Update: Nature has just published a thoughtful commentary on the report
The Inter-Academy Council report on the processes and governance of the IPCC is now available. It appears mostly sensible and has a lot of useful things to say about improving IPCC processes – from suggesting a new Executive to be able to speak for IPCC in-between reports, a new communications strategy, better consistency among working groups and ideas for how to reduce the burden on lead authors in responding to rapidly increasing review comments.
As the report itself notes, the process leading to each of the previous IPCC reports has been informed from issues that arose in previous assessments, and that will obviously also be true for the upcoming fifth Assessment report (AR5). The suggestions made here will mostly strengthen the credibility of the next IPCC, particularly working groups 2 and 3, though whether it will make the conclusions less contentious is unclear. Judging from the contrarian spin some are putting on this report, the answer is likely to be no.
Rod B #195:
> (but it is what I’m currently trying to learn,
That would be the day… in the two years I have seen you frequent this blog, I have yet to see you honestly try to learn anything. So, go ahead, surprise us. Waste your own time instead of ours.
Geoff Wexler @192 — Yes, on millennial scales you have it about right. Using linear systems thoery and a one reservoir model with (small) positive feedback one doesn’t need more than pencil & paper to illustrate what is happening.
On longer time scales, millions of years, temperature follws CO2 concentrations; something which needs to emphasized to the contrarians (who fail to learn enough geology).
Bob #198, seeing that you’ve chosen to waste your time :-) , here’s a hint:
http://geoflop.uchicago.edu/forecast/docs/Projects/modtran.orig.html
Remove everything except CO2. Then, try a doubling of CO2, and a re-doubling. See what it does to the absorption band profile. Remember, what counts, what tells you how much energy is not getting to space, is the area contained in the profile, not what’s happening in the core. Look at the number Iout on top.
Saturation is bunk. Hope this helps.
Rod B., First, there is absolutely nothing controversial about the fact that CO2 absorption is not saturated. You will not find any serious paper in the past 20 years that argues for saturation.
Second, even a small broadening of the spectral absorption lines represents a very large amount of energy absorbed.
Third, even if all the energy from the surface were absorbed in the first 10 meters, you would still have the energy radiated by the atmosphere.
Personal incredulity does not equate to or validate skepticism.
195 (Rod B),
Please provide a citation for that statement.
#203, is there a bug with the calculations on that page – the Iout changes, but the Ground T, K value stays the same no matter what input parameters are used (apart from changing the location, which changes to a different fixed value for each location)?
203 (Martin Vermeer),
[Rod B, please don’t take this the wrong way… even though I know you’ll eventually bring up the Medieval Warm Fantasy and tick me off by doing it…]
I believe that some serial deniers, like serial killers, actually commit their crimes as a plea for help. Deep down, they want to be stopped, but they can’t help themselves.
So I see Rod B’s persistent presence here as a cry for help.
And, to paraphrase Blanche Deboise, from that famous Tennessee Williams play A Streetcar Named Deniers, “I’ve always depended on the climate of skeptics.”
Anyway, it’s a slow day at work (since I’m the only one working today). I’m trying to debug a batch script that takes 20 minutes to run through and reveal the sixteenth bug that was lurking behind the last fifteen of them. Seventeen. Eighteen…
That, and I really, really like the molecular level aspects of GHE. It’s cool, and once someone really understands it, I think they start to take the other stuff with a much larger grain of proverbial, IR absorbing salt.
Of interest:
http://www.science20.com/news_articles/greenland_west_antarctic_ice_caps_melting_half_speed_previously_predicted
#Rod B
I know you said you stated your last name in the past. if it’s not to terribly inconvenient, can you refresh my memory again.
Also, I think there are so many tired old arguments out there that it is really hard for people to cut through to the good stuff. But you are here with some truly knowledgeable people and they have been directing you very well.
It seems you keep digging for gold in the wrong places and end up finding fools gold. Try to remember, just because it’s shiny, does not mean it’s valuable.
Try this little nugget:
https://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/
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“Scientists say CO2 absorbs 100% of its primary IR radiation within 10 meters” – 195
And what happens to the heat emitted from the atmosphere from within that 10 meters?
208 (Jacob Mack),
Good news, for a change!
Stuart #206, no, you have to manually change the “ground T offset” to restore equilibrium, i.e., bring Iout back to the same value. How much, tells you what the surface temperature effect of a given atmospheric composition change is.
This is a very simple, 1-D model: don’t take it too seriously. E.g., the effect of humidity on the lapse rate seems to be lacking. But the radiative transfer code is used by remote sensing folks including the military, and if there is anything wrong with it, climatologists aren’t the only ones in trouble ;-)
185, Bob (Sphaerica): It will be an interesting (and sad) day, however, when an IPCC ARx comes out with an entire section (“Possible Climate Effects To Date”) that assigns a statistical probability to some percentage of a series of events (droughts, storm and wild fire frequency and strength, expanding/changing ecosystems, etc.) as being a result of climate change (based purely on an analysis of what tended to happen in the past, to what degree and how often, compared with the “present world” of ARx).
Why sad?
You have introduced a concept like “attributable deaths” in epidemiology: granted that a 10% gain in weight increases heart attack risk by 10% (that’s neither exact nor very far wrong), how many of the heart attacks among those who were 10% overweight at the time of their heart attacks might reasonably be said to have been caused by their excess weight?
David B. Benson (184), I may be a bit confused, but did you say that the study I referenced did not determine temperature in the miocene by using current general forcing and sensitivity equations in models, even though that’s what the authors said? Or did I miss your point?
I simply overlaid Vostok graphs from NOAA since 450,000 bp and in many obvious areas temperature is leading CO2; in some areas it looks like it might be the other way, and in many areas eyeballing isn’t sufficient given the granularity and sharp variations.
You’re correct that I need more geology. And I can see how your conclusion might be drawn. But to move it to a class of irrefutable a fait accompli (“That’s it! Game over! We won! No more questions!”) is grossly unwarranted.
Richard Ordway, a minor clarification: while you will find high-ranking and mid-ranking individuals on both side of the AGW question, the military does not have a position on whether AGW is true (Commander-in Chief not withstanding). They do have (or are making) contingency plans to respond to AGW caused conflicts.
Bob (Sphaerica) (194), none of your three points apply to me.
Bob (Sphaerica) (198), good points. I have always felt that CO2 molecule acting as a bucket brigade, while having its own problems, is better argument in support of unsaturation. My reaction was to a plethora of responses that said/say broadening does it.
Your second point has long been at the forefront of my mind. I am not able to reconcile the different radiations between the layers with specific narrow band radiation being absorbed by CO2. Just one question: you say “re-emitted” — what exactly is the emission, from what gas at what frequency, in what you call re-emission? (I’m not sure of the “re” part.) (With apology for getting into detail on the wrong thread.)370020 robils
Martin Vermeer, well I am studying — I’m just slow, though as you know climatology is very tough. You’re confusing what looks to you as my not learning with my unacceptance of the “scientific” statement that basically says, “Is too!” or something akin. Or my not accepting a true scientific assertion because maybe that same person recently asserted something that was way off the chart hyperbole and has lessened credibility.
Plus, as I said a couple of years or so ago, I have the responsibility to dig it out as best I can with maybe a scattering of help here on RC (which is the only blog I spend more that trivial time on). Bottom line, the RC posters and moderators have no responsibility to teach me; most have more important things to do.
John P. Reisman (OSS Foundation), Surely, I’m easy!
Sincerely,
Rod W. Brick
Scientists need to directly confront the liars where they are. There should be a coordinated attack on Fox News, Matt Drudge, Rush Limbaugh, etc. because that is where the majority (of Americans) gets their disinformation from. It is not enough to respond with intellectual arguments on a blog. Polls of Americans show that fewer and fewer people accept global warming. Murdoch is winning and you are losing.
The forces of Murdoch aren’t going to stop until they defund your research. Scientists need to fight back much harder in order to prevent this from happening.
Just listen to what Glenn Beck says on Fox News on a weekly basis. He’s not simply a denier. He wants to take down science itself.
Ray, you made strange claims…
“Rod B., First, there is absolutely nothing controversial about the fact that CO2 absorption is not saturated. You will not find any serious paper in the past 20 years that argues for saturation.”
It is obviously saturated in the most intense lines – now of course in any spectrum there are unsaturated weak lines and the wings are – by definition- not saturated.
”
Second, even a small broadening of the spectral absorption lines represents a very large amount of energy absorbed.”
huuh? small broadening represents a small amount on energy absorbed, of course ! just the extra fraction of power absorbed, which can be nothing but small if the broadening is small.
”
Third, even if all the energy from the surface were absorbed in the first 10 meters, you would still have the energy radiated by the atmosphere.”
The energy is *never* absorbed, or almost not. It is absorbed and reemitted, that is eventually transmitted. It is true that if you increase the concentration, the equilibrium temperature at a given height will slightly increase because the height of the last scattering surface will increase (and the TOA temperature must keep approximately constant, barring effects of sphericity), but this corresponds only to a small amount of energy absorbed, and most important, it does not increase indefinitely. Meaning that this small amount of energy, once absorbed, gives a vanishing *power* (energy absorbed per unit time) when averaged over the new steady state equilibrium (i.e. infinite time). So the net absorbed *power* is actually, strictly speaking, zero.
John P. Reisman #209, I know Rod B’s longer (real?) name; Prof. Google never forgets. But if he wants to be semi-anonymous, grant him that. Reputation attaches to the handle…
Vendicar #210, it may well be true that the path length of an IR photon in the core of the absorption band is 10 m. CO2 is extremely absorptive there. What it means is that the level that radiates directly to space at that wavelength is very high up in the stratosphere, where it is very cold (which is why we see an absorption band looking down from space).
But there are many other wavelengths, and then there is convective heat transport: the atmophere is three-dimensional.
Meanwhile, Monbiot is back on form. I haven’t had time to keep up so I don’t know how widely his defence of Pachauri has been seen, but it’s pretty good.
This all arises out of the Sunday Telegraph article by Christopher Booker and Richard North, “Questions over business deals of UN climate change guru Dr Rajendra Pachauri”, that made sweeping unsubstantiated claims of how Pachauri is making millions out of climate change hence the IPCC must be a fraud.
It turns out the only fraud is that they get away with writing rubbish like this. More detail here.
Maybe a good moment to solicit more signatures for my stand up for climate science petition.
Richard Ordway 193,
Fox News is the propaganda arm of the Republican Party. This isn’t liberal paranoia. The CEO of Fox is Roger Ailes, and before he did that he was an electrion strategist for the GOP. When congressmen or senators are interviewed or are guests on Fox programs, 90% of the time they are Republicans.
Rod B 195,
Here are Essenhigh’s coefficients of absorption for CO2:
1.9-2.1 microns: 656 (m atm)^-1. 2.6-2.9 mu: 139.4. 4.1-4.5 mu: 18.37. 13-17 mu: 1.48
By Beer’s law, it’s easy to see that a concentration of 0.04% CO2 results in 99% absorption being reached in those bands at 18, 82, 625, and 7,800 meters, respectively.
The “within 10 meters” stuff refers to ONE PARTICULAR LINE. Each band has thousands of lines.
And even when all ground IR reaches saturation low down, CO2 is still a problem further up in the atmosphere, and it ALL interacts. For details, try here:
http://BartonPaulLevenson.com/Saturation.html
The saturation argument is WRONG. FALSIFIED. DOESN’T WORK. And we knew that by the 1940s.
Again, I renew my plea for anyone who has published peer-reviewed journal articles to look over my article before I submit it, and/or read over my book, The Case for Global Warming. If someone doesn’t answer on this blog, I will start individually emailing climate scientists. I need help, guys, and so far I’m not getting it.
Gilles, Do the math. You will find that energy absorbed does not saturate, but increases roughly logarithmically–as does temperature. This ain’t hard. The saturation argument does not even qualify as a zombie argument–it’s an ex-parrot argument in that it wouldn’t “voom” if you put 4 million volts through it. It’s a stiff, bereft of life. If it hadn’t been nailed to the perch, it would have been pushing up the daisies…It is an EX-argument.
Rod B (217),
First, the phrase “specific narrow band” isn’t really accurate. CO2 absorbs in a range which can be termed “narrow” or “wide”, depending on your point of view. Narrow as compared to H2O, yes, but it is significant in relation to the range of IR emitted by the surface of the earth, at least in terms of being able to interfere with cooling. And it’s not just one exact wavelength, but rather a range (or, rather, a collection of specific wavelengths within that range, due to various combinations of vibrational and rotational energy resulting from the geometry and bonds of the CO2 molecule).
Re-emission: In a nutshell, IR absorbed by a CO2 molecule causes it to vibrate (and maybe spin, but ignore that). This won’t last for very long (microseconds) before the molecule either collides with another molecule (most likely O2 or N2) and passes the energy to that molecule as translational energy (like a vibrating spring hitting a marble), or it re-emits that energy as another photon (in the same wavelength as the original).
Thus, the original photon emitted from the earth’s surface gets absorbed by the CO2 molecule, but then for all intents and purposes it either instantly heats the surrounding atmosphere, or else the CO2 molecule “shakes the photon loose” again.
That photon is then free to go in any direction: up or down or sideways, to go through the exact same process with another CO2 (or H2O) molecule, and eventually to either heat the atmosphere, hit the ground again (and start all over), or to escape out into space.
Your “bucket brigade” analogy works well here, with the exception that the guys in the line are really, really sloppy, so they may pass it backwards instead of forwards, or to another bucket brigade right next to theirs, and as often as not they spill it on the ground (an O2/N2 molecule gets accelerated/heated instead).
So it wouldn’t matter if every single photon got absorbed within 1 cm of the earth’s surface. It’s still heating the atmosphere, and step by step (bucket brigade) working it’s way up with a chance to escape. At some point, more CO2 is going to have an effect on this.
It should be pointed out that if this weren’t the case, if the first 10 meters simply went on absorbing all of the IR with nothing else going on, then that 10 meters of air would quickly have to heat up to the point where we all burst into flame. I haven’t actually seen a paper on the subject, so I can’t be sure, but I’m pretty sure it hasn’t happened yet. :)
> Gilles says: 7 September 2010 at 1:55 AM
> … energy is *never* absorbed …. TOA temperature must keep
> approximately constant, barring effects of sphericity) … small
> amount … does not increase indefinitely…. a vanishing *power*
> … new steady state equilibrium (i.e. infinite time)….
> actually, strictly speaking, zero.
Sokal?
Rod B #218, surely you’re joking… the readership here may not know your long history of studiously ignoring learning opportunities. From your debating skills you’re way too clever to be as slow as you claim ;-)
Ray, I think Gilles is doing a different sketch. And if you don’t ignore it, he shall taunt you a second time, you silly knnnigget.
:)
213 (Septic Matthew),
Because that will mean that that day will expose measurable, negative impacts on individual human lives, and it will mean that the selfish/ignorant delay that we engage in now will have made us all accomplices to unnecessary human suffering.
221 (Gilles),
The problem being that it is not always transmitted in the same form. In the stratosphere it is more likely to be transmitted as IR, and so eventually escape into space. In the troposphere it is more likely to be transmitted as translational energy to O2/N2, thus raising the temperature of the atmosphere. In the end, no matter now you slice it, more CO2 = more chance for IR to be passed into the atmosphere as heat than for it to escape into space.
So the net absorbed power by CO2 (as one component of the atmosphere) is actually, strictly speaking, zero, but the net absorbed power by the atmosphere, and evidenced as heat, is very definitely positive.
Bob (Sphaerica) (228), thanks for the help.
Whether the absorption band is wide or extremely narrow is a subjective judgement. From a simple broadening process I’d say the 15um line that extends from roughly 14.985um to 15.015um is very narrow. A back of the napkin calculation says within this band the earth emits about 0.00056 watts/m^2 — not a helluva lot of intensity even if all was absorbed. Though the vibrotation lines (bands) are another story.
However, the so-called bucket brigade greatly mitigates the above. some follow up on that: a CO2 molecule that absorbs a 15um photon is overwhelmingly likely to transfer that energy to kinetic (heated) energy through collision — mostly with N2 or O2. Very little will be re-emitted (btw, after a longer interval thereby slowing the bucket brigade — though not by much…). I agree with most of your qualitative description, but the re-emission seems very sparse with only half of that returning to the earth.
Rod W. Brick (Thank you for #219)
I too, like #205 Bob (Sphaerica) would like to know which
and which
in what peer reviewed papers?
Some citations would help also. Your argument is ‘they say’ by, ‘they’ is ambiguous and impossible to counter. Please provide citations so others can take a look at what ‘they say’.
Since it is pretty clear that the science on the saturation argument was largely settled in the 40’s and 50’s. Which brilliant new minds have overturned the established science?
I think more than a few of us here would like to know?
Also, if you read the Saturated Gassy Argument and its associated Part II
https://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/
https://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/
which Raypierre and Spencer Weart did a wonderful job on (including citing Arrhenius, Hulbert, Plass)
Also your layers question is very well addressed.
Did you read the above discussions regarding saturation?
If so, then I have to concur with Rays response to Gilles
http://www.youtube.com/watch?v=Oj8RIEQH7zA
It is an EX-argument, dead, bereft of life, deceased, not resting, not stunned. It’s not tired, sleeping or pining for the Fjords. It’s bleeding demised, it’s passed on, it is no more, it has ceased to be, expired, gone to see its maker, a late argument, it is an EX argument.
Now I’m hoping you are not about to inform us the reason that you have brought it up has nothing to do with anything you do or do not understand and that the only reason you have done so is because you actually always wanted to be a lumberjack in British Columbia.
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“. . .if the first 10 meters simply went on absorbing all of the IR with nothing else going on, then that 10 meters of air would quickly have to heat up to the point where we all burst into flame. I haven’t actually seen a paper on the subject, so I can’t be sure, but I’m pretty sure it hasn’t happened yet. :)”
Whew–for a moment, you had me
all het upworried there.Rod B @14 — I don’t doubt somebody has run climate models for the Miocene; I haven’t read that (those) paper(s). What is easily located, and to which I referred, is a paper comparing d18O with leaf stomata counts for the Miocene. The former is a proxy for temperature and the latter a proxy for CO2 concentrations. The results are as I state.
There are many aspects of climate, especially paleoclimate, which deserve further study; the role of CO2 is not one of them.
The case was already closed by Bob Callendar’s 1938 paper, but if more is actually required, all the spectral lines were resolved in the 1960s (see the Modtrans data, for instance). So it looks to me that you a seriously behind the times.
234 (Rod B.)
The point is not that 1/2 is returning to earth (which, BTW, is an inaccurate generalization). The point is that substantially less is escaping into space (i.e. exiting the system) until the temperature of everything (ocean, land, atmosphere) warms to the point that it emits IR at a rate that overcomes the effect (i.e. the new equilibrium).
Quantifying that equilibrium point is the goal of a whole lot of climate science.
But you should notice that you’ve fallen into a deep “feels like” trap. You said:
All of these generalities are unnecessary. The math exists and has been done. If you don’t trust it, you should work out the math yourself, not stop there because “it feels wrong.” There’s no reason to work based on how it feels. Work with actual numbers, and complex systems, and a final result, rather than eyeballing it. Of course, that’s where things start to get way more complex…
But, I think you should at this point be willing to accept the premise of this discussion, which is that the “saturation” argument is silly.
I’d then hope that this recognition would lead you to begin to treat other denier claims with a little more skepticism (i.e. don’t start out assuming the denial to be correct, until proven otherwise).
By “Bob Callendar,” David means “Guy Callendar,” I believe! See:
http://hubpages.com/hub/Global-Warming-Science-And-The-Wars
While I’m linking to my own stuff, I have a new “Thumbnail History of Global Warming” out today. It contains little that will be new to most here, but it may be useful as a very succinct summary of the the history of the science and politics prior to 1992. With fear and trepidation I broke Hank’s rule against citing to refute, structuring the thing in the context of Walter Cunningham’s (mis)understanding of the history. Check it out at:
http://hubpages.com/hub/Global-Warming-Science-A-Thumbnail-History
Nomination for new FAQ category:
“Frequently Answered ‘Rod B’ Questions”
It should contain the above posting, what Bob (Sphaerica) says: 7 September 2010 at 1:45 PM
https://www.realclimate.org/index.php/archives/2010/08/ipcc-report-card/comment-page-5/#comment-186051
Kevin McKinney @239 — Thank you for the correction; Guy it is.
Well done biography in the link!
“but the re-emission seems very sparse ” Rod B — 7 September 2010 @ 11:57 AM
Don’t forget that the energy absorbed by the CO2 (into molecular excitation modes), transferred into thermal energy of N2, O2, H2O, CO2, Ar, and whatever else is rattling around in the atmosphere, will also sometimes get transferred back into excited modes of other CO2 molecules, along with energy from other thermalized sources (H2O absorption, heat of condensation, convection, etc), and these “buckets” of energy will sometimes get radiated, in random directions – even back to the warmer surface where they originated. If the bucket of energy is the same size as a radiative mode of GHG excitation, it can get absorbed (if it’s a photon), radiated, or transferred kinetically. Your qualitative “sparse” is quantitatively about 33 degrees Kelvin greenhouse effect.
John P. Reisman (OSS Foundation), I’ve been working through a half dozen or so texts, partial texts, or lecture notes, and some papers. Almost all of the textbook type stuff talks of the difficulty and uncertainty to some degree of pressure broadening. A couple of examples: Zender, Tatum, Pierrehumbert.
David B. Benson (237), I’m just not as easily and quickly satisfied.
> Rod B says: 7 September 2010 at 10:47 PM
> I’m just not as easily and quickly satisfied.
Without doing the math, or trusting those who can, you can’t ever be satisfied; your feelings will guide you toward what you can grasp and hold onto firmly, in the absence of knowing or trusting the science.
For most people that’s their wallet or their politics, which may differ but often don’t.
Bob (Sphaerica) (238) you say a large band, I say a narrow band. That strikes me — no — rephrase — That is precisely a subjective judgement, either way. I can’t see the sin.
Pieces of the science ought to be explainable for the most part in simple rough understandable terms. If my question, isn’t the re-emission from an absorbing CO2 molecule very little, is not precise enough, what would be precise enough? The percentage of absorbing CO2 molecules within a square meter column of air at an altitude between 0 and 100 meters at a pressure of 1 atm at zero altitude but changing only every 10 meters (left in one less than exact calculation) at 296K (we’ll fudge that for the whole 100 meters) that are emitting a photon from their vibration energy (at what frequency and intensity) in the direction of the surface, per second? Do you know anyone who has calculated that with zero margin accuracy? (Good trick; if nothing else it is partly based on quantum mechanics which only gives probabilities.) You think the climate models do this? If the climate models didn’t make a rash of assumptions, averages, and groupings and the like, they probably (oops! there I go again!) could never complete a run, at least for a number of years.
A shorter simpler example: show me the precise math and physics that the forcing on a global average (I’ll even give you that) over the next few decades starting today will be exactly the natural log of the concentration ratio raised to the 5.35rd (if memory serves) power.
Bob: “In the stratosphere it is more likely to be transmitted as IR, and so eventually escape into space. In the troposphere it is more likely to be transmitted as translational energy to O2/N2, thus raising the temperature of the atmosphere. In the end, no matter now you slice it, more CO2 = more chance for IR to be passed into the atmosphere as heat than for it to escape into space.
So the net absorbed power by CO2 (as one component of the atmosphere) is actually, strictly speaking, zero, but the net absorbed power by the atmosphere, and evidenced as heat, is very definitely positive.”
I’m sorry, but this is definitely wrong, although it seems a very widespread idea. In a steady state energy transfer, there is nothing absorbed anywhere, and there is no change (statistically speaking) of anything, neither the number of photons, nor the translational or vibrational or internal energy. The only effect of increasing the CO2 concentration is to slow down the energy transfer rate, which at turn causes the ground temperature to be higher -but it is still steady. The net absorbed power absorbed by the atmosphere is zero, and its heat content doesn’t change. The effect of the IR absorption and reemission is just to hinder the propagation of energy, which
You probably all built once a small dam on a creek with small stones, when you were a child. When you add a stone, it slows down the flow of water, which raises the level above, because the water must flow at a constant (incoming from above) rate, and as the dam hinders the flow. So the water level need to be higher for the same result. Nobody says that the stones “absorb” the water, or produce it. The increase of the level is not due to an “increase” of the quantity of water. That’s the same with the energy output throughout the atmosphere, CO2 molecules are just “small stones” in the flow.
The argument that a CO2 molecule, after having absorbed a photon, will transfer more often its energy by collision than by radiative deexcitation is true on a microscopic level, for a single molecule, but wrong on a statistical one, for a large set of molecules : because you forget that this is compensated by the fact that CO2 molecules are *also* more often excited by collisions than by radiative absorption , and some of them will deexcite by emitting a photon (at least when you are close to LTE). And the number of photons reemitted after a collision compensates exactly the number of photons that “disappeared” because of a collisional deexcitation. Statistically, the number of excited molecules at LTE depends only on the temperature, and the number of absorbed and reemitted photons must be strictly equal (and determined only by the temperature).
Actually I agree that because of the temperature gradient, the troposphere is not strictly at the thermodynamic equilibrium, and so with the decrease of temperature , there is a decrease of excited molecules. So the different excitation and deexcitation process do not exactly cancel, and there is a small “transfer” between various degrees of freedom. But this is only a residual effect that adjusts spontaneously to adjust the required thermodynamic balance, and its magnitude is much lower than the number of primary “absorbed” photons : it is just a small difference between two much larger rates (absorption and reemission) that almost cancel.
actually I realized that what I say is not contradictory with what Bob said, because the atmosphere is optically thick only inside the saturated lines, and thus the radiation is thermalized only in these lines. In the transparent part of the atmosphere, IR photons escape freely without being coupled with the atmosphere translational temperature. So the real issue (and I agree with that) is that the increase of CO2 photons decreases the amount of energy that is directly transferred, without absorption, and increases the part that is transferred by thermal energy. However, it doesn’t change what I said, that the number of absorbed photon is almost equal to the reemitted ones, even if a single photoexcited molecule will more often loose its energy by collision. Increasing CO2 concentration increases the total number of absorbed AND reemitted photons – that is, increases the part of the spectrum that is thermally coupled with the atmosphere, because it broadens the absorption lines- but the two numbers remain very close.
Pieces of the science ought to be explainable for the most part in simple rough understandable terms.
Ah … the ‘way things ought to be’. Haven’t heard that one in a while. Straight out of the denialist’s handbook, written by the man himself.
Jim Bouldin: See: http://dotearth.blogs.nytimes.com/2010/09/07/extreme-weather-in-a-warming-world/
which links to http://www.esrl.noaa.gov/psd/csi/meetings/attrworkshop_2010/
which is about attribution research.
Your comments on the dotearth article would be most helpful.