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Real greenhouses
"This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature will drop considerably"
That example does not demonstrate that a greenhouse functions by reducing convection, rather it demonstrates that if you let hot air out of a greenhouse, it will be replaced with cooler air from the outside. To prove that the greenhouse effect is due primarily to convection, one would keep the windows closed and run a fan inside a greenhouse, which would be and example of forced convection. Convection is the physical transportation of energy from one place to another. Convection will not occur unless there is a temperature difference between two locations. Once that energy is transported, it is either radiated or conducted away from there -- as it must in order to maintain the temperature difference that created the convection to begin with. Only if there is no temperature difference in a greenhouse will there be no convection (as can be the case for small greenhouses, but not large ones).
The article itself refers to the technical description of the greenhouse. In this article the choice of the material is based on retaining the infrared radiation in the greenhouse. All long wave IR radiation (the heat) will be kept inside the greenhouse. 120.28.8.19 (talk) 16:03, 10 October 2009 (UTC)
Even if convection were suppressed inside a greenhouse (which would be desirable in order to reduce heat loss), the mechanism for radiation and conduction are not affected, and convection outside a greenhouse will cool it down every bit as much as convection inside a greenhouse. If the real greenhouse effect were due solely to suppressed convection, many tin roof half-round aircraft hangars should also exhibit the greenhouse effect, yet they do not.
It has also been demonstrated experimentally (Wood, 1909) that a 'greenhouse' with a cover of rock salt heats up an enclosure similarly to one with a glass cover
This information did not come from a peer-reviewed scientific journal, where the outcome has been replicated by anyone else in the scientific community. It is an example of an opinion and hearsay and therefore should be taken out of the article.
That is not the point. Empirical data is convincing enough. The explanation for the rise of temperature is wrong, but I don't know if this information is in the article itself. It is only said that the temperature will rise according to the article. 120.28.8.19 (talk) 16:03, 10 October 2009 (UTC)
"Greenhouses thus work primarily by preventing convection; the atmospheric greenhouse effect however reduces radiation loss, not convection"
If the atmospheric greenhouse effect operates differently from a real greenhouse, then it is not actually a greenhouse effect, but something else -- what is that "something else", i.e. -- if the "greenhouse effect" has only one meaning, then they are not operating differently, they are operating the same. If the "greenhouse effect" has more than one definition, that other definition was not conveyed.
Since the Earth exists in the vacuum of space, it cannot lose heat via convection or conduction, so it can only loose heat by radiation. If the atmospheric greenhouse effect "reduces radiation loss", that would imply that the Earth is not in steady state
The actual greenhouse effect is due to re-radiation of objects (or gases) as explained in numerous sites such as:
Planetary Radiation Budget and the 1-Layer Greenhouse Effect http://hope.simons-rock.edu/~geshel/physci134/1layer/1layer.html
Understanding the Greenhouse Effect http://www.ldeo.columbia.edu/~kushnir/MPA-ENVP/Climate/lectures/energy/Greenhouse_Effect.html
On the Phenomenon of Atmospheric Backradiation http://www.geocities.com/atmosco2/backrad.htm
- Here is a quote from the above referenced (internet, not peer reviewed) article:
////"Fig. 1 reminds us that the temperature in the troposphere decreases with increasing height, and may also call to mind the Second Law of Thermodynamics (in Clausius’ formulation): “Warmth can never pass from a colder to a warmer body unless another related change occurs at the same time” (cf. Baehr, [11]), or more simply “Warmth can never spontaneously pass from a body of low temperature to a body of higher temperature” (see Schmidt, [12]). The Law may raise doubts about how “atmospheric backradiation” can work. In fact, properly considered, it already suggests that “atmospheric backradiation” is a mirage."//// The author of the internet page does not understand thermodynamics and radiative transfer. The imbedded quotations are gross oversimplifications, the kind of thing that is taught in grade school. Actually, to a scientific mind, they're idiotic. The term 'warmth,' besides having no scientific meaning, is meant to indicate the relative amount of thermal heat as measured by a temperature difference. Warmth has no relation to power or radiation in this context, power and radiation having scientific meanings. To understand back radiation, you have to understand various scientific terms: power, as in radiated power, thermal energy, thermal conductivity (zero in a vacuum), radiative power transfer (can occur in a vacuum), temperature (where differences in temperature drives thermal energy from one place to another place within matter where the thermal conductivity is non-zero, i.e. sufficiently large given the time scale of interest). Once you understand how these various properties interact, the concept of back radiation is quite easy to grasp. You just have to be careful, clear, and avoid completely terms that are not well defined. And you have to follow the long version of the laws (esp. in thermodynamics), the one that have all the contraints to be met, and those constraints are sometimes expressed in a single word- which of course can not be ignored or misinterpreted. I'll stop here until I get some feedback that shows interest in approaching the subject with the required level of rigor. blackcloak (talk) 08:18, 26 June 2009 (UTC)
- The above comment is a resort to the logical fallacy of ad hominem. We can dismiss an article because we think it isn't peer reviewed, but we cannot dismiss an article if it is constructed using scientifically accepted principles of reasoning. There are excellent bibliographic references at the end of the article for the claims made, and those would need to be discredited as well, in order to discredit the entire article -- and that has yet to be done. The peer reviewed journal, SCIENCE, is "Internet reviewed", so being being "Internet reviewed" does not prove something has not been peer reviewed or cannot be peer reviewed -- in fact, we are peer reviewing Heinz Thieme's article as we speak. See http://en.wikipedia.org/wiki/Peer_review. Furthermore, it is not enough to claim that the author does not understand thermodynamics and radiative transfer, you need to prove it. Mere say so is not enough and is another example of ad hominem. The above comment finally ends with a challenge that "I know all there is to know about this [supposedly] extremely complicated topic but I am not going to share my knowledge [even though that is why we are here] unless you act and think like I tell you to" -- to which Albert Einstein would reply that, “If you can't explain it simply, you don't understand it well enough”. Obviously that challenge was a dodge and evade for giving us any actual facts or simple explanations. I don't play that game, so if we eliminate all the ad hominem from the above comment, what is left of the argument above? Nothing, so let me add something to demonstrate just how simple the concept of backradiation is, and therefore how well I understand it. Presume the glass used in a Greenhouse is transparent to shortwave radiation and opaque to longwave radiation. Any radiation absorbed by the glass will be re-emitted in all directions equally, therefore 50% of the radiation absorbed by glass will be re-emitted back into the Greenhouse. If 100% of the Sun's predominantly shortwave radiation is absorbed and the re-emitted as infrared radiation by objects in a Greenhouse, the glass will absorb and re-radiate 50% of that energy back into the Greenhouse. So now the total energy received by the objects inside the Greenhouse will be 150% that of the Sun alone. Now 50% of that 50% will be absorbed and re-emitted back into the Greenhouse, and so on and so forth until the limit of this geometrical series is reached, at which point the total sum of energy in the Greenhouse will be 200% that of the Sun alone. This is what is called the Greenhouse effect by way of backradiation. —Preceding unsigned comment added by HY1802D (talk • contribs) 19:25, 30 June 2009 (UTC)
- So? Go on. Finish your thought. Please. Do you see confirmation or contradiction? Don't make us guess. You know how to be direct, but can you be both complete and consistent? That is the question. (Sorry, poetic license.) blackcloak (talk) 02:24, 1 July 2009 (UTC)
- Tell me which word(s) didn't you understand in any of my comments and I will see if it is possible to help you answer your question. —Preceding unsigned comment added by HY1802D (talk • contribs) 20:43, 1 July 2009 (UTC)
- Did I say I had a problem with any of your words? Rest assured I understood every one of your words. It's your sequences of words, while strung together in gramatically correct fashion, that don't seem to lead to a clearly stated, logical, unambiguous conclusion. For instance, are you saying that one may infer that the 200% number means that conservation of energy is violated and therefore your (counter) example forces us to conclude that back radiation can not be the correct (dominate) explanation for the greenhouse effect? There are a bunch of other points in your discussion that should be challenged, but, before I attempt to show you where you've made mistakes, I want to understand precisely where you are trying to take us with your reasoning. blackcloak (talk) 08:25, 2 July 2009 (UTC)
- One of the many points I made is that just because the temperature of greenhouse will drop "considerably" when opening a small window near the roof of the greenhouse, does not prove that a greenhouse heats up due to lack of convection, as the Wikipedia article still incorrectly points out. No, to prove that assertion would require keeping the window closed and putting fans inside the greenhouse to see if the temperature would drop considerably -- as it must if the greenhouses-work-by-suppressing-convection "theory" were true. But of course the blind faith assertion that the greenhouse effect is due to a lack of convection isn't true at all, as evidenced by actual greenhouses in which convection is encouraged. A simple Google search for "greenhouse circulation fans" will reveal an overwhelming number of examples of actual greenhouses with circulation fans in them. Seeing as convection is a low volume phenomenon, the high volume circulation fans should completely destroy the greenhouse effect, but they don't. Is that simple enough for you, or do you need a still simpler explanation -- I can draw pictures for you if necessary (HY1802D (talk) 01:19, 2 August 2009 (UTC))
- I need a more coherent, not simpler, explanation. But just to set the record straight, let's figure out what your understanding is of the phrase "greenhouses-work-by-suppressing-convection." Is it your understanding that the phrase refers 1) to convection of air inside the greenhouse (i.e. outside air is not relevant), or 2) to preventing convective flow between air inside the greenhouse and the air outside the greenhouse? Please answer by telling us if you believe the phrase refers to number 1 or number 2. You don't have to say anything more, except if neither description matches your understanding. Your record of responding to questions directly is very poor. This makes you look like your modus operandi is evasion, which suggests that you have ulterior motives for participating in this forum. blackcloak (talk) 19:24, 6 August 2009 (UTC)
This explanation is very consistent with what the rest of the scientific community has always claimed about the greenhouse effect, and it is the same explanation given for a real greenhouse, as is for the atmospheric greenhouse effect. Furthermore, if you look at the radiation budget for the Earth, convection only accounts for 7% of that budget, whereas the rest is accounted for by other things such as the greenhouse gases. —Preceding unsigned comment added by HY1802D (talk • contribs) 22:02, 10 June 2009 (UTC)
"This mechanism is fundamentally different from that of an actual greenhouse, which works by isolating warm air inside the structure so that heat is not lost by convection." , needs a reference of convection based heat-loss on the earth unless only the surface temperatures are meant... Does the nightside of the earth lose molecules and atoms more than the dayside, what is the difference? True the convection rises water vapor which then rains but does this happen in the planetary level?? True the energy of the vaporization takes temporarily cools the nearby surface temperatures. 85.156.31.132 (talk) 07:04, 20 June 2009 (UTC)
- Suppressed convection is not the principle by which the greenhouse effect works -- neither in greenhouses nor for the Earth's Radiation Budget. Visit the links I posted above and read the proper explanation of the greenhouse effect as given there. —Preceding unsigned comment added by HY1802D (talk • contribs) 01:14, 2 August 2009 (UTC)
- Ok, so after all this discussion, why does the article continue to insist in the lede that "This mechanism is fundamentally different from that of an actual greenhouse, which works by isolating warm air inside the structure so that heat is not lost by convection." Quite apart from the many objections to this claim raised above, the Wikipedia article Solar greenhouse itself cites as the two main mechanisms of a solar greenhouse "1. Thermodynamically isolate the system to stop convection and conduction from equalizing the inside temperature with the outside temperature. 2. Provide a covering with a controlled difference between the transparency in the solar radiation band (280 nm to 2500 nm wavelengths) and the terrestrial thermal radiation band (5000 nm to 35000 nm), for the purpose of either raising or lowering the temperature inside the greenhouse." With regard to the latter it says "A greenhouse covering which is more transparent to the solar radiation band and less transparent to the thermal radiation band will result in a temperature higher than the surrounding environment, and a greenhouse covering which is more reflective of solar radiation and more transparent to thermal radiation will lower the temperature relative to the surrounding environment.[1]"
- Conservatives needing an outlet for their pet theories of how greenhouses "really work" have Conservapedia at their disposal for such misinformation; please use it, it is an excellent way of avoiding Wikipedia articles that flatly contradict each other. The Conservapedia article on greenhouses claims that "The heat comes from sunlight's infrared spectrum, which is used in the heat lamps that keep McDonald's french fries warm." This raises the interesting question, if thermal radiation (the kind McDonald's uses) comes from sunlight, what happens to the solar radiation (280 nm to 2500 nm) constituting over 98% of the heating energy of the Sun even before it reaches Earth? And how does this thermal radiation get through the atmosphere, which is opaque to thermal radiation but transparent to solar radiation? The truth of the matter is that the earth is heated essentially entirely by solar radiation defined as radiation from 280 to 2500 nm. The sort of thermal radiation used by McDonald's, which is at a wavelength an order of magnitude longer than solar radiation, is a really tiny component of sunlight's spectrum that contributes essentially nothing to the warmth of the Earth! No wonder conservatives are so muddle-headed about science when they run around repeating made-up science factoids like that to each other. --Vaughan Pratt (talk) 02:50, 7 November 2009 (UTC)
Why remove so much?
Boris, that is about half the article. I understand if you then link to the information elsewhere, but you didn't provide a link. What's up? Q Science (talk) 04:18, 7 July 2009 (UTC)
- It was just an unreadable mess -- not literally unreadable in the sense of not being parseable as English, but redundant and confusing. It was too convoluted for the layman and yet not meaty enough for an expert. I think the "basic explanation" is enough for this article and then we can go on to discuss anthropogenic effects, greenhouse effects on other planets, comparison to real (agricultural) greenhouses, and so on.
- Arguably there is room for a more detailed explanation but I considered the material beyond repairing in the usual incremental way -- better to blow it up and start from a clean slate. Short Brigade Harvester Boris (talk) 04:44, 7 July 2009 (UTC)
It is like the cheshire cat, soon there will only be a smile(y)!--Damorbel (talk) 05:41, 8 July 2009 (UTC)
Pure greenhouse effect not mentioned
Although the article (properly) says that absent the greenhouse effect, Earth's temperature would be around -17 deg C, it nowhere mentions that without the extensive climatic heat-dumping mechanisms of convection, evaporation, condensation, precipitation, and atmospheric circulation generally, the greenhouse effect would produce a temperature of around 70 deg C. Why not? -- Craig Goodrich 68.58.2.165 (talk) 19:43, 2 October 2009 (UTC)
- Well, I suspect because this is an article on the greenhouse effect, and not on atmospheric dynamics, general circulation, and general climate. Also, do you have a reliable source for that claim? 70°C where? I suspect there are a number of simplifying assumptions in any calculation coming to that result... --Stephan Schulz (talk) 21:10, 2 October 2009 (UTC)
- Do I understand you correctly Stephan, the Greenhouse Effect can be described without reference to "atmospheric dynamics, general circulation, and general climate"? I would agree that predicting a mean temperature of 70°C might prove a tad difficult but surely not much more challenging than the already massive 33°C increase generally attributed to the GHE.--Damorbel (talk) 19:22, 10 November 2009 (UTC)
The GHE can indeed be usefully described wihtout ref to atmos dynamics. However, does anyone have a clue what CG means by "...would produce a temperature of around 70 deg C", and a ref for it? William M. Connolley (talk) 21:07, 10 November 2009 (UTC)
- I have struggled without success to find any explanation (or a ref.) for the GHE with the answer "+33°C" increase due to GHE radiation"; lots of assertions, hypotheses, probabilities etc. but no maths.
- CG's "70 deg C" is just over double the highly improbable 33°C of the GHE when just a °C or so change is enough to start a hurricane, so why must he have a ref. for it? --Damorbel (talk) 21:41, 10 November 2009 (UTC)
- We know, from repeated discussions, that you either don't understand or intentionally reject the widely accepted and fairly basic physics of the greenhouse effect. I'm not giving it another try. If he wants it in the article he needs to have a ref per WP:V. --Stephan Schulz (talk) 21:55, 10 November 2009 (UTC)
- If you've struggled without success, you haven't looked too hard. Try http://en.wikipedia.org/w/index.php?title=Climate_model&oldid=24670575, the "Zero-dimensional models" (unfortunately some bozo has broken the current version) William M. Connolley (talk) 23:02, 10 November 2009 (UTC)
- Thanks for the link. The relevants errors in this "explanation" are to be found in this quotation from your link:-
- "It is possible to obtain a very simple model of the radiative equilibrium of the Earth by writing
- where
- the left hand side represents the incoming energy from the Sun
- the right hand side represents the outgoing energy from the Earth, calculated from the Stefan-Boltzmann law assuming a constant radiative temperature, T, that is to be found,
- and
- S is the Solar constant - the incoming solar radiation per unit area - about 1367 Wm-2* a is the Earth's average albedo, approximately 0.37 to 0.39
- r is Earth's radius - approximately 6.371×106m
- π is well known, approximately 3.14159
- s is the Stefan-Boltzmann constant - approximately 5.67×10-8 JK-4m-2s-1
- The constant πr2 can be factored out, giving
- "
- Like all the other Greenhouse effect science your explanation is based on a false assumption, namely that the Earth radiates heat like a black body (in the infrared). This assumption is mistaken, when considering radiation a body cannot be partially "black", either it is black or it is not. If it reflects (or transmits) any radiation it is not a black body.
- Your formula has, quite rightly, the Earth absorbing that fraction of the Sun's radiation not reflected (as the albedo). But the absorbing of radiation is done by the same mechanism as emission, the acceleration of separated electric charge. Not all material can absorb because it has no separated electric charge to accelerate; thus some radiation is reflected or more accurately: scattered. Since it does not absorb, it cannot radiate either because it lacks separated charge. More information about separated charge here electric dipole moment. This is the science behind Kirchhoff's law of thermal radiation that, when properly applied, informs us that the actual equilibrium temperature of a planetary body, without an internal heat source, is independent of its albedo.
- What causes a lot of confusion is the apparent temperature of a planetary body when its infrared signature is used as a measurement. The infrared signature of a body is only accurate for a body that really is black (by Kirchhoff's definition, thus neither reflecting nor transmitting). Two bodies in the same orbit, one of black carbon (albedo 0.05) and one gold plated (albedo 0.95) will have the same actual temperature but wildly different infrared signatures, giving appartently equally wildly different temperatures. To find the real temperature you need to find either the emmissivity or the absorbtance of the bodies, which can be very difficult.
- I recommend you think about this "black body (in the infrared)" idea because I suggest "you haven't looked [at it] too hard". A yellow coloured body is not "black" in the blue part of the spectrum nor is a red body black in the green and the blue.
- Correcting this mistaken "black body (in the infrared)" assumption means that the Earth's equilibrium temperature should be calculated at about 279K, not the 246K to 248K predicted in your link. Using the temperature derived by the correct analysis leaves precious little room for the greenhouse effect.--Damorbel (talk) 12:51, 11 November 2009 (UTC)