A very interesting article questioning the very existence of the CO2 Greenhouse Gas Effect has been published in the International Journal of Modern Physics:
Falsification Of The Atmospheric CO2 Greenhouse Eff ects
Within The Frame Of Physics
Version 4.0 (January 6, 2009)
replaces Version 1.0 (July 7, 2007) and later
Gerhard Gerlich
Institut fur Mathematische Physik
Technische Universitat Carolo-Wilhelmina zu Braunschweig
Mendelssohnstrae 3
D-38106 Braunschweig
Federal Republic of Germany
g.gerlich@tu-bs.de
Ralf D. Tscheuschner
Postfach 60 27 62
D-22237 Hamburg
Federal Republic of Germany
ralfd@na-net.ornl.gov
I have long been dissatisfied with the explanations I have read about how the greenhouse gases are supposed to cause warming of the atmosphere and the earth's surface. I have now read about half of this long article and will comment on it when I have finished reading it. It appears that my doubts were justified.
One thing that strikes me as wrong about the usual approach to justifying a greenhouse gas effect based on a black body model (which the above paper also says is wrong, but has not yet in my reading suggested in quite what way), is that it is assumed that the radiative cooling of the earth through re-emission of infrared radiation occurs from the earth's surface. If the greenhouse gas theories were correct, this would not be the case. The primary radiation loss would have to be from a layer which was at a considerable altitude over which there was little remaining water vapor and CO2. Yet these calculations like to say that the radiative black body cooling would be at about 15C or 288K if there were no greenhouse gas effect. But this would not be in balance with what they calculate the sun's radiation to be. The temperature in black body radiation balance with the sun's radiation is calculated to be lower and the difference in temperature is attributed to the greenhouse gas effect.
But, one can just as easily argue that of course the surface temperature is not the radiative black body cooling temperature. It is air convection that acts to cool the surface air temperature as the warmed surface air rises up to higher altitudes. As it does so, air molecules collide and pass energy from the molecules recently warmed at the surface to those which had dwelled longer in the upper atmosphere. Finally as molecules reach a high enough altitude, convection loses its cooling ability due to the low density of molecules and radiative cooling becomes the means by which further energy is lost. Much of the black body radiation at this altitude is emitted into space and the earth cools on net balance. But, this black body radiative cooling of course happens at the much cooler temperatures found at higher altitudes. At a mid-latitude location, the atmospheric temperature is already about 10C lower than at the surface at an altitude of about 2 km.
In other words, with no net greenhouse gas effect, if radiative cooling mostly occurs at altitudes a few kilometers up, then the calculated black body temperature will be significantly lower than the surface temperature. The lower calculated black body temperature for the earth cannot be used as proof of a greenhouse gas effect!
Greetings!
ReplyDeleteI don't know what explanations you have been reading, but it is stock standard in physical accounts of the atmospheric greenhouse effect that the vast majority of the infrared radiation going out into space from the Earth is emitted within the atmosphere... not the surface. This is fundamental to how the atmospheric greenhouse works.
In simplest terms, the atmosphere is transparent to incoming solar radiation, and opaque to outgoing infrared. Hence radiation from the surface is absorbed by the atmosphere. As the paper you are citing notes, it is not reflected. Much of that paper seems to be aiming at a strawman of how physics is actually used by climatologists; it might be useful for rebutting simple gradeschool level misunderstandings; but the paper goes horribly wrong in casting this as a criticism of actual climatology; and makes a number of very elementary errors itself.
As an atmosphere absorbs energy, it heats up; and radiates itself by virtue of its temperature. Some of the radiation is emitted upwards, and some downwards. There is, in consequence, an additional flux of infrared radiation from the atmosphere back to the surface, and from the atmosphere back out to space. One measure of the extent of the greenhouse effect is the altitude in the atmosphere that is most characteristic of the radiation emitted back into space; and as the greenhouse strength increases, so does this altitude. This characteristic altitude varies over the Earth's surface also.
Since you have a strong technical background in physics, and an active mind, I recommend you try material on climatology aimed at a high level of technical understanding, rather than the simple popular expositions. There's good on-line textbook, called "Principles of Planetary Climate", by R.T. Pierrehumbert at the Uni of Chicago, used for advanced undergraduate course work. It deals with physical basics that can be applied to any planet. It is at http://geosci.uchicago.edu/~rtp1/ClimateBook/ClimateBook.html (and look for the 13.6 Mbytes download of the working draft).
In the book, the concept of "effective radiating level" for an atmosphere is introduced in section 3.3 (page 112). It represents a kind of mean depth from which photons escape into space. The more greenhouse effect, the higher up in the atmosphere is this mean.
Your closing paragraph describes the normal features of any planet for which an atmospheric greenhouse effect is at work – the atmosphere is cooler than the surface (because it is being heated from the surface), and the radiation out into to space is from cooler and higher altitudes in the atmosphere. But then you describe this as a contradiction of greenhouse effects! What you are describing is CLASSIC greenhouse effect.
Without a greenhouse effect, the surface radiates direct to space, and the surface temperature matches blackbody emission temperature. Add an atmosphere that absorbs in the infrared (an atmospheric greenhouse). Suddenly that surface radiation is absorbed… and re-radiated. Some goes out into space, some goes back to the surface. The surface heats up a bit more in response, until an energy balance is attained, in which the atmosphere is heated from below, the surface is warmer than the atmosphere, and the radiation into space is from the atmosphere rather than the surface.
Read the book, seriously. It's hard work, but I found it a tremendous help in sorting out the background physics behind the popular disputes. The paper you are describing here is a very misleading guide indeed. Good luck with it all and best wishes – Chris.
Chris,
ReplyDeleteThanks for your comment. I will take a look at "Principles of Planetary Climate." I do not disagree with what you say about radiation processes, but I do find myself dubious about this having the climate implications which are often attributed to it.
According to the idea of the greenhouse effect you are implying there is a greenhouse effect if light energy absorbed at the earth's surface and converted into infrared radiation is not radiated back into space with less than 100% efficiency. This does not happen when an infrared-absorbing gas is present in the atmosphere, such as water vapor and CO2. Therefore, we have a greenhouse effect.
I believe the authors of this paper, which I hope to get back to sometime this evening, are going to complete their argument along the lines of this: The incoming radiation from the sun is half visible and half infrared. If no infrared-absorbing gases were in the atmosphere, near twice as much energy would be deposited on the earth's surface. But water vapor and CO2 are absorbing most of the in-coming infrared radiation and most of it is therefore radiated back into space already from higher altitudes. The half of the sun's energy in the form of light is passed on. [That much smaller part which is UV is mostly not incident at the surface so I have ignored it for simplicity.] The infrared absorbing gases in the atmosphere do then shift the altitude higher for the effective point at which the incoming light energy is then irradiated back into space as infrared radiation, but this whole effect is operating on only half the initial energy from the sun in the first place. Those same greenhouse gases have already rejected half the energy from the sun and as more of them is added to the atmosphere, the altitude from which the half of the sun's incoming energy due to infrared radiation is re-radiated back into space also increases.
This is very different than a real greenhouse, because the real greenhouse is only working with that part of the sun's energy which is in the form of light from the beginning. If IR and light unimpeded from the sun fell on the greenhouse, but the greenhouse did not allow the IR radiation inside somehow, then whatever it did with the light energy it would not be able to warm the inside relative to what it would be without the greenhouse, except insofar as the structure interfered with air convection.
This argument may still be simple-minded since I am not sure that infrared absorbing gases do not still have important effects on where in the atmosphere the incoming radiation is deposited as heat as a matter of distribution, etc. In fact, I understand that there have been problems in finding the atmospheric heating at the altitudes which is supposed to be found according to such calculations as have been done.
This is important, but I have not seen calculations or explanations that are more than hand-waving. If we are to wreck our economy and shackle our freedoms in the name of CO2 infrared radiation absorption, then we had better first be sure that these calculations are on a very solid footing. There are enough computer modeling experts now saying they are not and there are enough discrepancies between predictions and observations that it would seem apparent that some gross errors are to be found in these radiation calculations.
Another point the authors in the paper I referenced above seem to be making is that if you are interested in the surface temperature given that you already have a lot of water vapor and a certain amount of CO2, the important effects for the surface temperature are that air has a low thermal conductivity and a low specific heat, so convection is the dominant means for removing the heat deposited by sunlight from the surface and dissipating it up into the atmosphere. Adding more CO2 will not much change either the thermal conductivity or the specific heat, so what CO2 additions do is to have effects upon the temperature of higher altitude air. This need not have much effect on the surface temperatures.
Thanks for pointing out Pierrehumbert's book.
Thanks for a generous welcome.
ReplyDeleteYou say: "The incoming radiation from the sun is half visible and half infrared. If no infrared-absorbing gases were in the atmosphere, near twice as much energy would be deposited on the earth's surface."
But that is just false. The incoming radiation from the Sun is a classic blackbody spectrum: a Plank distribution characteristic of 5700K. It peaks in the visible spectrum; and there is far far more energy there than in the infrared. The majority of solar radiation passes easily through the atmosphere. The Earth's surface is much cooler, at around 300 K. It radiates almost nothing in the visible, and peaks in the infrared, and very little of this can get directly into space. It is absorbed and then re-emitted by the atmosphere. It is this difference that makes an atmosphere so important for determining the temperature at the surface of a planet.
Your whole comment above is premised on this simple and basic error. The book I've suggested starts out with some background thermodynamics, which is needed to deal with this level of technical understanding.
By the way, of course the atmospheric greenhouse effect works differently from a real greenhouse. It's what I meant previously about the paper perhaps having some value in addressing grade school level miscomprehensions.
But the paper also makes a complete mess of the real physics of thermodynamics of planets and atmospheres. The physics of climate which we are describing that of atmospheric absorption and re-emission of radiation. Let's stick to that and get it right.
The comments on convection are very odd. Of course CO2 has negligible contributions to convention or specific heat. That's totally irrelevant to the real contribution of CO2 for a planet, which is all about absorbing and remitting radiation. The effects of H2O for latent heat are a very important part of the energy balance as energy moves between the surface and the atmosphere; and H2O also has a large contribution to the greenhouse effect that keeps our planet so warm. This is all described also in the book I have suggested. But these are details.
The fundamental stumbling block seems to be recognizing that there really is a strong surface warming effect when an atmosphere is much better at absorbing infrared radiation than visible radiation. This is called an atmospheric greenhouse effect, which is rather a misnomer because the physics involved is not at all that of a glass greenhouse. But it's certain real and it is basic physics.
Cheers -- Chris
Hi Chris,
ReplyDeleteYes, the critical issue is the distribution of the incoming solar radiation. Figure 7 of this article gives the black body spectrum for a temperature of 5780K. This spectrum peaks in the visible range, but has a long tail through the infrared portion of the electromagnetic spectrum. The authors claim that the breakdown between UV, Visible, and IR radiation is 10.0%, 44.8%, and 45.2%, respectively. The UV plays little role with little reaching the earth's surface. So, the visible radiation and the infrared radiation are about equal in intensity according to the authors. They note that this fact is commonly ignored in other people's treatment of the problem.
They take the visible portion of the spectrum to be from 380 to 760 nm. Possibly from the relevant standpoint of what radiation reaches the ground this is not the correct boundary for the energy integration. What is important is determining that part of the spectrum which reaches the ground and that part which does not. Perhaps some of the shortest wavelength IR does reach the ground, so the normal bound for visible light is not really the correct bound here for calculating the power of the radiation reaching the ground. Maybe, they have made an unrealistic assumption on this issue. Is this something addressed by Pierrehumbert?
Yes, the convection issue is not important for the sum total of energy for the planet. It is only important if we care about where the energy is distributed in the atmosphere. Since this is important, the fact that most thermal energy near the surface is dissipated by convection rather than by radiation is very important.
Yes, the effects of water's heat of vaporization are very important. Yes, the gas absorbing most of the IR radiation is water, which is one of the reasons why adding further CO2 to the atmosphere has less and less effect on the ground temperature.
The critical issue here is what part of the power from the sun's spectral irradiance reaches the ground given our normal, pre-industrial CO2 concentrations or those now due to natural phenomena other than man. If only visible light reaches the ground, the complete story is that IR absorbing gases have prevented half the power of the sun's radiation from reaching the ground even before we consider what happens to the visible part of the spectrum. The IR absorbing gases are then cooling via half the power spectrum and warming with some partial degree of effectiveness on the other half of the spectrum, assuming the author's partition along Visible versus IR lines is not too simple-minded.
Chris, thanks for your input. It has been helpful in terms of my clarifying my thinking on this problem and I do appreciate the reference, which I will try to get to after I finish reading this paper.