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Comments 51 to 93 out of 93:

51. suibhne at 18:12 PM on 24 April, 2010
    jibal at 16:48 PM on 22 April, 2010 Jabal refers to another site where the imminent release of a comment by Halpern, Smith, Colose and three others was promised (March 20). As this has not happened as yet it might out of courtesy to them be better to wait for its release. http://scienceblogs.com/deltoid/2009/03/gerlich_and_tscheuschner_oh_my.php
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52. chris at 19:08 PM on 24 April, 2010
    re: suibhne at 18:03 PM on 24 April, 2010 Not really suibhne. Arctic sea ice is on a downward trend. Sea ice area coverage will obviously show considerable interannual variation; however as the downward trend progresses strongly warming years will eat into old ice which requires several sufficiently cool years to recover, and so sea ice volume is likely to be diminishing without the amount of interannual variability of sea ice area. Thus, as pointed out by Peter Hogarth evidence indicates that total sea ice (i.e. sea ice volume) in March was the lowest March sea ice volume on record: Polar Science Center, Univ. Washington re: suibhne at 18:12 PM on 24 April, 2010 suibhne, jibal was referring to your curious reluctance to address straightforward questions on the Deltoid thread. He wasn't referring to the in press comment on the dodgy IJMBP paper.
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53. suibhne at 01:15 AM on 25 April, 2010
    chris The anticipated comment to which I refer; The reference is: Joshua Halpern, Christopher M. Colose, Chris Ho-Stuart, Joel D. Shore, Arthur P. Smith, Jörg Zimmermann (2010) Comment On “Falsification of the Atmospheric CO2 Greenhouse Effects within the Frame of Physics”, (to appear in) International Journal of Modern Physics (B), Vol 24, Iss 10, March 30 2010. The six authors put in some hard work to find any alleged "flaws" in the G&T paper. The previous "refutations" unfortunately did not cut the mustard. I for one was rather surprised by the approach of some of previous attempts. I think any reasonable person would agree that it is wrong to prejudge the as yet unpublished comment. If and when it is published however I would expect to have some observations which I will share with the Deltoids.
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54. KR at 02:41 AM on 29 April, 2010
    suibhne, did you read my reply on G&T on the "Is CO2 a pollutant?" thread? You did not respond there. I took the time to read their article thoroughly, which was... rather painful. G&T display an appalling lack of understanding of the physics of thermodynamics, particularly radiative equilibrium - a concept dating to 1791, well understood and acknowledged as a scientific consensus. The core of their paper uses a strawman argument conflating convection blocking greenhouse effects with radiative greenhouse effects (not true, demonstrable in any freshman thermodynamics class), and from that stating that since they are not the same thing, radiative greenhousing doesn't exist. That's a pure logical fallacy. They make (by my estimate) ~2 errors, logical fallacies, or outright physics howlers (I'll refrain from labeling them lies, but it's hard to understand how such basics are misunderstood) per page. I'll enjoy further comments from people with better physics skills than mine, but IMO G&T isn't worth the paper it's written upon. I put some references to radiative equilibrium in my previous post (linked above) - I would strongly recommend them, as they're important elements of what we disagreed upon in the CO2 thread.
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55. suibhne at 09:06 AM on 30 April, 2010
    KR Sorry I didn't catch you at "Is CO2 a pollutant?" ......G&T display an appalling lack of understanding of the physics of thermodynamics, particularly radiative equilibrium..... Strangely enough Kevin Trenberth is recently finding his sums don’t work out within radiative balance. However he should relax, there is no such law in physics. A much more realistic picture was given recently by Richard Lindzen. “Evidence Suggests Man-Made Warming Greatly Exaggerated” In the article Lindzen pointed out that radiative equilibrium is seldom observed. People everyday experience temperature changes of 20 degrees or so and yet the IPCC gets alarmed at a rise of less than a degree in the past century. This prompted me to do a simple calculation based on the planet having no radiative balance whatsoever. This illustrates the sheer thermal inertia of the bulk of the planet. I have used a very simple model of the Earth made of uniform material with reasonable conductivity If the Earth absorbed all the Suns radiation that landed on it and absolutely no heat ever escaped. How long would it take for the temperature to rise by 1 degree centigrade. Formula used Pxt =cm(temperature rise) P=1367W/m2x(crosssectional area of Earth) t =time in seconds C = specific heat capacity = 1000 (you can tweak this number if you like) m = Mass of Earth =6×10power24 When calculated it turns out to be 1080 years.
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56. KR at 00:14 AM on 1 May, 2010
    Hmm... I'm reminded of a joke about a farmer (with milk production problems) asking a physicist for ideas, leading to a discussion of "spherical cows". The Earth's core is already pretty warm (think lava) from radioactivity and residual heat; it would be interesting although irrelevant to calculate how long before we melted once we stopped losing radiative energy to space. It was my understanding that Trenberth has refined his data and estimates, based on temperature variation and a fourth-power rule for heat radiation (to use the Max Planck term). That's science - always improving your results with further study. G&T, on the other hand, seem to claim that radiative heating doesn't exist at all, which would overturn ~220 years of scientific consensus, contradicts _all_ the experimental evidence and measurements, and is certainly not proven by their collection of errors, logical fallacies, and outright junk. It reminds me somewhat of the Transformative Hermeneutics of Quantum Gravity paper, 'tho with less overall humor. And once again, short term variations are quite large - that doesn't change the facts about long term temperature shifts of the center-point around which those variations are based.
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57. suibhne at 01:25 AM on 1 May, 2010
    KR I think you must have missed recent post in which Kevin Trenberth frankly admitted that he couldn't account for what he called the "missing heat" and further worried that unless it is found "it could come back and haunt us". I on the other hand like Richard Lindzen do not believe in radiative equilibrium hence the post above. The very simple model excluded geothermal and gravitational effects such as tidal flows etc which would only detract from the focus on these points. I have exaggerated many physical effects to make radiative equilibrium as big a problem as I can make it. If you can think of any further reasonable inflation of the problem please let me know and I will include it. Including non related phenomena only make the case for human induced CO2 as a major problem much weaker. Reasonable conductivity given the time scale of 1000 years should enable the one degree rise in temperature.
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58. suibhne at 01:30 AM on 1 May, 2010
    KR ......G&T, on the other hand, seem to claim that radiative heating doesn't exist at all, which would overturn ~220 years of scientific consensus, contradicts _all_ the experimental evidence and measurements, and is certainly not proven by their collection of errors, logical fallacies, and outright junk........ What makes you think that G&T "claim that radiative heating doesn't exist at all" Quote a page number or such like.
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59. Doug Bostrom at 02:18 AM on 1 May, 2010
    Suibhne, you don't believe in radiative equilibrium? Can you describe how the planet sheds energy, or is it being stored somewhere inside the globe?
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60. suibhne at 04:52 AM on 1 May, 2010
    doug_bostrom The planet can heat up and cool down over geological periods. Heating up means gaining internal energy. Cooling down means losing internal energy.
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61. Doug Bostrom at 05:44 AM on 1 May, 2010
    Suibhne, perhaps I should ask the question a different way. Does energy leave planet Earth? If so, how?
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62. suibhne at 07:46 AM on 1 May, 2010
    doug_bostrom By longwave em radiation
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63. Doug Bostrom at 04:36 AM on 2 May, 2010
    Suibhne, you understand that Earth must lose energy somehow and that it appears it does so by radiative emissions but at the same time you don't believe in the notion of radiative equilibrium? Surely you'll want to qualify that remark? If the Earth is not shedding energy roughly as fast as it gains energy, surely we would expect some change in temperature here at the surface?
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64. suibhne at 08:29 AM on 2 May, 2010
    doug_bostrom I don't believe in the necessity of the notion of radiative equilibrium? We will ignore for the moment the fact that radiant energy can be transformed into other energy forms. If the Earth gains more radiation than it loses, its temperature will increase very slowly, see post 55. Likewise if the Earth loses more radiation than it gains, its temperature will decrease slowly.
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65. KR at 12:54 PM on 3 May, 2010
    suibhne - first of all, my apologies, I was thinking of the wrong Trenberth reference. I believe that the "missing heat" thread is discussing that issue. As to your thought experiment of heating the entire earth and the large time constants - crust temperature rises ~20C per kilometer for the first ten kilometers, figure ~200C hotter than the surface 10 kilometers down, when you get to the mantle, where convection currents drop the gradient to 0.3C/kilometer. That means you would only see heating in the top kilometer or so; the rest of the planet is already much hotter, with the upper crust cooling through radiation to space. You won't be heating the mantle, let alone the core (5000-6000C). Warming the crust just slows the cooling of the core, it doesn't heat it. So if you run your calculations with the top 10km (a generous depth) of crust rather than the entire planetary mass, I suspect you will find the time constant for full solar irradiation heating much much smaller. I get a time constant of ~5 years for a 1C temperature rise, not 1080. If you just consider the top 1km, as the crust is 20C hotter below that, your time constant would be six months/degree C; actual thermal conduction speeds in the crust mean that the surface would be much hotter. That makes the 0.7C rise over the last 70-80 years attributable to a very small portion of total irradiance. Incorporating the entire planet in thermal inertia calculations makes no sense when 99.5% of the planet is 200-5500C hotter already. Radiative equilibrium simply describes a steady state situation where incoming radiation matches outgoing radiation - a simple balance of energy. I believe that's what you've described in your last post - an Earth system that cools or warms until it reaches equilibrium. I just have to disagree with your time constants.
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66. KR at 03:32 AM on 4 May, 2010
    In regards to G&T's more outrageous points, I find Arthur Smiths rebuttal quite clear. Even a single layer of IR scattering (absorbance/emisison) atmosphere can be very simply shown to produce a greenhouse effect, and a more realistic thick layer with temperature gradients and convection will be even more effective. G&T's major confusion seems to be about "heat radiation", aka thermal radiation, emitted by anything above 0K. In section 3.9.3 their misunderstanding (amazing if it isn't intentional) is quite evident, and leads to their claim that heat radiation and energy flow balancing somehow contradicts the 2nd law of thermodynamics. This is a clear attempt on their part to confuse heat flow (net energy changes) with heat radiation.
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67. suibhne at 04:29 AM on 4 May, 2010
    KR On the thought experiment. Like all these gross simplifications it is fetched pretty far. But then so are calculations about the Earths atmosphere that ignores Oceans and so on. I thought it would be interesting though to get a simple value for the Earths thermal capacity or the amount of energy required to increase its temperature by one degree c. A slightly more realistic one for the Oceans gives 30years for a rise of one degree. Assumptions 10% imbalance in radiative equilibrium and using the value of surface radiation 168 w/m2. Both calculations show a large value of thermal inertia.
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68. suibhne at 04:38 AM on 4 May, 2010
    KR On G&T ....G&T's major confusion seems to be about "heat radiation", aka thermal radiation, emitted by anything above 0K...... I think G&T have been misunderstood on this point. They say radiation can go from a lower temperature body to a higher temperature body. However they say HEAT cannot go from a lower temperature body to a higher temperature body. This is simply stating the "bleedin" obvious in terms of standard thermodynamics.
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69. KR at 04:56 AM on 4 May, 2010
    Take a look at the Arthur Smith paper. I've spent a number of hours on G&T (sigh - time I'll never get back, time that would have been better spent with a decent beer); Smith's paper is only 9 pages and very clear. G&T say that there is no such thing as a radiative greenhouse effect. They are quite simply wrong. The magnitudes and numbers for heating via LW radiation trapping and total radiative imbalances are well established by numerous sources; not much I can add there.
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70. suibhne at 05:24 AM on 4 May, 2010
    KR Yes Ive read Arthur Smiths paper and still prefer G&Ts version of reality. One thing for me sums up the departure of AGW advocates from reality is the figure of 324W/m2 Back Radiation. Why is this huge magnitude of photons not put to some useful work? If this could be shown I would have to reconsider the whole issue.
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71. KR at 06:50 AM on 4 May, 2010
    suibhne, take a look at the EPA response, particularly Volume 3, Comment 3-45 and Response 3-45 on page 38. You're welcome to take it up with the EPA, but the vast scientific consensus is that G&T are full of, um, hot air... As to the 324 back radiation discussion, AGAIN!!! - I would love to put that energy to work, preferably in my car. Unfortunately, that's part of the sea-level radiative balance, and there are no cold sinks to divert it to, no opportunity to extract work from it. See the definition of "work", under "Zero work", for this situation. 'Nuf said, suibhne. We went around and around on this under the "Is CO2 a pollutant" thread, you've had the same argument on other blogs, and in each case you've repeatedly refused any physics not from G&T, changed the subject, or just left the discussion midstream when it became clear that nobody found your arguments persuasive. You seem to have a basic misunderstanding of 'zero work' situations of steady state systems, and repeated raise issues of 'work' when there is zero net energy flow. That's really a freshman physics error, and if you don't/won't get it, there's nothing anyone here can say to you... My apologies for the harshness of my reply; I'm more than willing to have a discussion, but you haven't shown a willingness for that. It's quite frankly not worth my time.
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72. KR at 07:49 AM on 4 May, 2010
    To clarify my previous comment: the EPA document, Volume 3, Comment 3-45 and Response 3-45 on page 38 is a direct response to the issues in Gerlich and Tscheuschner (2009).
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73. suibhne at 08:10 AM on 4 May, 2010
    KR You made my point for me, the "back radiation" cannot do any work. This means it cannot be described as heat. I see you followed my version of the Alamo at Deltoid. Two reasons for the pause in my contributions; 1. The article by H=>Z has still not been published. 2. While you can have a rational discussion with Sylas, Arthur Smith and Stu there are others on that site who simply want to hurl abuse behind the safety of the internet. Thank goodness for a site like Skeptical. While I have not fundamentally changed my position it is not the same as it was say two months ago. All the best.
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74. Riccardo at 08:21 AM on 4 May, 2010
    suibhne, infrared photovoltaic detectors work like photovoltaic solar panels and could in principle be used to produce electricity. Whatever the type of IR detector used, radiation from the atmosphere can, and indeed is, measured. It's energy, no doubt.
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75. Doug Bostrom at 04:45 AM on 5 May, 2010
    Just to amplify Riccardo's remark, one could in principle arrange an array of photovoltaic IR detectors to liberate mechanical energy via an electric motor, aka "do work" in the most prosaic sense. With such an apparatus pointed skyward on a cloudy night, even if the detector array IR radiation temperature was higher than the cloud IR radiation temperature one would still be able to see a net increase of electrons flowing from the IR detectors and ultimately liberating their energy as heat at the motor, compared to the same arrangement pointed at a clear sky. Photons arriving at the detector array neither know nor care about the temperature of the array itself. They are not somehow driven back because the detector is warm, they plow into the surface regardless where they stand the usual probability of bouncing an electron. G&T's paper lacks perspective.
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76. suibhne at 07:42 AM on 5 May, 2010
    doug_bostrom As I said to KR in post70 ............... the figure of 324W/m2 Back Radiation. Why is this huge magnitude of photons not put to some useful work? If this could be shown I would have to reconsider the whole issue. Yes and I stand by this statement.
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77. Riccardo at 08:09 AM on 5 May, 2010
    suibhne, we're way offtopic here. The short answer is costs and efficiency.
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78. KR at 10:14 AM on 5 May, 2010
    doug, Riccardo, folks, my apologies - I referred to an earlier topic without sufficient attribution/context. The 324W/m2 number comes from an earlier thread, Is CO2 a pollutant, where suibhne argued at length against GHG heating, using as a reason the G&T paper. My most recent (and sadly a little rough) posting was in response to seeing G&T arguments against greenhouse gas heating again; not the energy flows at Earth's surface. And yes, you can extract some energy using the photoelectric effect (which is how the detectors for IR work), but that energy isn't usable in a heat engine without a cold sink. suibhne, it turns out that the G&T paper was NOT PEER REVIEWED; it appeared in International Journal of Modern Physics B as a review paper, not a research paper - invited by the editor(s) on a topic of their interest, and very definitely not subject to a peer review process. No peer review, hence no checks by anyone actually knowledgeable in the field, hence I have even less reason to take any arguments from G&T seriously.
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79. KR at 10:21 AM on 5 May, 2010
    Incidentally, that's an abuse of IJMPB's own editorial system. A "review" paper should consist of describing the state of the art in a field, listing significant contributors, seminal papers, and directions for future research. If you want to claim that the last 100 years of thermodynamics, radiation equilibrium, and climate theory are WRONG, that's original research (certainly an original opinion), and deserves peer review - which G&T did not get. The editors of IJMPB simply published a long polemic - one that had been solidly refuted ages ago by people with actual knowledge in the field.
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80. Doug Bostrom at 11:21 AM on 5 May, 2010
    Suibhne, what you said is that back radiation cannot do any work. In order for your assertion to be true, photons emitted from a lower temperature source must somehow be unable to interact with surfaces radiating at a higher temperature. Can you describe the mechanism that isolates and sorts photons in this way?
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81. KR at 15:41 PM on 5 May, 2010
    The IJMPB review paper policy is described here - Gerlich and Tscheuschner (2009), FALSIFICATION OF THE ATMOSPHERIC CO2 GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS, was definitely not peer-reviewed. And, sadly, it's junk...
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82. suibhne at 06:44 AM on 6 May, 2010
    KR This is what your link led me to! To ensure top quality, review articles are by invitation only and all research papers undergo stringent refereeing. We welcome you to submit your research papers to IJMPB for publication. You say further .....If you want to claim that the last 100 years of thermodynamics, radiation equilibrium ... are wrong. Who wants to claim such nonsense. The boring thing is that G&T are just applying traditional thermodynamics and find that the CO2 AGW theory just does not stack up.
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83. suibhne at 06:53 AM on 6 May, 2010
    doug_bostrom In order for your assertion to be true, photons emitted from a lower temperature source must somehow be unable to interact with surfaces radiating at a higher temperature. Well they just don't. KR (78) puts it quite well. Here's my guess from Quantum Mechanics. The higher temperature energy levels will already be full from bottom up. Lower energy photons will not find any "slots" to fill and will be at something of a loose end.
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84. Riccardo at 07:30 AM on 6 May, 2010
    suibhne, nice reply: "they just don't". In fact they do, as already shown. P.S. review your quantum mechanics and in particular how bosons work.
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85. Doug Bostrom at 08:13 AM on 6 May, 2010
    Suibhne, in order to say "they just don't", you must also say what they do. What do photons emitted from a cool body do when they encounter a warmer body?
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86. kdkd at 10:42 AM on 6 May, 2010
    suibhne #83 Please excuse my rusty chemistry, but I think you've made a fundamental error. Please correct the below if it's wrong. The IR absorption of CO2 has very little to do with the electron energy levels (except from the context of forming the bonds in the first place). The bond energy in the CO bonds in a co2 molecule is around 1500kj per mole of CO2. So in order to break the bonds of the co2 molecule you have to supply 1500kj of energy to 1 mole of co2 molecules before the bonds break, and the energy levels of the electrons come into play again. Again, my chemistry is very rusty, but this is my understanding. I really don't think that quantum effects are relevant at all in the way that you are claiming they are.
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87. scaddenp at 11:06 AM on 6 May, 2010
    "The boring thing is that G&T are just applying traditional thermodynamics and find that the CO2 AGW theory just does not stack up." They are misinterpreting classical thermodynamics. Consult a text book. ( eg Fundamentals of Heat and Mass Transfer). This was covered well at: The imaginary second law
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88. suibhne at 18:35 PM on 6 May, 2010
    scaddenp Thanks for the link. Read Terry Oldbergs comments in the Tread he puts the case for G&T much better than I can.
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89. suibhne at 18:59 PM on 6 May, 2010
    doug_bostrom ...What do photons emitted from a cool body do when they encounter a warmer body? ....... Think of the basic physical reality of the situation. 1. The mass of the Earth against the mass of atmospheric CO2 2. The ability of the Earths surface to radiate at all wavelengths within its spectrum centred around 15c. 3. The restriction that CO2 can only emit at a few wavelengths. The energy envelope of CO2 centred around -10c Would the tiny number of low energy photons from CO2 make any difference to the massive number of higher energy photons leaving the Earth. I don't think that even the most sensitive measuring device could detect any effect in the Earth surface temperature. However being a practical man if you can produce a realistic device that does work from the "backradiation" I will find your viewpoint much more convincing
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90. Ned at 22:15 PM on 6 May, 2010
    suibhne writes: However being a practical man [...] With all due respect, an actual "practical man" knows that when he's in a hole it's time to stop digging. There are many less nonsensical arguments against the IPCC consensus than the one you've chosen to make your stand on. I'm not going to speculate about what motivates you to be so persistent and vocal in defense of obvious error, but practicality pretty clearly has nothing to do with it. Steve McIntyre is a very practical man. You don't see him posting about G&T on his blog (in fact, he's banned discussion of it because he knows that hosting that kind of nonsense would damage his site's credibility). There's a lesson there.
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91. suibhne at 23:18 PM on 6 May, 2010
    Ned Steve McIntyre is very good with numbers as the Hockey Stick man has found out. He is a mathematician not a Physicist. I think he was suggesting that people go to a site where Physics was the main thread. Perhaps he felt uncomfortable in a discussion where his own expertise was not central
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92. KR at 00:40 AM on 7 May, 2010
    suibhne, if you fully read the link I provided, the journal policy states: "One unique feature of this journal is its review section which contains articles with permanent research value besides the state-of-the-art research work in the relevant subject areas. To ensure top quality, review articles are by invitation only and all research papers undergo stringent refereeing." (emphasis added) Note the difference between review papers, invited by the editors, and research papers that undergo refereeing. G&T was a review paper, invited by the editors, and not peer-reviewed. Note the difference. G&T claim that the last 100 years of climate research, GHG heat retention, and radiation thermodynamics are wrong. They are sadly mistaken, and their 150+ page polemic does nothing to support their position except push a bunch of incorrect jargon. (Seriously - if you have something to say in science you can usually state it in under 30 pages or so!) I do not agree with you about the photon selection issue, incidentally - that's quite a misread of what I said; I clarified my statements in #78. Heat engines cannot work without a temperature gradient, but photon excitation/emission events certainly occur. The energy flows in each direction are easily detected; you can't extract work from them in a case of radiative equilibrium because the net energy flow is zero. That's the basis of radiative equilibrium, a link you apparently haven't followed yet. Your statements in #83 about "all high energy levels being full" are complete nonsense. See an excellent description of heat radiation here. Ned, well put in #90.
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93. sylas at 19:30 PM on 10 May, 2010
    The formal rebuttal to Gerlich and Tscheuschner has now been published, along with their reply. The two papers appear in IJMP(B), Vol 24, Iss 10, Apr 20, 2010. The references are: [1] Comment On "Falsification Of The Atmospheric Co2 Greenhouse Effects Within The Frame Of Physics", by Joshua B. Halpern, Christopher M. Colose, Chris Ho-Stuart, Joel D. Shore, Arthur P. Smith and Jörg Zimmermann, pp 1309-1332, doi:10.1142/S021797921005555X [2] Reply To "Comment On 'Falsification Of The Atmospheric Co2 Greenhouse Effects Within The Frame Of Physics' By Joshua B. Halpern, Christopher M. Colose, Chris Ho-Stuart, Joel D. Shore, Arthur P. Smith, Jörg Zimmermann", by Gerhard Gerlich and Ralf D. Tscheuschner, pp 1333-1359, doi:10.1142/S0217979210055573 I am collecting blog and journal links at Duae Quartunciae: Published rebuttal to Gerlich and Tscheuschner 2009 and will keep extending the list. I am also hosting discussion of the rebuttal and reply at a new bulletin board: Climate Physics Forums, which I have recently established to host substantive and courteous discussion of matters relating to the practice of climate science. I am a co-author of the rebuttal; my own name is Chris Ho-Stuart. In my opinion, an elementary familiarity with basic physics and thermodynamics is more than sufficient to see that Gerlich and Tscheuschner's paper and reply are without any scientific merit at all. However, it has an lot of technical material which can make it appear more credible than it really is, and daunting to many readers. Their hypothesis represents an extreme view which has no prospect whatsoever of having any genuine scientific impact. In fact, I believe our rebuttal paper will be their first proper citation for the original paper! I note that Steve McIntyre is mentioned here; Steve has more than sufficient basic understanding to appreciate why Gerlich and Tscheuschner's work is a dead end. The speculation that Steve feels out of his depth is quite implausible. Neither Gerlich nor Tscheuscher have any standing in this field either; they are writing well outside their normal areas of professional competence. The whole episode has been extremely silly. However, I am hopeful that discussion of the paper might help people who do feel out of depth, and I will be ensuring that any discussion at the new board is maintained at the highest levels of personal courtesy. Ideas are fair game, but I will strive to keep all members, of any persuasion background or level of ability, safe from personal ridicule or abuse.
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94. WRyan at 21:44 PM on 24 July, 2014

    just read this article and comments. With regard to the hypothetical photovoltaic IR panel, it would work if it was cooled below the temperature of the emitting body (the earth's surface, in this case.) PV panels work because they are cooler than the Sun's surface, which is where the light originates.

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95. WRyan at 21:49 PM on 24 July, 2014

    p.s. With regard to my previous comment. The temperature difference requirement applies only to thermal radiation.

    A PV panel can absorb light from a light source like an LED or a fluorescent light without having ot be cooler than the light source. This is because the light from those sources is not being produced by a thermal process.

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96. Tom Curtis at 23:31 PM on 24 July, 2014

    WRyan @94&95, that is the trap of thinking in terms of the temperature of the emitting source rather than the energy of the photon.  The Sun also emitts IR radiation, for example.  A PV cell behind such a filter would react in the same way to the IR photons from the Sun as it would to IR photons from any other source.  Light from an LED or fluorescent light is carried by high energy photons, even though the method of emission is not thermal.

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97. CBDunkerson at 04:36 AM on 25 July, 2014

    WRyan... how does the photon know the temperature of the object it would eventually impact if it were emitted? I mean... it could have to travel hundreds of light years to get there. Say a photon emitted from a distant star is going to hit the International Space Station, but if the station hadn't been constructed (hundreds of years after the photon was emitted) then it would have just passed through empty space and continued on to hit the Sun (which in this hypothetical is hotter than the emitting star). How does the photon instantaneously 'know' something that won't happen for hundreds of years? For that matter... how is it NOT emitted just because it will eventually strike a warmer object?

    You should really publish on this. Among other things it allows faster than light communication. Aim a laser at a target location and then raise or lower the temperature of that target to higher/lower than the laser's temp and the laser will instantaneously stop emitting when the temperature is higher... regardless of the distance involved. Messages could thus be 'transmitted' instantly to the laser end by changing the temperature at the target end.

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