fredag 25 juni 2010

AGW Myth of Back Radiation

AGW alarmism is  based on an idea of "back radiation" or "re-radiation" from an atmosphere with greenhouse gases, but the physics of this phenomenon remains unclear. 

To test if  "back radiation" is a real phenomenon, we suggest the following experiment: On a night with moon-light so feeble that you can cannot read a newspaper, place yourself in front of a mirror letting the moonlight reflect from the newspaper to the mirror and back again, and check if you can now read. You will probably find that the paper is still unreadable, as if "back radiation" does not give more light.

To give this experiment theoretical support we consider the mathematics of wave propagation from a source at x=0 (Earth surface)  to a receiver at x=1 (atmospheric layer) described by the wave equation (as a model of Maxwell's equations describing light as electromagnetic waves):

U_tt - U_xx = 0 for x in the interval (0,1)

with solution U(x,t) being a combination of waves traveling with velocity +1 and -1 along the x-axis, and with subindices indicating differentiation with respect to space x and time t. The boundary condition at the receiver may take the form

AU_t(1,t) + U_x(1,t) =0

with a positive coefficient A signifying:
  • A = 0: soft reflection with U_x(1,t) = 0
  • A large : hard reflection with U_t(1,t) = 0
  • A = 1: no reflection: transparent absorption of all incoming waves at x = 1.
The basic energy balance is obtained by multiplying the wave equation by U_t and integrating 
with respect to x to give:

E_t + AU_t(1,t)^2 = -U_x(0,t)U_t(0,t) = Input Energy.

where E(t) is the energy of the wave over the interval (0,1). Assuming that E(t) stays constant so that energy is no accumulating in the interval (0,1), we have that 

Output Energy = A U_t(1,t)^2 = Input Energy.

In particular, with soft reflection with A = 0, the Input Energy is also zero. We learn that  it is not possible to "pump the system" by reflection at x = 1: If you change from transparency with A = 1 to reflection with A = 0, the system reacts by refusing to accept Input Energy.

Ergo: Reflection/back radiation cannot increase the insolation to the Earth surface. 

(Back radiation seeks support in a description of light as a stream of particles proposed by Newton, which was replaced by Maxwell's wave theory in the late 19th century).

52 kommentarer:

  1. En liten limerick, håll till godo:

    The Hothouse Limerick

    There was an old man named Arrhenius
    Whose physics were rather erroneous
    He recycled rays
    In peculiar ways
    And created a "heat" most spontaneous!

    Timothy Casey, 2010

  2. (Back radiation seeks support in a description of light as a stream of particles proposed by Newton, which was replaced by Maxwell's wave theory in the late 19th century)....

    And later replaced by Einsteins photons, BUT... If people take care in working out the momentum balance equations the effect would probably disappear anyway.

  3. Your thought experiment is meaningless; it only proves that whatever reflected light there is still is insufficient for reading, not that there is no reflected light. And it is obvious that there is indeed reflected light, which rather destroys the argument anyway.

    Very simple logic may help you here. Here's the truth:

    1. The Earth, at a temperature of about 300K, radiates infrared photons. They go upwards.
    2. Some molecules in the atmosphere absorb infrared photons.
    3. Conservations of energy requires that the energy absorbed be re-emitted.
    4. There is no physical mechanism to restrict which direction it is re-emitted in, and therefore it is re-emitted isotropically.
    5. Therefore, some proportion of that re-emitted energy is re-emitted back towards the Earth.

    It's really not hard. It amazes me that someone would seek to deny this.

  4. Is infrared radiation really a stream of photons?

  5. Roger,
    Since you noted that GHGs re-emit isotropically, lets hear your explanation why the Trenberth/IPCC Earth energy budget shows GHG emit 95% of the energy input from the Sun Unidirectionally to the earth and not an equal amount to outer space.

    Here's another simple experiment along the same lines:

  6. 4. There is no physical mechanism to restrict which direction it is re-emitted in, and therefore it is re-emitted isotropically.

    Roger, have you heard about momentum conservation? That is why photons are more likely to pass through the medium, an in case it is absorbed it results in an expansion of the gas which leads to cooling. Amazing that this is not understood. That is why there are no temperature gradients formed in a glass of water on the table.

  7. "Is infrared radiation really a stream of photons?"

    If it is not, then what is it, and - more importantly - how does that affect the logic?

    Anders, momentum conservation has no bearing on the issue. An atom or molecule in the atmosphere which has absorbed energy will re-emit it isotropically. If you want to deny that, you would need to believe that these particles know which direction the earth is in, and know that they have to re-radiate the energy in directions which do not reach the Earth. How do they do that?

    MS: I fear you misunderstand the diagram. You do appear not to have noticed that it also includes radiation upwards from the atmosphere. Also, "back radiation" naturally includes radiation reflected from clouds, as well as re-emitted by greenhouse gases. In any case, if you don't believe it, you would do far better to e-mail Kevin Trenberth and ask him, rather than me. Have you done so already? If not, why not?

  8. It is electromagn waves and the message of the post is that waves do not support backradiation.

  9. Never mind that your insistence on EM radiation as a wave phenomenon only is a hundred years out of date; it has no bearing at all on the logic I presented above.

    In your view, if the atmosphere absorbs radiation it re-emits it only away from the earth. In reality. the atoms and molecules in the atmosphere do not know which way is up, and they re-emit their absorbed energy isotropically.

    A couple of trivial observations which invalidate your viewpoint include the ease with which you can measure infrared radiation coming from above, on any clear, cloudless night; and the observation that the Moon's night side is far colder than the Earth's night side. In your view, these facts cannot be understood.

  10. In terms of CO2's bands.
    Upwards radiation simply becomes part of the energy to and fro between molecules that exchange constantly as they convect. In the lower atmosphere the predominant exchange must be through contact transfer due to molecule density whereas e.g. at the tropopause due to the distance between molecules, radiation becomes more apparent.
    Radiation doesn't get a free pass through the atmosphere, the energy from it gets convected and collisions produce IR with increasing frequency as the molecule density reduces.

    How does the IR survive a downward journey to heat something that is already at a temperature that is unreceptive? Convection must always defeat downward radiation. Near the surface has a density of CO2 sufficient to convert all emitted radiation to either a lower frequency or another energy form that convects so no downward radiation is going to get anywhere near the ground.

    Roger, a stimulated molecule will rise a little and that fact would bias radiation upward.
    The atmosphere is curved. That also biases upwards.
    Rising air currents must bias radiation upwards

  11. What exp shows radiation from above a clear night?

  12. An example of measurement of night sky infrared emission:

    Clothcap: if a molecule is moving in a certain direction, that does not make it more likely to emit a photon in that direction. The curvature of the earth and atmosphere only means that the solid angle covered by the earth as seen from anywhere within the atmosphere is less than 2π radians; it doesn't make any particles radiate anisotropically. And rising air currents again do not affect the radiative properties of the atmosphere. They carry heat upwards, certainly, but the particles continue to radiate isotropically.

    "How does the IR survive a downward journey to heat something that is already at a temperature that is unreceptive?"

    No matter what temperature a body is, it can still absorb energy. There is no such thing as a "temperature that is unreceptive".

  13. I don't see that the measured emission lines of the OH radical tells anything about backradiation of greenhouse gases. Do I miss something?

  14. Roger,
    Good idea - I will email Trenberth to ask why his diagram does not show GHGs emit isotropically and see if he responds. His diagram shows GHG emit 342 Wm-2 to the earth and only 165 Wm-2 to outer space. This is what I am questioning and believe was disproven by RW Wood and others long ago.

  15. Roger, you're a fast replier!
    It's not a question of a photon direction, it's a Q of what height it is more likely to meet another molecule. If the molecule impacted moves up, a downward emitted photon is more likely to meet a molecule at a greater height than a photon emitted from the emitting molecule's original position.
    Curvature. Light travels in straight lines. The net product of lateral emission must also be in a straight line. Following a lateral straight line, a photon will meet successively thinner air so escaping faster than a photon emitted laterally at a lower altitude. A bias due to curvature.

    I don't disagree that a photon can impact a molecule vibrating at a higher frequency but it would have the effect of reducing, not raising that molecule's frequency. If my ringing bell idea is correct.

    At the end of the day it is about whether the level of the ground emission can be raised by downward radiation.

    Actually that is only relevant to the environment where we are. In reality it is how long the additional CO2 delays the escape of radiation and as photons travel at light speed, allowing for momentary delays for reemission after impact I would imagine not very long or it may be that additions produce a net negligible cooling.

  16. "I don't see that the measured emission lines of the OH radical tells anything about backradiation of greenhouse gases. Do I miss something?"

    Yes, I think you do. The observation is of energy absorbed by the atmosphere being re-emitted. This is the very phenomenon you seek to deny, is it not?

    Clothcap and MS, you both seem to be confusing microscopic and macroscopic concepts. The bulk flow of energy in the atmosphere is not isotropic. Heat escapes from the Earth at night. But spontaneous emission of photons is isotropic, and thus some radiation from the atmosphere reaches the ground. Conservation of energy means that the radiation that reaches the ground warms it up.

  17. How big is then the reradiation from the night sky?

  18. Roger,
    No doubt GHGs do re-radiate IR and somewhat less than 50% (due to curvature of the earth) comes back to the earth's surface. However, Trenberth et al apparently do not fully account for the slightly more than 50% of the GHG IR re-emission to outer space. Also, the Clausius formulation of the second law of thermodynamics "Heat generally cannot spontaneously flow [i.e. the net vector] from a material at lower temperature to a material at higher temperature" precludes heating from back radiation. Another way of stating this is "energy from the hotter body has left that body - it therefore cools down. The smaller amount of energy from the cooler body cannot fully replace that lost energy; it just slows the rate of cooling."

    Do you doubt the classic findings of RW Wood and others?:

  19. "How big is then the reradiation from the night sky?"

    How big do you think it is?

    MS: why is the night side of the Earth hotter than the night side of the Moon?

    RW Wood only demonstrated that the greenhouse effect could be considered a misnomer, and not that it doesn't exist. Pencil lead is not lead, but that doesn't mean you can't make a mark on a page with one.

  20. Roger, my previous comment I compared to a molecule at a lower height, I meant compared to a flat earth atmosphere. Hard day at the office.

    I'm not a physicist so if I say what seems dumb, don't jump on it, I learn from mistakes.
    I think a photon is at the crossover between energy and matter. Impact transforms it to pure energy. The lower frequency will take from the higher frequency increasing its amplitude, the higher frequency amplitude is lowered in the process. A larger volume but at a lower frequency.

    CO2, that there is near total absorption of emitted IR in under 30mtrs - what does absorption mean? If a same frequency photon was emitted, there would be no absorption. Does absorption mean 100% is reflected downwards? No. The energy is still there but it is now kinetic or potential, what are the prospects of it being emitted in CO2's bands? If you talk to me about energy levels, once IR is in the other energy forms it convects. Ir is produced in the convection process but adding to kinetic or potential speeds convection. I think near the surface atm density favours energy loss by collision rather than emission.
    Downward IR from above 30mtrs must transform before reaching the ground. That must add to the kinetic and potential E pool and enhance convection.
    Adding to the CO2 volume would lower the height of absorption. That means the IR gets transformed faster, enhancing the convection process to my mind.

  21. Wood proved much more than that it is a misnomer - as elaborated in the post and won't be repeated again here. To answer your moon question see:


    (ignore political rant)

  22. Clothcap: I'm sorry but I just don't understand most of what you're saying about photons and energy. Could you clarify what your opinion is, please? Do you believe that there is a greenhouse effect? Do you believe that the atmosphere absorbs infrared radiation? Do you believe that an IR-absorbing layer around an IR-emitting body affects the temperature of the IR-emitting body?

    MS: pick any position, no matter how untenable, and you can find someone on the internet who will argue vehemently in favour of it. Far better to quote from the peer-reviewed literature. Peer review doesn't guarantee correctness but it does at least ensure that the results presented have passed the first test of being not obviously wrong. Nothing resembling the ideas you've linked to appears in the peer-reviewed literature.

    An example of a real investigation into the surface temperature of the Moon can be found if you google "Near-Surface Temperatures on Mercury and the Moon and the Stability of Polar Ice Deposits".

  23. A cloud layer can affect the ground temperature in the same way as
    insulation can affect the inside temperature of a house, with only flow of heat from warm to cold thus without backflow of heat from cold to warm.

  24. Roger,
    You didn't offer any criticism of the links other than they are not peer reviewed. So here are four peer reviewed papers which show GHG back radiation cannot further warm the earth:

  25. OK Roger: Which are the key peer-reviewed articles demonstrating the
    global warming effect of CO2?

  26. MS: I certainly did offer criticism. I showed you a paper that carries out a proper analysis of lunar surface temperatures.

    You found only three peer-reviewed papers. They are easily shown to be mistaken.

    1. This paper assumes implicitly that CO2 does not absorb infrared radiation.

    2. Transparently ridiculous, as shown in the peer-reviewed literature here:

    3. Not peer-reviewed as far as I can tell.

    4. Wrongly states Kirchhoff's law, wrongly claims that a semi-infinite atmosphere has been assumed by all previous investigations, among numerous other basic errors.

    Your beliefs contradict basic physics. If the atmosphere radiates, then it cannot fail to warm the Earth, and yet you believe that this is not so. Have you read any textbooks about planetary atmospheres?

    Claes: To ask such a question you must presumably be not be at all familiar with the literature. It is a mistake to imagine that there are a small number of key articles that have established theories of how planetary atmospheres behave. However, a good overview of how the science has developed can be found in "The discovery of global warming" by Spencer Weart.

  27. If there are no key articles proving CO2 global warming, then the science
    of this effect is missing. I have asked the same question to the Royal Swedish Academy of Sciences, with the same empty response. Give me
    an article or give up.

  28. Like many aspects of science, our understanding of planetary atmospheres has developed in smaller or larger steps over many decades. You're asking for a small number of papers describing giant leaps that never happened.

    Have you already read "The discovery of global warming" by Spencer Weart, as I recommended?

  29. Yes I have, but I did not find any answers and my question thus remains.

  30. Really? You did not find any enlightenment at all? You found no answers in the story of the work of Fourier, Tyndall, Arrhenius, Chamberlin, Milankovitch, Callendar, Plass, Revelle, Keeling, Manabe, Ramanathan, Hansen, and countless others? Not a single one of the 2000+ references satisfied your demand for papers demonstrating the global warming effect of CO2?

    It is not easy to believe you really read it. At the very least, you cannot possibly have read it with an open mind. Would you agree with that, or would you in all honesty describe yourself as open-minded?

  31. Roger,
    Your criticism of the Chilingar paper is false - start reading on page 2 "...when the infrared radiation is absorbed by the greenhouse gases..."

    Smith's paper is refuted by Kramm's paper - what specifically do you find wrong with Kramm's paper (other than not yet peer reviewed)?

    What specifically is wrong Miskolczi's statement of Kirchhoff's law?

  32. BTW, Miskolczi has a new peer-reviewed paper coming out this momth & here is the abstract:

  33. Roger
    Rather than get into how molecules work lets stay with what I believe.
    The whole atm is what reduces the incoming solar radiation. Some reaches the surface and provokes IR emission.
    The energy emitted as IR by the surface cannot further warm the surface.
    Any influence on T of additions to CO2 as a GHG is not detectable. In any case additions to CO2 volume are irrelevant to the atm. heat content because of saturation.

  34. Give me an article or give up.

  35. Claes,
    Here's two of the AGW "seminal" papers so you can see how flimsy the arguments are (they are both entirely based upon arbitrary computer models):

    James Hansen's "seminal" 1988 paper:

    Kiehl & Trenberth's paper on the energy budget which still adheres to the greenhouse "heat trapping" gases behave like a pane of glass theory disproven by Wood in 1909:

  36. MS: the errors are so basic and so numerous that it would take an extremely long time to go through them all. If you really want to know why they are all mistaken, then post your e-mail address and I'll contact you.

    Clothcap: how does the earth know where the energy that falls on it came from?

    Claes: I gave you a whole textbook, and a list of some 2000 articles and papers. Your demand for a single "seminal" paper is a bit ridiculous. Perhaps you could explain why you think there should be just one paper that describes the entire science of planetary atmospheres?

  37. Roger,
    I don't post my email address on public web pages. How about just showing in detail specifically what you consider to be the most egregious flaw for each of the papers by Chilingar, Kramm, and Miskolczi...just pick one single flaw for each paper...and doing it here for all to evaluate?

    Claes- I have also not been able to find any paper proving the physics of AGW - The IPCC relies on arbitrary computer models to provide whatever result is desired - and admits in the fine print that few read (section 8.6.4) that it isn't even clear which diagnostic tests are critical to assess confidence in the models. The section concludes by saying that the things necessary to assess confidence in feedbacks simulated by different models have yet to be developed. In other words, the scientists can't make any assessment whatsoever of confidence of the models at the heart of the IPCC "consensus" on AGW.

  38. and here's why we shouldn't have confidence in said models:

  39. Roger, as a spokesman for AGW don't you understand that by failing to give key scientific references you pull the carpet for CO2 climate alarmism?

  40. I am not a "spokesman for AGW". You only started demanding "key references" when you could not answer simple questions about your original post. I gave you references. That you now deny this only demonstrates your own insincerity.

    Perhaps you could tell me the exact number of "key references" that you consider sufficient. Perhaps you could also give me an estimate of how many climate-related papers and textbooks you've read already.

  41. One key reference is enough. Give me that or give up acting like a AGW spokesman. My person is irrelevant as concerns the existence of scientific support of AGW.

  42. One key reference certainly isn't enough. Few branches of science can be trivialised in this way. I pointed this out in a comment on another of your blog posts.

    Still, I may as well point you towards Arrhenius's paper of 1896, "On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground".

  43. If the Arrhenius paper is the best you can come up with, CO2 alarmism
    is dead.

  44. Yes, I rather suspected that whichever paper I gave you, you would not be happy with. Nonetheless, you can at least withdraw your preposterous claim that "there are no key articles".

    As you do not give any indication of what you don't like about it, I assume that you have neither read nor understood the Arrhenius paper.

  45. I have read and understood that it presents a simple radiative model which in no way describes global climate.

  46. Unfortunately you have misunderstood the scope and the point of the Arrhenius paper.

  47. Roger, please, once again the Arrhenius paper was ripped to shreds by RW Wood:

    So who is the one who has not read the literature with an open mind?

    Still waiting on your detailed analysis of one single flaw (pick any flaw at all of your choice)in each of the three papers and please don't continue to state that the flaws are just too numerous to even elaborate on one single flaw.

    Climate "science" has an incredible hubris found in no other area of science of stating it is "settled" with an "over 90%" confidence based entirely upon arbitrary computer models, while quietly admitting said models have no validation or confidence and which in fact contradict empirical observations. Just unbelievable!

  48. Once again, RW Wood only showed that "greenhouse effect" could be considered a misnomer, not that the effect did not exist.

    I already pointed out some major flaws in those papers. Carrying on with that is way off topic for this thread.

  49. Roger, wrong wrong wrong yet again on RW Wood!!! You obviously have not read nor understood or desire to understand his work (and others that confirmed it) so I'm done here. You obviously also do not have any ability to back up your blanket statements about flaws "too numerous to mention" and which are now are "off topic".

  50. "Back radiation" or DLR (downward longwave radiation) is measured in many locations around the world.

    Typically the values are around 300W/m^2 -

    The spectral analysis of DLR shows that it is emitted by water vapor, CO2, ozone, NO2 in the atmosphere -

    And a simple example that everyone can understand which demonstrates how a system can have higher radiation from surfaces within than is supplied to the system as a whole -

  51. Roger,

    Can you let me know how the colder CO2 molecules can force the warmer surface to increase its temperature? Doesn't heat flow from warm to less warm?

    Live well and prosper