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Post by heatsink on Feb 9, 2009 3:04:53 GMT
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Post by steve on Feb 9, 2009 11:11:05 GMT
Fascinating. How much by? 1/sqrt(2). I said "If you uniformly double CO2 concentrations". I didn't say how uniform CO2 is. But it's quite uniform especially in the parts of the atmosphere I'm referring to. Nope. 1/sqrt(2) is of course wrong because there are other greenhouse gases. I guess that's why you need to use a radiation model (there's that scary word for people to latch onto) on a typical atmosphere profile.
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Post by tallbloke on Feb 9, 2009 11:22:22 GMT
Nope. 1/sqrt(2) is of course wrong because there are other greenhouse gases. I guess that's why you need to use a radiation model (there's that scary word for people to latch onto) on a typical atmosphere profile. I take it the 'nope' is directed at yourself not me Steve, after our previous exchange about your statement: Steve: By uniformly doubling CO2 concentrations you decrease the mean free path of an emitted photon throughout the atmosphere. Tallbloke: Fascinating. How much by? How 'uniform' are co2 concentrations in the real world? Steve: 1/sqrt(2). I said "If you uniformly double CO2 concentrations". I didn't say how uniform CO2 is. But it's quite uniform especially in the parts of the atmosphere I'm referring to. Tallbloke: So the photon finds it's mean free path decreased by 1/sqrt(2) after a doubling of co2. Hmmm. Thats 0.707. Which unit's are we talking here Steve? And are we talking about the atmosphere as a whole, or the co2 element of it? Which parts of the atmosphere are you referring to? ---------------------------------------- I'm not sure why you didn't simply quote my previous post. maybe it was to make it look like I'd misunderstood it rather than you? Once again Which parts of the atmosphere are you referring to?
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Post by steve on Feb 9, 2009 16:15:30 GMT
Yes, the Nope is directed at me. I'm happy to admit when I get things wrong, and apologise if my quote selection might have not made it clear.
Please note. I am just trying to apply basic physics here. I'm not any sort of expert in radiative transfer theory (though I've done modelling studies of gamma ray absorption in various materials which is what guides my thinking).
The mean free path of photons of a given frequency will be reduced when CO2 is doubled, because the extra CO2 increases the opacity at a large range of IR frequencies.
So if the mean free path at a particular location for a particular frequency was 1 metre, it will now be less than 1 metre. I suppose the proportional reduction will always be such that the new path is less than the original but more than 1/sqrt(2) (~70%) of the original.
The difference will depend on the relative importance of CO2 as compared with other gases. In places where there is a lot of water vapour, the difference will be small. In dry locations it may be larger.
The same principle should apply throughout all the atmosphere.
I imagine there are secondary effects, though I'd have thought at the current small CO2 partial pressure, most would be minimal.
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Post by tallbloke on Feb 9, 2009 21:47:25 GMT
Damn good answer, thanks Steve.
Curses, more reading to do. ;D
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Post by nautonnier on Feb 10, 2009 0:55:21 GMT
Kiwi, I sincerely hope that I have never said that CO2 "traps" infrared. The surface and all levels of the atmosphere are emitting and absorbing infrared. A substantial proportion of the IR spectrum is quickly reabsorbed at lower levels. Emission from a given location is proportional to the fourth power of the temperature and is in all directions. Therefore, at the higher and colder levels of the atmosphere there is less emission. By uniformly doubling CO2 concentrations you decrease the mean free path of an emitted photon throughout the atmosphere. This means that from any given layer of the atmosphere from which a proportion of IR is escaping to space, the proportion reduces. But because the higher layers are colder, they emit less, and cannot balance out the reduced proportion of photons escaping from below. # As a second way of thinking about it. If you view the earth with infrared eyes (using regions of the spectrum that are reasonably well saturated), then the earth will look foggy. The temperature of the fog will be the temperature of the depth of atmosphere from which much of the radiation is escaping. Talking technically for a moment, a rule of thumb would be that you are observing the atmosphere at a level where the optical depth is 1. If you double CO2, the fog gets slightly thicker, and you can see less deeply. By seeing less deeply you are seeing colder layers. These layers emit slightly less energy because they are colder. The difference in temperature will be about 1C, equating to 4W/m^2. Precisely this sort of calculation is done when observing any hot gaseous object, including the sun. "Emission from a given location is proportional to the fourth power of the temperature and is in all directions. Therefore, at the higher and colder levels of the atmosphere there is less emission."Modified by the emissivity. And of course for CO 2 it is only in 3 narrow bands (two of which are overlapped by water vapor absorption) that cover around 8.3% of the IR spectrum. Or more than 90% of the IR spectrum is unaffected by CO 2. "A substantial proportion of the IR spectrum is quickly reabsorbed at lower levels."Of the 8.3% of the IR spectrum absorbed by CO 2 or are you including water vapor in your "substantial proportion" ? As with all of the 'its only radiation' group, you have TOTALLY forgotten convection. Warm air rises, sometimes extremely fast. Convection carries more heat energy to the tropopause than radiation and even warmed (or kinetically excited) CO 2 lowers the density of the volume of atmosphere it is in and causes it to rise. The entire reason that there are winds is due to the huge convective cells in the atmosphere but no- these are disregarded even though AGW proponents are demanding windmills that are driven by the wind that is due to convection. It is the tradewinds and their strength that causes the La Nina/El Nino oscillations and these winds are due to the Hadley Cells and the Coriolis force. The clouds that are formed as the water vapor condenses out also have a negative forcing that can be far more than any positive forcing from CO 2 or CH 4. The concentration CO 2 radiative forcing and total disregard of convection reminds me of the advertisement for Fosters Lager that was run in UK for some time. Two Australian herdsmen leaving a bar with cases of Fosters to a battered pick up truck loaded high with many more cases of Fosters. One of the herdsmen is carrying 3 bottles of sherry. "For the Sheilas!" he says as he puts the bottles onto the cases of Fosters. As he puts them down there is a crack and the back drops as the truck suspension fails. The second herdsman says "Too much sherry!"
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Post by nautonnier on Feb 10, 2009 1:12:54 GMT
Yes, the Nope is directed at me. I'm happy to admit when I get things wrong, and apologise if my quote selection might have not made it clear. Please note. I am just trying to apply basic physics here. I'm not any sort of expert in radiative transfer theory (though I've done modelling studies of gamma ray absorption in various materials which is what guides my thinking). The mean free path of photons of a given frequency will be reduced when CO2 is doubled, because the extra CO2 increases the opacity at a large range of IR frequencies. So if the mean free path at a particular location for a particular frequency was 1 metre, it will now be less than 1 metre. I suppose the proportional reduction will always be such that the new path is less than the original but more than 1/sqrt(2) (~70%) of the original. The difference will depend on the relative importance of CO2 as compared with other gases. In places where there is a lot of water vapour, the difference will be small. In dry locations it may be larger. The same principle should apply throughout all the atmosphere. I imagine there are secondary effects, though I'd have thought at the current small CO2 partial pressure, most would be minimal. "The mean free path of photons of a given frequency will be reduced when CO2 is doubled, because the extra CO2 increases the opacity at a large range of IR frequencies."
True if your definition of large is about 8.5% of the IR spectrum. I suppose that is large for some but its nowhere near the spread of water vapor which just happens to cover around 3% of that 8.5% and is much much higher concentration in most volumes of the atmosphere. So what we are really talking about is around 5% of the IR spectrum that is affected by CO 2 I won't get into saturation as I don't want to inflame your dyspepsia
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Post by steve on Feb 10, 2009 12:38:34 GMT
Kiwi, I sincerely hope that I have never said that CO2 "traps" infrared. The surface and all levels of the atmosphere are emitting and absorbing infrared. A substantial proportion of the IR spectrum is quickly reabsorbed at lower levels. Emission from a given location is proportional to the fourth power of the temperature and is in all directions. Therefore, at the higher and colder levels of the atmosphere there is less emission. By uniformly doubling CO2 concentrations you decrease the mean free path of an emitted photon throughout the atmosphere. This means that from any given layer of the atmosphere from which a proportion of IR is escaping to space, the proportion reduces. But because the higher layers are colder, they emit less, and cannot balance out the reduced proportion of photons escaping from below. # As a second way of thinking about it. If you view the earth with infrared eyes (using regions of the spectrum that are reasonably well saturated), then the earth will look foggy. The temperature of the fog will be the temperature of the depth of atmosphere from which much of the radiation is escaping. Talking technically for a moment, a rule of thumb would be that you are observing the atmosphere at a level where the optical depth is 1. If you double CO2, the fog gets slightly thicker, and you can see less deeply. By seeing less deeply you are seeing colder layers. These layers emit slightly less energy because they are colder. The difference in temperature will be about 1C, equating to 4W/m^2. Precisely this sort of calculation is done when observing any hot gaseous object, including the sun. "Emission from a given location is proportional to the fourth power of the temperature and is in all directions. Therefore, at the higher and colder levels of the atmosphere there is less emission."Modified by the emissivity. No it's not. The proportionality has nothing to do with the emissivity. References? Relevance? Calculations expect a drop of outgoing longwave of 1.6% for a doubling of CO2, so you're in the right ballpark.
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Post by nautonnier on Feb 10, 2009 14:51:35 GMT
Come off it nautonnier. This is a discussion about the radiative effects of adding CO2, not about convection or, indeed, the whole earth system. Either you don't believe that climate scientists ignore convection, and you are being obtuse and obstructive. Or you believe that they do ignore it, in which case you need to read up a bit more. The climatology models with slab atmospheres and instantaneous doubling of CO 2 are hardly realistic. The main thing that is missed is the impact of convection which immediately starts as soon as any volume of atmosphere is warmed and it transports the heat upward to the troposphere. I was not being deliberately obtuse (as if I would ) - but you could go back through the threads here and find only discussion of radiation on the 'AGW' side and nothing about convection. You are all like one-club golfers. How much energy is carried to the troposphere by Hadley and Ferrel cells in equivalent watts per square meter? How much energy is consumed by the polar vortex? You can tell me off the top of your head Stefan Boltzmann constant and Beers Lambert issues for CO 2 and argue in depth about saturation of radiation bands in the atmosphere. If convection is so well known in climatology you will be able to quote the same kinds of formulae and quantification as well. But you can't. Its the elephant in the climatology room that is not discussed because its untidy - you cannot easily have a formula or algorithm to quantify the tradewinds and the clouds also formed by convection are still not well defined despite their huge effects on climate. If these quantifications were carried out then it may be noted how small the effect of CO 2 actually is in the climate as a whole.
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Post by steve on Feb 10, 2009 15:31:14 GMT
Nautonnier,
This thread is about whether scientists are ignoring things that disprove the theory.
You appear to be merely providing distraction from the fact that a core part of the theory is soundly based. It was suggested that the saturation argument was a disproof, and I'm challenging the suggestion.
You can waffle on about the uncertainties with regard to convection, but of relevance to this thread is that a) convection is taken into account by models - not all models are "slab models" with "instantaneous increases in CO2" (though such models have useful parts to play). b) there is no *firm* evidence that changes in convection etc. are strongly countering the CO2 effects and c) there is *reasonable* evidence that changes are adding to the effects.
Plugging a Roy Spencer blog and a few papers by Schwartz, Douglass, Svensmark and claiming these destroy the AGW theory won't get you anywhere with Popper. Nor does pointing out the real or potential flaws in Santer, Steig, Mann, Parker, Peterson etc.
You need more and better evidence.
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Post by ron on Feb 10, 2009 15:32:46 GMT
Don't the AGWs expect more frequent and more powerful storms as a result of warming? By that aren't they saying there will be increased convection?
I don't recall, however, seeing "more frequent and more powerful storms" listed as a negative feedback in that IPCC chart that keeps getting linked.
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Post by poitsplace on Feb 10, 2009 17:33:04 GMT
Don't the AGWs expect more frequent and more powerful storms as a result of warming? By that aren't they saying there will be increased convection? I don't recall, however, seeing "more frequent and more powerful storms" listed as a negative feedback in that IPCC chart that keeps getting linked. Indeed..thunderstorms (and other storms) dump huge amounts of heat off high in the atmosphere.
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Post by steve on Feb 10, 2009 17:49:51 GMT
Don't the AGWs expect more frequent and more powerful storms as a result of warming? By that aren't they saying there will be increased convection? I don't recall, however, seeing "more frequent and more powerful storms" listed as a negative feedback in that IPCC chart that keeps getting linked. I think you're referring to the chart of radiative forcing components. Feedbacks are not radiative forcing components, so wouldn't be listed there. But surely you must have heard the sceptic mantra that "AGW predicts more rapid warming in the upper troposphere that is unproven by satellites". It's usually referred to as "lapse rate feedback", and is indeed thought to be a negative feedback (that is not out of line with, though not proven, by satellites). But more vigorous convection would also result in higher levels of water vapour in the upper troposphere which is a positive feedback. So these two effects can partly cancel out.
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Post by ron on Feb 10, 2009 22:35:21 GMT
Don't they list solar activity in that chart??? I gotta go look at it again.
If you move heat up and out of the atmosphere, how are storms' convection not a negative forcing for the heat that would have radiated at lower levels in the atmosphere?
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Post by nautonnier on Feb 10, 2009 23:32:11 GMT
I have posted this research before - but I'll copy it here too ....
Journal of Climate - Article: pp. 4495–4511; Tropical Convection and the Energy Balance at the Top of the Atmosphere
Dennis L. Hartmann, Leslie A. Moy, and Qiang Fu; Department of Atmospheric Sciences, University of Washington, Seattle, Washington
Its conclusion states inter alia:
"The corresponding cloud net radiative forcings at the top of the atmosphere for these cloud types range from +20 to −119 W m−2. This great variation in net radiative effect arises mostly from the reflectivity of the clouds, which is primarily dependent on the water and/or ice content of the clouds." and
"We have verified that the cloud radiative forcing in regions of suppressed convection in the deep Tropics is small even when the abundance of low clouds is substantial. These conclusions follow if the convective and nonconvective areas are nearly in equilibrium with each other. If the circulation is forced by significant ocean heat transport, as in the east Pacific, or by strong dynamical forcing associated with land–sea contrasts, as in the Bay of Bengal area, then the net cloud radiative forcing in the convective regions can be significantly negative (e.g., Fig. 1 ). The net radiative effect of tropical convective clouds is thus dependent on the nature of the large-scale circulation within which they are embedded, and may respond to circulation anomalies associated with El Niño, for example.
The implications of this feedback process for the sensitivity of tropical climate need to be explored more fully. "
So some clouds can give more than --100WM-2 of feedback compared to something less than 5WM-2 maximum that CO2 radiative forcing could give.
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