Subject: Re: Global Warming; CO2:-mechanism and relative importance From: ogryzlo@Chem.ubc.ca (Elmer) Newsgroups: sci.environment [ #6170 ] Date: Tue, 13 Jun 1995 13:53:51 -0800 Organization: UBC Message-ID: In article <11@iconoclast.win-uk.net>, ahughes@iconoclast.win-uk.net (Andrew Glynn Hughes) wrote: > I seem to recall an article in a British publication, New Scientist, > some two years ago where a senior academic of Chemistry from Imperial > College, London cast doubt on the role of CO2 as significant > greenhouse gas. > > Would any chemists or physicists out there like to comment? In a later issue of the new scientist there was a response which made sense to me. Here are my notes on the subject: Jack Barrett who is at Imperial College in London (and was supposed to publish these ideas in Spectrochemica Acta, ~1994) said something like this: - The lowest thirty meters of the troposphere already contains sufficient CO2 and H2O to absorb all the radiation emitted by the Earth's surface (except in the "10 micron" {7.5-14 5m} window). -When CO2 absorbs the emitted radiation it does not re-emit it because in its radiative lifetime (105s) it suffers 104 collisions, which are enough to transfer the energy to N2 and O2 which do not emit IR radiation. Hence emission of IR from the Earth's surfaces to outer space is prevented at all wavelengths except in the 10 micron window. Under such circumstances further additions of CO2 to the atmosphere would be expected to have little effect on the average global temperature. For example, the burning of all the fossil fuels on earth would raise the CO2 level to 1400 ppm, from its current level of about 355 ppm. If the above reasoning is true this could cause vegetation to flourish, as it did during the Cretaceous period (144-65 million rears ago, when dinosaurs roamed the Earth) and when it is now thought that the temperatures were not too different from what they are currently (Nature 370, 453(1994)). Here is the response that came later: Barrett's analysis assumes that global warming is driven by changes in the radiation balance at the Earth's surface. This is not so. What happens is something like this: It is true that the CO2 molecule suffers many collisions between the time that it absorbs radiation from the solid Earth, and re-emits it in all directions. This means that it is in thermal, and radiative equilibrium with its surroundings at each altitude. As we go up in the troposphere, the temperature of that atmosphere drops, and hence the temperature of the CO2 at greater elevations also drops. At these lower temperatures found at the top of the atmosphere, the energy is radiated into space because there is so little CO2 above it that the atmosphere is essentially transparent at these emitting wavelengths. However, at that altitude the intensity of the emitted radiation is decreases (recall the Steffan-Boltzmann law says that: I is proportional to T4). Thus the loss of radiative loss of energy to space from this altitude drops, because of the presence of the CO2 in the atmosphere. If now more CO2 is added to the atmosphere then the level from which the emission occurs rises. Since the temperature of the emitting CO2 is even lower, radiation leaving the Earth is reduced. The climate then warms until once again the input of solar radiation just balances the radiative loss to space. The fact that near sea level the CO2 concentration is sufficiently high to absorb all the radiation in the main CO2 band is therefore irrelevant! ***** Subject: Re: Global Warming; CO2:-mechanism and relative importance From: rtp1@quads.uchicago.edu (raymond thomas pierrehumbert) Newsgroups: sci.environment [ #6245 ] Message-ID: Reply-To: rtp1@midway.uchicago.edu Organization: The University of Chicago References: <11@iconoclast.win-uk.net> Date: Thu, 15 Jun 1995 04:31:14 GMT I concur with Elmer's description of CO2 radiative saturation and the relative role of surface and TOA budgets. For an optically thick atmosphere, it is the TOA budget plus the lapse rate that dominantly control the surface temperature. The surface budget is relatively unimportant. Another way of looking at it is that the atmosphere is so opaque to IR that the radiation to space is determined by just the first one optical depth from the top, which, loosely speaking, reaches into the mid trop. If Barrett's argument were correct, it would be difficult to account for the very high surface temperature of venus. Just one clarification, though: > during the Cretaceous period (144-65 million rears ago, when > dinosaurs roamed the Earth) and when it is now thought that the > temperatures were not too different from what they are currently > (Nature 370, 453(1994)) It's only the tropical temperatures which may (repeat MAY) have been not much more than the present values. The poles, of course, were ice free and perhaps 20C warmer than the present annual mean. ***** Subject: CO2 Controversy From: B.Hamilton@irl.cri.nz (Bruce Hamilton) Newsgroups: sci.environment Date: Wed, 29 Nov 1995 09:49:21 GMT Organization: Industrial Research Limited Lines: 95 Message-ID: <49h734$j6m@zephyr.grace.cri.nz> Well, this is my penance for yesterday's nonsense post.... It started out innocently enough, in a rather boring, staid, scientific journal ... " The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere " Jack Barrett Dept. of Chemistry. Imperial College, London Spectrochimica Acta v.51A, p.415-417 ( 1995 ) However, the conclusions were somewhat startling:- "The implications of this re-interpretation of the roles of CO2 and H2O in atmospheric warming and cooling is that any increase in the CO2 content of the atmosphere will not affect the average temperature of the troposphere..... A proper scientific conclusion would be that any effects of the 25% increase in atmospheric CO2 on the Earth's average surface temperature cannot be distinguished from the background of natural variability. All the energy that can be absorbed by the atmosphere is being absorbed under present conditions. Any additional CO2 cannot alter the 100% absorption of terrestrial radiation, nor will it interfere with the main mechanism of cooling, which is the direct radiative loss of energy from the Earth via the 7.5-14um window" Wow! Just as dogmatic as any sci.environment claims.... Sure enough, the knight came rushing.... " Comment on "The roles of carbon dioxide and water vapour in warming and cooling the Earth's troposphere" " John Houghton Spectrochimica Acta v.51A, p.1391-1392 ( 1995 ) Sir John very politely, and carefully points out the problems, and goes on to explain that as the concentration of CO2 in the atmosphere increases, so too does the average height (about 6km) from which CO2 emits radiation in space. Since atmospheric temperature in the lower atmosphere falls with altitude, if nothing changes other than the amount of CO2, the amount of radiation to space is reduced. For atmospheric CO2, this reduction is about 4Wm^-2. To restore the Earth's energy balance the temperature thoughout the lower atmosphere has to increase - hence the enhanced greenhouse effect. There is also a response from K.P.Shine, whose "constructive criticism of a previous version of this paper" is acknowledged in Barrett's paper. He notes that the previous paper had been submitted to another journal, and he "firmly recommended rejection of that paper and continue to profoundly disagree with the conclusions he reaches" in his review. He then goes on to repeat the points of Sir John, with another couple added for good measure. All in good, clear English that is too often missing from such journals. ( Spectrochim.Acta Part A 51 p.1393-4 (1995) ) As is usual, the original author is given the final right of reply (Spectrochim.Acta Part A 51 p.1395 (1995)), and Dr. Barrett continues to claim that his paper is valid. All very genteel, and no blood anywhere..... So it was with some surprise that I noted that a much more acrimonious debate in Chemistry in Britain, November 1995 letters section "CO2 Controversy" had J. Emsley ( also of the Chemistry Dept at Imperial College ) citing the Barrett paper and noting, "The mechanism by which CO2 behaves as a greenhouse gas is not the simplistic one of emission-absorption that the IPCC bases its hypothesis on, and I refer the authors to J. Barrett's recent paper on the subject for the correct mechanism...... Like many chemists I find it hard to accept the CO2 global warming theory of IPCC and Greenpeace for another simple reason. If every molecule of oxygen in the atmosphere is there because of photosynthesis of a molecule of CO2, then in the past the Earth's atmosphere must have contained orders of magnitude more CO2 than today, perhaps even being as high as 200,000ppm. I should point out that the many members of the European Science and Environment Forum are soon to publish their report on CO2 and global warming, and that this flatly contradicts the IPCC/Greenpeace view." Aside from the fact that most IPCC members are probably now walking around holding crosses in front of themselves because they have been mentioned twice as accomplices of GP, that's a pretty strong claim for a paper that had been subsequently answered. One could suppose they are seeking US Senate funding at IC... Coming as it does after a full frontal assault on the IPCC conclusions in the NZ Institute of Chemistry Journal ( such a journal is unlikely to cause the IPCC global concern :-) ), chemists really are demonstrating that they should stick to their last, and concentrating on important matters like the names of the transfermium elements :-). Bruce Hamilton ***** Subject: Re: CO2 Controversy From: rparson@spot.Colorado.EDU (Robert Parson) Newsgroups: sci.environment Date: 2 Dec 1995 19:32:13 GMT Organization: University of Colorado, Boulder Message-ID: <49q9jt$qao@peabody.Colorado.EDU> In article , Steinn Sigurdsson wrote: > I haven't seen Barrett's paper but there was buzz in > the media here about it. Essence as I heard it is that > collisional de-excitation of CO2 makes the incremental > opacity irrelevant to radiative forcing. My understanding > is the argument is flawed but subtly, haven't bothered to **Subtly**?!! You're an astrophysicist; do you remember the letters "LTE"? [Editor's Note: LTE = Local Thermodynamic Equilibrium] Of _course_ collisional deactivation is much faster than radiative decay; if it weren't LTE wouldn't apply and the radiative transfer calculations really would be wrong. If you didn't have collisional deactivation you couldn't get the radiative energy into thermal energy! Take a look at the Barrett paper (it's just a little over 2 pages long) and his response to the comments. It really is amazingly bad. Since Barrett believes that increasing CO2 has no effect on temperature - not a sublinear effect, *no* effect - I wonder how he explains Venus. (Yeah, there was this comet that popped out of Jupiter about 4000 years ago...) ------ Robert ***** Subject: Re: CO2 Controversy From: rparson@spot.Colorado.EDU (Robert Parson) Newsgroups: sci.environment Date: 2 Dec 1995 23:02:00 GMT Organization: University of Colorado, Boulder Message-ID: <49qlt8$r6@peabody.Colorado.EDU> In article , Steinn Sigurdsson wrote: > The radiative transfer is non-gray, LTE is not an issue > at all, rather where the opacity is. In principle if self-absorption > from CO2 was incorrectly handled then the transfer calculations > could be wrong, I didn't think they were, rather the atmosphere > get warmer (as observed). I heard Houghton give a talk on > the radiative transfer calculations couple of months ago, > I thought they were being done correctly, hence I though Barrett's > point was wrong, without having read the paper. I think you're being too generous, Barrett does claim (incorrectly) that rad. transfer calculations treat molecules as cavity radiators (he even cites "unpublished work" of his own to support the utterly pedestrian statement that the absorption spectrum of CO2 at 1 at pressure consists of discrete bands) but he also seems hung up on the time scales for radiative vs. nonradiative transfer: "The currently perceived mechanism of operation of the so-called greenhouse gases, carbon dioxide and water, is dependent upon the atmosphere behaving as an emitter of continuous radiation as would a cavity of the same temperature and upon vibrationally excited carbon dioxide and water molecules being deactivated mainly by the emission of fluorescence radiation at all altitudes." (From the abstract) [ ... ] > Since Barrett believes that increasing CO2 has no effect > on temperature - not a sublinear effect, *no* effect - I wonder how > he explains Venus. (Yeah, there was this comet that popped out > of Jupiter about 4000 years ago...) > > Ah, I hadn't heard that. That is just stupid. Here's the quote: "The implication of this re-interpretation of the roles of carbon dioxide and water in atmospheric warming and cooling is that any increase in the carbon dioxide content of the atmosphere will not affect the average temperature of the troposphere."