Talk:Greenhouse effect

This page has an arbitration committee decision associated with it. Please see the following archived arbitration case for more information: Wikipedia:Requests for arbitration/Climate change dispute#Use of metaphor.

Inconsistent

The figure showing scattering losses and absorption is very low resolution and does not show absorptions and windows in the mid-IR. Anyone have a better figure??

CO2 lifetimes

158.169.131.14 wrote:

NOT correct. The lifetime of CO2 is in the order of FIVE years, not hundreds. If you don't believe me, look at http://www.icsu-scope.org/downloadpubs/scope13/chapter01.html. This gives some figures. The atmospheric reservoir of CO2 is now about 750 Gigatonnes. Photosynthesis uses some 100 Gigatonnes/year (both land and marine plants). Exchange with the ocean comes to another 100 Gigatonnes/year. Lifetime is the reservoir size divided by turnover rate. Work it out yourself)

First of all 158.169.131.14 it woud be a good idea to get yourself an account. Second, to put comments like that in the talk page (here) not the article.

Secondly, your calculation of the lifetime is too simplistic. What is of interest is the lifetime of a CO2 anomalty in the atmosphere, not the individual CO2 molecules. See Greenhouse_gas; http://www.grida.no/climate/ipcc_tar/wg1/016.htm. IPCC tar says the lifetime is "5-200" years (FWIW sar says 50-200) and no single lifetime can be determined. It refers you to ch 3 for the details but they are elusive...

==: Please, IMHO, the lifetime of CO2 or any other atmospheric gas is not relevant to describing the greenhouse effect, nor is the precise quantitative measure of any energy transport method. These issues should be discussed somewhere else ... say for example news on global warming or in Atmosphere Chemistry. We should stick to known science and refrain from speculations in areas that are obviously still basic research. Tanuki

First Paragraph

How about: "The greenhouse effect, discovered by Joseph Fourier in 1824 and first investigated quantitatively by Svante Arrhenius in 1896, is the process in which the emission of infrared radiation by an atmosphere warms a planet's surface." When do I get my brownie points?

Millenddoug

Greenhouse effects is a compilated subject to understand. The whole cycle/process is very confusing. I hope staring at the computer page will help me understand. With confidence, Tino

Clarification needed re effect vs greenhouse operation

From my reading, there is a lot of confusion out there because actual greenhouses do not in principle or practice actually employ the real greenhouse effect re reradiation of infrared. A one sentence clarification to this effect in the first para would be helpful imho. Otherwise it takes a lot of reading to get this important point. (Assuming I am not myself just as confused) —The preceding unsigned comment was added by 167.191.250.81 (talk) 18:45, August 20, 2007 (UTC)

Are you sure real greehouse does not apply greenhouse effect at all? So tell me what is the temperature in a greenhouse that does not trap radiation and it's inbound and outbound radiations are balanced and equal? Wouldn't it bee the same than outside? 82.128.226.51 (talk) 17:47, 29 October 2008 (UTC)

Heat Transfer

The question of re-radition (or not) is not particularly important to an article describing the Greenhouse Effect. The right question to put is "Does the Greenhouse Effect require the transfer of thermal energy aka heat from the troposphere to the surface? And must this occur with sufficient intensity to raise the surface temperatue by 33C?" This transfer, should it be required, requires the extraction of heat energy from tropospheric gas at -19C, which would cool it further, and transferring it to a gas on the surface generally agreed to be at 14C or thereabouts; all this without any external work being done!--Damorbel (talk) 20:52, 8 October 2008 (UTC)

You are aware, I hope, that the whole system runs on solar power. I'm not sure what you mean by "without external work being done," but do keep in mind that there's an incident power of 1.3 kW/m2 driving the entire system. The whole system-- incident heating, greenhouse effect, convection, radiation--all comes from that incident energy falling downhill.

You ask "Does the Greenhouse Effect require the transfer of thermal energy aka heat from the troposphere to the surface?" If, by "transfer of thermal energy" you actually mean "transfer of net thermal energy, then the answer is no: energy flows both directions, but (by the Stefan-Boltzmann law) more energy flows from the surface to the upper atmosphere than flows from the upper atmosphere to the surface, so the net transfer of energy is from the surface upward. However, subtracting the downward flow from the upward flow means that the net flow upward from the surface is less than it would be with no atmosphere, and so the surface temperature has to be slightly hotter compensate, and to stay in thermal equilibrium. This is the greenhouse effect.

Clear? Geoffrey.landis (talk) 21:26, 8 October 2008 (UTC)

Having participated in the thermal design design of Earth orbiting satellites I am quite well aware of many matters connected with heat transfer. And you?

I've taught it. Geoffrey.landis (talk) 13:49, 9 October 2008 (UTC)

You say "If, by "transfer of thermal energy" you actually mean "transfer of net thermal energy, then the answer is no: energy flows both directions". Heat transfer is by nature "net", there is no other kind.

Photons move both directions, upward and downward. Net heat transfer is the difference between the energy carried by the two. If, as you say, you wish to define net heat transfer at the only kind of heat transfer (which you can do if you like to define it that way), then the answer to your question is "NO". The net heat transfer is from ground to atmosphere, not vice versa. The greenhouse effect reduces the net heat transfer upward, but does not make it go the other way. --GL

When a system is in thermal equilibrium there are no thermal transfer processes taking place, no temperature differences, no heat transfer, this is the basic science of heat and also common experience.

Should the Sun heat the troposphere, making it warmer than the Earth's surface, heat would be transferred by radiation from CO2, H2O etc. to the surface, this radiation would tend to cool the troposphere because it would remove thermal energy from it; the surface would tend to become warmer.

When the Sun heats the surface it becomes warmer than the troposphere thus heat transfers from the surface to the troposphere, this tends to cool the surface. But the lapse rate, more or less constant over the global surface, ensures that it is always warmer than the troposphere above. Where then is the mechanism that is supposedly warming the surface by 33C? There is nothing coming from the troposphere to the surface that is going to raise the surface temperature!

If the troposphere is at some temperature greater than 0K, it is going to radiate energy according to the Stefan-Boltzmann equation, P= epsilon sigma T^4 A. If you do thermal design of spacecraft, surely you are aware of this; this is the fundamental equation of heat transfer in vacuum. --GL

There is no interpretation of the redundant term "net" that is going to do this!--Damorbel (talk) 06:25, 9 October 2008 (UTC)

Oh dear, not this again. We can try the very very simple explanation, and see if it helps: "the earths surface receives radiation from two sources: the sun, and the atmosphere. It is therefore warmer than if it received radiation from the sun alone". Happy now? William M. Connolley (talk) 07:15, 9 October 2008 (UTC)

At night, the surface of the Earth cools much faster than the atmosphere. After an hour or so, the lower troposphere is warmer than the surface. The resulting radiation keeps the minimum nightly temperature higher than what would result without an atmosphere. This is easy to demonstrate by observing that clear nights are colder than overcast nights because clouds keeps the surface from cooling as fast. (They block the IR windows.) Q Science (talk) 15:41, 9 October 2008 (UTC)

"Oh dear, not this again". Who is claiming that there is no radiation from the troposphere? (I suggest "troposphere", it is more precise.) The whole of my contribution was about heat transfer, the predictions of the Greenhouse Effect are about temperature rise. It is the nature of the heat transfer that governs the rise or fall of temperature. Heat may or may not be transferred by EM radiation, the temperatures of the sources of EM radiation govern the transfer, the mere presence of EM radiation is insufficient to cause heat transfer.

If the Greenhouse Effect is confusing EM radiation with heat transfer then it is indeed necessary to look at "this again".--Damorbel (talk) 09:28, 9 October 2008 (UTC)

EM radiation, by which I assume you mean thermal infrared, is indeed a significant mechanism of heat transfer; and it's the one that's key in understanding the greenhouse effect.

"Darmorbal" wrote: "There is nothing coming from the troposphere to the surface that is going to raise the surface temperature!"

If the troposphere is at some temperature greater than 0K, it is going to radiate energy according to the Stefan-Boltzmann equation, P= epsilon sigma T^4 A. That's the law of physics; everything radiates. The troposphere too; no exceptions. If you do thermal design of spacecraft, surely you are aware of this; this is the fundamental equation of heat rejection in spacecraft. The analysis of the greenhouse effect consists of simply taking careful account of each of the mechanisms of heat transfer upward and downward.

All I can suggest is, do the thermal analysis before you continue. In fact, you can treat this as a spacecraft thermal transfer problem. Start by considering a thermal box in vacuum. Assume that it has an heat dissipation load of, say, 200 watts/m2. Assuming that this load is dissipated entirely by radiation, and let's assume an emissivity (epsilon) of, say, 0.65. What is the equilibrium temperature of the surface? OK, once you've calculated that, suppose that the thermal engineer decides that this is too low, and wants to increase the temperature by putting a single layer of MLI material around it. Assume that this MLI has an absorptivity (in the infrared) of 0.1, emissivity of 0.1, reflectivity 0.85, transparency 0.05. What is the surface temperature now?

Once you've come up with those two answers (equilibrium temperature with no MLI, equilibrium temperature with one layer of MLI material) we can move on and look at the case of planetary atmospheres. If, as you say, you've done spacecraft thermal transfer analyses, this one will be very easy. Feel free to use the Matlab thermal transfer module or even NASTRAN if you've got it (although it's hardly worth firing up NASTRAN for such a simple problem), but keep in mind that you need to make sure that the code you run includes emissivity, reflectivity, and also transparency for the MLI. Geoffrey.landis (talk) 14:12, 9 October 2008 (UTC)

Your equation P= epsilon sigma T^4 is that giving the power into a void at OK. To get the heat transferred between two surfaces you should account for the temperature of the sink also. You do this by taking the difference of the 4th power of both temperatures (T_a⁴ - T_b⁴). It is put better here: [1] where you can play about with some figures to convince yourself. --Damorbel (talk) 15:09, 9 October 2008 (UTC)

You taught thermal transfer and you used P= epsilon sigma T^4 as heat transfer? Did you mention that this only gives the heat transfer into 0K? For a real thermal analysis you need to replace T^4 with (T_a⁴ - T_b⁴).

As I said earlier, infrared travels both directions. When you say " you need to replace T^4 with (T_a⁴ - T_b⁴)", what you are saying here is that you need to account for the absorbed infrared flux as well as the emitted flux, so since the atmosphere is radiating downward a flux proportional to its temperature to the fourth power, you have to subtract a term for the downward flux.

Exactly. We're saying the same thing, two different ways. You're on the right track here.

So: can you solve the simple thermal equilibrium problem I posed earlier? Go ahead and solve it using an engineering simplification if you like, that's fine. Matlab may help. Once you solve the case of a simple single-layer insulation, you are halfway there to solving the greenhouse effect for a semitransparent atmosphere. I encourage you: do the numbers. There is no better way to understand the physics than to work through the problems, with numbers. Geoffrey.landis (talk) 03:03, 10 October 2008 (UTC)

What do you mean "Photons move both directions, upward and downward."? Do you feel that an analysis with photons will show that the cold troposphere is warming the Earth's hotter surface somehow? This is absurd! Did your students not pull you to bits about this? --Damorbel (talk) 15:59, 9 October 2008 (UTC)

You wrote (at least I presume it was you; it isn't signed properly) "The greenhouse effect reduces the net heat transfer upward, but does not make it go the other way. --GL" Would you care to describe just how you see the "Greenhouse Effect" actually reducing the net heat transfer upward? I have such difficulty accepting that a cold surface can make a net transfer heat by radiation to a warm surface in order to raise its temperature by 33⁰C. The IPCC claims this to be due to "backradiation" [2] , is there a conflict here? --Damorbel (talk) 16:43, 9 October 2008 (UTC)

Can we please take talk to the physics of the greenhouse effect off this talk page? This isn't an atmospheric physics class. - von Atmoz (talk) 17:18, 9 October 2008 (UTC)

Greenhouse effect isn't physics! I know for some it is just politics now but the logic Atmoz's suggestion there would be no place for the whole article. Do you have a reason for dumping the physics discussion, Atmoz? --Damorbel (talk) 17:28, 9 October 2008 (UTC)

WP:NOTFORUM and WP:SOAP come to mind. - Atmoz (talk) 17:36, 9 October 2008 (UTC)

Point taken. This is a controversial matter with manifest technical contradictions. I have attempted to place a section listing a small number; this section lasted a few minutes. Is there a Wiki policy on this? I understand that controversial matters in Wiki should have some place for sound objections, my objective for the moment is to check the matter out in order to be as constructive as possible, I have no taste for edit wars and so forth.--Damorbel (talk) 18:12, 9 October 2008 (UTC)

I have attempted to place a section listing a small number; this section lasted a few minutes. Don't know what you mean. Can you point to the diff please? the predictions of the Greenhouse Effect are about temperature rise - not really; we're mostly talking about steady state here William M. Connolley (talk) 07:51, 10 October 2008 (UTC)

The section I contributed (and its deletion!) it to be seen here [[3]] 8 minutes, even though discussed beforehand. Error - "a small number of deficiencies;

William, a "temperature rise" is also a rise when it is above the equilibrium. Being a knowledgeable authority on Greenhouse matters you will know that the alleged rise has been occuring with time also, but with a short perpective this appears as a "steady state".--Damorbel (talk) 08:52, 10 October 2008 (UTC)

Oh right, well your addition was obviously unacceptable. Lets try getting the time-dependent confusion out of the way: in the real world, things do vary with time, and the GHE effect varies as concnetrations of GHG's change. But we can forget all about that for a moment while we discuss the basics, specifcally your objection The greenhouse effect is described in this article as “ the process in which the emission of infrared radiation by the atmosphere warms a planet's surface”. Such a process would breach the second law of thermodynamics. So: we can consider the steady state. I wrote above: the earths surface receives radiation from two sources: the sun, and the atmosphere. It is therefore warmer than if it received radiation from the sun alone. Do you have any problem with that, in the time-independent case of an idealised non-rotating planet with only radiative transport? William M. Connolley (talk) 09:44, 10 October 2008 (UTC)

Mr. Connolley, you wrote (09:44, 10 October 2008) "time-independent case of an idealised non-rotating planet with only radiative transport? "Idealised non-rotating planet? with only radiative transport?" What is this? Yet another Greenhouse effect? Do try again, I know you can do better.--Damorbel (talk) 11:37, 10 October 2008 (UTC)

It seems like a better idea to study the idealised version first, and agree on that. Maths is below, also here, do let us know how you get on William M. Connolley (talk) 12:07, 10 October 2008 (UTC)

Geoffrey wrote (14:12, 9 October 2008) "In fact, you can treat this as a spacecraft thermal transfer problem" Not remotely, it is an planetary problem of multiple heat transfer processes in an atmosphere (gas in a gravitational field). The matters you mention are irrelevant to the defects I have identified. The Greenhouse Effect claims radiation from the troposphere raises the surface temperature above its equilibrium. I object to this because it requires a heat transfer process never previously observed. I invite you to substantiate the claimed warming effect in the light of my objection. You may of course agree with me, and let a note of my objection be put in the article.--Damorbel (talk) 08:28, 10 October 2008 (UTC)

It can be treated, in simplified form, as a very basic problem indeed. See the maths, which I provided here. Do you disagree with any of that? With your background you will have no trouble understanding it and pointing out any problems William M. Connolley (talk) 11:21, 10 October 2008 (UTC)

Checked your maths, provided here. Actally I looked in the archives [[4]] to find the full background. Your maths is good but it is the wrong physics. Heat flows according to the energy of the photons, i.e. the temp., not the intensity (W/m²) basics are here at hyperphysics. From this you should be sure you get the full meaning of the (T_a⁴ - T_b⁴) term. The explanation you gave in the archives just adds the intensities (W/m²) e.g. "the radiaton downwards at the sfc is S1 + erU^4" and "The radiation up is rT^4; hence rT^4=S1+erU^4 " But the heat transfer is zero unless T⁴ and U⁴ are different, this is what the hyperphysicslink is all about. I have been pushing the temperature hard because GH effect article does not pay attention to it. The argument is the same as that used by a certain Mr. A Einstein when explaining the Photo Electric Effect It is also the basis of the Second Law of Thermodynamics. --Damorbel (talk) 15:01, 10 October 2008 (UTC)

At night, the atmosphere is warmer than the surface. You are trying to use a static analysis and are ignoring the fact that the Earth turns. Q Science (talk) 17:57, 10 October 2008 (UTC)

Q: I certainly am, for these purposes, as a simplification. D: OK, good, we are onto the maths. I'm afraid its not clear to me exactly where you think the (simplified) physics is in error. You accept that (a) the downward radiation at the sfc is S1+erU^4; and that the upwards radiation at the sfc is (b) rT^4. Therefore, in my world, in equilibrium we must have the two terms being equal. You say "But the heat transfer is zero unless T⁴ and U⁴ are different" and refer me off somewhere else. I don't know what you disagree with. Once you have accepted (a) and (b) I don't see what you can do. Please write down what you believe to be the radiation balance of the sfc, in that situation. And if you use titles, get them right: E wasn't a Mr, of course William M. Connolley (talk) 22:28, 11 October 2008 (UTC)

The GHE article [[5]] claims:- "The surface temperature will rise until it generates thermal radiation equivalent to the sum of the incoming solar and infrared radiation" Because the so-called GHGs radiating in the troposphere are at a lower temperature than the surface, this warming claimed for the GH effect is contrary to Einsteins analysis of the Photoelectric Effect and the Second Law of Thermodynamics. The PE effect and 2nd Law both state very clearly that the lower temperature (thus lower energy) radiation cannot increase the temperature (energy) of material already at a higher temperature. To clarify the PE effect. Einstein noted that, however many (many = power) photons struck a surface, no electrons would be ejected unless the individual impacting photons had higher energy than surface (i.e. came from a hotter source). If you don't know about this you should get a course in quantum mechanics [[6]] In your calculations you bundle radiation from the Sun and the Troposphere without taking account of the different temperture of the sources (downward radiation at the sfc is S1+erU^4) S1 is radiation from a source @5780K, U is radiation from a source @254K S1 has no problem warming the surface to 288K but the Troposphere cannot warm the surface to 288K because it is only @254K, you should not really need QMech. to understand this.

A lot of words, but no substance. Once again: I've written down my surface radiation balance, from which my conclusions follow. I've asked you to write down yours, and you haven't. Please do (and for bonus points, also calculate your predicted surface temperature in terms of the given quantities) William M. Connolley (talk) 20:41, 12 October 2008 (UTC)

Ah, I think I see you mistake. Never mind, we can thrash it out later, for now just write down your sfc radiation budget and we'll take it from there William M. Connolley (talk) 21:38, 12 October 2008 (UTC)

By the way, Einstein did this work in 1905, almost certainly before he got his PhD since he submitted his thesis in April. [7] I think he published his PE paper [8] in March 1905, so it was perhaps Herr Einstein, not Mr. --Damorbel (talk) 18:09, 12 October 2008 (UTC)

Yes, if you're going to weasel out of not using Dr/Prof, you need to use Herr. In no way is Mr appropriate William M. Connolley (talk) 20:41, 12 October 2008 (UTC)

Radiate vs. reradiate again

The radiate/reradiate discussion seems to have dies down, but I present the following in case of a flareup. In the spring 2003 edition of the The Wilson Quarterly, V. Ramanathan and Tim P. Barnett describe the greenhouse effect as:

Atmospheric gases, such as water vapor and carbon dioxide, absorb infrared energy emitted by the planet's surface that would otherwise escape to space. These gases also emit infrared energy into space, but because the surface of the planet is, on average, much warmer than the atmosphere, the eventual result is a net trapping of infrared energy within the atmosphere. (Atmospheric gases absorb some incoming solar radiation as well, but this has only a negligible impact.) This reduction of the outgoing infrared energy by atmospheric gases is what we call the greenhouse effect.

Their description is very similar to the wording that is currently used in the lead and the basic mechanism section [9].- Atmoz (talk) 14:00, 11 October 2008 (UTC)

Ramanathan & Barnett make the same mistake as the Wiki article, even claiming an equivalence between the downward radiation/m² and that of a 250W lamp! No account at all is taken of the difference of temperatures, 254K for the Troposphere and 2700K for a tungsten lamp. As noted above, there can be no surface warming effect from radiation originating in the Troposphere on account of its lower temperature.--Damorbel (talk) 18:44, 12 October 2008 (UTC)

I suspect Ramanathan knows radiative transfer and its implications better than >99.999999% of Wikipedia editors. But if you're convinced he doesn't even understand basic principles such as this, you would be doing him a favor by emailing him with an explanation of how he's managed to get everything wrong for the past 40 years. Short Brigade Harvester Boris (talk) 20:08, 12 October 2008 (UTC)

I am not here to cite authorities. If you wish to believe that a cold surface can raise a surface already warmer to an even higher temperature by radiation then that is your belief, but it there is no experimental evidence for this. For more than 100 years this zany has only been found in the domain of perpetual motion, it will take a lot more than the GH hypothesis to displace one of the most solid laws in science. http://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Quotes Good luck, but don't count on it!

Another thought, since there so much confidence in your guru. Have there ever been measurments to show this kind of heat transfer taking place? I mean, everything I have read on AGW seems to be based on this "back radiative heat transfer mechanism" and similar propositions such as the Earth emits as a black body. This latter is equally impossible. Most of the Earth's heat is emitted by CO2 and H2O vapour which are about as far from the black body model as you can get. --Damorbel (talk) 21:25, 12 October 2008 (UTC)

You've been raising this same tired issue for over a year now, and convinced no one. Has it not occured to you that perhaps you are the one who is misunderstanding thermodynamics? There is no conflict between the second law and the greenhouse effect. The only conflict that exists is the one you have invented in your head by misunderstanding the implications of the second law. Dragons flight (talk) 22:13, 12 October 2008 (UTC)

Dragons flight, may I have relevant details of what you object to in my contribution, then we can compare them? For the moment you seem to be hiding them! Do you have anything to say about the surface being warmed by the troposphere? Let us hear it! And be so kind as to give the version of 2nd Law of thernodynamics that you use (there are a number).--Damorbel (talk) 07:57, 13 October 2008 (UTC)

Raval, A. and V. Ramanathan (1989), Observational determination of the greenhouse effect, Nature, 342, 758 - 761, doi:10.1038/342758a0 - Atmoz (talk) 02:11, 13 October 2008 (UTC)

Atmoz, do you have full access to your link? I can't get a copy. Does it explain the warming process, or just the radiation balance?. If Ramanathan can show that there is a surface temperature rise due to radiation from the colder troposphere it would revolutionise science.

Further note for Dragonsflight. If the cold troposphere were shown to warm the hotter surface the whole of physics would be revolutionised! If you could show this you would become v. famous, you would wipe Einstein off the face of science! Is this what you mean by a tired issue . The fact that you don't recognise the importance of the issue would suggest that you haven't actually studied thermodynamics. --Damorbel (talk) 08:19, 13 October 2008 (UTC)

The cold troposphere was known to contribute heat to the warm surface in the 19th century (Arrhenius 1896 [10], and probably others). Hardly revolutionary. As to my objecions, you already have them in the previous times you have raised this nonsense. The second law deals with the systemwide transfer of energy. In a thermodynamically coupled system the net transfer of heat is always from warm to cold (in the absense of applied work). However, the internal transfers of energy can and do consist of both an upward and a downward flow and it is only the net transfer that is constrained by the second law. You repeatedly have said their can be no downward flow at all. This is simply wrong, and you have never given any justification for it other than repeating your tired interpretations of what you mistakenly believe the second law means. Dragons flight (talk) 15:01, 13 October 2008 (UTC)

For the surface to be warmed by radiation there has to be a net transfer of energy away from the troposphere to the surface. If the troposphere is colder than the surface, how does it happen? --Damorbel (talk) 19:53, 13 October 2008 (UTC)

No, the point of the greenhouse effect is that surface is warmer than if there was no atmosphere. The downward radiation from the troposphere partially offsets the radiation that the surface will emit regardless. It is still a net transfer from warm to cold, but the warm body disspiates heat less rapidly than if the atmosphere didn't exist and the Earth was simply radiating directly into space. Since the sun is ultimately pumping heat into the system, the ability to dissipate heat less rapidly due to the atmosphere has the effect of causing the Earth to reach a higher steady state temperature. Dragons flight (talk) 20:02, 13 October 2008 (UTC)

You suggest "the warm body disspiates heat less rapidly than if the atmosphere didn't exist" I think you are close to the real reason why the Earth is at 288K and not 254K. The argument for 254K is made here [[11]] but it has a serious defect, clear in the first line where it says "planet with the power emitted by a blackbody of temperature T". But the Earth is far from being a blackbody, it is covered with water, clouds and CO2, it reflects quite a lot of radiation (albedo) and has a very irregular spectrum [[12]] in the infrared, nothing "black" at all. The fault is in this formula $T=\left({\frac {L(1-A)}{16\pi \sigma D^{2}}}\right)^{\tfrac {1}{4}}$ the term (1-A) is equal to the absorptivity of a material "α" that is not perfectly black (the non absorbed radiation is the albedo). Kirchhoff's law states that, for a body in thermal equilibrium, the absorptivity equals the emissivity, (α=$\epsilon$). So the term (1-A) should be replaced by α/$\epsilon$=1 since a planet can only receive and lose heat by radiation. The equilibrium temperature is thus about (279+3)=282K (3K cosmic background). Thus by taking the correct emissivity there is no need postulate the questionable Greenhouse Effect to account for a massive 33K rise in surface temperature above a (supposed) equlibrium of 254K.

I already have a copy of your reference to Arrhenius 1896 [13], it isn't very clear that he describes the GHE as it is now understood, particularly the 254K equilibrium temperature. What seems to me the important mistake is not using Kirchhoff's law as his point of departure, i.e. the same mistake as the GHE. --Damorbel (talk) 08:39, 14 October 2008 (UTC)

So your argument here is because replacing 1-A with 1 gives 277 K instead of 255 K that ignoring the Earth's albedo is the natural way to explain our temperature of 288 K, and hence we should ignore all those details like the absoprtivity and reflectivity of the atmosphere and any notion of a greenhouse effect? Kirchoff's Law only implies that appropriately averaged over wavelength absorptance and emissivity must be equal, there is no requirement that they both equal 1. Dragons flight (talk) 09:17, 14 October 2008 (UTC)

"no requirement that they both equal 1." That is correct, it is only the ratio is also equal to 1, otherwise there would be a net heat inflow which could never escape and the temperature would always reach that of the source; however far away. No net outflow either because the temperature would then drop to that of the sink, 3K.

Any symmetrical object, even a glass or metal ball, illuminated by a star will stabilise at the equilibrium temperature of the given distance. The temperature distribution in the object may be such that only a small part is actually at this equilibrium temperature but that is another matter. For example, the atmosphere affects the surface temperature because gravity gives it a natural temperature gradient, the lapse rate. Because of this the average surface temperature is above the equilibrium. Venus has a much hotter surface because its atmosphere is 90 times more massive.

Kirchhoff's law is quite consistent with EM theory which states that all radiation absorption and emission comes from accelerating charges. For a planet it is the same accelerating charges that absorb and emit, there are no others!--Damorbel (talk) 11:41, 14 October 2008 (UTC)

$1-A\approx \alpha \approx 0.7$. Albedo is directly a measure of the reflectivity of sunlight and hence 1-A is directly related to the absorptivity of sunlight. You don't get to ignore the fact that 30% of sunlight is reflected back into space just because it would be more convenient in making your numbers work out. So the above gives 255 K. Dragons flight (talk) 16:28, 14 October 2008 (UTC)

That is OK if you can show that Earth radiates like a black body. But you know that most of the radiation comes from CO2 and H2O which only radiate in bands which mean its "coloured". A black body is the most efficient radiator possible, it is so efficient because it radiates in all bands with its characteristic shape. Gases aren't like a blackbody because there are gaps in their emission spectrum where no energy can pass, that why they are less efficient than a blackbody. A less efficient radiator will have to get to a higher temperature than a blackbody to get the same heat out. You remarked yourself "ability to dissipate heat less rapidly due to the atmosphere has the effect of causing the Earth to reach a higher steady state temperature". Well that is true, it is to a great extent because the atmosphere is a less efficient radiator than a supposed blackbody than the Earth, it is why the Earth is at a higher temperature than a black body emitter.--Damorbel (talk) 19:41, 14 October 2008 (UTC)

And now you are so close to describing the greenhouse effect... --Stephan Schulz (talk) 11:51, 18 October 2008 (UTC)

So close indeed but without GHGs. The full implication of Kirchhoff's law means that the equilibrium temperature is independent of the albedo, completely at variance with most versions of the GH Effect.--Damorbel (talk) 19:06, 19 October 2008 (UTC)

Question - Does Kirchhoff's law of thermal radiation apply to gases that also get heat from conduction? It seems that, in that case, the gas can radiate more heat than absorbed from radiation alone. Q Science (talk) 00:37, 20 October 2008 (UTC)

Yes, it can get a little confusing but Kirchoff's law still applies. Note that Kirchoff's law deals with emissivity, i.e., emission of radiation in proportion to that of a black body emitting at the same wavelength, and not emission. Same emissivity (per Kirchoff) but higher temperature = more total emission. Short Brigade Harvester Boris (talk) 01:19, 20 October 2008 (UTC)

Thanks Q Science (talk) 02:29, 20 October 2008 (UTC)

"get heat from conduction?" Kirchhoff's law of thermal radiation is for matter in Local Thermal equilibrium, i.e. no other heat source or sink, the condition closely reproduced in an orbiting planet--Damorbel (talk) 16:33, 1 November 2008 (UTC)

Re:

Gases aren't like a blackbody because there are gaps in their emission spectrum where no energy can pass, that why they are less efficient than a blackbody. A less efficient radiator will have to get to a higher temperature than a blackbody to get the same heat out.

I believe this comment in the talk above is an incorrect view of what is going on in greenhouse effect. The SURFACE of Earth is hotter, but the gases higher in the atmosphere --that absorbed heat from the earth-- are at lower pressure and hence temperature; the lower temperature they are radiating at is what makes them a less efficient radiator. I'm looking at sources now, to clarify this detail in the article (there is some mention of temperature differences, but it could be sharpened).ToolmakerSteve (talk) 09:16, 3 November 2008 (UTC)

Hi Damorbel. I've read quite a lot of this discussion, and don't pretend to understand most of the maths (I'm a biologist, we're generally not too strong on that stuff!). However, I do think I can see where you're coming from and would like to try an analogy to see if it helps.

As far as i can tell, the following is the crux of your argument - 'there can be no surface warming effect from radiation originating in the Troposphere on account of its lower temperature'. Now my understanding is that this comes from the net transfer of heat always being from hotter to colder (forgive the layman's terminology!).

This sounds to me a little like diffusion - which you probably know is the net movement of molecules from a region of higher concentration to a region of lower concentration by random molecular motion. However, while the NET movement is to the region of lower concentration, there are some molecules which do just the opposite (the motion is random!). The very fact that diffusion is the 'net' movement implies there is motion in more than one direction.

Hmm...not quite as clear as it was in my head (and not being a physicist there migh be something i don't know about that makes this analogy nonsense), but hopefully it will help. ````

It is actually simpler than that. In the morning the ground is colder than the atmosphere a few hundred feet above. (See Lapse Rate - Plot and Definitions, drag the zoom controls in the lower panel to see the morning temperature inversion.) Thus, every night heat follows from the atmosphere to the ground. This keeps the ground from getting as cold as it would without the atmosphere and results in an increase in the average surface temperature. The confusion results from applying static equations to a dynamic problem. Q Science (talk) 21:15, 13 November 2008 (UTC)

I like he explanations of the Lapse rate and the analogy of diffusion. These should be mentioned on these pages Greenhouse effect and Earth's energy budget.Veteran0101 (talk) 03:33, 10 December 2008 (UTC)

Thermal equilibrium vs steady state

The very first sentence in this article is wrong because it confuses thermal equilibrium with steady state. In thermal equilibrium there is no greenhouse effect, because that would be a violation of 2.law of thermodynamics and Kirchhoff law. This also seems to be a source of confusion for many people who discuss on this page. If Earth received certain amount of energy from the Sun and radiated this energy back to Sun, that would be thermal equilibrium; if it receives some energy from Sun and radiates this energy into [colder] space, so that its temperature stays constant, it is known as steady state.213.220.211.183 (talk) 10:45, 20 January 2009 (UTC)