Arguments
Lu Blames Global Warming on CFCs (Curve Fitting Correlations)
Posted on 5 June 2013 by dana1981
A paper just published in an obscure physics journal by the University of Waterloo's Qing-Bin Lu (2013) has drawn quite a bit of media attention for blaming global warming not on carbon dioxide, but rather on chlorofluorocarbons (CFCs, which are also greenhouse gases). However, there are numerous fundamental flaws in the paper, which is based almost entirely on correlation (not causation) and curve fitting exercises.
Lu's hypothesis can be disproven very simply. He argues that the radiative forcing (global energy imbalance) from CFCs matches global surface temperatures better than that from CO2 over the past decade. This is because as a result of the Montreal Protocol, CFC emissions (and emissions of other halocarbons) have been flat over the past decade, and global surface air temperatures have also been essentially flat during that short timeframe, while CO2 emissions have continued to rise.
However, a global energy imbalance doesn't just impact surface temperatures. In fact, only about 2% of global warming is used in heating the atmosphere, while about 90% heats the oceans. Over the past decade, ocean and overall global heating have continued to rise rapidly, accumulating the equivalent of about 4 Hiroshima atomic bomb detonations per second (Figure 1).
Figure 1: Land, atmosphere, and ice heating (red), 0-700 meter OHC increase (light blue), 700-2,000 meter OHC increase (dark blue). From Nuccitelli et al. (2012).
So while CFCs might match surface temperature changes better than CO2 emissions over the past decade, CO2 emissions better match the relevant metric – overall global heat accumulation. Since a global energy imbalance influences global heat content and not just surface temperatures, this by itself is sufficient to falsify Lu's hypothesis.
But let's dig into the details of the paper to see how Lu built his case and where he went wrong.
Unphysical Curve Fitting, Misrepresenting Cited Research, and Circular Logic
Here at Skeptical Science we have previously examined several cases of curve fitting. This describes the practice of scaling several variables without any sort of realistic physical constraint until the model closely matches the observational data, and then declaring that you've proven that those variables caused the changes in the observations. Loehle and Scafetta used this strategy to blame global warming on astronomical cycles, and Roy Spencer used it to blame global warming on ocean cycles.
In this paper, Lu used curve fitting to blame global warming on a combination of solar activity and CFCs. First he randomly scaled a total solar irradiance (TSI) reconstruction to match the surface temperature record as closely as possible. He claimed that this practice was justified by Solanki and Krivova (2003). Lu says:
"...it can be seen that the global temperature indeed closely followed the TSI variation up to 1970; the y-axis for TSI can be scaled so that the magnitudes of the temperature and TSI variations are similar during 1850-1970. This was actually shown previously by Hoyt and Schatten50 and Solanki and Krivova52, and an excellent linear correlation with coefficients of 0.83~0.97 between the TSI and the temperature was obtained.52 This implies that the TSI values can be converted into temperatures using the linear correlation.52 The observed data indicate that the solar effect played the dominant role in climate change prior to 1970."
But Solanki and Krivova didn't say TSI can be scaled willy nilly to fit the temperature data. They tried a similar approach in their 2003 paper simply to show that using the most generous possible assumption, solar activity still can't explain recent warming (emphasis added).
"We have shown that even in the extreme case that solar variability caused all the global climate change prior to 1970, it cannot have been responsible for more than 50% of the strong global temperature rise since 1970 through any of the channels considered here. We believe that even this fraction is too high."
There is a proportional relationship between changes in TSI and changes in surface temperatures, but it's a physical relationship. You can't just choose whatever proportionality is convenient for your argument. In fact what Lu has done is assume that TSI explains most pre-1970 global surface warming, and then claim that he's proven this is the case. It's circular logic, like fixing a card game and then claiming you're a great card player when you win.
The only reason Lu's TSI model matches the surface temperature data is because he forced it to match through curve fitting – by refusing to apply any physical constraints to his model. Then when his unphysical model fits the temperature data reasonably closely, he declares that he's shown "that the solar effect played the dominant role in climate change prior to 1970." In reality he's shown no such thing, he's simply assumed that his conclusion is true.
Lu also uses a solar reconstruction from Hoyt and Schatten (1993) in his curve fitting exercise. Why use the results of 20-year-old study? Perhaps because it helps Lu arrive at his end conclusion that global warming isn't due to CO2. The Hoyt and Schatten paper claims that the equilibrium climate sensitivity to doubled CO2 is a mere 0.19°C – a factor of 15 lower than today's best estimates.
Perhaps the gold standard of TSI reconstructions comes from Wang, Lean, and Sheeley (2005), updated by Kopp and Lean (2011), whose data are available here. They estimate that the increase in the amount of solar radiation reaching Earth from 1860 to 1970 was not very large (a radiative forcing of less than 0.2 Watts per square meter, compared to the 1.7 Watts per square meter CO2 forcing from pre-industrial times to Present), and only sufficient to account for approximately 0.07–0.15°C average global surface warming. Thus TSI can probably only account for less than half of the observed 0.3–0.4°C surface warming during that time, contrary to the 100% solar attribution Lu claims based on his curve fitting exercise.
Yet More Circular Unphysical Arguments, Curve Fitting, and Misrepresentation of Cited Research
Lu faced the conundrum of having to explain how the increased greenhouse effect from CFCs can cause global warming while the much larger increased greenhouse effect from rising CO2 can't. To accomplish this, he used what the climate scientists at RealClimate have described as the saturated gassy argument – claiming that increased CO2 can't cause more warming because there is already so much in the atmosphere that its greenhouse effect has become saturated. However, as the climate scientists at RealClimate (and we at Skeptical Science) have explained, that argument is quite clearly wrong – disproven by observational data.
Here Lu is again guilty of circular, unphysical logic. He doesn't actually physically demonstrate why he thinks the CO2 greenhouse effect is saturated. Rather he merely argues that because CFCs seem fit the surface temperature data better than CO2, that means CO2 can't be causing global warming, which means the CO2 effect must be saturated. Once again he has merely assumed his conclusion is true rather than actually providing physical evidence for it.
Perhaps worse, Lu claimed that a paper by Anderson et al. (2004) supported his saturated gassy argument, claiming the CO2 absorption band is missing from the observed spectrum data. On the contrary, Anderson et al. concluded,
"The spectra in Fig. 8a are the result of a superposition of two different effects. First, there is an increase of greenhouse gases from 1970 to 1996 that gives rise to recognizable bands in the observed spectrum..."
And once again, Lu tried to demonstrate that CFCs can account for the recent global surface warming through unphysical curve fitting, multiplying the CFC forcing by whatever value allowed the CFC data to best fit the temperature data. When using physical constraints, CFCs (included in "halocarbons" in Figure 2) can account for only about 20% as much warming as CO2.
Figure 2: Global average radiative forcing (RF) in 2005 (best estimates and 5 to 95% uncertainty ranges) with respect to 1750 for CO2, CH4, N2O and other important agents and mechanisms, together with the typical geographical extent (spatial scale) of the forcing and the assessed level of scientific understanding (LOSU). From the 2007 IPCC report.
In his Figure 11, Lu also exaggerates the difference between expected CO2-caused warming and observed temperatures by plotting the observational data against the surface warming we expect at equilibrium. This is wrong because there is a global energy imbalance, which means there is more warming "in the pipeline" for several decades to come before we reach that equilibrium state. In reality the Earth has warmed as expected from the increased CO2 greenhouse effect.
Why did the Media Cover this Paper?
Frankly this paper should not have passed peer-review, but was perhaps aided by publication in a physics rather than climate journal, and in fact in the physics journal with the lowest impact factor by a wide margin. The paper was then trumpeted by a University of Waterloo press release and a Science Daily article, both of which used exaggerated language like "Lu’s theory has been confirmed." The Science Daily article did not discuss any of the problems with the paper that we have detailed in this post, or ask any climate experts about it.
ABC did a better job, talking to climate scientist David Karoly, who expressed appropriate skepticism about a paper which purports to overturn decades and even centuries of well-established physics and climate science in one fell swoop. Characteristically, The Australian then criticized ABC for failing to be "fair and balanced" because they interviewed an actual climate expert about the paper.
Frankly, the paper is a non-story. It may seem like news due to the grandiose claims of overturning the vast body of scientific evidence supporting CO2-caused global warming, but it is very rare for a single paper to accomplish this type of feat. More often the single paper claiming to overturn the body of established scientific research is wrong. That is clearly the case for Lu (2013), which is based on assuming rather than proving the hypothesis, unphysical curve fitting, and misrepresenting the cited research.
Moreover, this study isn't new. It's actually the third Lu has published about his CFC warming hypothesis. The first two were addressed by RealClimate, two peer-reviewed published responses, Skeptical Science, and others. Andrew Gilkson at The Conversation, Climate Science Watch and Rabbett Run (here and here) are also good resources for debunking Lu's latest effort.
As we've previously discussed, the media need to be more careful in avoiding single study syndrome, misinforming the public by overhyping a single supposedly game-changing study before it has survived the scrutiny of the scientific community.
Note: this post has been incorporated into the rebuttals to the myth "it's CFCs"
Thanks Dana for going by numbers dissecting this roadkill of a study.
1) The journal that published this also published Falsifiation Of The Atmospheric CO2 Greenhouse Effects within The Frame Of Physics, Gerlich, G. and R. D. Tscheuschner (2009). Needless to say, it did not accomplish that goal, but one has to wondre about the journal.
2) The most puzzling is why on Earth U Waterloo, generally a fine scholl in science and engineering, put out big press release on this. Professor ought to be free to publish what they can get accepted ... but I don't think a university is *required* to create a gushing press release for every paper. Sadly, this diminishes U W's reputation in my mind, anyway.
The journal IJMP-B is a low impact journal, yes; but it serves well in its particular focus; which is mainly condensed matter physics, superconductivity and the like. The problem is most likely somewhere within the editorial board, allowing this otherwise respectable if low impact journal to be a soft touch for pseudoscientific climate denial. It is something the editorial board really needs to look at seriously.
Declaring my own personal interest: I'm one of the six people who helped put together a response to the nonsensical Gerlich and Tscheuschner (2009) at IJMP-B, with Joshua Halpern as the main author of the rebuttal piece.
The other fitting step that QB Lu from U of Waterloo applies is a crucial 9-year lag from halocarbon increase to temperature effect. Below is my attempt at reconstructing what Lu attempted to do via the 9-year lag. Note that he also uses R instead of R^2 to make the correlation look better. As Dana said, the lag is not there in the OHC data.
Climate Science Watch has a page up entitled Response by Qing-Bin Lu to “Qing-Bin Lu revives debunked claims about cosmic rays and CFCs” On it, Lu says he is not aware of any experimental evidence of "the physical mechanism by which CO2 warms the planet". His actual words were: "I do not know who has done such experiments".
Joe Farman, the first person to observe the Antarctic ozone hole, critiqued Lu's idea that cosmic rays cause it, in 2002 (with Harris and Fahey, in Comment on "Effects of cosmic rays on atmospheric chlorofluorocarbon dissociation and ozone depletion"). Lu's idea then was that CFCs were observed to be in lower concentration over Antarctica therefore cosmic rays must cause this, therefore cosmic rays, not UV photolysis, was the cause of the ozone hole. It was as solid as that. It had something to do with something Lu thought must be going on on the surfaces of the polar stratospheric clouds, i.e. ice particles that ozone scientists suddenly realized were there. He had no measurements. Farman said no one has ever measured anything like what Lu is talking about on the surfaces of ice particles in the stratosphere over Antartica, or in a laboratory, and Lu is not citing measurements now. Farman said CFCs are "strongly hydrophilic" and therefore why should they suddenly be attracted to solid water particles? Farman stated that the observed concentration of CFCs in the atmosphere over Antarctica was consistent with the idea that UV photolysis breaks up CFCs mainly in the tropical and subtropical stratosphere and with what is known about the movement of air from the troposphere to the stratosphere and within the stratosphere.
What amazed me was that the Dean of the Faculty of Science at Waterloo allowed the Waterloo News to publish his statement that he, Terry McMahon, has swallowed Lu's gibberish, hook, line, and sinker. Waterloo has a good reputation in Canada, especially in computer science. If its Dean of Science claims one of the scientists there has come up with a paper overturning 150 years of climate science, it is no wonder that some newspapers covered it. The question is, who were the "peer" reviewers, and how has Lu palmed off his work all these years as something Waterloo would want to be associated with? McMahon must believe Lu is something like Einstein, the discoverer of a new way to see.... No wonder the human race is doomed.
He describes himself as:
Qing-Bin Lu, PhD
Professor in Physics, Chemistry and Biology
Canadian Institutes of Health Research (CIHR) New Investigator
Department of Physics and Astronomy
University of Waterloo
GFW,
Lu's profile page at UW places him as an associate at the faculty of Physics & Astronomy, and he looks on the picture as a young person (certainly not "emeritus" type ala Singer), nothing about his tenure but I guess as an associate he doesn't have one yet.
One thing is certain, he tries to apply his Astronomy skill to the field where he lacks basic knowledge and it's surprising that he's been able to do it (publish poor work) three times. I wonder, Mike Mann style, if he has certain other affiliations business or political or such, that make him so biased in this filed unknown to him.
Andrew Gilkson, Earth and Paleo-Climate Scientist at the Auatralian National University, has also writtten a devastating critique of Lu's paper.
Gilkson's critique, Are CFCs responsible for global warming? was posted on The Convesation on June 5.
Gilskson and Dana cover much of the same ground in their respective posts.
The usual progression in Canadian universities is:
- hired as an untenured assistant professor
- get tenure, get promoted to associate professor. Sometimes a single step, sometimes two, depending on the university - but usually they happen at roughly the same time. In very rare cases, I have seen faculty get tenure, then sit at the assistant professor level for years.
- continue to develop your fiefdom and accumulate enough papers/grad students/research grants to get promoted to full professor (i.e., "professor", with no assistant or associate prefix). (Alternatively, languish as a tenured assistant professor for the rest of your career.)
On this basis, my guess is that Lu has tenure. Number of publications often counts more than quality...
Oops. Make that "Alternatively, languish as a tenured assistant associate professor ..."
John H @9 - thanks for that link, yes, Gilkson does a nice job debunking this myth as well. I notice he has an Escalator link in there :-)
Are the powers-to-be at the Univesity of Waterloo under the thumb of the Harper government?
David Lewis @6
Just to cut down on the confusion factor, you probably mean that CFC's are "strongly hydrophobic."
Harris Farman and Fahey actually used the word "hydrophobic". Duh. One reason CFCs and other ozone destroying substances make it up into the stratosphere is they do not mix with water molecules in the troposphere to be rained out. Lu needs CFCs to appear on the surfaces of the ice particles that make up the polar stratospheric clouds found in Antarctica so the reaction he believes in can take place. Ice isn't liquid or gaseous water, but the Farman paper states the claim "seems very unlikely".
I found a correlation between global temperatures and the quantity of headlines about the private life of celebrities. I think the obscure journal may be interested in it - but I'll see if I get a better offer from Energy & Environment.
Science Daily, here I come!
Lu is an experimental electron scattering guy who thinks that he can use that to explain everything. He also seems to be a bit of a self promoter. BTW, the CFC+HFC forcint is flat since about 1992, so that is twenty years.
@17 - Eli- Sort of reminds me of one Will Happer. Yes? Except of course, Happer hasn't published on climate science....just opined.
And the saturated gassy argument is sooooo old. As Spencer Weart notes- that argument was had between Arrhenius and Angstrom.
"You can't just choose whatever proportionality is convenient for your argument."
You mean like Foster & Rahmstorf 2011? TSI is only a proxy for solar activity. In their paper F&R also looked at another proxy, SSN, but made no attempt to cross-check theorectical TSI forcing against their coefficient. Why should Lu be held to a higher standard?
By assuming TSI is the only effect that solar can possibly have, you eliminate indirect solar effects which may also correlate with TSI, like UV modulation of stratospheric temperature.
Klapper @19 - no, not even remotely similar situations. F&R used multiple linear regression for all of the primary short-term natural temperature influences (solar, volcanic, ENSO). Lu just randomly scaled up one forcing - an old and inaccurate representation of the forcing at that - ignored all other forcings, and didn't even use any statistics.
There's also no research or physical evidence suggesting that indirect solar effects have a non-negligible impact on global temperatures, especially one that's not correlated with TSI. It would be generous to say your comment is on shaky scientific footing.
Klapper @19, you yourself say that F&R11 use TSI as a proxy of solar activity, and do not check against forcing. It follows from that that any indirect solar effect correlated with TSI is included in F&R11's TSI regression. To then turn around and claim F&R2011 "assum[e] that TSI is the only effect that solar can have" simply contradicts yourself (in addition to being false). You may, of course, suspect indirect effects that do not correlate with TSI; but if they do not correlate then they weaken, rather than strengthen, the TSI forcing.
I don't know if the crew here have seen this:
http://science.nasa.gov/science-news/science-at-nasa/2012/22mar_saber/
But there are a few sites that claim this falsifies global warming....because CO2 in the thermosphere is called a "coolant" in the article. But anyhow, I think this is the kind of activity that Klapper may be referring to. The footnote at the end of the article points out:
ootnote: (1) No one on Earth’s surface would have felt this impulse of heat. Mlynczak puts it into perspective: “Heat radiated by the solid body of the Earth is very large compared to the amount of heat being exchanged in the upper atmosphere. The daily average infrared radiation from the entire planet is 240 W/m2—enough to power NYC for 200,000 years.”
I'm not sure also what UV effects on the stratosphere is supposed to mean. UV is included in the TSI satellite measurements, so it's not like it's missing from the TOA energy budget. Is this some kind of 'wings of the butterfly' effect that is supposed to do something else? Or is this more unicorn chasing....the endless parade of "what ifs" that don't actually formulate a hypothesis.
@Dana81 #20:
"There's also no research or physical evidence suggesting that indirect solar effects have a non-negligible impact"
Doesn't AR4 admit indirect solar is poorly understood. That is we don't know enough to conclude it has no effect?
[DB] "Doesn't AR4 admit indirect solar is poorly understood"
Citation, please.
@Tom Curtis #21:
'claim F&R2011 "assum[e]........'
Where do I claim that? I'm talking about this Skeptical Science analysis when I say "you", meaning Dana is the one making the assumption that the TSI effect can only be direct, i.e. the delta W/m2.
As for the possibility that indirect solar effects don't correlate with TSI, at least cycle to cycle, that might be true. I'm going to start by checking the aa index vs SSN over the period of the F&R2011 paper.
[DB] "Doesn't AR4 admit indirect solar is poorly understood"
Citation, please.
Klapper @24
Dana said:"There's also no research or physical evidence suggesting that indirect solar effects have a non-negligible impact"
You replied: "Doesn't AR4 admit indirect solar is poorly understood. That is we don't know enough to conclude it has no effect?"
Don't you see the logical fallacy in your statement? You have converted Dana's comment involving something with shades-of-grey into a black and white statement then responded to that. That is a strawman argument.
Nobody suggests that there cannot be any impact from indirect effects such as the impact on UV. That mechanism certainly has plausibility, particularly given that the UV part of the solar spectrum varies by a more significant percentage than overall TSI. However admiting the possibility of a mechanism that might have an impact of some magnitude does not necessarily mean that such a mechanism would necessarily have a significant magnitude, which was Dana's point.
If any mechanism associated with the Solar Cycle; TSI, Stratospheric changes due to UV, whatever, exists, one would expect to be able to extract its significance from the data using Multiple Regression. When F+R regress against TSI they are effectively regressing against the Solar Cycle since TSI is very highly correlated with the cycle. So their analysis will necessarily find the impact of all mechanism that correlate with the Solar Cycle.
One thing you could consider is doing similar regression analyses of Solar Cycle versus the various satellite temperature records for the various levels in the stratosphere which you could get from here. You would still need to include Volcanic activity in this since the impact of the El Chichon and Pinatubo eruptions is clearly visible in the stratospheric data.
As for non-Solar-Cycle related indirect solar effects, how do you look for them? What would you be correlating against, and what mechanism would make them plausible; at least solar-cycle related effects have a plausible mechanism? If there is no plausible mechanism, isn't looking for some such hypothetical equivalent to speculating that dust storms on Mars might influence Earth's climate. One can speculate idly as much as one likes, but a conjecture needs at least some degree of plausibility before one even considers it.
[DB] "Doesn't AR4 admit indirect solar is poorly understood"
Citation, please.
Table 2.11, Page 202, Chapter 2 of AR4 lists "Cosmic Rays" as LOSU = very low, consensus = 3, evidence = C. Even direct solar effects (irradiance) are listed as LOSU = low, consensus = 3, evidence = B. In section 2.7.1.3, UV modulation is also mentioned but it does not receive extensive discussion, nor is it included in Table 2.11.
@Glenn Tamblyn #26:
I meant to say "non-neglible effects" not "no effects". The CERN experiments on cosmic rays are going on because currently there is a very low level of scientific understanding in this area.
Also I didn't say indirect effects are not solar cycle related, I said they didn't necessarily correlate with the secular trend in TSI, or that's what I meant to say. For example what if the peak TSI drops from one cycle to the next but the aa-index does the opposite, even though it still honours the same period.
The point of all this is that I don't think you can ignore indirect solar effects, nor can you assume the relationship between TSI and indirect solar effects is constant over the last 100 years. If I interpret this post correctly, Lu's paper is being de-constructed primarily because TSI can't possibly raise the temperature as much as Lu claims prior to 1970. Yet indirect and direct solar effects are rates as having "very low" and "low" levels of scientific understanding according to the IPCC.
Klapper
If I had to focus on the most important aspect of Lu's paper that seems faulty, it is simply his claim that CFCs correlate with warming because CFCs have dropped and warming has dropped. His basic error is in equating surface temps with total system warming. Surface temps constitute only 2% or so of the total system warming with the bulk of this occurring in the oceans.
If his hypothesis wrt CFCs being the dominant driver of warming, not CO2, is to have any legs then he needs a correlation between CFCs and the major effect of warming which is total heat content. That correlation simply isn't there; CFCs have plateaued, warming hasn't, the oceans are still warming.
He has another problem in that he dismisses the GH Effect impacts of CO2 without ever giving a satisfactory reason why, just vague allusions to Saturation. And his claim that OLR readings don't match what is expected is a flat out misrepresentation of Anderson et al.
Additionally he merely uses correlation to suggest that CFCs can have the magnitude of GH Effect that he claims when he could have used to known properties of CFCs to actually calculate this using any of the many Radiative Transfer Codes available.
In a reply to a criticism of his paper at Climate Science Watch here he makes the following statement (my emphasis)
"5. “In contrast, there is strong experimental evidence of the physical mechanism by which CO2 warms the planet, evidence that (as scientists have mentioned already in response to Lu) dates back 150 years.”
Response: I do not know who has done such experiments."
That is an absolutely stunning statement from a researcher involved with Atmospheric Physics! He actually doesn't know the literature of the field he is operating in!
As for his actual theories about Cosmic Ray genesis for Ozone depletion, I don't have an opinion. It seems most of his peers reject that claim, and have done so in the past but I don't know enough to actually comment on that. But his other claims about CFCs vs CO2 and the GH Effect have more holes in them than a block of Swiss Cheese.
Klapper @28 - Lu is criticized for arbitrarily scaling the TSI forcing to "prove" his assumption. Now you're arguing that maybe that arbitrary scaling is coincidentally correct, because [hand waiving other solar effects]. For that to be true, you would need these other effects to more than double the TSI forcing. There's just no evidence for it. You're arguing it hasn't been conclusively disproven - that's all fine and dandy, but there's no evidence supporting it either. Nobody has disproven my hypothesis that unicorn farts are causing global warming either. That doesn't make it plausible.
As for GCRs, all the evidence so far indicates that they have a very small if any impact on global temps.
I just read Solanki and Krivova (2003) and found the following:
"[10] In Figure 2 we have scaled the irradiance such that the magnitudes of the temperature and irradiance variations are similar between 1856 and 1970. To be precise, we minimize the X2 between irradiance and temperature prior to 1970. This implies converting irradiance into temperature using a linear regression."
There is essentially no difference from Fig. 9 in Lu (2013).
And dana1981 (Dana Nuccitelli ?) also used a similar presentation in this post, "IPCC Draft Report Leaked, Shows Global Warming is NOT Due to the Sun", 14 December 2012 by dana1981 (http://www.skepticalscience.com/ipcc-draft-leak-global-warming-not-solar.html ).
Aren't there double standards??
Moreover, the results presented in his Figs. 12 and 13 of Lu (2013) are the temperatures observed and CALCULATED using the IPCC radiative-force equation for CFCs, rather than based on correlations between temperature and CFC concentrations.
Please stop damaging the reputation of IPCC.
[JH] Please lose the snarky tone.
John,
Regarding your second point, I think you are mistaken.
To arrive at the curves plotted in figure 12, one has to convert concentration to radiative forcing via eq 7, and convert radiative forcing via eq 6.
There are three parameters. The parameter chi in eq 7 is the only one obtained using WMO radiative transfer codes. alpha on the other hand is a parameter, and Lu chose alpha = 0.9 K/Wm-2 because it fitted the observations the best (see figure 6 of his 2010 paper in Journal of Cosmology), not based on any physical model. So it was a curve fitting exercise.
Ian,
Good point.
Aren't there large uncertainties in the climate sensitivity (alpha) in IPCC climate models?
When one says that there would be 1 or 4 deg C increase in temperature corresponding a doubling of CO2 concentration, how sure for this assumption? Were the results not called CALCULATED results in IPCC climate models? Did we call them curve fitting correlations?
John001 @31 - you're missing a key difference. Solanki and Krivova and the part of my blog post you reference weren't trying to determine how much global warming has been caused by the sun. We were looking at correlations and/or trying to figure out the maximum possible solar contribution. What Lu did was assume that the maximum possible solar contribution is reality, without providing any evidence to support that assumption.
The difference with respect to Foster and Rahmstorf is that F&R also accounted for all other known large natural temperature influences in their multiple regression.
John001 @33 - equilibrium climate sensitivity is a physical output from a climate model. It's not based on 'curve fitting' at all.
Co2 above the tropopause (e.g. in the stratosphere and thermosphere) is a coolant because it radiates after collisional excitation, but there is little upwelling radiation in spectral regions where it can absorb. Net result is that it pushes more radiative energy out to space than it absorbs from below and acts as a coolant. See, for example
http://www.atmosphere.mpg.de/enid/20c.html
Recently, Eli asked Leif Svagaard about
"Has anyone worked on adjusting pre 1979 solar irradiance reconstructions based on Kopp and Lean (2011)?
http://www.dtic.mil/dtic/tr/fulltext/u2/a535690.pdf
http://rabett.blogspot.com/2013/03/the-blog-of-new-sun.html
which drops the solar constant to 1361 W/m2, decreases the peak to minimum intensity a bit and straightens out time history since 1979 and basically makes anything said about TSI previously, both for before 1979 and after wrong, and got this reply
"yes, almost all the old stuff is obsolete. That does not deter the enthusiasts, of course"
Prof. Lu is very enthusiastic. Not very well informed, but very enthusiastic
John,
First off, IPCC does not develope climate models, and they only summarize published results; the model themselves are developed by independent research groups all around the world.
One thing that you have to understand about climate sensitivity itself is an idea that helps us understand and characterize the bulk behaviour of climate models, and it is not a parameter that can be set a priori.
The parameter alpha, which I think is the same as the Plack response, describes how the earth will warm/cool according to a change in radiative force, whether due to sun or greenhouse gases, in the absernce of feedback. This is very well constrained, as it is from (relatively) simple physics. All climate models agree on this very well; and you can see it from a graph from Dufresne and Bony 2008: all models gives a planck feedback of 1.1 degrees.
The real uncertainly is on the feedback (beta), and this is entirely responsible for the range of uncertainties: 2.3-4.2 degrees for doubling of CO2. Even this can be broken into its components: surface albedo (ice cover etc.), water vapour, and cloud feedback. You can see that the most of the uncertainty comes from changes to clouds; this is is of course a known limitation to current climate models.
To reiterate, climate sensitivity cannot be set and it simply reflects our understanding of the various aspect of climate physics, and the uncertainty in climate sensitivity reflects uncertainty in our understanding as well as constraints on our ability to quantify this understanding through a climate model.
Whether 2.3-4.2 degrees is large depends on what you are looking at. From a purely scietific point of view it is rather large, but from a broader perspective it is not: what matters is that we are quite certain that it is above 1, and likely above 2, which is more important from a policy point of view.
Also I shold clarify that curve fitting can be very informative if done correctly, and the results are interpreted with care. Unfortunately Lu's paper is not one of them IMO.
Hi Ian,
Very good interpretation of the climate sensitivity and good comment on Lu's paper.
But I still have one question. Suppose that the equilibrium climate sensitivity finally to calculate the temperature change due to a radiative force is equal to the value of alpha times beta. You say that alpha =1.1 deg with good certainty. But if beta has a large range of uncertainties, then the equilibrum climate sensitivity still has a large range of uncentainties. And you would probably agree that in the literature, researchers sometimes just use the equilibrium climate senstivity without separating alpha and beta.
Thanks.
Well, this is embarrassing. Not only do I currently attend the University of Waterloo, but I’m also physics major. Professor Lu’s main research areas are:
I took those directly from his department profile page. The last one seems oddly out of place as compared to the others, though his past study of ozone depletion would explain his predisposition toward CFCs.
Hi John,
Indeed there is still a large uncertainty in the equilibrium climate sensitivity (ECS), primarily due to cloud feedback, which dominates the uncertainty: the range of cloud feedback in 12 models is almost as large as the spread in ECS itself; I think this is unlikely to converge until we get to the point where clouds can be modelled somewhat explicitely.
Even though the spread among model is large, the important thing is that even if you pick out the best case scenario for each feedback aong the models in Dufresne and Bony 2008 (i.e. model 1 for surface albedo and water vapour+lapse rate, model 2 for cloud feedback, you will still get a warming that is very close to 2 degrees. In other words, there is very strong evidence that warming will not be less then a degree.
Climate model is really just a way for us to quantify our physical understanding. Skeptics often point to the uncertainty as a problem, but I think the right way to look at the spread is that we can implement our current knowledge in 12 different ways, and under no circumstances is the warming neglible.
Yes, most of the time ECS is used instead of splitting it up to alpha and beta, I think the reason is that you can't in reality increase the temperature without the water vapour feedback, so making the distinction between the two is pointless for most applications.
Calling the Science Daily piece an 'article' is generous - it's just a reprint of the press release, which is all Science Daily does. Of course, this didn't stop it being cited as supporting the research by The Australian's consistently abysmal Cut & Pate column.
Dave@23 UV effets is a handwave at the change in the proportion of UV radiation in the solar spectrum within the solar cycle. The increased UV below 306 nm then does increased photochemistry. Lu does little more than handwave
IanC#40: Thank you, Ian. You made good points.
John000 - I would suggest looking at the Climate Sensitivity thread, where the various uncertainties are discussed.
Estimates for climate sensitivity come from model results, from observations over the instrumental period, from responses to volcanic eruptions/aerosols, and paleo observations over the last few ice age cycles. Not just models! The climate sensitivity values used in such discussions are, in general, the synthesis of many lines of evidence, which is one of the reasons why extrema estimates such as Lu's tend to raise eyebrows.
Extraordinary claims, counter to large collections of existing work, require extraordinary evidence - Lu has not supplied the same, nor answered earlier criticisms of his work.
Its a thing both odd and very ambitious to be using "Curve fitting" as a pejorative in science. At least this fellow found a curve that fit.
"Extraordinary claims, counter to large collections of existing work, require extraordinary evidence -"
This phrase is from Carl Sagan. (-snip-). Its actually a plea for a handicap. And to make such a plea would indicate that ones hypothesis needs a handicap. (-snip-). (-snip-).
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Chordotonal wrote "With Lu there is nothing wrong with the evidence so far."
Far from it, as discussed in the article itself. If you want to engage in the discussion and support Lu's work then identify a specific flaw in the article and discuss it.
I suggest you read the comments policy, particular the item about sloganeering. If you make posts that make arguments that are not backed up by evidence they are likely to be deleted.
(-snip-).
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(-snip-). I don't think Lu 's hypothesis will pan out by the way. But the process by which you prove things like this is going to involve curve fitting and correlation. Its very strange to be clziming otherwise.
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What you have, Chordotonal, is a scientist presenting a hypothesis and the proceeding to support that hypothesis by picking and choosing whatever evidence seems to support the hypothesis (don't look too closely) and ignoring whatever doesn't support it. Need to get rid of CO2 as a GHG? Ok, go all Angstrom and use the saturation argument. Ignore the fact that it is completely unsupported in the literature.
I imagine it passed peer review because it was reviewed by Lu's peers -- people who were not experts in the field and who had little idea of the mess that Lu was creating out of the existing literature.
(-snip-). Falsification is okay but it ought to be convergent. And falsification is not nearly as important as verification. What we want is convergent verification. I don't think that Lu is going to get convergent verification. I suspect that its just a matter of luck. But to pretend that finding a correlation for an hypothesis is not even a valid part of the process appears "a bit rich" as it were.
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