, who one could call a member of the “hockey team” based on his strong past opinions related to AGW and paleoclimatology.
Andrew Revkin published the email today at the NYT Dot Earth blog as a comment in that thread, so now I am free to reproduce it here where I was not last night.
Below is the comment left by Andy, quoting Annan’s email, bolding added:
The climate scientist James Annan sent these thoughts by email:
‘Well, the press release is a bit strange, because it sounds like it is talking about the Aldrin et al paper which was published some time ago, to no great fanfare. I don’t know if they have a further update to that.
Anyway, there have now been several recent papers showing much the same – numerous factors including: the increase in positive forcing (CO2 and the recent work on black carbon), decrease in estimated negative forcing (aerosols), combined with the stubborn refusal of the planet to warm as had been predicted over the last decade, all makes a high climate sensitivity increasingly untenable. A value (slightly) under 2 is certainly looking a whole lot more plausible than anything above 4.5.’
And this is what many have been saying now and for some time, that the climate sensitivity has been overestimated. Kudos to Annan for realizing the likelihood of a lower climate sensitivity.
The leader of the “hockey team”, Dr. Michael Mann will likely pan it, but that’s “Mikey, he hates everything”. I do wonder though, if he’ll start calling James Annan a “denier” as he has done in other instances where some scientist suggests a lower climate sensitivity?
UPDATE: over at Annans’ blog, now there is this new essay expounding on the issue titled: A sensitive matter, and this paragraph in it caught my eye because it speaks to a recent “leak” done here at WUWT:
But the point stands, that the IPCC’s sensitivity estimate cannot readily be reconciled with forcing estimates and observational data. All the recent literature that approaches the question from this angle comes up with similar answers, including the papers I mentioned above. By failing to meet this problem head-on, the IPCC authors now find themselves in a bit of a pickle. I expect them to brazen it out, on the grounds that they are the experts and are quite capable of squaring the circle before breakfast if need be. But in doing so, they risk being seen as not so much summarising scientific progress, but obstructing it.
Readers may recall this now famous graph from the IPCC leak, animated and annotated by Dr. Ira Glickstein in this essay here:
Yes, the IPCC is “in a bit of a pickle” to say the least, since as Annan said in his comment/email to Revkin:
…combined with the stubborn refusal of the planet to warm as had been predicted over the last decade, all makes a high climate sensitivity increasingly untenable.
UPDATE 2: Annan also speaks about lying as a political motivator within the IPCC, I’ve repeated this extraordinary paragraph in full. Bold mine.
Note for the avoidance of any doubt I am not quoting directly from the unquotable IPCC draft, but only repeating my own comment on it. However, those who have read the second draft of Chapter 12 will realise why I previously said I thought the report was improved 🙂 Of course there is no guarantee as to what will remain in the final report, which for all the talk of extensive reviews, is not even seen by the proletariat, let alone opened to their comments, prior to its final publication. The paper I refer to as a “small private opinion poll” is of course the Zickfeld et al PNAS paper. The list of pollees in the Zickfeld paper are largely the self-same people responsible for the largely bogus analyses that I’ve criticised over recent years, and which even if they were valid then, are certainly outdated now. Interestingly, one of them stated quite openly in a meeting I attended a few years ago that he deliberately lied in these sort of elicitation exercises (i.e. exaggerating the probability of high sensitivity) in order to help motivate political action. Of course, there may be others who lie in the other direction, which is why it seems bizarre that the IPCC appeared to rely so heavily on this paper to justify their choice, rather than relying on published quantitative analyses of observational data. Since the IPCC can no longer defend their old analyses in any meaningful manner, it seems they have to resort to an unsupported “this is what we think, because we asked our pals”. It’s essentially the Lindzen strategy in reverse: having firmly wedded themselves to their politically convenient long tail of high values, their response to new evidence is little more than sticking their fingers in their ears and singing “la la la I can’t hear you”.
Oh dear oh dear oh dear…
Philip Shehan says:
February 2, 2013 at 6:58 pm
Mark Bofill says:
February 2, 2013 at 5:48 pm
“If someone falsified evidence in a cause I really believed in I’D certainly want that someone exposed, discredited, and disassociated from my cause ASA”
Yes Definately. Annan should name him/her. Not simply because such a person should be exposed, and given the opportunity to defend himself, but also because in the absence of specific allegations, people such as yourself can portray that hundreds of other honourable scientists as cockroaches.
The fact is, as I pointed out on another thread, I have been a whistleblower on corrupt conduct (scientific and administrative) in a university department. As a result of my insistance that my allegations be properly investigated and that due process be followed, I was subjected to worse than usual attacks, including false criminal charges (acquitted) and ultimate vindication when the department suddenly collapsed and the financial cupboard found to be bare.
———————————–
Fair enough. Out of curiosity, what do you make of my argument that nobody in their right mind would make a statement like that to their peers without having a confident expectation that such a statement would be acceptable? Point taken that I am entirely taking Annan’s word about the incident, I will think that through carefully, but assume for the sake of argument he’s speaking the plain truth.
I apologize for my presumption in suggesting that you’d prefer to see the matter buried then, thanks for clarifying your position.
Mark
davidmhoffer: It is a funny thing that AGW skeptics often claim that conventional climate scientists are too focused on radiation…and ignore things such as convection…because not only is this false, but your post betrays the fact that you (and many other skeptics in my experience) are the ones who actually do this.
What conventional climate scientists understand is that it is essentially only via radiation that the Earth communicates with the rest of the universe, hence the importance of understanding the “top-of-the-atmosphere” radiative effect of a CO2 doubling. However, once you are talking about how that radiative imbalance gets translated into changes at the surface, in surface temperature (and other weather), you can’t remain stuck in a radiation-only point of view. So, no, I don’t see W/m^2 at the surface as a particularly plausible metric…and since it has very little relationship to how we experience the climate, you then have the disadvantage of losing connection with our intuition while gaining little in return. (I don’t know about you, but I don’t walk around thinking about how many W/m^2 the Earth in Rochester is radiating today; I think in terms of what the temperature is.)
So, I would say that if this metric seems particularly useful to you, then by all means go ahead and do some analyses and show us how this is a better metric than the temperature metric, but frankly I don’t really see it.
The never ending arguments put forth by joelshore are simply an indication of his unalterable belief system. In the final analysis, it is what the planet is telling us that settles the argument, because the planet is the ultimate Authority.
The Authority is telling us that CO2 is insignificant. But some folks just can’t handle the truth, so they argue incessantly. It is their way of avoiding reality.
John M.
There is nothing selective in the quote I gave.
Of course the 2008 review does not rule out sensitivities higher than 4.5 C. The sentence is superfluous when the 2 -4.5 is given as the “likely” range, that is higher or lower figures cannot be ruled out.
I do not know what temperatures Annan is declaring “untenable”. That is rather an unscientific term for a parameter which is subject to such a high level of uncertainty. On those two grounds I reject the use of the term “untenable”.
Certainly Annan believes sensitivity will be at the low end. Personally I hope Annan is correct. The lower the sensitivity the less the adverse effects on global climate from continuing greenhouse gas emissions. The odd thing is he accepts the basic theory of AGW and is using mainstream arguments to come to a lower figure, to the enthusiastic applause of those who normally rubbish climate theory.
If we are going to talk about selective quoting, Annan does not make any extravagant claims for his conclusions here:
”Of course, this still leaves open the question of what the new evidence actually does mean for climate sensitivity. I have mentioned above several analyses that are fairly up to date. I have some doubts about Nic Lewis’ analysis, as I think some of his choices are dubious and will have acted to underestimate the true sensitivity somewhat.”
(Not to mention the bit left out about concerning his condemnation of deliberate misrepresentation of the sensitivity – “Of course, there may be others who lie in the other direction…”)
Annan’s speculation of how his opinions will be greeted by people at the IPCC does not qualify as science.
joeldshore;
To summarize, I think that the basic problem is you imagine some simple relationship between the 3.7 W/m^2 number and some increase in radiation from the surface due to some change in surface temperature.
>>>>>>>>>>>>>>>>
You’d be wrong. Again, I summarized for brevity. If we use the simple average earth surface temperature of 15 C, 3,7 w/m2 only achieves an increase of 0.6 degrees. It is more complicated than that. How many times have I pointed out that the IPCC AR4 report specifically states RF and surface forcing are two different things? I’ve lost track. Nor does quantifying it at TOA change the problem much, it just quantifies it from a different perspective. In fact, the IPCC doesn’t even quantify it at TOA either. The quantify it as the sum of all downward flux (that otherwise would not have existed) less the sum of all upward flux (that otherwise would not have existed) and as such it isn’t quantified at TOA or at surface, it is quantified across the atmospheric air column.
joeldshore;
It is a funny thing that AGW skeptics often claim that conventional climate scientists are too focused on radiation…and ignore things such as convection…because not only is this false, but your post betrays the fact that you (and many other skeptics in my experience) are the ones who actually do this.
>>>>>>>>>>>
I did no such thing. You want me to summarize the physics problem in its entirety for the purpose of this discussion in a blog post? C’mon. You’re raising arguments that you know very well I understand and am conversant with and which are simply a diversion from the central issue.
We’re tracking surface temperatures in an effort to determine if CO2 increases are causing a significant energy imbalance at the surface. Are you proposing we measure surface temperatures to determine if there is an energy balance elsewhere? Obviously that’s not possible. And, you your own comment points out, the relationship is incredibly complex. You’ve not made the case that measuring temperature and temperature anomalies at surface is of any value, if anything, you’ve demonstrated that it doesn’t have value.
Once again, please make the case that for measurement at surface, there is a better single metric than w/m2. All you’ve done so far is muddy the waters.
joeldshore;
and since it has very little relationship to how we experience the climate, you then have the disadvantage of losing connection with our intuition while gaining little in return.
>>>>>>>>>>>>>>>>>>>
Frankly Joel, I cannot believe you said that.
If we relied on intuition, the sun would circle the earth.
The whole point of science is to discard intuition in favour of facts.
Mark: I don’t know what goes on inside some people’s heads I know that deeply flawed individuals in powerful positions think they can, and often do get away with anything, even when they betray themselves in unguarded moments. I found that out to my considerable cost.
I do not doubt Annan’s report of the incident, It’s unfortunate that he cannot supply more details of the circumstances and reactions but perhaps confidences, concern for collateral damage to innocent bystanders who may reluctantly be called to make an invidious choice between telling the truth and self preservation (a real problem and a good way to lose friends), being sent to profressional pergatory (been there, not nice) or concern about defamation proceedings render that difficult. I hope there was a collective intake of breath when the statement was made. But I am aware that stunned silence or the psychological state of denial can be the collective reaction to outrageous conduct.
I note that David Hoffer — admittedly a self-educated lay person — is giving physicist joelshore a pretty thorough pummeling in this thread.
Philip Shehan says:
February 2, 2013 at 8:31 pm
…
——–
Thanks, I appreciate your taking the time to share your views with me on this.
Regards
Here is the latest from Climate scientist Lennart Bengtsson, Today he is Visitin Professor at Uppsala Universitet but still Prof. emeritus at the Max Planck Institutet Hamburg and also former member of the group which initiated the early ‘studies’ re. Climate for UN’s climategroup today IPCC. The translation below is a quick version using Google Translate:
– The warming Earth experienced the last hundred years is so small that it was not noted if the meteorologists and climatologists informed about it. It indicates that the climate sensitivity is probably lower than climate models, at least initially adopted, says Bengtsson.
UN climate panel says in its latest report that a doubling of carbon dioxide levels likely to result in a warming of around 3 degrees. So far, the 0.8 degrees since the 1800s, and then ten fifteen years, the curve has become flatter, while greenhouse gas emissions continued at the same pace as before.
– There is no doubt that humans have an impact. What we are not sure about is why the warming is so slow. It is possible that the planet cools more efficiently than we had previously expected. It is also possible to store more heat in the deep sea, so that there is inertia.
Vi skapar en väldig ängslan utan att det är befogat/ we are creating a huge anxiety without justified, Prof Lennart Bengtsson on DN.se February 3 2013
Now accepting that the alarm was to strong, Lennart Bengtsson still can’t accept that the overall problem is the way the issues for the data models were put together without all factors known from 1899 to be taken into consideration. Nor has it occured to him that faked, sorry corrected data, can’t be used when the corrections made origin from instrumentsreading on a vulcan…..
When the fox counts the chickens, Norah4you page
He do have problem understanding that we humans arent as important for changes in weather and climate as many would have wished… Mother Nature isn’t as easy understanding as expected!
Is it really any wonder why no one has been able to actually explain global warming or any climate forcing using “radiative physics”, when it is based on a false analogy like the concept of a GHG?
I am starting to think that the theory of radiation heating caused by CO2 has been some what exaggerated. I have thus far found no proof that it has any effect for it is overwhelmed by that other evil heating gas water vapour.
It seems that some on the team are starting to have second thoughts as their pet theory is falling in a hole as the earth refuses to co-operate. This man obviously knows the first rule of holes.
1. When in a hole stop digging.
davidmhoffer says:
February 2, 2013 at 5:12 pm
joeldshore says:
February 2, 2013 at 5:59 pm
The value (324 w/m2) comes from various global satellite data projects and was the original claim ( Kiehl & Trenberth, 1997.) The 150 w/m2 is based on theory, but there is nothing better than observed data admittedly with errors. Therefore I am pointing out the flaw using observed satellite data projects and the 1.2c per doubling. I used the older value because I thought this one was well known to folks on here.
A more recent update puts the value at 333 w/m2.
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/BAMSmarTrenberth.pdf
If 150 w/m2 was taken into account instead, still basically gives 0.81c per doubling without taking different climates zones into account. The data analyzed using satellite projects already takes into account the cold and warm regions of the planet and how 3.7w/m2 is affected there.
joeldshore:
I am copying your entire post at February 2, 2013 at 6:19 pm so it cannot be asserted that my response is taken out of context.
My question was clear, straightforward, unbiased, and simple.
You have not answered it.
Hence, I make the reasonable deduction that
(a) There is no length of time with no discernible global warming that would induce you to reject your notion that increasing atmospheric CO2 concentration is causing global warming
Or
(b) You don’t know how long such a time would be
Or
(c) You are being deliberately evasive for some unstated reason
Your claim that my “very phrasing biases the question” is untrue: it does not and you do not suggest how it could.
You say,
So what? I anticipated that evasion and when I posed the question (at February 2, 2013 at 12:07 pm) I listed the various estimates of no discernible warming (at 95% confidence).
The range of various estimates of recent no discernible warming (at 95% confidence) is over 17 years for GISS to over 23 years for RSS. As I stated, they are ALL statistically significant at 95% confidence. And they are ALL at least 3 years longer than your “12-14” years.
And you make a false assertion when you say
Firstly, we are talking about a “trend” over more than 17 years but you are discussing trends of “12-14” years. And longer should NOT “happen now and again” if increasing atmospheric CO2 is causing significant global warming. Indeed, there must be some other effect constraining the global warming from CO2 if there is no discernible global warming for such periods: and that is the reason for my question.
You claim the CO2 effect is significant but have not said what you think is stopping it from causing global warming.
And then you put your head in a noose by saying
That is a very different but also very important question. And it was answered for you on another thread. Wisely, you don’t link to that other thread where you made a complete fool of yourself by trying to misrepresent the clear and unambiguous falsification criterion stated by NOAA in its 2008 Report On ‘The State of The Climate’. And, contrary to your assertion, it was you and ONLY YOU who “completely convoluted interpretation of what their criterion” which I note you also wisely fail to quote.
The thread where you made yourself a complete laughing stock is
http://wattsupwiththat.com/2013/01/14/has-the-met-office-committed-fraud/
The NOAA falsification criterion is on page S23 of its report at
http://www1.ncdc.noaa.gov/pub/data/cmb/bams-sotc/climate-assessment-2008-lo-rez.pdf
It says
So, the climate models show “Near-zero and even negative trends are common for intervals of a decade or less in the simulations”.
But, the climate models RULE OUT “(at the 95% level) zero trends for intervals of 15 yr or more”.
But reality has had (at the 95% level) zero trends for more than 17 years whether or not one interpolates across or extrapolates back across the 1998 ENSO peak.
In that thread you wriggled in every possible way – and some impossible ways – in attempt to claim the NOAA falsification criterion means other it says and I quote here (people wanting a laugh at your expense may want to read that thread).
The facts are clear.
According to the falsification criterion set by NOAA in 2008, the climate models are falsified by the recent period of 16+ years of (at 95% confidence) zero global temperature trend. This is because NOAA says the climate models simulations often show periods of 10 years when global temperature trends are zero or negative but the simulations rule out near zero trends in global temperature for periods of 15 years. What the models “rule out” nature has done.
The climate models are falsified: this contradicts your superstitious belief in AGW, and you need to come to terms with it.
Richard
CO2 doubling produces a +3.7 W/m2 increase in energy levels in the troposphere (well some mythical layer anyway) from a doubled CO2 which increases the temperature of that level by +1.2C (after the stratosphere fully adjusts apparently).
Then we have feedbacks of +1.75 W/m2/1.0C from water vapour increases, +0.75 W/m2/1.0C from cloud albedo reduction, +0.25 W/m2/1.0C from surface albedo reduction, -0.3 W/m2/1.0C from a decreased Lapse Rate.
So, after our initial +3.7 W/m2 of direct CO2 forcing (and another +0.5 W/m2 from the other GHG increases like methane), we get another +7.5 W/m2 in energy levels from the feedbacks.
All together, the 240 W/m2 troposphere layer increases in energy by +11.6 W/m2. This is enough to increase thetemperature in the layer by +3.0C. There is really no explanation about how that affects the surface except that it is supposed to increase in temperature by almost exactly the same level. That is the whole story (except for the part about volcanoes and sulfate aerosols getting in the way as well).
What could possibly go wrong with that?
The actual response data to date says a lot could go wrong with that.
I could start listing them, but that would make for a long, long post.
richardscourtney says:
February 3, 2013 at 3:23 am
joeldshore:
Richard, you are of course spot on but fighting someone like shore, so blinded by his religious need of funding and self assurance, is headbanging territory.
The head climate druids have been saying for a few years that the models predict/project periods of zero or no trend but what they deliberately omit to say is that none of those periods were shown to be due right now.!! That is their thimble trick on this one.
Reblogged this on The GOLDEN RULE and commented:
It seems that the “rock” on which the house of cards is built, “97% scientists can’t be wrong” besides being incorrect anyway, is about to become sand.
What Joel has said at the end of his post of 6:19 on February 2nd gave me a good chuckle. To suggest that the basic way the NOAA’s criterion reads is a convoluted interpretation whereas the way he interprets it, which is the very definition of convoluted and requires numerous additional explanations and qualifications which are lacking in the report itself, isn’t convoluted, is pretty outrageous.
Steve Mosher,
We are agreed on the 1.2C number. I do not agree that it is a lower bound.
Let me talk electronics which I know a couple of things about. I can design an amplifying system which when given a 1.2 Volt input produces a 1.2 Volt output. I could modify the design to get .012 volts out or 12 volts out.
Depending on the feedbacks the lower bound could be close to zero. From my studies (not near as in depth as yours I admit) my estimate of the gain of the system is around .5 – i.e. a 1.2C “forcing” will give a net of .6C rise.
My point? Your lower bound is incorrect. Which is not to say my estimate is correct. Just that it is a possibility. And of course I rate that possibility as more likely than the others. One of my clues is homeostasis. A system with a gain of less than one will be more stable than a system with a gain greater than one. Are perturbations damped or amplified?
Let me talk nuclear reactors here which I also know something about. Reactors with a persistent gain of greater than one are slag heaps. What does that tell you? That a sensitivity >1 is not very likely.
When bringing up cold iron ROs (reactor operators) like to bump up the reactivity very very slightly above one and hold it until the negative temperature coefficient of reactivity kicks in. Then you bump it again and wait. Strict limits are placed on the rate of rise (neutron multiplication) until the reactor is well into the “thermal range” i.e above 100 deg C or so. Then you can get a little more aggressive. But not much. Once in the thermal range rod position controls temperature not reactivity per se. This is why reactor start ups are 4 to 8 hour events. I have participated in a hot restart after a scram. But civilian reactors are not allowed to do that due to the danger. Things like Xenon build up confound the calculations. And if you wait too long you have to wait until the Xenon decays before you restart as the reactivity will not get any where close to one. The wait is about 3 days minimum.
Anyway the time constant of the system along with the rate of change of reactivity with temperature is critical for adequate control. Without delayed neutrons ( making immediate reactivity less than one) the system is unstable. If immediate reactivity is greater than one you get a very undesirable condition called prompt critical.
So at the very least the immediate gain of the system is less than one.
Stephen Richards:
As a reaction to my post addressed to joeldshore at February 3, 2013 at 3:23 am,
your post at February 3, 2013 at 4:28 am says to me
Yes, I agree and I know.
However, for the information of onlookers it is important to expose the falseness of the assertions of head climate druids and their acolytes (e.g. Joel Shore).
As Shore’s response to my question shows, there is no evidence that will reduce his superstitious belief in dangerous CO2-induced AGW.
Of course CO2 must induce some warming, but (as I say in my post at February 1, 2013 at 1:26 pm) if climate sensitivity is less than 1 deg.C for a doubling of CO2 then any possible CO2-induced warming is so small that it would be undetectable. And measurements show climate sensitivity is less than 1.0 deg.C.
The climate models are constructed so they project dangerous global warming from increased atmospheric CO2 concentration. Evidence continues to mount that the models don’t work and – as Annan’s admission demonstrates – rodent disembarkation is occurring.
As you say, excuses are mounting, too. Any claim that the models predict periods with lack of global warming such as is now happening is a lie: the models only predict shorter periods. As the NOAA reported in 2008, the models “rule out” lack of warming for a period as long as 15 years and that has happened. It does not matter when such ‘stasis’ happens: now or elsewhen. The models say it cannot happen and it has.
The truth of ‘global warming’ needs to be stated and those who deliberately misrepresent the truth need to be exposed.
Richard
joeldshore says:
February 2, 2013 at 5:59 pm
Your justification of averaging is unscientific. For temperatures as well as for fluxes. You end up with a meaningless number. Temperatures and therefore greybody radiation fluxes as well are not normally distributed; therefore the Law Of Large Numbers does not apply and there is no defined average.
http://chiefio.wordpress.com/2012/12/10/do-temperatures-have-a-mean/
The number you come up with serves only your propaganda purposes. Therefore not part of science. Well, if we count sociology and the art of mass manipulation as a a science, then yes.
With a little help from Maxwell’s Demon we can boil the oceans. Problem is, nobody’s seen the little imp.
A bit of rudimentary logic: I think the advancing certainty about climate sensitivity being markedly less than formerly believed, must make lukewarmers out of fire breathing dragons and neutral to microwarmers out of the former lukewarmers like Mosher. Let’s hear it! Are you former lukewarmers now more tepid or are you illogical.
davidmhoffer says:
That it is what “top of the atmosphere” means…It means that one is comparing all of the radiative flux coming into the atmosphere vs all leaving it.
Actually, if you want to look at the energy imbalance, the best way to do that is to look at the accumulated heat content change in the ocean, where the vast majority of the excess energy due to that imbalance is accumulating.
Others, like Trenberth, have tried to look directly at the incoming and outgoing radiation, but as he has noted, we can’t yet measure these precisely enough to directly measure the radiative imbalance.
That example is a red herring. My point is that in this case, there is no right or wrong answer for what sort of figure-of-merit best represents the change due to greenhouse gases. So, one ought to at least go with one that people have some intuition about.
But, if you want to do it some different way, nobody is stopping you from doing your own analyses and reporting the results that you would like to see.