Bishop Hill Sans science, sans maths, sans everything
Jan 12, 2015 Climate: sensitivity Over at Lucia's place, there has been some interesting conversation in the comments about the technical abilities of some of those on the other side of the climate debate. This originally arose in connection the host of And Then There's Physics, who had apparently reduced Blackboard regular Paul K to laughter in a post about a paper on climate sensitivity by Craig Loehle and a response to it, Cawley et al, which was written by five of the denizens of Skeptical Science. This amusement was followed by others chipping in with their own surprise at ATTP's comments. It's all good family fun. However, it turns out that it's not only ATTP who is struggling. Nic Lewis has added a comment to the thread about the Cawley paper itself which is astonishing.
First a bit of background. Loehle's paper described a model developed in an earlier paper (Loehle and Scafetta 2011) and used it to derive an anthropogenic warming trend from the mid-20th century onwards. The paper then derived an estimate of transient climate response (TCR) of 1.1°C by relating the anthropogenic trend rise in temperature to the increase in anthropogenic radiative forcing, and went on to derive an estimate of equilibrium climate sensitivity (ECS) of 2.0°C. The Skeptical Science response appeared about six months later and was written by Gavin Cawley, Kevin Cowtan, Robert Way, Peter Jacobs and Ari Jokimäki. This is the key part of the abstract.
We demonstrate that the Loehle and Scafetta model systematically underestimates the transient climate response, due to a number of unsupportable assumptions regarding the climate system. Once the flaws in Loehle and Scafetta’s model are addressed, the estimates of transient climate response and equilibrium climate sensitivity derived from the model are entirely consistent with those obtained from general circulation models, and indeed exclude the possibility of low climate sensitivity, directly contradicting the principal conclusion drawn by Loehle. Further, we present an even more parsimonious model for estimating climate sensitivity. Our model is based on observed changes in radiative forcings, and is therefore constrained by physics, unlike the Loehle model, which is little more than a curve-fitting exercise.
Nic notes that one of the key issues that Cawley et al raise concerns Loehle's estimate of the forcing that has produced the recent warming:
The paper notes...that Loehle assumed aerosol and non-CO2 greenhouse gases and other forcings approximately cancel each other out, and accordingly used only CO2 forcing. The Cawley et al. authors dispute the validity of this assumption, saying about the IPCC AR4 chart of 1750–2005 forcings that Loehle cited in support of it:
This does not however imply that these forcings have approximately cancelled over the period from 1951 to 2010, used to estimate the anthropogenic warming after 1950. The RCP8.5 forcings (Meinshausen et al., 2011), shown in Fig. 3(a) suggest that total anthropogenic forcing since 1950 has risen appreciably faster than the forcing from CO2 alone by a ratio of approximately 1.145:1.
Nic agrees with this this point, and in fact goes on to note that even Cawley et al's figure is too low.
Cawley et al. are correct in their assertion that total anthropogenic forcing since 1950 has exceeded that from CO2 alone. However, they understate the difference over the stated period, for two reasons. First, 1.145 is the ratio of the RCP8.5 increase between 1950 and 2010 in total forcing (including solar and volcanic), not anthropogenic forcing, to that in CO2 forcing. The correct ratio is 1.245. Secondly, the RCP forcings dataset does not represent current best estimates. Based on the IPCC AR5 forcing dataset, the ratio of the increase in total anthropogenic forcing over 1950–2010 to that from CO2 alone is 1.361 times.
But this is where it gets rather hilarious. In simple terms, transient climate response is calculated as follows:
TCR = Temperature change/change in forcing
So if, as everyone agrees, Loehle got his forcing too small then his TCR figure is actually too large not, as the crack team at Skeptical Science seem to think, too small as well.
I was rather nonplussed at this point in my reading of the Cawley paper. Its main thesis was that Loehle had underestimated transient climate response (TCR) and hence equilibrium climate sensitivity (ECS). But Loehle derived TCR by dividing the estimated anthropogenic warming by the estimated change in anthropogenic forcing (relative to that from a doubling of CO2 concentration) over 1959–2013, which is broadly consistent with the generic definition of TCR given in AR5 (10.8.1). Obviously, if the change in forcing were greater than Loehle had assumed, that would imply an overestimate of TCR and thereby of ECS, not an underestimate. Very odd. But then I read on:
As a result of this assumption, the method of LS14 underestimates climate sensitivity by about 13%...
Unbelievable! Instead of adjusting the Loehle TCR estimate by dividing it by 1.145, to reflect Loehle's underestimate of forcing by that ratio, Cawley et al. have multiplied the sensitivity estimate (which is for TCR here, not ECS) by 1.145. On that incorrect arithmetical basis, Loehle's method of working from just the increase in CO2 forcing would indeed have underestimated TCR by 13%. But the correct conclusion should be that Loehle's method overestimates TCR by 24.5% (rather than 14.5%) based on the RCP8.5 forcing data – or by 36.1% based on the more up to date AR5 forcing estimates.
Interestingly, Craig Loehle has noted in the subsequent comments that he was not given the opportunity to respond to Cawley et al before the paper was published.
Bishop Hill
In the comments, WB notes that Robert Way posted a series of tweets about Loehle's paper last year. Concatenated, they read:
Last year, this rubbish [i.e. the Loehle paper] was published in an out-of-topic journal that contained the author on its advisory board. Beyond the 4-month timeline from receipt to published, clear statistical errors showed it had not been scrutinized enough during review. Reimplementing their analysis showed a number of methodological flaws and assumptions to the point where a response was necessary. Enter Cawley et al (2015) who show how fundamentally flawed Loehle (2013) was in reality.
Too funny.
Bishop Hill
ATTP is doing some hilarious handwaving:
I think that is a genuine error in the Cawley et al. paper, in that they got that Loehle’s method under-estimates TCR, rather than overestimates it (by mutiplying rather than dividing). A silly mistake I imagine since it is trivial, and I don’t doubt all those involved in the paper could easily do this. Of course, what Nic Lewis fails to point out is that the Loehle paper is rubbish and full of completely unjustified assumptions. That it’s already low TCR estimate should actually be lower if he’d done it with more reasonable numbers, just highlights this even more. Would be nice if he focused on the interesting part of the Cawley paper, which I discuss here, rather than nit picking something minor and rather trivial (however, this does seem to be his normal style, so not surprised).
Reader Comments (71)
Kevin Marshall at 10.05 pm
You are mistaken, but your confusion is very understandable.
As Section 8.3.2.2 of AR5 states, the radiative forcing (RF) of methane in 2011 (c/f 1750) was 0.48 W/m2, the same as in 2005 per AR4. The 0.97 in Figure SPM.5 shows RF attributable to methane emissions, whereas the 0.48 is RF from methane concentration in the atmosphere. Emitted methane only remains as such for 5-10 years, before getting broken down, leading to the production or destruction of other gases. So part of the 0.97 is RF from impacts of methane emissions on ozone, CO2, stratospheric water vapour, sulphate aerosols and CFCs/HCFCs. It is not to do with any difference between RF and effective radiative forcing (ERF). RF and ERF for greenhouse gases are identical in AR5,
So, if I've understood this correctly, there's an assumption in the calculations that the measured temperature is equal to the (anthropogenic warming + natural cooling).
What is causing the natural cooling? Shouldn't they be caclculating that as well?
I think they'd have a problem trying to equate it to lower solar radiation + cooling oceans (particularly as the Atlantic has been in a warm phase, and La Ninas haven't been evident). Is there some volcanic activity which balances?
After Nye's (failed) high-school physics, we get ATTP's trivial and minor elementary-school (incorrect) math.
I have been doing an intense statistical survey of the USHCN, and I have been having to derive (some of) the logic myself. All I can say is that I am prone to some very stupid errors. A clear majority of the time, my stupid errors conform with my own confirmation bias (that Great Enemy of the scientist).
Having said that, this is a very stupid error, and it is surprising that it made it as far as publication. It speaks poorly that not only none of the authors detected this, but that the answer to subsequent criticism is couched in such arrogance.
All told, the authors should have caught it. And if somehow or other, they didn't, peer review should have caught it. This is one of those situations where the throw is high to third, and the backup man isn't there.
Bad peer review is like bad education. It doesn't prepare one for the real world. And even if you fiddle with peer review, it always, always comes back to bit you in the ass. Peer review has (and always has had) fleas. But it's the best game in town, and the most honest one. It is far from ideal, but it is (in the fullness of time), self-correcting.
And you can pull all the cheats you wants during peer review -- but you can't fool independent review.
Basic mistakes can be made by anyone, especially if the result confirms your bias.
Maybe instead of getting sympathisers to rubber stamp the peer review they may consider requesting a peer reviewer from maths for dummies.com?
It shocks me that it took Nic Lewis to find this error. There are about seven billion humans out there capable of understanding this fiasco. If we double the number of humans will we halve the time to catch further such foolishness?
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Thanks anng @ 11:08. I think this is a tremendously, and possibly tragically, neglected point. Also, it is useful to remember now and then that the higher the sensitivity, the colder we would now be without man's effect.
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I think you'll find that "Climate Science" has moved on from the tired old debate about the relevance of coefficients being greater or smaller than unity. Just another minor and trivial nit picking "red herring", which confuses the uninformed.
Anyone know what ATTP's first language is?
I will need some persuading that he is not a native of Gibber
A tweet from Jokimäki says:
“Yes, we noticed this back in December and an erratum is in the works.”
“Yes, we noticed this back in December and an erratum is in the works.”
Oh yeah, just like Gergis et al... These guys really see this as war where one is not allowed to concede an inch.
Ridiculous!
ATTP's discounting of the Cawley et al multiplication/division error as 'silly' is nonsense, especially, since the authors go out of their way to note that with their "correction" (AKA their multiply/divide error) even Loehle's incorrect model gives results consistent with the sensitivity values from CGCM's. So they are claiming even 'a terrible model' diagnoses high sensitivity... after they 'correct' it.
But the Cawley et al 'minimum model' that ATTP defends generates very doubtful results because 1) it depends on wildly uncertain assumed historical forcing data during the "calibration period", and 2) if the current AR5 best estimates for net forcing were used in the model (rather than the lower, out-of-date estimates they actually used), the model's calculated current warming rate would be too high compared to reality. Sort of like... well... the CGCM projections of the current warming rate that are also too high compared to reality. Which suggests their simple model and the CGCM's both suffer from a serious GIGO problem..... consistent with a hefty dollop of confirmation bias influencing the otherwise impeccable 'climate science'.
Paul Matthews at 3.42 pm
That is not quite the impression I got from Gavin Cawley, who responded to my email to him pointing out the error by thanking me for spotting it and saying that this error "has also been pointed out by another reader".
I feel a bit sorry for Gavin Cawley; he comes across as a decent chap.
Paul Matthews
“Yes, we noticed this back in December and an erratum is in the works.”
"The Time Warp"
Worth pointing out that Gavin Cawley had some cordial exchanges with BH commenters in the discussion forum some time ago.
"So, if I've understood this correctly, there's an assumption in the calculations that the measured temperature is equal to the (anthropogenic warming + natural cooling).
What is causing the natural cooling? Shouldn't they be caclculating that as well?"
If I understand TCR (to doubling of CO2) correctly, it involves only the positive radiative forcing theoretically calculated from the increase in atmospheric CO2 plus an array of positive and negative feedbacks which are a direct consequence of the increase in CO2 radiative forcing. I am guessing that this would include increases in other associated GHGs (+ve feeback) and increases in aerosols from fuel burning (-ve feedback). Though natural variability (external and internally generated - including the cooling effect of naturally produced aerosols) would affect the final temperature achieved, this would not affect the calculation of TCR as long as natural variability is accounted for. So solar, volcanic activity, ENSO/AMO etc. are independent of TCR and any measurement of TCR would presumably have accounted for their (presumed estimated) effect upon global temperatures.
The situation we have here is that the cooling effect of man-made aerosols has declined appreciably as CO2 emissions and other GHGs have increased, so we would expect even greater warming, which hasn't happened. Hence TCR must be lower than previously thought. Of course, it could be argued that natural variability since 1951 has been appreciably greater than that which is estimated by the IPCC, and that this may explain part or all of the observed reluctance of temperatures to rise as quickly as they have been predicted to rise using AGW forced models. In which case a higher estimate of TCR could be argued. But this requires natural variability to have contributed a net negative influence on global temperatures over that period. If it has been net positive - which looks more likely - and greater in magnitude than assumed by the IPCC in their calculations, this will put even more pressure on the downward revision of TCR.
Some research on signs of life at ATTP
“Why are they laughing? That thread at Lucia’s is, in places, venomous.” Found the quotes, 2 different articles at ATTP
ATTP January 12, 2015 at 5:26 pm Re cartoon
BBD, Yes, I had wondered if while Nic Lewis is happy to refer to others as “SkS activists” I should allow people here to refer to him as a “GWPF stooge”. Maybe we could even get some kind of cartoon drawn.””
WebHubTelescope says:January 12, 2015 at 5:58 pm
“Why are they laughing?”
ATTP January 12, 2015 at 5:26 pm cartoons that simply mock others with whom you typically disagree is a little infantile.
Joshua says: January 12, 2015 at 6:23 pm
What’s juvenile about cartoons that simply mock others with whom you typically disagree?
WebHubTelescope says: January 12, 2015 at 6:56 pm
“It is only going to get worse:”
IN REFERENCE TO
“http://wattsupwiththat.com/2015/01/12/monday-mirthness-more-sceptical-science-kids-scienz/”
BBD says: January 12, 2015 at 7:29 pm
” NL intended the term pejoratively. Second, since he is indubitably an activist himself, he is demonstrating a remarkable lack of self-awareness.”
BBD says: January 12, 2015 at 7:31 pm
“And you can stuff the tone-trolling. That thread at Lucia’s is, in places, venomous.”
Pekka Pirilä says: January 13, 2015 at 7:33 am
When you think that something that you read is wrong, you develop eagerly counterarguments and are even ready to publicize them using arguments that are actually very weak and do not show at all what they are claimed to show is common. Trying to make the arguments simple and strong makes them actually wrong.
russellseitz says:January 13, 2015 at 8:42 pm
“While the Tyneside coal baron’s court jester ,Josh, has drawn a literally juvenile cartoon celebrating this gaffe,”
BBD says: January 13, 2015 at 8:46 pm
“Here’s Nic Lewis commenting on the error at Lucia’s. Not sure where else this has got to, but doubtless there will be much premature and inappropriate noise.”
…and Then There’s Physics says:January 13, 2015 at 8:49 pm
“Yes, someone on Twitter pointed out that Josh can draw but doesn’t seem very bright.”
Victor Venema (@VariabilityBlog) January 13, 2015 at 9:03 pm
“Was is necessary to write a reply to a paper like Loehle et al. (2014)? It is not as if such a paper could trick a real scientist into thinking it was legit, ”
…and Then There’s Physics January 13, 2015 at 9:43 pm
” Picking on inconsequential mistakes and suggesting that they are important is indeed ClimateBall and is not the behavior one would expect from a scientist. Indeed.
Richard Tol (@RichardTol) January 13, 2015 at 10:02 pm
“Just because X made a silly mistake doesn’t invalidate the rest of their paper.”
Some pretty contorted post-normal science thinking going on over at ATTP in an attempt to gloss over this affair. ATTP says:
"They also discuss how Loehle et al. (2014) only used the forcing due to CO2, rather than due to all anthropogenic influences. Consequently, Loehle et al. underestimated the change in forcing by about 13%.
Here’s where there was a mistake. Rather than pointing out that this would have reduced Loehle’s estimate for climate sensitivity (making it even more unrealistic), they suggested it would have increased it. A mistake. However, this didn’t influence the minimal model that they presented . . . . "
The minimal model they presented was, in their own words, "based on observed changes in radiative forcings", so it's hard to see how these observed changes, which they wrongly attributed to increasing the estimated TCR, could not have affected their model. It's also hard to see how Cawley et al would have written a paper attempting to rebut Loehle and Scafetta's paper if they had realised from the word go that the erroneous assumption made by Loehle and Scafetta, if corrected, would have resulted in a lower estimate for TCR. They obviously attacked the paper because they believed it underestimated TCR, not overestimated it. But, such are the goings on in the parallel Universe of AGW climate science and its defenders.
By the way, the quote from Richard Tol was a sarcastic restatement of what ATTP had said earlier in the main body of the post.
ATTP,
The post modernist pub landlord
How does one make a mistake in a rebuttal paper?
The only, possible reason: confirmation bias.
That alone is enough to flush this down the toilet.
Jaime Jessop,
Thanks for the details. I was taking a more simplistic view:-
IPCC AR5 says:- “The best estimate of the human-induced contribution to warming is similar to the observed warming over this period … The observed warming since 1951 can be attributed to the different natural and anthropogenic drivers and their contributions can now be quantified.
So, using the IPCC estimates for the observed warming since 1951, total anthropogenic warming was in range -0.1 to 1.4, so, assuming actual warming = 0.4, then natural variability was in range 0.3 to -1.0°C.
But they can't explain the physics for the natural warming.