Rod, take a lump of anything.
Put it on the table in front of you.
What “frequencies” do you think it’s emitting?
What does a “frequency” mean to you?
Patrick 027says
Re Rod B. – coming into the conversation midpoint, note that a blackbody radiation flux – unpolarized, incoherent, isotropic, an intensity in amount and spectral distribution fitting the Planck function, be produced, at least approximately (maybe nearly isotropic except for some directions), with one or more methods:
Take a large isothermal opaque empty box or empty ball or whatever, and put a tiny hole it. Even with nonzero albedos, even large nonzero albedos at some frequency, polarization, etc, the path that a photon would have to take to go in, be reflected, and come out without absorption, will, with some possible exceptions in some directions, require many reflections. With some exceptions, each interaction with the material offers some probability of absorption. The same path offers the same probability of emission in the opposite direction. (PS I would think that many multiple interactions would also allow some equilibration of photons to non-photons even via Raman scattering and fluorescence) So the tiny hole, if tiny enough relative to the size of the chamber and for it’s inner surface’s albedo, can act approximately like a blackbody (PS maybe not for the wavelengths which are sizable relative to the hole; if the temperature is high enough, or the hole is allowed to be larger by using a less reflective material or larger chamber, then most of the energy will not be affected much by diffraction out the hole).
Alternatively, an isothermal path that is sufficiently long to be nearly opaque, through a material with small single-scatter albedo – or the radiation seen from within a vast isothermal expanse, whatever scattering may occur.
PS radiation is quantized in the sense that there are photons – whatever energies the photons have.
Rod Bsays
t_p_hamilton, WHAAA??! So, I’ll take the integer one (or two if you’d like) and since there is (evidently) an infinite range of allowable frequency differential (even smaller than 10^-100 Hz) I have an infinite number of quantum levels. I dunno, but that seems to defeat the whole purpose…
Theo Kurtén, probably correct about the one Hz break. I wasn’t at all central to my point and is totally insignificant — like angels on the head of a pin. I did think it telling though that to counter my argument of a quanta at 20THz to the nearest whole Hz I was chastised for not including 2.00000000000004 Hz! There still seems to be something amiss. But, maybe you (and t_p_hamilton) are more correct… [scratch, scratch]
Yes, you interpreted my central argument correctly (although this argument is a side bar to the initial question of planck radiation versus line spectral radiation and one I would have preferred not have come up — but my fault), which essentially says gases (or everything) can radiate ala Planck.. Though as I said, probably little in most cases (though I doubt as near infinitesimal as you are suggesting) and certainly requires at least enough atoms/molecules to make up a normal Boltzmann distribution.
One of the things that bothers me (and I can’t so far get a crisp answer to) is how can 396 watts in a full planck spectrum emitting from the earth (and supplemented by 78watts coming from the sun into the atmosphere) physically generate a back radiation of 333 watts reaching the earths surface from only the narrow radiation bands of greenhouse gases (though admittedly H2O is pretty substantial) — and all of the details that attend this.
Rod Bsays
Ray Ladbury, answers:
1) I heard you the first time you said JPL is not an authoritative source.
2) Probably so, though I don’t see how Landau and Lifshitz are necessarily more authoritative than others.
3) After 30 years I would have guessed you’d be more up on stuff. ;-)
4) I agree it’s pretty hard for a single atom or molecule to radiate in a continuum.
5) You can get something like a Boltzmann distribution which can generate a distribution of frequencies.
Rod Bsays
Brian Dodge, thanks for your #387. I started into the Ventura article and it seemed pretty scientifically astute. Then I stumbled across some pretty goofy sounding stuff and decided I’d catch it later, now with your critique to help.
siddsays
Mr. Rod B commented on Landau and Lifshitz. I really like the whole series. Particularly: Vol. 10: Physical Kinetics. I recall fondly the discussion of detailed balance which helped me immensely when a calculation went pear shaped. I must warn that it takes a grad school level of technical proficiency, and it helps if you have a mentor for the sticky bits.
sidd
Didactylossays
Rod B: Your own quotation contradicts you. “the intensity and frequency distribution of the radiation depends on the detailed structure of the body”
Lord knows I’m not a physics expert, but I’ve always found reading comprehension a useful skill.
Even your original quote contradicts you: “the amount of radiation emitted at each frequency (or frequency band) depends on the temperature of the material”
Of course, I could have misunderstood your own position. Reading comprehension is only useful when there’s something there to comprehend.
I did notice that you elided the words “(although not equally)”. It’s almost as if you aren’t being honest. Oh wait….
If you are relying on an introductory workbook, don’t you think that’s a big clue that you’re out of your depth? Knowing when you’re out of your depth is a really useful thing to know.
Rod Bsays
Ray L, picking up some of the pieces:
Finding something ambiguous and disagreeing with something are NOT the same thing.
Yes gas is a body; a single atom not so much.
Emissivity causes deviations from the classic continuous blackbody radiation curve, and CAN be a function of wavelength and temperature and physical structure.
Rod Bsays
Hank a lump at 300K radiates theoretically from 0 to maybe ~10^50 Hz, practically from about 10GHz to about 100THz with a peak intensity around 20THz. I don’t know the quanta though they’re pretty small. What’s your point?
t_p_hamiltonsays
RodB:”t_p_hamilton, WHAAA??! So, I’ll take the integer one (or two if you’d like) and since there is (evidently) an infinite range of allowable frequency differential (even smaller than 10^-100 Hz) I have an infinite number of quantum levels. I dunno, but that seems to defeat the whole purpose…”
Purpose of what – quantization? Quantization was at first an ad hoc principle applied by Planck to get the blackbody radiation curve correct. It was with a continuous frequency spectrum – to verify this just look at the equation – do you see any integer type numbers or indices? No, you will not.
The quantization idea is this:
Say you have $100 and I have $1. This is analogous to available energy (temperature). We wish to buy sodas that cost $0.50 (a small amount, like the amount of energy in the infrared). Essentially you can buy as many as you want within reason, because the quantum required ($.50) is insignificant compared to the available energy ($100). Now for the ultraviolet (like buying a new car), you and I can buy exactly the same amount – zero. In classical physics making up any amount of payment was possible (so you could by 100/25,000 th of a car), because there were no requirements to buy an integer number of items. The concept of items (quanta) did not exist. This theory gives infinite energy for high frequencies, whereas the actual observed amount approaches zero. This is more than just a little disagreement.
Patrick 027says
Re Rod B. quoting Wikipedia in 399 When the molecules bump into each other, they change direction. A change in direction is equivalent to acceleration. As stated above, when charged particles accelerate, they emit electromagnetic radiation.
I would like to hear what a physicist would say about that; neutral molecules may have dipoles (temporary and permanent) and changes in spin and vibration would accelerate charge (and collisions can do that), but the acceleration of the whole molecule in some direction doesn’t do that if the molecule is neutral. An oscillating dipole emits radiation; I’m not clear on what happens with an accelerating dipole (translation, not accelerating the oscillation).
Vibrations and rotations are quantized, though. (? I would imagine translational states might be quantized when other molecules are around, perhaps only with significant effect in sufficiently dense packing, as in solids and liquids (? – phonons?).)
PS it has sometimes been said that, when there are quantized states, other states aren’t available and the system jumps instantaneously from one available state to another – but actually, the solution for the time-independent Schrodinger equation is what describes the available states; the process of transition from one such state to another must be described by the time-dependent equation; a continuum of states are available so long as the state is changing and thus the system is in the process of emitting or absorbing energy or … but that process can not be completed until the system reaches a state that is available when the state is not changing – so far as I know.
“Any body at any temperature above absolute zero will radiate to some extent, the intensity and frequency distribution of the radiation depending on the detailed structure of the body….
…
… Einstein took the next step: he conjectured that all oscillators are quantized, for example a vibrating atom in a solid. This would explain why the Dulong Petit law, which assigns specific heat 3k to each atom in a solid, does not hold good at low temperatures…. The specific heat falls, as is indeed observed. Furthermore, it explains why diatomic gas molecules, such as oxygen and nitrogen, do not appear to absorb heat into vibrational modes—these modes have very high frequency….
…
… the two measures, per unit interval of frequency and per unit interval of wavelength, are different, so a claim that, say, sunlight is most intense in the yellow has to specify which is being used (actually it would be wavelength, frequency would give the near infrared).”
Buy a textbook (not any random article you find on the Internet that supports the misunderstanding you already have).
Read.
Concentrate.
Learn.
Then come back and we’ll talk.
[I cannot believe a bunch of PhD physicists and chemists have been sucked into arguing about this with you, when A) your understanding is so tragically, comically warped, B) you are so unwilling to listen, reason and learn and C) you actually attack people who do understand the subject! Just amazing.]
Patrick 027says
Re Rod B – about energy being quantized, see last paragraph of my last comment. The energy is quantized in that individual systems only have a discrete set of allowable states (when not in the process of interacting with other systems or things – note that a larger system can be defined to include that interaction, though – right?). A sufficiently large system (solid of large number of atoms) may have so many closely-spaced energy levels that it may seem like a continuous band. Different systems that may otherwise be identical may be perturbed in different ways so that the photons emitted and absorbed don’t fit the same identical set of energy levels, or be moving relative to each other, so that emitted photons are red- or blue-shifted differently. Then there’s the uncertainty principle. As explained by someone else on another thread, a shorter finite time a photon emission occurs within requires some range of frequencies for that photon (a shorter pulse of wave amplitude is the superposition of a larger range of wavelengths).
The energy is also quantized in the sense that it is carried by or consists of particles, or something which acts like particles even if it is also waves.
Patrick 027says
PS Rod B. – remember that the radiation emitted toward the surface from the atmosphere will be, at frequencies where the atmosphere is more opaque (or else when there are lower-level clouds) coming from layers that are generally warmer (aside from inversions). Peaks (or if there is an inversion that is sufficiently optically thick, dips) in the spectrum of downward radiation reaching the surface may fit a Planck function for temperatures found near the surface.
Joe Cushleysays
Maybe it’s time for Rod B’s contributions on this to be sent to the Bore Hole? I’ve learned a lot from the attempts by Patrick, Rays, Hank, Theo etc to educate him on this matter (unintended pun). He hasn’t.
Rod Bsays
Patrick 027 (411), sounds good. An oscillating dipole is an accelerating dipole.
Rod Bsays
Hank, I’ve been asserting for years that physics doesn’t allow for warming due to increasing CO2 based on this notion that 396 watts in a full planck spectrum emits from the earth, you say??? Where did that come from? You clearly have me confused with somebody else? I’ve never said, implied, or thought such.
> Rod
> a lump at 300K radiates theoretically from 0 to maybe ~10^50 Hz,
> practically from about 10GHz to about 100THz with a peak intensity
> around 20THz.
300K, 80.33F
A lump of what, Rod? Glass? Aluminum? Soot? Ice? White paint?
You really don’t believe there’s any difference?
Why’s Stephen Chu suggesting white roofs, then?
“… If one assumed that Maxwell’s theory of electromagnetic radiation, which worked well in the macroscopic world, was also valid at the microscopic scale (tenths of nanometers), then these oscillating charges would radiate, presumably giving off heat and light….
…
… A full understanding of how this works needs quantum mechanics, but the general idea is as follows. There are charges-electrons-in glass that are able to oscillate in response to an applied external oscillating electric field, but these charges are tightly bound to atoms, and only oscillate at certain frequencies. It happens that for ordinary glass none of these frequencies correspond to those of visible light, so there is no resonance with a light wave, and hence little energy absorbed. Glass is opaque at some frequencies outside the visible range (in general, both in the infrared and the ultraviolet). These are the frequencies at which the electrical charge distribution in the atoms or bonds can naturally oscillate…..
…
… Heated bodies radiate by processes just like the absorption described above operating in reverse. Thus, for soot heat causes the lattice to vibrate more vigorously …. On the other hand, the electrons in a metal have very long mean free paths, the lattice vibrations affect them much less, so they are less effective in radiating away heat….
At sufficiently high temperatures, all bodies become good radiators. Items heated until they glow in a fire look much more similar than they do at room temperature. For a metal, this can be understood in terms of a shortening of the mean free path by the stronger vibrations of the lattice interfering with the electron’s passage.
…
… Any body at any temperature above absolute zero will radiate to some extent, but the intensity and frequency distribution of the radiation depends on the detailed structure of the body. To make any progress in understanding radiation, we must specify the details of the body radiating…..”
You’re obscuring the detail by talking about “a lump” Rod — the hotter you get the material, the less its detailed structure limits “the intensity and frequency distribution” because the details — the dimensions/connections/distances between bits of the structure — vary more and more, the hotter it gets.
Brian Dodgesays
“…not clear on what happens with an accelerating dipole…” Patrick 027 — 12 Feb 2011 @ 4:00 PM
“…or be moving relative to each other, so that emitted photons are red- or blue-shifted differently.” Patrick 027 — 12 Feb 2011 @ 5:12 PM
The emission from an oscillating dipole which is accelerating in the observers frame of reference would be chirped; increasing frequency if it is accelerating towards the observer, decreasing if it is accelerating away – changing doppler shift as its velocity changes.
Ray Ladburysays
Rod, So an gas is a body, but not an atom of a gas. How about 2 atoms? 3? 4? If so, what is different about the multi-atom assembly from the single atom case? How many atoms are needed? OK, now look at a hydrogen vapor lamp. Do you see a continuum spectrum? Why, no. We see a Balmer series. Why?
And, Rod, I would appreciate it if you would actually do me the courtesy of reading what I write and not distorting it. What I said is that the particular JPL presentation you cite is intended for a lay audience, and so is not precise in its phrasing. And even then, it does not support what you say.
Patrick, collisions that would distort the energy levels of an atom sufficiently for it to radiate will outside its allowed energy levels would be extremely rare. As I said to Rod above, if you look at a vapor lamp, you see emission in a line spectrum. This is why thay have to put phosphors on mercury vapor lamps to get anything even remotely approaching full spectrum lighting.
Patrick 027says
Re 421 Brian Dodge – Thank you; actually though I was wondering about a dipole whose translation is being accelerated and is not necessarily oscillating. If the charges are closely spaced relative to wavelengths being emitted then their radiation should largely cancel out, but …?
Re 422 Ray Ladbury – thank you (about collisions). But how about the vibrational/rotational states of molecules (I haven’t reviewed pressure/collisional broadenning in a while; that is what I was thinking of)?
PS Re Rod – vibrational/rotational energy levels of relatively simple molecules (like CO2) can produce huge numbers of closely spaced absorption/emission lines.
What’s the temperature of the surface? Everything that passes through the atmosphere is intercepted in the surface and changed into heat. The surface is at a temperature in the infrared range.
> (and supplemented by 78watts coming from the
> sun into the atmosphere) physically generate a back radiation of
> 333 watts reaching the earths surface from only
Here’s another problem:
> the narrow radiation bands of greenhouse gases
What’s the temperature of the atmosphere? The earth is bright in the infrared. That energy is intercepted in the greenhouse bands, and if you look at the lines they cover most of that infrared range. That energy is intercepted, passed to nitrogen and oxygen, averaging out the temperature, and passed back to greenhouse gases, winding them back up to where they emit infrared.
> (though admittedly H2O is pretty substantial)
> — and all of the details that attend this.
That’s the problem you keep raising — you
can’t see how the greenhouse effect works.
Your theory doesn’t allow you to see how it works.
Try doing it as a hypothetical.
If energy behaved as the physicists are telling you it does — would that make sense to you? Do you follow the argument except you don’t believe the surface heat is radiated in the infrared at the surface temperature?
Or is this where you say heat isn’t temperature and temperature isn’t heat?
–> What would have to be true, for you to believe the picture? <–
Ray Ladburysays
Patrick, Collisional/pressure broadening can cause some of the lines to coalesce, but it doesn’t come close to absorbing a continuum. But basically, the higher the density, the more interaction, and the more of the spectrum that gets absorbed. However, even in a liquid, you don’t really get continuum absorption. And in a solid, the energies are in bands, so it’s close. That’s why you use a metal filament in a lightbulb. Even here, though, not quite a blackbody.
“… our atmosphere is only partially transparent to infrared wavelengths. Filled with water vapor, carbon dioxide, and methane, our atmosphere absorbs almost all infrared light …. These molecules grab infrared light and trap it, preventing it from passing through the atmosphere (which is why they are called greenhouse gases)….
… The final problem posed by our atmosphere for infrared astronomers is that it — and the Earth itself — is warm. Infrared light is characteristically emitted by room-temperature objects. Objects like you and I glow brightly in infrared light, and so does the Earth and its atmosphere. If you could see in infrared light, the night sky would look as bright as daylight!”
Bob (Sphaerica), so you’re saying in #414 that I’m idiotic to believe some article written by JPL when I have you to listen to instead??
[editorial comment: OK, we’re going to ask everyone here to tone down the rhetoric from here forward. Anything further that is personal/ad hom is going to be edited out]
“The atmosphere is transparent to visible light, but mostly opaque to infrared.
Infrared “opacity” comes from absorption bands of H2O, CO2, CH4 and others molecules. Zoom into the near-Infrared (1-6micron) showing specific molecular bands ….
“Photons are absorbed by the ground, heating it up
The warm ground radiates infrared photons (Wein’s Law)
The atmosphere, however, is mostly opaque to infrared photons
Most of the infrared photons emitted by the warm ground get absorbed by the atmosphere on their way out, heating the atmosphere.”
“A black body is a theoretical object that absorbs 100% of the radiation that hits it…. In practice no material has been found …. It is also a perfect emitter of radiation…. It would emit at every wavelength of light as it must be able to absorb every wavelength to be sure of absorbing all incoming radiation.”
Rod Bsays
Patrick 027, I think your #415 is about right. The various numerous energy states of a crystal stems from bounding a piece of the crystal, as I understand it (which I understand is perfectly proper for analysis). I agree with your red shift/blue shift or uncertainty factor in radiation analysis. But this applies whatever the genesis of radiation. Also, from a practical matter with atmospheric absorption/emission, they have virtually no effect.
I don’t fully follow your ‘radiation into opaque frequencies’ thought. GHGs radiate at rather precise frequencies determined intrinsically by the GHG molecule, not by what is in the path of the radiation. Or are you saying that CO2 (e.g.) in the path is far more likely to absorb backradiation from other CO2 molecules and therefore present a more opaque path. Can you better explain your thought?
Rod Bsays
Hank, were you just trying to catch me off guard with a veiled gotcha?? My lump answer (for your lump) was for a blackbody. In real lumps emissivity and therefore planck function intensity CAN vary with temperature, wavelength of physical makeup, as I clearly said earlier. I find nothing in the main of your #420 that I disagree with.
Rod Bsays
Ray, I’ve answered your points in #422 at least twice. I would appreciate it if you would actually do me the courtesy of reading what I write and not distorting it before lambasting it.
“is not precise in its phrasing.” Is that spinmeister’s words for lying through their teeth and making stuff up? If such an article had been written by a so-called denier, how would you have characterized that? ‘Not precise in their phrasing???’ Just curious.
Rod Bsays
Patrick 027, “hugh” is an imprecise subjective term. I’d by “lots;” Maybe a ‘whole lot’… I agree and have said that the combined vibration-rotation spectral lines form a band like spectra much better than uncertainty, doppler and even collisions (which usually get the credit.)
“is not precise in its phrasing.” Is that spinmeister’s words for lying through their teeth and making stuff up?
No, Rod, it’s not. When you are explaining things to beginners, you can’t be fully precise because the result will be information overload and zero comprehension.
Hence, pedagogical simplifications are useful in a great many subject areas–from radiation physics to music theory. (Which I mention because that is where I personally have had the most occasion to deploy pedagogical simplifications.)
And I’m not making that up. . .
Ianashsays
Could I ask the experts – what are your views on the Berkeley Earth Surface Temperature project (a new global temp data set)?
Rod Bsays
Hank, the upwelling surface radiation IS a full spectrum planck type. The earth is considered to have an emissivity of near 1.0 and hardly wavelength dependent — so much so that 1.0 is assumed in most analyses taking earth as a blackbody at 288K +/-.
I know fully how the greenhouse gas theory works. It’s the specific numbers that seem to me to have a problem. (And I mean “seem.” Can’t say with certainty that they do have a problem.)
Yes, heat isn’t necessarily temperature but I’m not sure that’s a factor here…
Your referenced statement that “…our atmosphere absorbs almost all infrared light…” might sum up my questions here. I know that’s what the models say (absorbs roughly 90% of the full spectrum emitted watts), but if one looks at high resolution Spectracalc there are far more wavelengths with no (or extremely light) absorption in CO2, e.g. I haven’t done the math so I can’t say anything is wrong, but it raises questions because my sniff test is not good.
> gotcha
No, Rod, I’m sincerely trying to figure out why you keep bringing up this doubt of yours, over and over, repeatedly taking conversations away from climate change and the greenhouse effect, by saying there’s something you’re just a mite uncertain about, something you can’t quite see how it could be so, something that just couldn’t work the way all these physicists think so some little error must have crept in.
Then we go ’round and ’round with you and — nothing gets figured out.
And a few months later, you bring it up again, but never get clear.
What, as clearly as you can say, is it that you don’t believe or doubt or don’t think adds up?
Whatever it is you’re trying to say — can you please say it?
“The emissivity of most natural Earth surfaces for the
wavelength range covered by the five ASTER TIR bands between 8 and 12 μm
(Table 1) is from 0.65 to close to 1.0.”
The North American ASTER Land Surface Emissivity Database (NAALSED) Version 2.0(http://emissivity.jpl.nasa.gov) has now been released ….
dhogazasays
Just say it. Clearly as possible
How about this: RodB doesn’t understand, therefore he doesn’t except mainstream climate science.
This is *much* better than those who say, \I don’t understand, therefore climate science is a fraud\.
flxiblesays
“Do you know how much trouble it is for me to pretend to care about facts?” Rod B
Do you know how boringly irritating it is for the majority here to have to scroll past all your “efforts” in order to find comments relevent to Unforced variations actually concerning climatology?
Hank and Ray, in particular, please stop feeding the troll!!
[Response: Not defending Rod B, who appears to be just spinning things along in an attempt to create an impression that there’s something not understood here (Rod, prove me wrong, it would make me happy!), but the quote up there seems to have been from somebody posting as a parody, under the name “Rod B-“. I deleted that since I thought it might cause confusion. Note that although I’ve made a cameo re-appearance, I don’t propose to start moderating this thread with comments again. Just issuing a put-up or shut up. –raypierre]
One Anonymous Blokesays
dhogaza #438. Accept, not except. And I think you’re wrong about Rod B. I think his statements are insincere from the start: none of his positions are genuine; it’s not that he doesn’t understand, I think his interest lies elsewhere. However, I am learning where he is not, so I value the answers to his drivel.
raypierresays
I’m not making an attempt to moderate this thread, but I happened to notice (rather to my astonishment) that the gabfest between Rod B and others on thermal emission is still going on, but seems to be going nowhere. Some useful references for people to read have emerged, but I see an awful lot of confusion here (most, but not all by Rod B) on points of the statistical mechanics of radiation and how that relates to quantum states (lines) that are in fact completely understood and have been for a long time. I don’t want any casual readers (if there are any left after roughly 450 comments) to drive by and think there’s anything really unresolved in the physics here. In fact, after taking a quick look at the exchanges, I can’t figure out just what Rod B is really complaining about. The closest thing to a statement about what is confusing him is the statement about where the back radiation is coming from (and I don’t fully understand the question).
So, Rod B, could you please state, concisely and clearly, what (if anything) there is in your conception of radiative transfer that leads you to think that some of the numbers in the basic greenhouse theory don’t (as you put it) quite “add up”? If you can’t do that, we might as well just shut down this discussion, since it’s not going anywhere. Rod B., if you are not getting answers to the questions you are posing, it is because most of us cannot figure out what you are trying to get at.
JCHsays
Science of Doom and a Rod B discussed the subject.
[Response: Hmmm. The discussion of back-radiation by Science of Doom was really excellent, and I see that Rod B didn’t manage to learn anything from that exchange and is just repeating the same points of confusion here. I’d love to be proven wrong, but I’m beginning to doubt Rod B is going to make any more progress this time than last time (assuming charitably that he really wants to make progress). –raypierre]
Pete Dunkelbergsays
How did Arrhenius do it? He managed to figure out the greenhouse effect on climate very well without quantum mechanics. I am not proposing to explain Arrhenius. Perhaps a future RC post (or short series?) explaining how Arrhenius did it and then showing how to do it even better with QM would add greatly to the understanding of all RC readers.
[Response: You don’t need a post. There is a very in-depth discussion of this in the chapter on Arrhenius in The Warming Papers. The upshot is that it’s perfectly possible to make use of physical laws based on observation before one has understood the microscopic origin of those laws in statistical mechanics. Specific heats depend on quantum theoretical effects, but people were making predictions based on specific heat long before quantum theory. The Stefan-Boltzman radiation law was well established experimentally long before its origins in the Planck hypothesis were understood. Similarly Kirchhoff’s laws and the spectrum of emission of various non–black radiating bodies and gases. What Arrhenius was lacking to do the calculation completely correctly was not so much quantum theory as accurate measurements of the spectroscopy of water vapor and CO2. –raypierre]
raypierresays
I am a fool for jumping back into this, and I don’t intend to stay long, but I want to lay to rest Rod B’s concern that the back-radiation can be greater than the net solar radiation. He also seems concerned about comparison to the solar radiation absorbed in the atmosphere, rather than the total, but that confusion, like the rest, is because he forgets that whatever is absorbed at the surface — solar or IR — is given back to the atmosphere in the form of turbulent heat fluxes plus upward infrared. To make things clearer, let’s look at the extreme case of Venus, for which so little solar radiation reaches the surface we can practically neglect it in the surface term. In this case, moreover, the CO2 density is so high that it is optically thick throughout nearly all the spectrum. Then, the back-radiation at 727K is a whopping 15838 W/m**2, way in excess of the 163 W/m*2 of solar radiation absorbed by Venus (remember the high albedo!). But there’s no problem energetically, since the ground is radiating upward also at very nearly the same temperature, giving the back radiation right BACK to the atmosphere, which absorbs it because it is optically thick. All that energy just keeps shuttling back and forth. No problem. Never was, never will be.
In the Earth’s tropics, the situation is rather similar, except most of the opacity of the low level atmosphere is provided by water vapor and low level clouds. Further, for Earth, a significant proportion of the energy exchange between surface and atmosphere is by turbulence, not radiation.
But nobody should think any of this is a good route to understanding the greenhouse effect. The greenhouse effect is best understood in terms of the top-of-atmosphere budget. See the discussion of the Surface Budget Fallacy in our book, The Warming Papers, or in Chapter 6 of my book Principles of Planetary Climate.
Joe Cushleysays
Hey, Fred Pearce seems to redeem himself slightly here…
The play is on just up the road from me, and I’m booking tickets. ‘Greenland’ at the National Theatre is another outing I’ll be making soon…
John E. Pearsonsays
Raypierre, I’d really like to hear more on what you were getting at with regard to the microscopic origins of Kirchoff’s law!
John E. Pearsonsays
oops. sorry. I meant Ray (Pierrehumbert) I’d really like to hear what you were getting at with regard to the microscopic origins of Kirchoff’s law!
[Response: It might be better to hold that thought for the next Unforced Variations open thread. At this point I don’t think many others are still listening in, and anything we say will reach only a limited audience. Mind, I’m not saying there’s anything wrong with Kirchhoff’s Law, just that it’s something which has a lot of subtlety to it. It’s something that people really ought to feel a bit confused about, until they’ve studied it in depth. –raypierre]
“… the second law of thermodynamics has not appeared anywhere in this argument. That’s because it’s entirely microscopic, whereas thermodynamics is a macroscopic theory. Nevertheless, one can show, via statistical mechanics, that when the relationships described here hold at the microscopic level, then the macroscopic properties will obey the laws of thermodynamics. We don’t need to invoke thermodynamics because we’re guaranteed that anything that we calculate from the microscopic theory will, as long as we do not make a mistake or an inappropriate approximation, obey thermodynamics.
Thus, I view Kirchhoff’s and Boltzmann’s original derivations of Kirchhoff’s law and the Stefan-Boltzmann law, which did invoke the laws of thermodynamics as, in some sense, having been superseded. By requiring that macroscopic properties obey thermodynamics, Kirchhoff and Bunsen derived relationships that any microscopic theory of radiation-matter interactions would have to satisfy. This was of enormous importance for the historical development of the microscopic theory. Nevertheless, we now have a successful microscopic theory the interactions between radiation and matter. As noted above, Dirac wrote down the essentials in 1927.”
443, Raypierre, in comment: The upshot is that it’s perfectly possible to make use of physical laws based on observation before one has understood the microscopic origin of those laws in statistical mechanics.
I am glad that you wrote that.
Septic Matthewsays
444, Raypierre, in comment: See the discussion of the Surface Budget Fallacy in our book, The Warming Papers, or in Chapter 6 of my book Principles of Planetary Climate.
I have read chapter 9, because it’s short and deals with a subject that is treated more fully in another book that I recently bought. I have been reading chapter 4, and the lively thought-provoking exercises. So I took his advice and scanned chapter 6 as well.
If anyone is still seeking enlightenment on the exchanges between Rod B and others, I recommend we all follow Raypierre’s advice — leave here, and read his book.
Rod, take a lump of anything.
Put it on the table in front of you.
What “frequencies” do you think it’s emitting?
What does a “frequency” mean to you?
Re Rod B. – coming into the conversation midpoint, note that a blackbody radiation flux – unpolarized, incoherent, isotropic, an intensity in amount and spectral distribution fitting the Planck function, be produced, at least approximately (maybe nearly isotropic except for some directions), with one or more methods:
Take a large isothermal opaque empty box or empty ball or whatever, and put a tiny hole it. Even with nonzero albedos, even large nonzero albedos at some frequency, polarization, etc, the path that a photon would have to take to go in, be reflected, and come out without absorption, will, with some possible exceptions in some directions, require many reflections. With some exceptions, each interaction with the material offers some probability of absorption. The same path offers the same probability of emission in the opposite direction. (PS I would think that many multiple interactions would also allow some equilibration of photons to non-photons even via Raman scattering and fluorescence) So the tiny hole, if tiny enough relative to the size of the chamber and for it’s inner surface’s albedo, can act approximately like a blackbody (PS maybe not for the wavelengths which are sizable relative to the hole; if the temperature is high enough, or the hole is allowed to be larger by using a less reflective material or larger chamber, then most of the energy will not be affected much by diffraction out the hole).
Alternatively, an isothermal path that is sufficiently long to be nearly opaque, through a material with small single-scatter albedo – or the radiation seen from within a vast isothermal expanse, whatever scattering may occur.
PS radiation is quantized in the sense that there are photons – whatever energies the photons have.
t_p_hamilton, WHAAA??! So, I’ll take the integer one (or two if you’d like) and since there is (evidently) an infinite range of allowable frequency differential (even smaller than 10^-100 Hz) I have an infinite number of quantum levels. I dunno, but that seems to defeat the whole purpose…
Theo Kurtén, probably correct about the one Hz break. I wasn’t at all central to my point and is totally insignificant — like angels on the head of a pin. I did think it telling though that to counter my argument of a quanta at 20THz to the nearest whole Hz I was chastised for not including 2.00000000000004 Hz! There still seems to be something amiss. But, maybe you (and t_p_hamilton) are more correct… [scratch, scratch]
Yes, you interpreted my central argument correctly (although this argument is a side bar to the initial question of planck radiation versus line spectral radiation and one I would have preferred not have come up — but my fault), which essentially says gases (or everything) can radiate ala Planck.. Though as I said, probably little in most cases (though I doubt as near infinitesimal as you are suggesting) and certainly requires at least enough atoms/molecules to make up a normal Boltzmann distribution.
One of the things that bothers me (and I can’t so far get a crisp answer to) is how can 396 watts in a full planck spectrum emitting from the earth (and supplemented by 78watts coming from the sun into the atmosphere) physically generate a back radiation of 333 watts reaching the earths surface from only the narrow radiation bands of greenhouse gases (though admittedly H2O is pretty substantial) — and all of the details that attend this.
Ray Ladbury, answers:
1) I heard you the first time you said JPL is not an authoritative source.
2) Probably so, though I don’t see how Landau and Lifshitz are necessarily more authoritative than others.
3) After 30 years I would have guessed you’d be more up on stuff. ;-)
4) I agree it’s pretty hard for a single atom or molecule to radiate in a continuum.
5) You can get something like a Boltzmann distribution which can generate a distribution of frequencies.
Brian Dodge, thanks for your #387. I started into the Ventura article and it seemed pretty scientifically astute. Then I stumbled across some pretty goofy sounding stuff and decided I’d catch it later, now with your critique to help.
Mr. Rod B commented on Landau and Lifshitz. I really like the whole series. Particularly: Vol. 10: Physical Kinetics. I recall fondly the discussion of detailed balance which helped me immensely when a calculation went pear shaped. I must warn that it takes a grad school level of technical proficiency, and it helps if you have a mentor for the sticky bits.
sidd
Rod B: Your own quotation contradicts you. “the intensity and frequency distribution of the radiation depends on the detailed structure of the body”
Lord knows I’m not a physics expert, but I’ve always found reading comprehension a useful skill.
Even your original quote contradicts you: “the amount of radiation emitted at each frequency (or frequency band) depends on the temperature of the material”
Of course, I could have misunderstood your own position. Reading comprehension is only useful when there’s something there to comprehend.
I did notice that you elided the words “(although not equally)”. It’s almost as if you aren’t being honest. Oh wait….
If you are relying on an introductory workbook, don’t you think that’s a big clue that you’re out of your depth? Knowing when you’re out of your depth is a really useful thing to know.
Ray L, picking up some of the pieces:
Finding something ambiguous and disagreeing with something are NOT the same thing.
Yes gas is a body; a single atom not so much.
Emissivity causes deviations from the classic continuous blackbody radiation curve, and CAN be a function of wavelength and temperature and physical structure.
Hank a lump at 300K radiates theoretically from 0 to maybe ~10^50 Hz, practically from about 10GHz to about 100THz with a peak intensity around 20THz. I don’t know the quanta though they’re pretty small. What’s your point?
RodB:”t_p_hamilton, WHAAA??! So, I’ll take the integer one (or two if you’d like) and since there is (evidently) an infinite range of allowable frequency differential (even smaller than 10^-100 Hz) I have an infinite number of quantum levels. I dunno, but that seems to defeat the whole purpose…”
Purpose of what – quantization? Quantization was at first an ad hoc principle applied by Planck to get the blackbody radiation curve correct. It was with a continuous frequency spectrum – to verify this just look at the equation – do you see any integer type numbers or indices? No, you will not.
The quantization idea is this:
Say you have $100 and I have $1. This is analogous to available energy (temperature). We wish to buy sodas that cost $0.50 (a small amount, like the amount of energy in the infrared). Essentially you can buy as many as you want within reason, because the quantum required ($.50) is insignificant compared to the available energy ($100). Now for the ultraviolet (like buying a new car), you and I can buy exactly the same amount – zero. In classical physics making up any amount of payment was possible (so you could by 100/25,000 th of a car), because there were no requirements to buy an integer number of items. The concept of items (quanta) did not exist. This theory gives infinite energy for high frequencies, whereas the actual observed amount approaches zero. This is more than just a little disagreement.
Re Rod B. quoting Wikipedia in 399 When the molecules bump into each other, they change direction. A change in direction is equivalent to acceleration. As stated above, when charged particles accelerate, they emit electromagnetic radiation.
I would like to hear what a physicist would say about that; neutral molecules may have dipoles (temporary and permanent) and changes in spin and vibration would accelerate charge (and collisions can do that), but the acceleration of the whole molecule in some direction doesn’t do that if the molecule is neutral. An oscillating dipole emits radiation; I’m not clear on what happens with an accelerating dipole (translation, not accelerating the oscillation).
Vibrations and rotations are quantized, though. (? I would imagine translational states might be quantized when other molecules are around, perhaps only with significant effect in sufficiently dense packing, as in solids and liquids (? – phonons?).)
PS it has sometimes been said that, when there are quantized states, other states aren’t available and the system jumps instantaneously from one available state to another – but actually, the solution for the time-independent Schrodinger equation is what describes the available states; the process of transition from one such state to another must be described by the time-dependent equation; a continuum of states are available so long as the state is changing and thus the system is in the process of emitting or absorbing energy or … but that process can not be completed until the system reaches a state that is available when the state is not changing – so far as I know.
> 396 watts in a full planck spectrum emitting from the earth
You’ve been asserting, for years, that physics doesn’t allow for warming due to increasing CO2 based on this notion — right?
“Any body at any temperature above absolute zero will radiate to some extent, the intensity and frequency distribution of the radiation depending on the detailed structure of the body….
…
… Einstein took the next step: he conjectured that all oscillators are quantized, for example a vibrating atom in a solid. This would explain why the Dulong Petit law, which assigns specific heat 3k to each atom in a solid, does not hold good at low temperatures…. The specific heat falls, as is indeed observed. Furthermore, it explains why diatomic gas molecules, such as oxygen and nitrogen, do not appear to absorb heat into vibrational modes—these modes have very high frequency….
…
… the two measures, per unit interval of frequency and per unit interval of wavelength, are different, so a claim that, say, sunlight is most intense in the yellow has to specify which is being used (actually it would be wavelength, frequency would give the near infrared).”
http://galileo.phys.virginia.edu/classes/252/black_body_radiation.html
Rod B,
Wow. Just wow.
Suggested recipe for education:
Buy a textbook (not any random article you find on the Internet that supports the misunderstanding you already have).
Read.
Concentrate.
Learn.
Then come back and we’ll talk.
[I cannot believe a bunch of PhD physicists and chemists have been sucked into arguing about this with you, when A) your understanding is so tragically, comically warped, B) you are so unwilling to listen, reason and learn and C) you actually attack people who do understand the subject! Just amazing.]
Re Rod B – about energy being quantized, see last paragraph of my last comment. The energy is quantized in that individual systems only have a discrete set of allowable states (when not in the process of interacting with other systems or things – note that a larger system can be defined to include that interaction, though – right?). A sufficiently large system (solid of large number of atoms) may have so many closely-spaced energy levels that it may seem like a continuous band. Different systems that may otherwise be identical may be perturbed in different ways so that the photons emitted and absorbed don’t fit the same identical set of energy levels, or be moving relative to each other, so that emitted photons are red- or blue-shifted differently. Then there’s the uncertainty principle. As explained by someone else on another thread, a shorter finite time a photon emission occurs within requires some range of frequencies for that photon (a shorter pulse of wave amplitude is the superposition of a larger range of wavelengths).
The energy is also quantized in the sense that it is carried by or consists of particles, or something which acts like particles even if it is also waves.
PS Rod B. – remember that the radiation emitted toward the surface from the atmosphere will be, at frequencies where the atmosphere is more opaque (or else when there are lower-level clouds) coming from layers that are generally warmer (aside from inversions). Peaks (or if there is an inversion that is sufficiently optically thick, dips) in the spectrum of downward radiation reaching the surface may fit a Planck function for temperatures found near the surface.
Maybe it’s time for Rod B’s contributions on this to be sent to the Bore Hole? I’ve learned a lot from the attempts by Patrick, Rays, Hank, Theo etc to educate him on this matter (unintended pun). He hasn’t.
Patrick 027 (411), sounds good. An oscillating dipole is an accelerating dipole.
Hank, I’ve been asserting for years that physics doesn’t allow for warming due to increasing CO2 based on this notion that 396 watts in a full planck spectrum emits from the earth, you say??? Where did that come from? You clearly have me confused with somebody else? I’ve never said, implied, or thought such.
> Rod
> a lump at 300K radiates theoretically from 0 to maybe ~10^50 Hz,
> practically from about 10GHz to about 100THz with a peak intensity
> around 20THz.
300K, 80.33F
A lump of what, Rod? Glass? Aluminum? Soot? Ice? White paint?
You really don’t believe there’s any difference?
Why’s Stephen Chu suggesting white roofs, then?
http://www.engineeringtoolbox.com/emissivity-coefficients-d_447.html
Try this version:
http://wien.nobelpr.com/1.htm
Wilhelm Wien
The Nobel Prize in Physics 1910
“… If one assumed that Maxwell’s theory of electromagnetic radiation, which worked well in the macroscopic world, was also valid at the microscopic scale (tenths of nanometers), then these oscillating charges would radiate, presumably giving off heat and light….
…
… A full understanding of how this works needs quantum mechanics, but the general idea is as follows. There are charges-electrons-in glass that are able to oscillate in response to an applied external oscillating electric field, but these charges are tightly bound to atoms, and only oscillate at certain frequencies. It happens that for ordinary glass none of these frequencies correspond to those of visible light, so there is no resonance with a light wave, and hence little energy absorbed. Glass is opaque at some frequencies outside the visible range (in general, both in the infrared and the ultraviolet). These are the frequencies at which the electrical charge distribution in the atoms or bonds can naturally oscillate…..
…
… Heated bodies radiate by processes just like the absorption described above operating in reverse. Thus, for soot heat causes the lattice to vibrate more vigorously …. On the other hand, the electrons in a metal have very long mean free paths, the lattice vibrations affect them much less, so they are less effective in radiating away heat….
At sufficiently high temperatures, all bodies become good radiators. Items heated until they glow in a fire look much more similar than they do at room temperature. For a metal, this can be understood in terms of a shortening of the mean free path by the stronger vibrations of the lattice interfering with the electron’s passage.
…
… Any body at any temperature above absolute zero will radiate to some extent, but the intensity and frequency distribution of the radiation depends on the detailed structure of the body. To make any progress in understanding radiation, we must specify the details of the body radiating…..”
You’re obscuring the detail by talking about “a lump” Rod — the hotter you get the material, the less its detailed structure limits “the intensity and frequency distribution” because the details — the dimensions/connections/distances between bits of the structure — vary more and more, the hotter it gets.
“…not clear on what happens with an accelerating dipole…” Patrick 027 — 12 Feb 2011 @ 4:00 PM
“…or be moving relative to each other, so that emitted photons are red- or blue-shifted differently.” Patrick 027 — 12 Feb 2011 @ 5:12 PM
The emission from an oscillating dipole which is accelerating in the observers frame of reference would be chirped; increasing frequency if it is accelerating towards the observer, decreasing if it is accelerating away – changing doppler shift as its velocity changes.
Rod, So an gas is a body, but not an atom of a gas. How about 2 atoms? 3? 4? If so, what is different about the multi-atom assembly from the single atom case? How many atoms are needed? OK, now look at a hydrogen vapor lamp. Do you see a continuum spectrum? Why, no. We see a Balmer series. Why?
And, Rod, I would appreciate it if you would actually do me the courtesy of reading what I write and not distorting it. What I said is that the particular JPL presentation you cite is intended for a lay audience, and so is not precise in its phrasing. And even then, it does not support what you say.
Patrick, collisions that would distort the energy levels of an atom sufficiently for it to radiate will outside its allowed energy levels would be extremely rare. As I said to Rod above, if you look at a vapor lamp, you see emission in a line spectrum. This is why thay have to put phosphors on mercury vapor lamps to get anything even remotely approaching full spectrum lighting.
Re 421 Brian Dodge – Thank you; actually though I was wondering about a dipole whose translation is being accelerated and is not necessarily oscillating. If the charges are closely spaced relative to wavelengths being emitted then their radiation should largely cancel out, but …?
Re 422 Ray Ladbury – thank you (about collisions). But how about the vibrational/rotational states of molecules (I haven’t reviewed pressure/collisional broadenning in a while; that is what I was thinking of)?
PS Re Rod – vibrational/rotational energy levels of relatively simple molecules (like CO2) can produce huge numbers of closely spaced absorption/emission lines.
> Rod
> One of the things that bothers me (and I can’t so
> far get a crisp answer
> to) is how can 396 watts
> in a full planck spectrum
See, there’s your first problem, you assume a “full planck spectrum” describes the energy pictured in the classic chart
http://chriscolose.files.wordpress.com/2008/12/kiehl4.jpg?w=480&h=350
> emitting from the earth
What’s the temperature of the surface? Everything that passes through the atmosphere is intercepted in the surface and changed into heat. The surface is at a temperature in the infrared range.
> (and supplemented by 78watts coming from the
> sun into the atmosphere) physically generate a back radiation of
> 333 watts reaching the earths surface from only
Here’s another problem:
> the narrow radiation bands of greenhouse gases
What’s the temperature of the atmosphere? The earth is bright in the infrared. That energy is intercepted in the greenhouse bands, and if you look at the lines they cover most of that infrared range. That energy is intercepted, passed to nitrogen and oxygen, averaging out the temperature, and passed back to greenhouse gases, winding them back up to where they emit infrared.
> (though admittedly H2O is pretty substantial)
> — and all of the details that attend this.
That’s the problem you keep raising — you
can’t see how the greenhouse effect works.
Your theory doesn’t allow you to see how it works.
Try doing it as a hypothetical.
If energy behaved as the physicists are telling you it does — would that make sense to you? Do you follow the argument except you don’t believe the surface heat is radiated in the infrared at the surface temperature?
Or is this where you say heat isn’t temperature and temperature isn’t heat?
–> What would have to be true, for you to believe the picture? <–
Patrick, Collisional/pressure broadening can cause some of the lines to coalesce, but it doesn’t come close to absorbing a continuum. But basically, the higher the density, the more interaction, and the more of the spectrum that gets absorbed. However, even in a liquid, you don’t really get continuum absorption. And in a solid, the energies are in bands, so it’s close. That’s why you use a metal filament in a lightbulb. Even here, though, not quite a blackbody.
Maybe this will help:
“… our atmosphere is only partially transparent to infrared wavelengths. Filled with water vapor, carbon dioxide, and methane, our atmosphere absorbs almost all infrared light …. These molecules grab infrared light and trap it, preventing it from passing through the atmosphere (which is why they are called greenhouse gases)….
… The final problem posed by our atmosphere for infrared astronomers is that it — and the Earth itself — is warm. Infrared light is characteristically emitted by room-temperature objects. Objects like you and I glow brightly in infrared light, and so does the Earth and its atmosphere. If you could see in infrared light, the night sky would look as bright as daylight!”
http://www.jpl.nasa.gov/wise/amy.cfm
Bob (Sphaerica), so you’re saying in #414 that I’m idiotic to believe some article written by JPL when I have you to listen to instead??
[editorial comment: OK, we’re going to ask everyone here to tone down the rhetoric from here forward. Anything further that is personal/ad hom is going to be edited out]
And these may help:
http://lasp.colorado.edu/~bagenal/1010/graphics/earth_ir_emission.gif
http://bouman.chem.georgetown.edu/S02/lect23/blackbody.png
“The atmosphere is transparent to visible light, but mostly opaque to infrared.
Infrared “opacity” comes from absorption bands of H2O, CO2, CH4 and others molecules. Zoom into the near-Infrared (1-6micron) showing specific molecular bands ….
“Photons are absorbed by the ground, heating it up
The warm ground radiates infrared photons (Wein’s Law)
The atmosphere, however, is mostly opaque to infrared photons
Most of the infrared photons emitted by the warm ground get absorbed by the atmosphere on their way out, heating the atmosphere.”
http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit5/atmos.html
Yet another: http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html — “every wavelength” is for a theoretical object, not reality.
“A black body is a theoretical object that absorbs 100% of the radiation that hits it…. In practice no material has been found …. It is also a perfect emitter of radiation…. It would emit at every wavelength of light as it must be able to absorb every wavelength to be sure of absorbing all incoming radiation.”
Patrick 027, I think your #415 is about right. The various numerous energy states of a crystal stems from bounding a piece of the crystal, as I understand it (which I understand is perfectly proper for analysis). I agree with your red shift/blue shift or uncertainty factor in radiation analysis. But this applies whatever the genesis of radiation. Also, from a practical matter with atmospheric absorption/emission, they have virtually no effect.
I don’t fully follow your ‘radiation into opaque frequencies’ thought. GHGs radiate at rather precise frequencies determined intrinsically by the GHG molecule, not by what is in the path of the radiation. Or are you saying that CO2 (e.g.) in the path is far more likely to absorb backradiation from other CO2 molecules and therefore present a more opaque path. Can you better explain your thought?
Hank, were you just trying to catch me off guard with a veiled gotcha?? My lump answer (for your lump) was for a blackbody. In real lumps emissivity and therefore planck function intensity CAN vary with temperature, wavelength of physical makeup, as I clearly said earlier. I find nothing in the main of your #420 that I disagree with.
Ray, I’ve answered your points in #422 at least twice. I would appreciate it if you would actually do me the courtesy of reading what I write and not distorting it before lambasting it.
“is not precise in its phrasing.” Is that spinmeister’s words for lying through their teeth and making stuff up? If such an article had been written by a so-called denier, how would you have characterized that? ‘Not precise in their phrasing???’ Just curious.
Patrick 027, “hugh” is an imprecise subjective term. I’d by “lots;” Maybe a ‘whole lot’… I agree and have said that the combined vibration-rotation spectral lines form a band like spectra much better than uncertainty, doppler and even collisions (which usually get the credit.)
Rod, #431–
No, Rod, it’s not. When you are explaining things to beginners, you can’t be fully precise because the result will be information overload and zero comprehension.
Hence, pedagogical simplifications are useful in a great many subject areas–from radiation physics to music theory. (Which I mention because that is where I personally have had the most occasion to deploy pedagogical simplifications.)
And I’m not making that up. . .
Could I ask the experts – what are your views on the Berkeley Earth Surface Temperature project (a new global temp data set)?
Hank, the upwelling surface radiation IS a full spectrum planck type. The earth is considered to have an emissivity of near 1.0 and hardly wavelength dependent — so much so that 1.0 is assumed in most analyses taking earth as a blackbody at 288K +/-.
I know fully how the greenhouse gas theory works. It’s the specific numbers that seem to me to have a problem. (And I mean “seem.” Can’t say with certainty that they do have a problem.)
Yes, heat isn’t necessarily temperature but I’m not sure that’s a factor here…
Your referenced statement that “…our atmosphere absorbs almost all infrared light…” might sum up my questions here. I know that’s what the models say (absorbs roughly 90% of the full spectrum emitted watts), but if one looks at high resolution Spectracalc there are far more wavelengths with no (or extremely light) absorption in CO2, e.g. I haven’t done the math so I can’t say anything is wrong, but it raises questions because my sniff test is not good.
> gotcha
No, Rod, I’m sincerely trying to figure out why you keep bringing up this doubt of yours, over and over, repeatedly taking conversations away from climate change and the greenhouse effect, by saying there’s something you’re just a mite uncertain about, something you can’t quite see how it could be so, something that just couldn’t work the way all these physicists think so some little error must have crept in.
Then we go ’round and ’round with you and — nothing gets figured out.
And a few months later, you bring it up again, but never get clear.
What, as clearly as you can say, is it that you don’t believe or doubt or don’t think adds up?
Whatever it is you’re trying to say — can you please say it?
Just say it. Clearly as possible.
hmmmm
“The emissivity of most natural Earth surfaces for the
wavelength range covered by the five ASTER TIR bands between 8 and 12 μm
(Table 1) is from 0.65 to close to 1.0.”
http://dx.doi.org/10.1016/j.rse.2009.05.005
http://www.sciencedirect.com/science/journal/00344257
Remote Sensing of Environment
Volume 113, Issue 9, September 2009, Pages 1967-1975
The North American ASTER Land Surface Emissivity Database (NAALSED) Version 2.0(http://emissivity.jpl.nasa.gov) has now been released ….
How about this: RodB doesn’t understand, therefore he doesn’t except mainstream climate science.
This is *much* better than those who say, \I don’t understand, therefore climate science is a fraud\.
“Do you know how much trouble it is for me to pretend to care about facts?” Rod B
Do you know how boringly irritating it is for the majority here to have to scroll past all your “efforts” in order to find comments relevent to Unforced variations actually concerning climatology?
Hank and Ray, in particular, please stop feeding the troll!!
[Response: Not defending Rod B, who appears to be just spinning things along in an attempt to create an impression that there’s something not understood here (Rod, prove me wrong, it would make me happy!), but the quote up there seems to have been from somebody posting as a parody, under the name “Rod B-“. I deleted that since I thought it might cause confusion. Note that although I’ve made a cameo re-appearance, I don’t propose to start moderating this thread with comments again. Just issuing a put-up or shut up. –raypierre]
dhogaza #438. Accept, not except. And I think you’re wrong about Rod B. I think his statements are insincere from the start: none of his positions are genuine; it’s not that he doesn’t understand, I think his interest lies elsewhere. However, I am learning where he is not, so I value the answers to his drivel.
I’m not making an attempt to moderate this thread, but I happened to notice (rather to my astonishment) that the gabfest between Rod B and others on thermal emission is still going on, but seems to be going nowhere. Some useful references for people to read have emerged, but I see an awful lot of confusion here (most, but not all by Rod B) on points of the statistical mechanics of radiation and how that relates to quantum states (lines) that are in fact completely understood and have been for a long time. I don’t want any casual readers (if there are any left after roughly 450 comments) to drive by and think there’s anything really unresolved in the physics here. In fact, after taking a quick look at the exchanges, I can’t figure out just what Rod B is really complaining about. The closest thing to a statement about what is confusing him is the statement about where the back radiation is coming from (and I don’t fully understand the question).
So, Rod B, could you please state, concisely and clearly, what (if anything) there is in your conception of radiative transfer that leads you to think that some of the numbers in the basic greenhouse theory don’t (as you put it) quite “add up”? If you can’t do that, we might as well just shut down this discussion, since it’s not going anywhere. Rod B., if you are not getting answers to the questions you are posing, it is because most of us cannot figure out what you are trying to get at.
Science of Doom and a Rod B discussed the subject.
[Response: Hmmm. The discussion of back-radiation by Science of Doom was really excellent, and I see that Rod B didn’t manage to learn anything from that exchange and is just repeating the same points of confusion here. I’d love to be proven wrong, but I’m beginning to doubt Rod B is going to make any more progress this time than last time (assuming charitably that he really wants to make progress). –raypierre]
How did Arrhenius do it? He managed to figure out the greenhouse effect on climate very well without quantum mechanics. I am not proposing to explain Arrhenius. Perhaps a future RC post (or short series?) explaining how Arrhenius did it and then showing how to do it even better with QM would add greatly to the understanding of all RC readers.
[Response: You don’t need a post. There is a very in-depth discussion of this in the chapter on Arrhenius in The Warming Papers. The upshot is that it’s perfectly possible to make use of physical laws based on observation before one has understood the microscopic origin of those laws in statistical mechanics. Specific heats depend on quantum theoretical effects, but people were making predictions based on specific heat long before quantum theory. The Stefan-Boltzman radiation law was well established experimentally long before its origins in the Planck hypothesis were understood. Similarly Kirchhoff’s laws and the spectrum of emission of various non–black radiating bodies and gases. What Arrhenius was lacking to do the calculation completely correctly was not so much quantum theory as accurate measurements of the spectroscopy of water vapor and CO2. –raypierre]
I am a fool for jumping back into this, and I don’t intend to stay long, but I want to lay to rest Rod B’s concern that the back-radiation can be greater than the net solar radiation. He also seems concerned about comparison to the solar radiation absorbed in the atmosphere, rather than the total, but that confusion, like the rest, is because he forgets that whatever is absorbed at the surface — solar or IR — is given back to the atmosphere in the form of turbulent heat fluxes plus upward infrared. To make things clearer, let’s look at the extreme case of Venus, for which so little solar radiation reaches the surface we can practically neglect it in the surface term. In this case, moreover, the CO2 density is so high that it is optically thick throughout nearly all the spectrum. Then, the back-radiation at 727K is a whopping 15838 W/m**2, way in excess of the 163 W/m*2 of solar radiation absorbed by Venus (remember the high albedo!). But there’s no problem energetically, since the ground is radiating upward also at very nearly the same temperature, giving the back radiation right BACK to the atmosphere, which absorbs it because it is optically thick. All that energy just keeps shuttling back and forth. No problem. Never was, never will be.
In the Earth’s tropics, the situation is rather similar, except most of the opacity of the low level atmosphere is provided by water vapor and low level clouds. Further, for Earth, a significant proportion of the energy exchange between surface and atmosphere is by turbulence, not radiation.
But nobody should think any of this is a good route to understanding the greenhouse effect. The greenhouse effect is best understood in terms of the top-of-atmosphere budget. See the discussion of the Surface Budget Fallacy in our book, The Warming Papers, or in Chapter 6 of my book Principles of Planetary Climate.
Hey, Fred Pearce seems to redeem himself slightly here…
http://www.guardian.co.uk/environment/2011/feb/11/the-heretic-climate-change-review
The play is on just up the road from me, and I’m booking tickets. ‘Greenland’ at the National Theatre is another outing I’ll be making soon…
Raypierre, I’d really like to hear more on what you were getting at with regard to the microscopic origins of Kirchoff’s law!
oops. sorry. I meant Ray (Pierrehumbert) I’d really like to hear what you were getting at with regard to the microscopic origins of Kirchoff’s law!
[Response: It might be better to hold that thought for the next Unforced Variations open thread. At this point I don’t think many others are still listening in, and anything we say will reach only a limited audience. Mind, I’m not saying there’s anything wrong with Kirchhoff’s Law, just that it’s something which has a lot of subtlety to it. It’s something that people really ought to feel a bit confused about, until they’ve studied it in depth. –raypierre]
John, try:
“… the second law of thermodynamics has not appeared anywhere in this argument. That’s because it’s entirely microscopic, whereas thermodynamics is a macroscopic theory. Nevertheless, one can show, via statistical mechanics, that when the relationships described here hold at the microscopic level, then the macroscopic properties will obey the laws of thermodynamics. We don’t need to invoke thermodynamics because we’re guaranteed that anything that we calculate from the microscopic theory will, as long as we do not make a mistake or an inappropriate approximation, obey thermodynamics.
Thus, I view Kirchhoff’s and Boltzmann’s original derivations of Kirchhoff’s law and the Stefan-Boltzmann law, which did invoke the laws of thermodynamics as, in some sense, having been superseded. By requiring that macroscopic properties obey thermodynamics, Kirchhoff and Bunsen derived relationships that any microscopic theory of radiation-matter interactions would have to satisfy. This was of enormous importance for the historical development of the microscopic theory. Nevertheless, we now have a successful microscopic theory the interactions between radiation and matter. As noted above, Dirac wrote down the essentials in 1927.”
http://scienceofdoom.com/2010/10/24/planck-stefan-boltzmann-kirchhoff-and-lte/
443, Raypierre, in comment: The upshot is that it’s perfectly possible to make use of physical laws based on observation before one has understood the microscopic origin of those laws in statistical mechanics.
I am glad that you wrote that.
444, Raypierre, in comment: See the discussion of the Surface Budget Fallacy in our book, The Warming Papers, or in Chapter 6 of my book Principles of Planetary Climate.
I have read chapter 9, because it’s short and deals with a subject that is treated more fully in another book that I recently bought. I have been reading chapter 4, and the lively thought-provoking exercises. So I took his advice and scanned chapter 6 as well.
If anyone is still seeking enlightenment on the exchanges between Rod B and others, I recommend we all follow Raypierre’s advice — leave here, and read his book.