Molecular Radiation and Collisional Lifetime

DeWitt Payne has kindly completed a nice post explaining how re-absorption of photons emitted by CO2 or other molecules doesn’t appreciably affect the ratio of energy transfer in the atmosphere due to IR emission vs absorption (or molecular collision).  It’s another commonly debated topic often improperly cited by critics of the warming effects of CO2. When it’s not expressed correctly, it’s a clue that the individual is less knowledgeable on the science than they may appear.  I’m sure everyone will agree that whatever your position on global warming, the basics are critical to making a sound, science based argument.

I’ve done a bit of reformatting for clarity–Jeff


Have you ever seen or heard the statement that CO2 can’t emit radiation in the atmosphere because the decay time for spontaneous emission is long compared to the collisional life?  Guess what, that’s completely wrong.  A molecule or atom in an excited state has no knowledge of its age.  The probability of decay is the same whether the excited state has existed for centuries or picoseconds.  The rate of decay of a collection of things in an excited state depends only on the number of things in the excited state, Ni, and the decay constant Kd. The decay constant has units of reciprocal seconds (s-1).





The decay constant is often expressed as the half-life or the amount of time it takes for half the initial number of things to decay.  The half-life is equal to ln(2)/Kd.

The difference between radioactive decay and molecular decay in an atmosphere is that for molecular decay, the number of molecules in the excited state is constant at constant temperature and pressure.  CO2 molecules are continually being raised to the excited state and the excited states are lowered back to the ground state by inelastic collisions with other molecules.  In inelastic collisions, kinetic energy is converted to vibrational energy and back.  Most molecular collisions are elastic and total kinetic energy is preserved.  Only about 1 in 10,000 collisions is inelastic at Earth surface temperature and pressure.  Since the mean time between collisions is about 1 ns under those conditions, that means the expected lifetime of a CO2 molecule excited to the 15 micrometer vibrational excited state is on the order of 1-10 microseconds.  This also means that only about 1 in 10,000 excited molecules decays by emission of radiation rather than collision.  For a system to be in local thermal equilibrium it is necessary for this ratio to be very small.

The decay constant for a molecular line is the Einstein A21 coefficient.  The value of A21 for any ghg molecular transition can be found in the HITRAN database.  The database can be searched using the extract data tab in the line browser feature of SpectralCalc ( ).  For the most intense CO2 line at 667.6612 cm-1, the A21 coefficient is 1.542 s-1 or a half life of 0.45 s.

The number of molecules in the excited state depends only on the energy of the excited state and the temperature through the Maxwell-Boltzmann distribution.   For the 667.6612 cm-1 CO2 line at 296 K:

Ni/N = exp(-Ei/kT) = exp (-hν/kT) =0.039

What does that actually mean in terms of radiance?

No significant absorption model:

Let’s take a very thin layer of gas so that self absorption can be neglected.  If we use surface atmospheric conditions with a CO2 volume mixing ratio (VMR) of 0.00038, the transmittance at the line peak according to SpectralCalc is 0.992 for a layer 2 mm thick.  The absorptance is 1-0.992 or 0.008.  For a surface area of 1 m2, that’s a volume of 0.002 m3.  At STP (1013 mbar and 273.2 K) there are 0.0224 m3/mole and 6.022E23 molecules/mole.  Correcting for the temperature difference between 296 and 273.2 and the VMR, there are (6.022E23*0.002*0.00038*273.2)/(0.0224*296)=1.89E19 CO2 molecules /m2 and 1.89E19*0.039=7.35E17 molecules in the excited state.  That gives 1.542*7.35E17=7.13E18 photons/sec.  The photon energy is hν=1.33E-20 and a radiance (ignoring layer thickness) of 7.13E18*1.33E-20/4π= 1.20E-03 W m-2 sr-1.

Bulk atmosphere model:

Now let’s take the same layer of gas and calculate the radiance using the Planck equation.  For an emissivity of 0.008, a frequency in cm-1 and radiance in W m-2 sr-1:

I(υ,T)= ε*(1.191427E-08*υ3)/(exp(1.438775*ν/T)-1)= 1.15E-03 W m-2 sr-1.

1.20E-03 W m-2 sr-1 approximately equates to 1.15E-03 W m-2 sr-1.

It’s distinctly possible I’ve made multiple errors here, but if I did, they appear to cancel out.

33 thoughts on “Molecular Radiation and Collisional Lifetime

  1. I think where a lot of people go wrong is they get stuck at “Step 2”, where “Step 1” is “CO2 molecules absorbs an IR photon, goes into excited state”, and “Step 2” is “excited CO2 molecule collides with non-CO2 molecule, transferring excitation energy to it”, which you calculate occurs 9,999 times out of 10,000.

    Of course, the question is what happens next. “Step 3” that they miss is “non-CO2 molecule collides with CO2 molecule, putting it in excited state”, so it can re-emit an IR photon.

    Come to think of it, if “Step 3” did not occur, the greenhouse effect would be much worse, as the N2 and O2 molecules that receive the energy from excited CO2 molecules cannot significantly emit in the IR themselves. If they just kept receiving kinetic energy from CO2 without being able to pass it back so it could be re-emitted, the air would get really hot…

  2. “Have you ever seen or heard the statement that CO2 can’t emit radiation in the atmosphere because the decay time for spontaneous emission is long compared to the collisional life? ”

    No. Can you point out some of these statements?

  3. Jae, I’ve said the last part of the statement lots of times and Jeff’s analysis (of DeWitt’s analysis) confirms it. But I’ve not seen this used for an excuse for claiming CO2 can’t emit radiation either. It’s just a matter of knowing that the emission constant is only a probabilistic value and the emission can be almost immediate or very long but the average decay time can be calculated easily. I wasn’t aware that the % of elastic collisions was that high, however. A good fact to know.

    Still the take-home point is that essentially all CO2 excited by IR from the ground is thermalized and therefore the operative temperature is that of the chunk of atmosphere emitting and not the temperature of the ground. Of course the IR bands which pass IR directly to space are important and many other things as well. Evaluating the affect of CO2 / IR is complex at best and the CAGW crowd are way too ready to assume all questions have been fully answered.

  4. Well, IMSimpleO, the important point is that the ghgs serve to “warm” all the other gases (thermalization) during each day, thereby storing heat to “get through” the next night. And, more importantly, much of the heat is stored in the water that dominates this planet. If water were opaque to sunlight, we would have a much different planet (well, “we” would not “be,” of course).

    The whole greenhouse gas theory falls to pieces when you consider the total theoretical radiation at noon in a place like Phoenix: 1200 watts directly from the Sun plus 400 watts of “backradiation” = 1600 watts total. That is equivalent to a blackbody radiating at 278 F (137 C). If this were true, I could design one hell of a power plant (steam turbine) to generate electricity in Pheonix or the Sahara. Something is WRONG with the frigging theory!

  5. The other thing to watch for are those that use the 1/2 up 1/2 down argument.

    The above discriptions also leads to a very short ir path length for the co2 band width. Almost all of the co2 energy is absorbed, and then either thru convection or h20 IR retransmission as determined by the atmospheric temp and pressure, is moved upward in the atmosphere quickly. Remember the top of the layer where h20 IR escapes the earth is around 6 Km. Co2 IR does not escape earth until the the stratopause (which is warm and heated by the sun).

    The various escape radiation layers (Chapman layers) coupled with the atmospheric temperature lapse rate set the earth temp. The primary paths in parallel are, the 10 micron IR window from ground, the water vapor from 0 to 10 km, the cloud tops, and co2 emission from around the stratopause. The 1/2 up 1/2 down argument you see by many is absolute BS. The earths temperature is determined by these parallel circuits and the atmospheric pressure. Note as the atmospheric pressure increases the radiation escape layers move higher meaning the IR escapes earth at a lower temperature rasing the temp of the earths surface.

  6. Curt,

    One of the other recent treatments of this problem (cannot recall where) pointed out that step 3 is unlikely, as the step 2 collision is very unlikely to impart the momentum in such a way that it is 100% available to another CO2 molecule, and anything less than 100% cannot provide the energy required for quantum re-emission (i.e. glancing collisions, rotations, etc).

  7. Let me get this correctly. The entire energy produced per second per meter squared per steradian is a whacking 0.001 J. And this is at standard temperature and pressure under optimum conditions?

  8. DeWitt Payne says

    ……”In inelastic collisions, kinetic energy is converted to vibrational energy and back. Most molecular collisions are elastic and total kinetic energy is preserved. Only about 1 in 10,000 collisions is inelastic at Earth surface temperature and pressure. Since the mean time between collisions is about 1 ns under those conditions,”

    Kinetic energy can also be transferred to other molecules in elastic collisions.
    Think of the famous Newtons Cradle steel balls display much loved by executives as desk furniture.

  9. DeWitt Payne says

    ……”In inelastic collisions, kinetic energy is converted to vibrational energy and back.”….

    Is vibrational energy not also kinetic energy?

  10. DeWitt Payne says

    Ni/N = exp(-Ei/kT) = exp (-hν/kT) =0.039

    ….”Have you ever seen or heard the statement that CO2 can’t emit radiation in the atmosphere because the decay time for spontaneous emission is long compared to the collisional life?”….

    Since at the temperature quoted most of the CO2 molecules will their KE in the translational form, I would expect that virtually all CO2 molecules would be capable of absorbing the 15um(667cm-1) and the 4um IR photons if provided.

    I also used my calculator to get a similar result to above but interpreted it as the fraction of co2 molecules who have attained the above average KE to enable them to emit a 15um photon.
    Another way of putting it is to say 4 emissions per hundred absorptions.
    Insistently the value for the 4um photon emission probability is 5 per million absorptions.

    My calculations are not concerned with decay times but with the number of CO2 molecules getting enough KE to enable them to emit the equivalent energy as an IR photon

    However if you follow Tom Vonk arguments because of quantum mechanical constraints absorptions = emissions

  11. Re: John A (Aug 18 09:12),

    That’s for a layer of atmosphere 2 mm thick and an effective line width of 1 cm-1. Emission in the thermal IR covers from about 50-3000 cm-1 and the atmosphere is a tad thicker than 2 mm. That line will be saturated so the emission seen at the surface will be 0.15 W m-2 sr-1 or 0.47 W/m2. Again, that’s just from a bandwidth of 1 cm-1. Integrated over the full CO2 band with a surface temperature of 296 K and 1976 US standard atmosphere temperature and humidity profile, the surface sees 32.9 W/m2 from 380 ppmv CO2 out of 282.5 W/m2 total DLR.

  12. Re: steveta_uk (Aug 18 08:43),

    Each molecule of gas experiences 10E9 collisions/sec at 1 bar surface pressure, ~10E5 of those are inelastic. So yes, it is unlikely that any one collision will excite a CO2 molecule. But there so many collisions that a constant fraction of CO2 molecules will always be in the 15 micrometer vibrational excited state. That’s what is meant by local thermal equilibrium.

  13. I am curious, seeing as ther appears to be some disagreement, what does MODTRAN model in this respect. ?

    I know “those that know” have had to sign a none disclosure agreement, but all the same, does anyone know..
    Will they say.

    AND, has anyone worked out how to separate 15 micron IR sourced from CO2, or liquid water in the atmosphere. ???

  14. Steveta:

    It’s been many years (and many beers…) since I studied this formally, but I think the key take-home point is that at this molecular level, these processes are completely reversible. With regard to photon absorption/emission, this is why absorption and emission at a given wavelength (photon energy level) is always the same. With regard to molecular collisions, if a particular transfer one way has a certain probability under given conditions, the reverse transfer is equally probable under those conditions.

  15. I think you over estimated the time between collisions. The density of air is
    1.2e-3 g/cm^3
    at STP. The mass of an N2 molecule is
    M = 28 amu x 1.66e-27 kg/amu = 4.65 E-23 g/N2.
    This gives a volume of
    = 4.65e-23g/N2 /1.2e-3gcm^-3 = 3.87e-20 cm^3/N2.
    The mean distance between N2 molecules is then
    = 3.38e-9m.
    The mean thermal velocity, V, of an N2 molecule can be computed from 1/2 M V^2 = 3/2 kT where k is Boltzmann’s constant. Sticking in numbers,
    V = 5.2e2 m/s
    The time between collisions then /V or
    t = 6.5e-12s
    two orders of magnitude smaller than your number. The expected lifetime would then be 60 nano seconds. Doesn’t change your argument at all, LTE still holds.

    All the emphasis on CO2 obscures the fact that the air mostly heats by conduction. Even if it were completely inert and IR transparent like the argon in the air, it would still heat up by contact with the ground, and much faster than due to the 0.47 W/m^2 in the 15 micron band.

  16. Dereck,

    MODTRAN was declassified a few years ago I believe.. I last used it in the 80s when I recall its classification being Secret. as opposed to the RCS codes which were TS/SAR

    and yes, C02 warms the planet.

  17. Re: Paul Linsay (Aug 18 16:48),

    Your estimate for volume seems a little high. The effective molecular diameter for N2 is about 0.3 nm, Van der Waals radius 1.55 angstroms, or 3e-8 cm giving a volume of 1.4e-23 cm3. There’s an applet here for calculating collision frequency and mean free path. With a diameter of 3E-10 m, a temperature of 296 K, a pressure of 101.3kPa and a molecular weight of 28 amu, the mean free path is 1.01E-7 m, the time between collisions is 0.2 ns and the collision frequency is 5E9/s. At 20 kPa, which is close to the pressure level at the tropopause, the collision frequency drops to 1E9/s.

  18. The important point about the decay time is that the gasses in the atmosphere are in thermal equilibrium and this includes Water Vapor. The situation of interest is what happens to the equilibrium when a little CO2 is added. What I think everybody has shown is that the water vapor must get warmer.

    My question is what happens to the tropopause when the water has not condensed as quickly because it is warmer? If the tropopause rises it gets colder if the lapse rate remains constant. The water in the stratosphere is controlled by the temperature of the tropopause so if it drops the stratosphere gets drier and water vapor is the most important IR absorber.

  19. #17, my mistake, I got the radius of the N2 molecule wrong. Putting in 0.3 nm gives the same result as yours.

  20. Re: Gary P (Aug 19 12:01),

    We’re drifting OT here but: An important negative feedback is the evaporation/precipitation rate and the resultant latent heat transfer from the surface. There’s a large spread of estimates from the different models. Models that predict a faster rate of increase of precipitation have a lower climate sensitivity. Correctly estimating the change in precipitation with temperature is related to how well the models do convection. Because of the very coarse grid size required to cover the whole planet and still do calculations in a reasonable amount of time, convection isn’t one of the models’ strong points. If they can’t get cloud cover right, and it seems fairly clear that models don’t, then it’s unlikely they’ll get precipitation right.

  21. *16 There really is no excuse for spelling someone’s name incorrectly Steven, except to disrespect them.
    I have come to expect no better of you, from your replies.

    MODTRAN is still only “accessable” by paying a fee, and signing a none disclosure agreement as I understand.
    That is not open or good science.
    MODTRAN to my view, is the turtle upon which the flat earth society of CO2 “dominating” climate rests upon.

    CO2 is modelled as warming the atmosphere Steven, yes, that is exactly my point……by MODTRAN not just GCM’s,
    which rely upon MODTRAN for their “physics”.. It’s a lot more than merely clouds that the climate modles do not “understand”.

    When the GWS forum is accessible again I will post a link to a page I recently read in this respect.
    MODTRAN now is not what it was in the eighties – it’s one heck of a lot better now supposedly.
    BUT, that does not mean a lot, if it still models GIGO, and admitted guesswork.

  22. Derek

    …….”CO2 is modelled as warming the atmosphere Steven, yes, that is exactly my point……by MODTRAN not just GCM’s,
    which rely upon MODTRAN for their “physics”.. It’s a lot more than merely clouds that the climate modles do not “understand”………

    Good point, the model replacing reality and people becoming dependent on conclusions based on false assumptions.
    Thank goodness for posters like Paul Linsay(15) who work it out from first principals with pencil and paper.

  23. Read this some time ago as part of a larger general interest piece. Some part are relevant –

    Types and Excitation of CO2 Lasers
    Basic Principles of Operation

    (Portions from: David Crocker.)

    The physical arrangement of most CO2 lasers is similar to that of any other gas laser: a gas filled tube between a pair of mirrors excited by a DC or RF electrical discharge. Metal coated mirrors (e.g., solid molybdenum or a gold or copper coating on glass or another base metal) may be used for the high reflector (totally reflecting mirror). However, at the 10.6 um wavelength, a glass mirror cannot be used for the output coupler (the end at which the beam exits) as glass is opaque in that region of the E/M spectrum. One material often used for CO2 lasers optics is zinc selenide (ZnSe) which has very low losses at 10.6 um. Germanium may also be used but must be cooled to minimize losses for high power lasers. Other materials that may be used for CO2 laser optics are common substances like NaCl (rock salt!), CaCl, and BaFl (but these are all hydroscopic – water absorbing – so moisture must be excluded from their immediate environment).

    Many details differ between a 50 W sealed CO2 laser and a 10 kW Transverse Excited Atmospheric (TEA) flowing gas laser machining center but the basic principles are the same. While HeNe lasers are based on excited atoms and ion laser use ions, CO2 lasers exploit a population inversion in the vibrational energy states of CO2 molecules mixed with other gases.

    Additional gases are normally added to the gas mixture (besides CO2) to improve efficiency and extend lifetime. The typical gas fill is: 9.5% CO2, 13.5% N2, and 77% He. Note how He is the largest constituent and CO2 isn’t even second! (This also means that leakage/diffusion of He through the walls and seals of the laser tube may be a significant factor is degradation of performance and/or failure of a sealed CO2 laser to work at all due to age.)

    The CO2 laser is a 3-level system. The primary pumping mechanism is that the electrical discharge excites the nitrogen molecules. These then collide with the CO2 molecules. The energy levels just happen to match such that the energy of an excited N2 molecule is the energy needed to raise a CO2 molecule from from the ground state (level 1) to level 3, while the N2 molecule relaxes to the ground state. Stimulated emission occurs between levels 3 and 2.

    The metastable vibrational level (level 2) has a lifetime of about 2 milliseconds at a gas pressure of a few Torr. The strongest and most common lasing wavelength is 10.6 um but depending on the specific set of energy levels, the lasing wavelength can also be at 9.6 um (which is also quite strong) and at a number of other lines between 9 and 11 um – but these are rarely exploited in commercial CO2 lasers.

    Here are some of the more subtle details. (Skip this paragraph if you just want the basics.) As well as the 3 energy levels of CO2 I referred to, there is actually a 4th involved, about midway between the ground state and level 2. After emitting, the CO2 molecules transition from level 2 down to this 4th level, and from there to the ground state (because a direct transition from level 2 to the ground state is forbidden by quantum rules). Level 2 is actually a pair of levels close together, which is why there are 2 separate frequency bands that a CO2 laser can operate on, centred around 9.4 um and 10.4 um (i.e., just above and just below 30 THz). Each of these bands is actually composed of about 40 different vibration/rotation transitions with frequencies spaced about 40 GHz apart. The strongest transition is the one called 10P(20), which is about 10.6 um, so a CO2 laser with no tuning facilities normally operates at this wavelength. It is possible to select a particular transition (and hence frequency) using a diffraction grating instead of one of the mirrors. The exact transition frequencies were known to an accuracy of about +/-50 kHz back in 1980.

    The helium in the mixture serves 2 purposes: (1) He atoms collide with CO2 molecules at level 2, helping them relax to the ground state; (2) it improves the thermal conductivity of the gas mixture. This is important because if the CO2 gets hot, the natural population in level 2 increases, negating the population inversion.

    Cooling of the gas mixture is critical to achieveing good power output. The gas at the centre of the tube is hottest and loses heat by thermal conduction through the surrounding gas to the walls. As the gas pressure increases, the thermal conductivity gets worse. So with a smaller tube, the gas pressure can be higher. This is why the power available from a properly-designed CO2 laser depends on the length of the tube but not the diameter (i.e., smaller diameter tube = higher pressure = greater density of CO2, which compensates for the smaller diameter).

  24. Geoff Sherrington

    A good article going into fine detail about the energy transitions of CO2,N2 and He and how they interact at the high temperature of a laser.
    Contrast this with what Climate Science has to say about the atmosphere!
    Where can we find a detailed explanation of the interactions of CO2,H2O,N2 and O2 at temperatures around 290K.
    Day and night conditions should be examined separately when solar spectrum and Earth surface spectrum effects can be teased out.
    All I have come across is vague generalisations leaving the door open for wide speculation such as illustrated by the Tom Vonk article and comments.

  25. As promised, GWS back up and running now (server upgrade meant forum software obselite apparently…)

    Regarding MODTRAN (4) software –…sp?id=7915

    MODTRAN – MODerate spectral resolution atmospheric TRANSsmittance algorithm and computer model

    Access to MODTRAN4 requires that a new Non-Disclosure Agreement (NDA) be signed and a fee paid.

    Military, model, algorithms, none disclosure.
    Alarm bells ringing anyone ?

    I would also note the use of words and phrases like,

    ” It remains the state-of-the-art ”

    ” development of MODTRAN was driven by a need for higher spectral resolution and greater accuracy than that provided by the LOWTRAN ”

    ” The current release is MODTRAN4, version 3.1. This version number connotes the additions of
    some errata and new physics since MODTRAN4 was first patented and released. ”

    ” now having a physical meaning. ”

    ” permit more accurate calculation of molecular absorption ”

    ” The updated Rayleigh scattering algorithm models the spectral dependence of the depolarization factor, and
    the refractivity (equal to one minus the real part of the index of refraction)
    now varies not only with water density but also with CO2 partial pressure. ”

    Earlier in the above linked to GWS forum thread I had also posted.

    Hi All,
    I have had a day “off” today, a long drive, and some pleasant family visits.
    However, long motorway cruises, on my own (the dog in the back of the car does not count), leaves me time to “ponder”.

    A very old phrase came to mind, namely,
    “X” is more than the sum of it’s parts.
    This can also be, as we all know care of lives experiences,
    “X” is less than the sum of it’s parts.
    It’s a phrase we all know.

    In a complex natural system however, “we” have all also “learnt” that,
    “X” can have no relationship at all to the sum of it’s parts,
    because of other relationships not shown in the individual components of the complex natural system, however they are “summed” together.
    Somewhere just past Preston this hit me. I forget the exact, and somewhat (admittedly) coloquial wording.
    But, boy, did it hit me, and specifically with regard to this thread.

    HITRAN are individual, in a closed system, isolated measurements,
    MODTRAN are “summed” HITRAN measurements with various assumptions added.
    The logarithmic effect of CO2 within the atmosphere upon temperature is derived from MODTRAN.
    “X” (log. effect of CO2 upon temp within the atmos.) is merely some varient of,
    1 – “X” is more than a sum of it’s parts.
    2 – “X” is less than the some of it’s parts.
    “X” can not be (if AGW is to stand a chance of being right),
    3 – “X” can have no relationship at all to the sum of it’s parts, because
    of other relationships not shown in the individual components of the complex natural system, however they are “summed” together.
    Because “we” do not know, not with any certainty, but to any reliable degree whatsoever,
    the various natural relationships of the various components in the open, real, mixed atmosphere.
    The question that this thread has moved towards, ie, Has it been shown that the MODTRAN measurements (and assumptions)
    apply to the real, open, and mixed atmosphere, is not merely academic, it is absolutely central, crucial infact.

    At this point it is obvious (to me at least), that, “we” ie, MODTRAN can not have
    all the natural relationships quantified, understood, or even known about yet.
    So, MODTRAN is educated guesses, at best (does this remind anyone of the “Do Global Energy Budegets make sense” thread..).
    How does MODTRAN stack up against reality ?
    Simply, MODTRAN does not “stack up”, not from a climate science point of view.
    CO2 has no proven effect upon temperature in the real, open, mixed atmosphere. It is that simple.
    MODTRAN says CO2 does have an effect upon temperature.
    MODTRAN does not (from a global temperature point of view) seem (except for distinct and very time scale limited “cherry picking”) to apply to the real, open, mixed atmosphere.
    AND, there is no proof (whatsoever – otherwise we would of heard about it by now….) that it does.

    Unsurprisingly, there are many major examples to back the idea up that MODTRAN does not apply to the real, open, mixed atmosphere, some examples follow.
    CO2 levels seem to follow temperature, not lead it.
    (This implies temps. effect CO2 levels, not the other way around.)
    Engineers state quite plainly that IR is the smallest form of heat loss, conduction and convection is next,
    and commonly, latent heat (of vapourisation of water) is by far the largest, by at least an order of magnitude.
    (AGW is constantly obsessed with IR, to the seemingly “exclusion” of latent heat in particular
    – MODTRAN (pro AGW) assumptions possibly..)
    How does / would (is it even possible) MODTRAN deal with latent heat in the first place ???

    MODTRAN used to derive the logarithmic effect of CO2 upon atmospheric temperature from a very basic level, is patently and very, very seriously flawed.
    This is obvious. So, why has it not been questioned vigourously before ???
    Even mild questioning SHOULD of made it obvious MODTRAN needed proving to actually apply to the real, mixed, open atmosphere.
    The “question” is not if the logarithmic effect of CO2 has been “questioned”, but
    how the heck has it survived intact the “questioning” so far.
    Alan Siddons says that most “skeptics” are simply not skeptical enough.
    I have to agree.

    This thread is reminding me of,
    the missing hot spot in the upper troposphere “basic AGW issue”,
    (it ain’t there)
    the assumed, modelled, but not shown, positive water vapour feedback mechanism “basic AGW issue”,
    (does not exist)
    the admitted as invented modelling cooling factors “basic AGW issue”,
    (key words here are “ADMITTED AS INVENTED” by UK Met Office in 1999)
    the greenhouse effect upon the moon “basic AGW issue”,
    (AGW effectively denies surface heat retention, and varying later release)
    “back radiation from clouds warms the earth’s surface “basic AGW issue”
    (How can a cooler thing (at quite a distance) warm a warmer thing – impossible)
    the all radiation is positive “basic AGW issue”.
    (it is supposedly different to all other forms of heat flow we can observe)
    etc, etc, etc, etc. It is all hocus pocus, politically correct and beneficial, make believe.
    AGW is based upon beliefs, as is the MODTRAN assumed logarithmic effect of CO2 upon atmospheric temperature.
    None are what we have actually, verifiably, empirically observed, and that makes AGW a religion. Full stop.

  26. Good work, Derek. I was tryng to hint to Jeff with his toy model that the walls of the experimental boc are not just an interference (they heat up), they are THE essence of the experiment because they pevent a simulation of the open atmosphere – which has always been the limit of a qauntitative global model.

  27. Re: Geoff Sherrington (Aug 22 07:22),

    If MODTRAN is somehow fatally flawed, how come the calculated spectra look just like the spectra measured by high resolution FT-IR spectrophotometers in the open atmosphere? Also, tell me how a molecular spectral line is going to have different characteristics in the open atmosphere compared to a lab or ab initio calculation for that matter. Things like Doppler and pressure broadening are built into the radiative transfer models in band models like MODTRAN and line-by-line models like SpectralCalc.

    As far as toy models, one usually specifies that the walls are perfect reflectors for radiation and collisions so energy in any form cannot be transferred to or from the walls. This is actually a fair approximation of no walls at all and parallel planes of infinite extent.

  28. Re DeWitt Payne said in post 28.

    1) ” If MODTRAN is somehow fatally flawed, how come the calculated spectra look just like the spectra measured by high resolution FT-IR spectrophotometers in the open atmosphere? ”


    2) ” walls are perfect reflectors for radiation and collisions so energy in any form cannot be transferred to or from the walls. ”

    1) Correlation is not neccesarily causation. Maybe MODTRAN at some levels does produce a similar “image” or “picture”, but what does that actually mean. Very little really. Proof that MODTRAN does apply to the atosphere is at present absent and still needed.
    I think the use of W/m2 figures does not help in this respect, these figures being annual “guesses” expressed as per second “movements”.
    Given such a distant view point from the actual variable reality it is not surprising a similar “image”, or “picture” can be drawn, but that does not give a single clue to it’s actually applicability.
    In the real world models and modelling have great problems looking forwards at any time scale, but rarely, if ever mange more than a couple of days.
    Does this not give a clue to how “relevant” MODTRAN / modelling actually are.

    2) Does this stop conduction warming the walls. ?
    I doubt it would. Therefore Geoff Sherrington’s point in post 27 seems to still stand.

    BTW – DeWitt sometime ago yourself and Ferdinand Engelbeen had a little discussion in a thread on this blog regarding how to show man’s impact upon global CO2 levels.
    Unfortunately I can not remember which thread that was, could you please point me in the right direction for that thread and it’s content please. – Thanks in advance,

  29. Derek August 22, 2010 at 5:17 am

    How can a cooler thing (at quite a distance) warm a warmer thing – impossible

    If the temperature of the “cooler thing” is equal to absolute zero, then it wouldn’t warm the warmer thing.

    Otherwise, it is obstructing a path to the absolute zero of empty space which does reduce the rate of heat transfer which would occur in its absence.

    Unless this obstruction also symmetrically obstructs an equivalent incoming heat transfer, the temperature of the warmer object will increase.

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