Discussion > An experimental demo of GHE.
Dung -
Really? Do you think he will be in drag at the pub when they meet in Oxford tomorrow?
I am looking forward to it already!
matthu
I thought of an improvement to the Berthold Klein experiment with the Mylar balloons with various concentrations of CO2. Based on things suggested by Lindzen I believe that there is a level of CO2 ppm above which there is no heating effect. I believe that this experiment proves that there is no heating effect at the current 400 ppm or at higher levels. However they did not perform this experiment with lower levels of CO2 which perhaps could have told us (if Lindzen is correct) at what level CO2 ceases to have any further effect.
Performing this experiment at lower levels of CO2 could either depress me totally or could end the argument about the GHE for ever hehe.
If the lower levels of CO2 in the balloons showed no warming at any level then we learn nothing since it could point to the experiment not being a reliable test. However if there was warming at low levels which ceased when a certain level was reached then the experiment is shown to be valid.
Dung
Dung
There is no doubt that CO2 and gaseous H2O (water vapour) absorb IR energy. However the energy absorbed does not increase the kinetic energy of the molecule and does not therefore increase the temperature of the atmosphere in which the CO2 etc, exists. The energy absorbed briefly excites a higher level vibration mode of the atoms within the molecule, it is at a precisely defined level, (quantum) and the same quantum of energy is released when the molecular energy collapses back to the ground state. In the unconfined global atmosphere, some of the re-emitted quanta will be absorbed by the earth but many will simply be re-absorbed and re-emitted by other receptive CO2 molecules during the overall mechanism of heat transfer of heat from the earth's surface to outer space.
At the relatively low temperatures which exist over the earth's surface, it is my understanding that forced convection (wind driven) and evaporation/condensation of H2O transport much more of the earth's surface temperature to the TOA where it is radiated to space by the clouds, water vapour and CO2 at that height. It would be nice if an engineer with experience of real world heat transfer calculations could comment on this.
I have couched this response in terms of CO2, but of course in the atmosphere, H2O is a much more effective absorber of thermal radiation by virtue of its multiplicity of internal vibrational energy modes and its greater concentration. In addition the property of water to change state from solid to liquid to gas at temperatures which all exist on earth and to absorb/emit very large quantities of latent heat in so doing provides a very strong set of feedback mechanisms to maintain the status quo!
Ronaldo
Dear Ronaldo
You are probably right however my point was that an easily verifiable experiment that PROVES you are right would be a good idea ^.^
Dung
Dung
Yes indeed, I agree.
Ronaldo
Recent threads on the main blog have led me to return to this great discussion as a means of silencing the "Increasingly Insufferable One" (sadly I can not claim to be the originator of that most apt title but the identity of that person shall remain secret ^.^).
My memory, particularly long term is pretty much shot to pieces, an ageing GP prescribed some antidepressants that were totally inappropriate and they did the damage :(
Hence I find myself half remembering stuff that I used to know perfectly well.
The point being that I seem to remember doing A level Physics and being told (something like) the following:
If you were to shine a powerful searchlight at a "screen" then if you viewed the screen it would appear to be a bright light (through reflection ofc). However if you then shone any number of other bright lights, none of which was as bright as the searchlight at the screen, the brightness of the screen would not change.
Can some noble Physicist add the actual scientific reason for this (or tell me my memory is even worse than we thought!).
I raise this because of the discussion that sprang up about the GHE in the Matt Ridley thread. I was reading up about heat transfer and the laws of thermodynamics etc etc (as you do). The Wiki entry stated the following:
There are only three mechanisms for heat transfer; conduction, convection and radiation.
conduction and convection obey the laws of thermodynamics.
radiation behaves in the same way as light.
If the atmosphere is cooler than the surface of the earth then convection and conduction can only warm the atmosphere and not the surface of the earth according to the laws of thermodynamics.
If my memory of my physics is right then back radiation (if it exists at all) can not affect the amount of radiation from the earth.
No GHE.
This would also mean that the laws of thermodynamics do indeed cover all three forms of heat transfer.
Dung
Dung, I can't pretend to say whether you are right or wrong. Some GHE explainers support the back-radiation meme, some state it in terms of a raising of the equilibrium level, warming at the surface beng provided by lapse rate. Maybe they are both merely illustrations to try to get the concept over than an exact description of the mechanism. Anyhow, both here and in the Oxford pub I've been told my quest for experimental proof is naive and unrealistic. I reject that. I believe it is scientific to say 'show me' and unscientific to support arguments with models and paleo when you cannot actually show your hypothesis working. Best evidence, as I call it.
Anyhow, this is on topic here on this thread, and I open it up to others to have a go at the challenge described on page one.
By the way. Aerodynamc lift is weirdly parallel to GHE. Plainly there IS aerodynamic lift, aeroplanes and birds use it to fly. But when it come to looking up how it works, you may still find references to Bernoulli effect and circulation theory. Maybe they are still being taught, I don't know. They are not right*, though, and never were.
*more accurately, not complete.
rhoda
"However if you then shone any number of other bright lights, none of which was as bright as the searchlight at the screen, the brightness of the screen would not change."
Dung - either your memory is foutu (as they say in France) or your physics teacher did not know what he was talking about*. That is the sort of thing you can read in "Slaying the Sky Dragon" - a dangerous book because it is full of nonsense of that sort that readers might take as fact.
* I think the latter, as faulty memory normally means that you forget things, not that you create fantasies.
Martin A
Martin A
Can you put me right then? Is it the case that the less bright light sources can increase the brightnes of the screen?
P.S.
My memory is truly FUBAR :)
Dung
OK - it's late here. I may rewrite it more comprehensively/coherently tomorrow.
The key thing is the the reflective screen is linear, so if you apply two electromagnetic waves a, b say, the response to a+b is the sum of the responses that you'd get if you applied a and b separately.
So even if b is tiny compared with a, the response to a+b still has more power than the response to a alone. (I used the phrase electromagnetic wave because linearity is a key concept in em theory. Light is an em wave so it applies to light.)
Does that convince?
Martin A
WARNING! this might be a long post.
Some BH contributors have taken the view that arguing that the GHE does not exist is somehow unacceptable, it is almost as if, on this issue at least, they are part of the consensus?
This is despite the fact that there is no experimental evidence to back up what is just a theory hence this discussion exists.
Since all the models based on the GHE fail to predict actual global temperature, there must be "something" wrong and the GHE becomes fair game for discussion by anyone at all. I think it would be great if BH contributors combined to analyse the GHE theory and see if we can tease out the flaws.
Martin A who is far better qualified than I am, does believe in a greenhouse effect although not a significant one, he is also able to delve into the math involved so if he and others get involved, who knows where we can get to?
I think the crux of the whole thing is back radiation and what effect if any it has on IR reradiated by the earth. There are probably as many graphic representations of the GHE as there are days in the year (perhaps people can submite their favourites?). This one at Wiki has figures in it and so makes a good target to start with http://en.wikipedia.org/wiki/Greenhouse_gas
When therealviffer made his posts about the laws of thermodynamics, the papers he referred us to talked about energy manufactured from nothing, the wiki graphic demonstrates what he is talking about I think.
According to the graphic the total input from the sun (to the whole atmosphere) is 235 watts/square metre. The amount of radiation eventually radiated to space also equals 235 watts/square metre. However the IR radiation at the earth's surface is a staggering 492 watts/square metre? How we do dis?
Well is it just me or should the radiation from the earth on the right hand side of the graphic include the feedback? I think not.
Whether or not the graphic is right or wrong you get back to the question of whether back radiation really exists and if it does, is there an effect on the radiation by the earth. At some point we must devise an experiment to test the theory. It could save us a lot of money ^.^
I have a proposal as follows
A chamber constructed with a soil floor, walls which are transparent to all wavelengths of IR, a ceiling that is transparent to all wavelengths of IR. In the ceiling a source of IR which should be as close to the suns IR wavelength as possible, adjacent to the IR source a sensor to detect IR from the floor of the chamber. The IR source should be thermally shielded so that none of its radiation can reach the sensor.
Air should be passed through the chamber at a known CO2 content, a known speed and a known and controlled initial temperature. The strength of the IR source should be constant. The system should run until a steady reading on the IR sensor occurs.
At this point the CO2 content should be increased but all other parameters should be held constant. Do we then observe any change in the sensor reading?
Dung
I just noticed an interesting implicit statement in the wiki graphic.
Looking at the IR from the sun; of the 235 watts/sq metre, 67 is "absorbed" by the atmosphere. Looking at the IR radiated by the earth 452 is absorbed by the atmosphere, of this combined total of 519, 195 is radiated into space and 324 is radiated back to the surface.
The graphic is stating that the radiation heats the earth and not the atmosphere, leaving any heating of the atmosphere to conduction and convection.
Dung
Dung, I think you'll find that the graphic has no basis in reality. For one thing it is averaged out over time and the whole planet. There is no place where these numbers are true and can be measured. There is no set of numbers available which apply to any given place and time of day and time of year and could therefore be checked. As far as I know there is no data about a change in these numbers over decades matching CO2 content. It's just a pretty picture. It is no more than a conjecture, unless someone here can tell me where I am wrong.
rhoda
Martin A who is far better qualified than I am, does believe in a greenhouse effect although not a significant one, he is also able to delve into the math involved so if he and others get involved, who knows where we can get to?
"...not a significant one... " I don't think I ever said that.
It seems that the greenhouse effect probably is significant since the average temperature at the earth's surface seems to be significantly more than it would be in the absence of an atmosphere.
I don't see any fallacy in the simple model that is often described - so far as I can see, its analysis is based on simple well understood principles and does not contradict any laws of physics. However, the model omits numerous effects that are undoubtedly significant - the earth's temperature is not uniform* in space or time, heat is transported around the atmosphere by mechanisms other than radiation, the atmosphere and the ground exchange heat by all sorts of mechanisms, the atmosphere is not a thin shell, and so on.
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* this has to be significant when you do calculations like integrate temperature raised to 4th power,
because [integral] T^4 dx can be very different from ([integral] T dx) ^4.
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The simplifications of the model mean (to me) that it serves merely as a plausibility argument to explain the GHE - producing figures ("33 deg C warmer") from the model and regarding them as reality seems just silly.
The bottom line, for me, is that if a thing has not been confirmed by physical observation and measurement, then it's just a hypothesis. So bon courage to your efforts.
PS - was my positive answer to "Is it the case that the less bright light sources can increase the brightnes of the screen?" convincing?
Martin A
Martin A
Your explanation was certainly convincing and I accept it ^.^ however in the process of my reading, I came to the conclusion that reflected IR would have little effect since it would be at the same wavelength as incoming IR and therefore pass through the atmosphere without heating it very much if at all.
rhoda
I am sure everything you said about the graph was correct but someone put it together and was careful to make the numbers add up. It must represent someone's"general idea" of what is happening in which case I ask again if the brown column on the right should actually include its own feedback? Is energy being manufactured from nothing in that graphic?
In addition the graphic does seem to say that all the radiation is heating the earth and not the atmosphere.
Dung
Martin A
You made this comment in the Ridley Response to Romm thread:
I don't know where the idea of "back radiation warms the earth" originated. www.realclimate.org perhaps?
Definition of Greenhouse Gases:
WIKI: A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect
THE ENCYCLOPEDIA OF EARTH: A greenhouse gas is one of several gases that can absorb and emit longwave (infrared) radiation in a planetary atmosphere. This phenomenon is often termed the greenhouse effect. Of the sunlight that falls on the Earth's surface, approximately 40% of that energy is reradiated upward into the atmosphere in the form of longwave radiation. Approximately 75% of that upward radiated longwave energy is absorbed by water vapor, carbon dioxide, methane and other greenhouse gases. Since this absorption process is molecular in nature, the subsequent reradiation of energy by these gases is multidirectional. As a result, about 50% of the longwave emission is reradiated back toward the Earth where it is once again turned into heat energy. Through this process, greenhouse gases contribute to the amount of heat energy released at the Earth's surface and in the lower atmosphere.
YOUR DICTIONARY SCIENCE: The retention of part of the Sun's energy in the Earth's atmosphere in the form of heat as a result of the presence of greenhouse gases. Solar energy, mostly in the form of short-wavelength visible radiation, penetrates the atmosphere and is absorbed by the Earth's surface. The heated surface then radiates some of that energy into the atmosphere in the form of longer-wavelength infrared radiation. Although some of this radiation escapes into space, much of it is absorbed by greenhouse gases in the lower atmosphere, which in turn re-radiate a portion back to the Earth's surface.
NOAA: The greenhouse effect is unquestionably real and helps to regulate the temperature of our planet. It is essential for life on Earth and is one of Earth's natural processes. It is the result of heat absorption by certain gases in the atmosphere (called greenhouse gases because they effectively 'trap' heat in the lower atmosphere) and re-radiation downward of some of that heat.
I do not say these are all the most reliable sources, I just say that back radiation seems to be fairly widely accepted and that it is the reradiation of IR received by greenhouse gases that makes them greenhouse gases. If that mechanism does not exist then there is no greenhouse effect, simply conduction and convection by all gases in the atmosphere.
Dung
Hi Dung -
Yes, I've seen all that stuff.
I don't have a problem with some of the radiation that leaves the Earth's surface coming back after being absorbed and then re-radiated in all directions by CO2 or H2O in the atmosphere and then needing to be re-radiated by the Earth's surface. It's inevitable if the system is to be in equilibrium.
My problem is with the back radiation "warming the Earth".
To start with, we are (or at least I am) considering that the system has reached equilibrium - so all the "warming" has already been done. Once it is equilibrium and the temperature of eveything is constant, there is no more "warming" going on, so far as I can see. (I assume "warming" = "heating up" = "the temperature is rising").
So far as I can see, all of the warming (prior to the system reaching equilibrium) was done by the radiation that arrived directly from the sun. The surface was then warmed by the Sun's radiation until equilibrium was reached ie the net W/m2 leaving the Earth's surface matched the W/m2 incoming radiation from the Sun reaching the Earth's surface.
[I really must write it up, if only to share with you. I've got sidetracked trying to track down an explanation of the absorption/emission of radiation by CO2 molecules, vibrations in CO2 molecules, and the transformation of such vibrational energy into heat. Any ideas?]
Martin A
Martin, of one thing I am sure, there is no equilibrium. The earth rotates too quickly, there is no time for anything to settle. I have occasionally wondered whether the 'extra warming due to CO2' just takes another five minutes to dissipate in the early hours of the following morning taking the temperature gradient to merely a slightly different place on the asymptote in search of equilibrium, to no detectable effect. But then I wouldn't need to speculate on this if somebody who propounds the theory got out there in the garden and damn well measured it. But they won't. Or they can't because it is too small to measure in the general noise. In which case what are we supposed to be worried about?
rhoda
Martin A
Can we just clarify what you said there because to me it seemed that you denied the GHE?
If the back radiation does not warm the earth then that "back" radiation can not warm the atmosphere.
I am not sure if you are treating the radiation by the CO2 molecules as wave energy or photons here (my rank amateur reading says it should be wave) but whatever it is my understanding is that its only effect on CO2 molecules is to excite the molecule causing it to reradiate the energy, there is no (or truly insignificant) warming?
Dung
Martin, of one thing I am sure, there is no equilibrium. The earth rotates too quickly, there is no time for anything to settle. (...)
Dec 31, 2012 at 9:28 AM rhoda
Rhoda - you are obvioulsy correct that there is no equilibrium - in the real system.
But I am talking about the idealised and over-simplified model, consisting of a black body assumed to be at uniform temperature, surrounded by a shell of atmosphere also at contant temperature. It is obviously a gross over-simplification and therefore anything derived from the model is (at best) suggestive of what might really be happening.
The many analyses of this model assume, either explicitly or implicitly, that things are in equilibrium - all temperatures are constant. The assumption of equilibrium is one of the things that makes the model unrealistic - but it permits a simple analysis.
Martin ACan we just clarify what you said there because to me it seemed that you denied the GHE?
If the back radiation does not warm the earth then that "back" radiation can not warm the atmosphere.
I am not sure if you are treating the radiation by the CO2 molecules as wave energy or photons here (my rank amateur reading says it should be wave) but whatever it is my understanding is that its only effect on CO2 molecules is to excite the molecule causing it to reradiate the energy, there is no (or truly insignificant) warming?
Dec 31, 2012 at 9:58 AM Dung
Dung - "Can we just clarify what you said there because to me it seemed that you denied the GHE?".
I don't think I did deny the GHE, since what I am saying is that the presence of the atmosphere (modelled as a thin shell around a black body) results in the black body being calculated as warmer than it would be without the shell surrounding it. This equates to the analysis of the model confirming that it describes a GHE. (But, as I said before, the model's confirmation does not say much about whether or not it exists in reality.)
To repeat what I said in a previous post:
- In the model, there is no warming taking place because everything is at constant temperature. Both the black body and the surrounding atmospheric shell remain, each one, at its own constant temperature.
Since (in the model) the temperatures are constant, it seems to me to be misleading to talk about "warming" going on. (To me "warming" means something is getting warmer - not that it is remaining at constant temperature. But I can see that other people might use the word "warming" in a different sense.)
Treat the radiation as either em waves or photons as you wish, whichever is easier to visualise - it gives the same result.
With the system (the modelled system - not the real system) in equilibrium. what you say is right - the temperature of the atmospheric shell remains constant and so all the energy it intercepts is re-radiated, the watts being intercepted exactly balancing the watts being re-radiated. This is completely consistent with the model saying that there is a GHE.
PS (added after posting) I really shall have to write this up so it can be followed step by step. So far as I can see, as the modelled system warmed up, in the process of reaching equilibrium, all of the warming was done by radiation arrivinf direct from the Sun. No need to fret about "back radiation" warming things up or the laws of thermodynamics being flouted.
Martin A
Martin A
Well one of us is befuddled by Christmas spirit here hehe. You say:
So far as I can see, as the modelled system warmed up, in the process of reaching equilibrium, all of the warming was done by radiation arrivinf direct from the Sun. No need to fret about "back radiation" warming things up or the laws of thermodynamics being flouted.
That statement is agreeing that back radiation is not an issue and therefore the GHE is not an issue ^.^
Dung
"Well one of us is befuddled by Christmas spirit here." That's not impossible.
Please clarify. Does "That statement is agreeing that back radiation is not an issue and therefore the GHE is not an issue" equate to "... therefore the GHE does not exist"?
If so, I don't agree. Analysis of the simple model says the GHE exists (in the simple model). The analysis does not depend on assuming that backradiation heats things.
Martin A
Martin A
It seems to me that our problem is that we do not agree on what the GHE actually IS.
I quoted WIKI and other places on greenhouse gases because they define those gases and the GHE soley by the mechanism of back radiation heating the earth.
If you give your definition of the GHE we might do better ^.^
Dung
Dung - yes, that's the problem. We obviously don't share a definition of the GHE.
Googling "greenhouse effect definition" comes up with numerous definitions involving "trapping energy" and the general bollocks that you seem to get when it's explained by people that don't seem to have studied physics to A-level. Some of them are laughably rubbish appearing to have been written by people who have not studied any physics at all (but perhaps have done some rote-learning of "climate science").
I find myself like one of those subjects in a psychologist's experiment where the rest of the audience put their hands up to say that they saw something that clearly did not happen. In most cases, the subject looks at the other 34 raised hands and then slowly raises their own hand, despite clearly having witnessed the non-occurrence of the thing the other 34 "subjects" (actually accomplices of the experimenter) indicate they saw. NONE of the definitions I found at a quick look satisfied me.
One that came near was (Yahoo Answers): The greenhouse effect is the heating of the surface of a planet or moon due to the presence of an atmosphere containing gases that absorb and emit infrared radiation.
I'd re-word it to say:
The greenhouse effect is where the average temperature of the surface of a planet or moon is, as a result of the presence of an atmosphere containing gases that absorb and emit infrared radiation, higher than it would have been in the absence of such an atmosphere.
I'd have thought (though I'm not certain) that my definition would be acceptable to people who use the other definitions that google comes up with on the first page.
Martin A
I may be asleep, in which case I am not writing this but I think Rhoda is just a made up name so Richard Lindzen can post on BH without being recognised.