Well, not my model exactly. I developed and host a web interface to the modtran model of atmospheric infrared radiation, an early example of a line-by-line code which I downloaded and use to teach and as part of a textbook. Now David C. Archibald from Summa Development Limited, Perth, WA, Australia claims that my “University of Chicago modtran facility” proves that global warming won’t happen.
Archibald begins by discovering that the IR light flux at the top of the atmosphere is more sensitive to changes in atmosphere CO2 when the concentration of CO2 is lower. This will come as no surprise to regular readers of realclimate who will know that the energy flux scales with the logarithm of CO2. The log dependence is why the climate sensitivity parameter is often posed as a temperature change for doubled CO2 concentration; to first order, a change from 10 ppm to 20 would have about as much climate impact as a change from 1000 to 2000 ppm. So Archibald is right on this score, clearly climate is more sensitive to CO2 when levels are lower. However, I think most climate models are aware that atmospheric CO2 is 380 ppm rather than 10 ppm, and they predict global warming anyway. If we were starting out from 10 ppm, the warming would be even worse.
Archibald then takes an atmospheric increase of 40 ppm which he thinks will happen by the year 2030. I’d have guessed 60 ppm by then at least, the way things are going, but whatever, we’ll see. He uses my setup of modtran to calculate that the IR flux to space would drop by 0.4 Watts / m2 as a result of this 40 ppm. Try it yourself. Run the model once with 375 ppm CO2 and another time with 415 ppm, and compare the Iout values in Watts / m2. The exact number you get depends on humidity, setting, clouds, etc. Formulas given in IPCC would say 0.5 Watts / m2; zeroing out water vapor in modtran gets the IR response up to 0.6 Watts / m2 for the default tropical atmosphere case. At any rate Archibald isn’t wildly off here either.
But then Archibald multiplies the radiative forcing by an absurdly low value of the climate sensitivity parameter. In this case he is using the parameter in units of degrees C per Watt / m2. The two forms of the climate sensitivity parameter that we have discussed here are related by a factor of about 4 Watts / m2 for a doubling of CO2. The value Archibald uses is 0.1 degree C per Watt / m2 which was “demonstrated” in a paper entitled “CO2-induced global warming: a skeptic’s view of potential climate change” by Idso, 1998. Translated, Idso’s climate sensitivity winds up to be 0.4 degrees for doubling CO2. IPCC finds it essentially impossible (yeah, I know, highly unlikely or whatever) that the climate sensitivity could be less than 1.5 degrees C for doubling CO2, and 3 degrees C is a best-guess value.
In the end, Archibald concludes that the warming from the next 40 ppm of CO2 rise (never mind the rest of it) will only be 0.04 degrees C. Archibald’s low-ball estimate of climate change comes not from the modtran model my server ran for him, but from his own low-ball value of the climate sensitivity.
Ray and others, Eli pointed to a new online textbook that goes into detail about how satellite instruments are used to detect sea surface temperatures in the infrared, it’s good info generally about how it’s done. Directly to that section: http://www.ccpo.odu.edu/SEES/ocean/ocean_lectures/sst_lecture/Part_2/index.htm
Ryan P. (87) re J. Galt
It would be helpful to include all natural sources and sinks of CO2 for comparison. Barton (88) added some. I thought Timothy would too in (94) but he just couldn’t make it past his diatribe [;-). I wonder (and have asked) the effect of carbonaceous rock as a sink. It also seems that because of the magnitudes involved, a slight anomaly in the natural source/sink process could have an impact. This is a pure speculative question, however. I agree that the argument from my fellow skeptics that ‘man adds just some tiny percent of the total added CO2’ is looking at just a piece of the puzzle, is a blind alley, and misleading.
> asked … carbonaceous rock as a sink …
Answered — explained by experts in the field
http://www.colorado.edu/GeolSci/courses/GEOL1070/chap04/chapter4.html
http://www.geo.arizona.edu/geo4xx/geos478/
From the discussion at http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/001004less_than_a_quarter_.html
Greenhouse gases are warming the planet and will continue to do so. Argue about the rate as much as you wish. This is a recent event only and was not significantly present beyond a century ago. Key point.
Some other influence(s)directly caused significant changes to global climate over the last 3000 years and longer – without greenhouse gases. Indisputable! Argue about this for as long as you like. It did happen.
Solar cycles appear to be directly related to the longer term global climate influences – this seems to be perfectly logical. Solar cycle 24 is already late and getting later. Fact.
It is to be appreciated that more than one influence impacts our climate – not only greenhouse gases.
The issue is ‘What have been the quantitative measures of the respective influences, and more importantly, what will they be in the future’.
It seems rather stupid for surposedly scientific commentary to focus on any particular influence or effect to the exclusion of others, rather than to be objective in assessments and presentations.
Can we please seek some definitive work(s) to provide meaningful information relating to the relevant factors that directly impact upon global warming or cooling.
Hank, Thanks for the reference on ocean temperature measurement. That fills in some blank spaces. I suppose that in looking at the atmosphere, the signal is the clouds and the ocean forms the background. They are now doing some interesting stuff with bandgap engineered semiconductors. These could be very useful for future instruments, but I’m not sure how closely you can tailor the bandgap.
Timothy,
Re: #97
Kirchoff’s Law is a bit of a nightmare. Well I think so.
It is also written down by different people in different ways and that does not help.
For a body in Local Thermodynamic Equilibrium whether in radiative equilibrium or not emissivity = absorptance. For a surface they are material properties, for a gas a function of material properties the volume, density, pressure. etc. The important point is that they are equal when the body is in LTE. For a blackbody they are constant and equal 1, for real materials they are not necessarily constant and are less than or equal to 1.
If the body is in LTE and radiative equilibrium then emission = absorption.
I think it is this last statement that reflects Kirchoff’s original idea.
The atmosphere is in, or close to, LTE and so emissivity = absorptance but not in radiative equilibrium so emission does not necessary equal absorption.
If the radiation background is “hotter” than the body absorption will be greater than emission, the body will warm in an attempt to attain radiative equilibrium. In the troposphere the major governing factor is probably the lapse rate not radiative equilibrium and so although LTE exists radiative equilibrium does not.
I hope this helps, to be honest whenever I feel I understand Kirchoff I find it best to lay down in a dark room until I am feeling better.
Best Wishes
Alexander Harvey
Alexander (Re: 106) Actually one of the clearest expositions I’ve read is in Landau and Lifshitz Stat Mech book. They state that the blackbody distribution is purely a product of the equilibration of the radiation field. However, photons do not interact with each other, so the only way for the field to come to equilibrium is via interactions with surrounding matter. So, the emissivity is entirely a property of the matter. In fact, emissivity does change with pressure, temperature, etc. in solids–just much more slowly. Here too, there is a continuum. The hydrogen atom has single lines. Bring in 2 electrons with helium, and the lines get split by spin-orbit effects lifting the degeneracy. Now put the atom in a molecule and the lines are further distorted and broadened. The molecule goes into a gas or liquid and you have pressure broadening, etc. In a solid, the atom-atom interactions are strong enough that energy lines become bands, which are themselves affected by pressure, strain stress, etc. Yesterday’s Nobel prize is an example of how tailoring the interactions of electrons can produce interesting and surprising properties.
David Norrish (#104)
A good place to start for an overview of the science involved in the picture of the current warming is the IPCCs fourth report (IPCC AR4, see the link at the top right of this page under “Science Links”).
The Working Group I “Summary for Policy Makers” has a nice chart (“Radiative Forcing Components”) for what they consider to be the relative influence on our recent climate changes. They include solar influence.
If you want to know how they arrived at their decisions, which papers they consider authoritative and why they did not consider others at this time; download WGI chapter 2 “Changes in Atmospheric Constituents and in Radiative Forcing”. It includes their discussion concerning solar influences in section 2.7.1.
Ray, I’m confused (I think). I thought the “line spectra” of, say, hydrogen, was caused by jumps in the electronic energy levels (with emission and/or absorption) and not directly related to Planck blackbody-type radiation. Or did I totally misread your 107??
Ray, on how they measure CO2 levels in the atmosphere from satellites,
I think it’s by selecting particular wavelengths (and comparing the satellite work to existing data).
For now all I can do is point to abstracts and hope one of the experts will come along. http://www.agu.org/pubs/crossref/2003/2003JD003439.shtml
(after the middle of next year sometime, the AGU back issues will be searchable online).
Here’s another hint:
http://www.nasa.gov/images/content/177888main_image_feature_833_ys_4.jpg
“Although originally designed to measure atmospheric water vapor and temperature profiles for weather forecasting, data from the Atmospheric Infrared Sounder (AIRS) instrument on NASA’s Aqua spacecraft are now also being used by scientists to observe atmospheric carbon dioxide. … using several methods to measure the concentration of carbon dioxide in the mid-troposphere (about eight kilometers, or five miles, above the Earth’s surface).
“This global map of mid-troposphere carbon dioxide shows that despite the high degree of mixing that occurs with carbon dioxide, the regional patterns of atmospheric sources and sinks are still apparent in mid-troposphere carbon dioxide concentrations.”
RodB, try reading these pages:
http://cfa-www.harvard.edu/~jbattat/a35/blackbody_color.html
http://cfa-www.harvard.edu/~jbattat/a35/cont_abs_em.html
____________excerpt_________
Key Points:
* Anything that absorbs also emits.
* A cloud of cool gas that absorbs certain colors from a blackbody will emit exactly those colors as the gas atoms de-excite
* If we look at the cloud without the blackbody in our line of sight, we will see an emission line spectrum.
* The lines of emission have the same color as the absorption lines in the absorption line spectrum
* If you added an emission line spectrum and an absorption line spectrum, you would get a continuous spectrum.
Rod B., electromagnetic radiation can come from atoms only where they can radiate–that is from transitions between energy states. Thus, a hydrogen atom at room temperature is going to be pretty inert. A hydrogen molecule, also will not do much radiation, although hydrogen in a gas can break the symmetry of the typical diatomic molecule and you might get some radiation due to rotational transitions. If you have a copy of Landau and Lifshitz, the exposition is pretty clear: the Planck distribution is a property of the photon gas in equilibrium, and it is a continuous distribution. However, the only way for it to achieve equilibrium since photons don’t interact with each other.
I think that you are still thinking that atoms have two mechanisms for emitting energy–“thermal” and “quantum”. To see why this is not true, consider the types of energy an atom or molecule can have: 1)kinetic–which is continuum, 2)electronic–quantized, 3)vibrational–quantized, 4)rotational (for molecules w/ more than 2 atoms or distorted diatomic molecules)–quantized. Exchanges of kinetic energy can occur continuously via collisions, but these do not involve emission of radiation. You can also excite a vibrational, rotational or electrical mode via a collision, but this energy will be quantized. All other energy transitions are quantized–from one quantized energy to another.
The Planck spectrum occurs because matter (solids, molecules, atoms, ions, etc.) absorb and radiate energy in their energy lines and bands. Collisions excite these same energy transitions, but the numbers of collisions that can do so varies with temperature. Thus, at room temperature, almost no collisions excite electronic transitions, but they can excite vibrational transitions. On the sun, most of the transitions are electronic and most of the photons are in the visible. Does this help.
Rod B. and Hank,
This is cursory, but the concept of emissivity is important for understanding how blackbody radiation relates to thermal radiation of real gasses/atoms.
http://en.wikipedia.org/wiki/Emissivity
Thank you Ray and Timothy and all
Your replies helped and did not help, the questions keep poping up.
I thought clouds could form at 5-6 km up, close to where IR could escape to space so that increased evaporation would give some negative feedback to temperature, but this appear not to be very significant. I know the reduction of IR would be small compared to the total IR.
An example that didn’t help:
Timothy’s “this is only because the time between collisions for any given molecule tends to be much shorter than the half-life of an excited state”, then another question appears; Ok, but isn’t this then just a transfer of IR energy from the ghg absoption bands to heat the rest of the spectrum?
But never mind, knowing I’m wasting time of some brilliant minds in here, can somebody point to another web site more for amateurs and ignorants? RC is probably more by and for experts and “true believers”.
Igl (114) — Scroll down the sidebar to the Other Opinions section to discover which site best meets your needs.
Ray, I think you’re right in saying to Rod:
“I think that you are still thinking that atoms have two mechanisms for emitting energy–”thermal” and “quantum”
Can you try for a fifth-grade level explanation (poetry, not math)?
I think the answer is — if we take a huge mass of hydrogen (enough to hold together by its own gravity) then its molecules are all constantly interfering with each other, so energy is being transferred among all possible forms.
Think of a ‘chaotic pendulum’ — several off-center masses each attached. Push any of them and the whole connected thing starts to move, but which piece moves which way and how fast? It varies constantly. Imagine shooting BBs at one of those — you’d get ricochets of all energies, some dead slow and some very fast.
I’m not sure that helps. But the point is that all radiation, all photons, are described by quantum mechanics. A hot dense mass (what we think of as normal solids, and hotter things) gives a broad average curve peaking at the ‘temperature’ which is also an average.
Hank, that’s a reasonable analogy. Physically what is going on is this. In an isolated single-electron atom, the electron exists only at certain energies because energy determines wavelength and the electron waves have to interfere constructively. Now add another electron–you get more interactions, more energies…
In a molecule, you now have vibrational and perhaps rotational modes. Put the molecule in a gas, and now the energy levels get further broadened. In a solid, energy lines interact with eachother and broadened still further until they meld into energy bands–so there’s a limited continuum–any energy in one band to any energy in another–of radiation. The point is that the more density increases, the more matter you get, the closer you get to a continuum–to a quasi-classical–result.
BTW, LGL–we’re all learners here. Keep asking questions.
lgl (#114) wrote:
Well, let’s see what we can do with the questions you have left. Believe it or not, this often helps me to understand things a little better as well.
lgl (#114) wrote:
The main negative feedback which comes from clouds is increased albedo where they scatter visible light back into space before it has a chance to reach the surface and get converted into infrared. Clouds will form at a variety of altitudes, although I would expect the bulk to be below the effective radiating layer of 6 km, with or without the enhanced greenhouse effect. However, clouds are also pretty close to being black bodies in the infrared spectrum, and when they absorb thermal radiation at lower altitudes, they actually tend to raise the ground temperature – then the temperature of the atmosphere.
*
At a more technical level, given the fact that in a local thermodynamic equilibrium, good absorbers at a given wavelength are equally good radiators (Kirchoff’s Law), the net direct effect of absorption and radiation would be neither to locally warm or cool the atmosphere But the atmosphere is also gaining thermal energy from moist air convection as well as thermal updrafts. This thermal energy stands an equally good chance of being radiated along with the energy coming from absorption. Likewise, there is the thinning of the atmosphere with altitude, resulting in longer paths between radiation and absorption. As such there tends to be an excess of radiation over absorption.
*
lgl (#114) wrote:
Bingo.
The question keeps popping up when the bit about the time between collisions being shorter than the half-life gets mentioned. I know this is something I had to think about. But I worry sometimes about repeating the more detailed answers – as the people who have been here longer than myself might get tired of reading my posts.
However, the key to the answer is already in the question itself.
Half-lifes.
GHG molecules don’t know how long they have been in an excited state, and as long as a certain percentage are in an excited, some of them will spontaneously decay. Essentially the coins of spontaneous decay keep getting passed around, and they keep getting flipped. Doesn’t matter which ghg has them at any given moment.
So yes, even when a GHG molecule becomes excited, either as the result of absorption or as the result of a collision, overwhelmingly the chances are that it will lose this energy by means of collisions before it has a chance to decay – but this is irrelevant as long as a certain percentage of ghg molecules are excited at any given time. Spontaneous decay will happen to some of them.
*
At a more technical level…
… for another Chris Cringle or two, it is also true that the vast majority of the thermal energy within the atmosphere (roughly 98%, I believe) is possed by molecules that in very large part are incapable of spontaneous emission. Nitrogen and oxygen are examples of this. Given the fact that they consist of only two atoms of the same element, they are incapable of entering the quantized states that GHG molecules are (e.g., vibrational, rotational, and vibrorotational, where pure rotational is possible only with permanently dipolar molecules, e.g., water but not carbon dioxide) and as such largely do not participate in thermal emission except by way of transfering their energy to greenhouse gases through thermal collisions.
However, locally all of the gases will be at the same temperature. The bulk of the atmosphere will be in Local Thermodynamic Equilibrium. This will be due to the air pressure being typically at 20 mb or above (where the surface air pressure being at 1013 mb), which means that the molecules are experiencing a million collisions or more within the half-life of the excited states which result in thermal emission. Given the high rate of collision, at the populational level the modes of excitation will share equally in the thermal energy, being at the same temperature as that of the atmosphere itself.
At altitudes where the air pressure is low enough that the atmosphere is no longer in local thermodynamic equilibrium, the temperatures of the various modalities begins to diverge. The biggest one to diverge first is the 15 μm of carbon dioxide at about 30 km, a strongly self-absorbing band of lines which will then (I believe) tend to diverge towards higher temperatures than the surrounding atmosphere.
*
lgl (#114) wrote:
With me its more tenacity than intelligence. And Real Climate is for anyone who wants to learn.
If you have questions at whatever level, you throw them out. If someone thinks they have an answer hopefully they will respond. But take whatever is said by the amateurs such as myself with a much larger grain of salt than the climatologists. We are in the same boat – just different seats.
*
Incidentally, here one thing to always keep in mind….
If given one argument or another greenhouse gases were able only to absorb but never radiate, energy would in very large part never be able to get out of the atmosphere – except I suppose with what little kinetic energy got transferred back to the surface. Neither convection nor can’t get thermal energy out of the atmosphere. But the atmosphere doesn’t keep heating up, and the good bulk of it is at a lower temperature than the surface.
So how is the thermal energy getting out of the atmosphere? The only way that it can get out of the climate system. It is either being radiated into space directly from the atmosphere or indirectly by being radiated back to the ground one or more times before finally being radiated back out into space.
*
But have we actually observed greenhouse gases emitting thermal radiation?
Definitely – by way of satellite and at various altitudes. Each line begins to escape into space as the atmosphere begins to go from being opaque to it to being transparent to it.
For a good number of examples to this including motion video, please see the links in my earlier comment #555 to Part II: What Angstrom didn’t know.
But have we actually directly observed the greenhouse effect?
Yep, at least in the case of water vapor.
Please see:
Valero, F. P. J., W. D. Collins, P. Pilewskie, A. Bucholtz and P. J. Flatau (1997),
Direct Radiometric Observations of the Water Vapor Greenhouse Effect Over the Equatorial Pacific Ocean,
Science, 275, 1773–1776.
*
Anyway, I hope this helps – and gives everyone more to peak their curiosity.
I cited the article:
Direct radiometric observations of the water vapor greenhouse effect over the equatorial Pacific Ocean
F.P.J. Valero, W.D. Collins, P. Pilewskie, A. Bucholtz, and P.J. Flatau
Science, 274(5307), 1773-1776, 21 March 1997
… in 118.
Actually, it turns out that what they were measuring wasn’t simply a greenhouse effect, but a “super” one.
Here is the abstract:
… and a teaser from the main text:
Alexander Harvey (#106) wrote:
Here is what Eli stated (comment 180 to The weirdest millennium) at one point:
It looks pretty solid, and it looks like it applies at the level of the individual wavelengths. Below 20 mb you are into non-LTE conditions where Kirchoff’s law no longer applies. However, the first big deviation begins to creep in with CO2’s 15 μm at about 30 km. Up until you get to that altitude the brightness temperature of the line is the same as that of the atmosphere itself, and all of the brightness temperatures for the different modes of CO2 excitation are the same as that of the atmosphere itself.
Anyway, we can both dig into this some more – I will be looking for the paper by Evans and Puckrin. But I don’t think I will be laying down Kirchoff’s law as of yet.
If you liked my June Lavoisier paper, then you will love my next one. The message remains the same – increased atmospheric CO2 is wholly beneficial.
http://www.lavoisier.com.au/papers/articles/ArchibaldLavoisierAGM.pdf
[[If you liked my June Lavoisier paper, then you will love my next one. The message remains the same – increased atmospheric CO2 is wholly beneficial.]]
Getting smashed in the head with a brick is wholly beneficial, too. I wish more global warming alarmists would realize that.
David Archibald, You make a blanket statement that increased atmospheric CO2 is wholly beneficial. The uncritical universality of your statement by itself establishes it to be fiction. Even if we were to grant some benefits, surely these benefits would not be uniform. Pacific Islanders are already coping with rising sea levels. Hunts of Eskimos are already failing due to dwindling sea ice. I suspect there will be winners who benefit from climate change. All the evidence points to there being far more losers than winners, though. But then, you clearly have never been about evidence, have you?
No adverse side effects are expected, eh?
Same claim you made in 2005 for the pills you were offering to men with prostate cancer.
How’s that going? Published results yet?
Hank, Ray, et al: I have to dig further into your-all’s posts to maybe find what I’m missing. But one simple roadblock keeps getting in the way. If blackbody/Planck-function radiation all stems from the quantum energy levels (electronic, rotational, vibrational) in an atom or molecule, how can the continuous spectrum be explained? The Sun as an example. First, whatever rotational and vibrational molecular levels might exist in the Sun, they predominately fall in the infrared or microwave range which we see little of in solar radiation. Second, then, the overwhelming amount of visible spectrum radiation would have to come from hydrogen electronic transitions. I’m assuming there are a dozen or two possible levels. Even with all of the potential “line spreading”, I can’t fathom those dozen lines spreading out for the full continuous very smooth spectrum from infrared to UV. Is that what you contend? Why does the formula for emittance cover every wavelength and have only temp as the independent variable — no molecular quantum energy levels or nothing? How does it work with the cosmic background? How does it work with solids, say a carbon cube or a rock painted flat black?
I didn’t fully get the Wikipedia reference. It looked like it was confusing transmission with emission, for one…
I appreciate your-all’s indulgence and help.
Rod, do you know an answer to “how does a photon get produced in the first place, and what happens when a photon is absorbed?”
That’s addressed in some of those prerequisite courses — the ones people need to pass before taking the radiation physics course.
I haven’t. That’s why I keep saying this is at best poetry, trying to find words that give some sense of what the math describes.
A photon started out as a bookkeeping entry. Einstein got his Nobel for work on the photoelectric effect.
Here’s a teaching example. See if this helps:
http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PHTEAH000042000006000340000001&idtype=cvips&gifs=yes
The method described worked for his class, who weren’t at all well prepared for even basic physics:
“In a subsequent class period, I distributed a collection of short passeges from all the student models for class discussion so they could see that they were describing the same phenomenon in somewhat different ways. I also included, as if it were taken from one of the student models, an excerpt3 from a translation of Einstein’s original paper on the photoelectric effect.4,5 Later I revealed to the students that the excerpt was from Einstein and that this was the paper that won him the Nobel Prize. This led to a discussion of how it was possible for them to arrive in two hours at a model that eluded the best scientists of the late 19th century for years.”
Rod, you’ve understood that when a molecule, or the atoms in a molecule, move in space, a quantum of energy (called a photon) can be kicked out and go traveling.
If the atom or molecule is floating all by itself, not interacting, then it can only move in a few particular ways limited by its own structure.
It has only its own individual energy, in discrete chunks.
A whole lot of atoms and molecules close together are interacting, and the banging and pulling and tugging and twisting among them increases the possible motions that parts of that mass of stuff can do in space. And with the mass of stuff all interacting, you can state an ‘average’ amount of energy there — that’s temperature.
And once the stuff that’s interacting so is doing it enthusiastically enough it has an ‘average temperature’ and the motions of the masses involved are so _huge_ compared to the little tiny motions of an individual molecule that the photons produced are overwhelmingly those from the big movements, the ‘temperature’ — and as the mass gets hotter the average temperature rises and we get infrared (huge amounts, perceptible heat, not just a band in a spectroscope) and then red – yellow – blue – ultraviolet as the mass gets hotter and hotter.
The little individual photons from the little individual motions of the molecules are still in there, but those molecules aren’t floating cold and alone, they’re also doing the mosh pit slam dance avalanche movements, and those create far more photons of all possible sorts.
Caveat: it’s doggerel, maybe poetry, just an attempt to find words. Let’s see if one of the radiation physicists can get the coffee out of his or her keyboard and say something more useful about this.
““how does a photon get produced in the first place, and what happens when a photon is absorbed?” is something like:
When a mass moves, the mass moving in space can make energy transfer through space.
Hank, I pretty much know what happens when a photon is absorbed, but have never fully grasped why a photon/light wave gets emitted when internal energy levels change… other than it makes sense to mirror the absorption. But then if you get far enough into the “whys”, physics runs out of answers!
Rod B., My previous several posts have touched on this. In a nutshell–the more particles you have interacting, and the more intense the interactions, the more the energy “lines” get distorted. Thus when you look at light escaping from a cavity, it has not only interacted with the material in the walls of the cavity, but with the gas in the cavity, etc. So when you look at this light, you don’t see the spectra characteristic of the wall material or the gas, but a pretty near blackbody spectrum.
As to your question of why you get a photon from a transition–it is because you can only have electronic/rotational/vibrational states at certain energies. If you got a molecule that tried to go to a forbidden energy, its wave function would destructively interfere with itself (in other words, it’s impossible). As to why you get spontaneous transitions from high to low energy in the first place, you can look at it 2 ways: 1)the low-energy state is more favorable 2)since the spontaneous high-to-low transition is energeticallly possible, it MUST happen (while of course the low-to-high transition cannot happen spontaneously). Now lot’s look at the Sun–it’s not just a ball of neutral hydroge, but rather a plasma–free protons and electrons along with and interacting weakly with other ions and neutral atoms. This is what removes the largely line character of the spectrum. Does this help?
“Why” is a question one can keep asking forever, that’s true. “If we do this we observe that” is about as good as it gets in science. That classroom teaching exercise I linked above shows how a class of ordinary students can, given the observations, can reason their way to the same answer Einstein did about what happens.
Hank, at first blush your 127 sounds neat. One picky problem (maybe). That individual molecule’s energy is in discrete chunks all right, but that has practical application only to rotation and vibration energies. The difference between the “chunks” of translation energy (1/2mv2 stuff) is so tiny those “quantums” are virtually indistinguishable, kind of like the quanta of an speeding automobile.
I want to thank everyone for the responses to my question. I’ve only recently started looking into AGW on a serious level. The inter-play between the two poles of the debate (or non-debate as realclimate contends)provides endless comedic value.
P.S.
and to Timothy Chase who asks “Who are you?”
As yet only a pretender.
It gets deep fast:
http://www2.slac.stanford.edu/vvc/theory/quantum.html
“… if we ask how much energy a beam of light of a certain frequency, f, deposits on an absorbing surface during any time interval, we find the answer can only be nhf, where n is some integer. Values such as (n+1/2)hf are not allowed.
“To get some idea of how counter-intuitive this idea of discrete values is, imagine if someone told you that water could have only integer temperatures as you boiled it. … It would be a pretty strange world you were living in if that were true.
“The world of quantum mechanics is pretty strange when you try to use words to describe it.”
So they draw pictures:
http://www2.slac.stanford.edu/vvc/theory/feynman.html
Here, we’ve been talking about photons. They say:
“…. traveling electromagnetic waves such as light … are electromagnetic waves and differ only in wavelength.
“In the quantum field theory, any changing electromagnetic fields or electromagnetic waves can be described in terms of photons.”
But:
“When there are many photons involved, the effects are equally correct (and more simply) given by the earlier non-quantum theory, namely Maxwell’s equations.”
Back from the brink of quantum theory — at least in the lower atmosphere. I can’t say whether radiation transfer in the upper atmosphere requires quantum theory to describe what’s happening in very thin air.
I suspect so.
True, Hank, but heating water does increase its temp by discrete steps, with intergers (or 1/2 intergers) part of the mathematics… along with Planck’s constant.
Rod B, We cannot say with certainty whether temperature is quantized, as the steps are too small to measure. For all practical purposes this can be treated classically. Quantum effects tend to manifest 1)for very small scales of mass, distance and time; 2)for systems confined to fewer than 3 dimensions. When a system is unconfined and sufficiently large and longlived, quantum effects are negligible.
Rod, c’mon.
Ray, I just can’t get it through my thick skull. The characteristic radiation as seen with a spectroscope shows extremely sharp and narrow lines (or voids), some wider than others, granted, but still very narrow compared to the visible-plus spectrum. This is true for the Sun and stars. The characteristic lines certainly do not go away and get lost in the mashing together of all the photons to make a complete blackbody spectrum. So we’ll have to leave this hanging out there.
I liked your explanation of why photons are generated with changing energy levels. Thanks.
re 135. I agree. It is impractical to think much about quantum steps in macro/classic physics stuff. Like it makes little sense to consider Uncertainty while parallel parking. [;-) But, none-the-less, ALL energy is quantized
http://www.newton.dep.anl.gov/askasci/ast99/ast99601.htm
Rod B., WRT the Sun, you have both a hydrogen plasma, but also neutral hydrogen–so you have a hydrogen absorption spectrum superimposed on a blackbody curve. You see similar features in the IR with Earth. There is no reason why a body as large as the Sun cannot exhibit both continuum and quantum features in its spectrum.
Even the Devil can quote scripture for his purpose – The Merchant of Venice. Thankyou for putting the MODTRAN facility together. We would be in the dark on the true extent of the log effect otherwise. And you are right, after that comes the climate sensitivity. What I like about Idso’s number is that it is derived from observations of nature, not models, which, no matter how diligently they are assembled and attended to, might leave something out, and thus be wrong, and lead us astray. Anyone who doesn’t like Idso’s sensitivity figure might care to read his paper, and determine where he went wrong. I don’t think you can, so his number stands. If you are true seekers of wisdom, this you will do.
[Response: I wonder if you notice the irony in your quote? The “true extent” of the log nature of CO2 forcing is well known and discussed in every IPCC report and included in every climate model – how is that keeping it in the dark? And as for climate sensitivity, Idso’s estimates suffer from all the same problems as those discussed here – you can’t just divide a temperature by a energy flux to get the global climate sensitivity. You need to do it on a global basis as discussed here – and those estimates (all drawn from observations) give numbers near 3ºC for 2xCO2. -gavin]
So, Rod, point to what you’re thinking you remember about bright line emissions in sunlight please?
You I think are remembering that spectral lines are _detectable_ (like helium, first discovered as a spectral line in the sun) and assuming that means they’re strong lines.
Not so. There are lines, but they’re the dark ones for absorbtion. http://ase.tufts.edu/cosmos/pictures/Explore_figs_5/Chapter1/fig1_21.jpg
That’s clearly explained above.
If you’re getting an explanation from some other source please post your source. If you’re making your mind up based on logic rather than relying on someone’s statements, you aren’t stating a basis for your thinking that you can point to.
It’s only in a cold thin gas where the individual spectral lines stand out. Like space or, I think, the top of the atmosphere.
A hot plasma like the sun, or a planet’s surface like Earth, aren’t diffuse thin gas and emit so much else that the individual clear lines are barely detectable.
Online references for standard spectra at top of atmosphere, and reference to nonstandard tools including MODTRAN (the atmosphere is a constantly changing filter):
http://rredc.nrel.gov/solar/spectra/
http://www.nrel.gov/rredc/smarts/
http://www.coseti.org/solatype.htm
Remember the discussion many topics ago about where the initial math for radiation transfer came from — work on solar atmospheres. There’s coursework, you can probably get the textbooks and do it if you want a real understanding. This is just throwing words at the subject here, you know.
Results — about 89,200 English pages for radiation transfer gas physics math. No “Wisdom” button available.
Graduate Courses in Astronomy – University of Michigan
The radiative transfer of the light in matter is developed and a subset of the … Introductory sections on particle, fluid dynamics and plasma physics are …
http://www.astro.lsa.umich.edu/Academics/Grad/desc.php
Physical processes in low density gases including radiation transfer, … and the interaction between gas and dust. P: Math 222 and Physics 205 or 241. …
http://www.wisc.edu/pubs/ug/10lettsci/depts/astron.html
David Archibald, The idea that an observation or even a set of observations is less likely to lead us astray than a model is pretty weird. I mean, after all, the model presumably is traceable to observations. Moreover, the observations you base your number on could just as easily neglect a factor that is unimportant on their timescale but very important on longer timescales. Models are based on observation, but suplemented with physical understanding (also with its roots in observation). This is the reason why science is more (and more effective) than a simple detailed logbook. If you don’t understand this, then you don’t understand science.
Ray (139) and Hank (138, 141), I fully agree with this. I was simply saying the sources of the continuous radiation and the discrete/quantum radiation are not the same. Specifically, the continuous “blackbody” radiation does not come from the “spreading” the molecular quanta radiation, as Hanks’s reference in 138 states. (Thanks.) You can have both (one way or another).
Nor do I disagree (nor did I say otherwise) that spectrography looks at discrete lines and/or discrete voids (blanks, black lines, whatever) depending on the situation. You get blank lines when the energy non-equilibrium causes the molecules/atoms to only absorb radiation from the continuous spectrum source into their internal quantum energy levels, gaining energy in the process, but not emit that energy (losing energy in that process) at its discrete wavelength(s) (to 4-7 decimal places in the nm range, BTW — before spreading).
Sorry guys but all the model you need is this:
El Nino add 0.2 oC, La Nina subtract 0.2 oC, and correct some for large volcano eruptions.
GISS data for low latitudes: http://data.giss.nasa.gov/gistemp/graphs/Fig_E.lrg.gif
clearly show the stepy nature of the temperature rise.
During periodes with more La Nina events than El Nino events, the temperature drops,
where they are in balance there is almost no change, and when El Ninos are in majority the temperature rise: http://virakkraft.com/ENSO1975.htm
From 1976 to 1983 there are two more El Ninos so temp anomaly goes from roughly -0.1 to 0.3, Then the next 15 years there are an even number of El Ninos and La Ninas so temp only increases some 0.05 oC per decade! Then the El Nino in 2002, without a following La Nina, brings it to 0.5 oC. The El Nino in 2006 was not very powerful so the present La Nina shold bring it down to around 0.3, and hey, we are almost there!
[edit]
Rod, look at what happens to the transitions of the hydrogen atom as you go to higher excited states. The energy levels get closer and closer until they are essentially a continuum. It’s not as if there is a definitive line that divides “continuum” and “quantum”.
The blackbody spectrum is the product of the photon gas coming to equilibrium with itself–but it does so by interacting through the matter around it. The more complicated the species in the matter and their interactions, the closer you get to a continuum.
Rod, the sources are “the same” in that the sources are movement of mass in space.
Isolated molecules move in very few ways and produce very specific emissions.
Crowded molecules in solids or dense gases move in all possible ways and produce emissions of all possible wavelengths, peaking at the average wavelength for the average movement, the “temperature”
I don’t have the prerequisite advanced math and physics, and you know this is just words, but do you agree that all energy emitted is due to masses moving in space? And the masses affected by other masses move in less precise increments so we get photons of all kinds of energies out?
Re: Climate Sensitivity
In response to David Archibald, Gavin wrote, “You need to do it on a global basis as discussed here – and those estimates (all drawn from observations) give numbers near 3ºC for 2xCO2.” (inline to 140)
Paleoclimate records say roughly 3 C.
Please see:
James’ Empty Blog
Climate sensitivity is 3C
by James Annan
Thursday, March 02, 2006
http://julesandjames.blogspot.com/2006/03/climate-sensitivity-is-3c.html
Thats evidence – not something dropping out of models.
lgl, So, what is the mechanism for your effect. How do you know that the causal arrow doesn’t point the opposite direction. Correlation is not causation. Correlation + an understood mechanism is a whole helluva lot closer.
Ray,
The mechanism is simply the winds and currents in the Pacific. For the last 30 years they have allowed less cold water from the deep to reach the surface. Then of course you ask for the mechanism behind that.
Maybe the three large volcanic eruptions play a role. It looks like about 5 years after those there are very strong El Ninos. In fact, the three stronges El Ninos after 1950 come 5-6 years after these three eruptions.
lgl (#144) wrote:
That’s called natural variability – and it don’t look “stepy.”
lgl (#144) wrote:
Why is it that the two charts don’t look the same?