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Post by steve on Apr 9, 2009 11:33:41 GMT
This paper is, I think, a good illustration of the greenhouse effect (that keeps the earth warm), and of the potential for the enhanced greenhouse effect (ie. AGW - the additional warming due to CO2 emissions. The title of the thread is in reference to: solarcycle24com.proboards.com/index.cgi?board=globalwarming&action=display&thread=546The paper is: Mid-infrared properties of Disk Averaged Observations of Earth with AIRS. Hearty et al To appear in Astrophysical Journal arxiv.org/PS_cache/arxiv/pdf/0810/0810.2957v1.pdfSee figure 4. This is not given as "proof" of AGW. It is merely an illustration to those uncertain of the basic physics, that the proposition is not as unreasonable as people make out. The basics of the theory are that much of earth's radiation is coming from the mid-troposphere where the temperature is about 250 or so Kelvin. Figure 4 illustrates the black body curve for 255K - the middle of the three light green curves. An important spectral line for CO2 is at 15 microns, and in Figure 4 a bite in the emission spectrum can be seen which is in part due to this spectral line. The area above the earth's spectrum and below the 255K line represents a rough measure of CO2's contribution to the greenhouse effect (the whole of which keeps the planet 30 or so degrees warmer than it would otherwise be). You need to multiply this area by 2pi (6.3) to get the value in Watts per metre squared. I think that it amounts to about 20-25 Watts/m^2 - the exact amount doesn't matter. The AGW theory is that if you increase CO2 to from current levels to 560ppm (a doubling from pre-industrial times), then the greenhouse effect will increase by a further 2 Watts per metre squared (on top of the current net forcing of 1.6) due to the CO2 increase alone. Some of this 2 Watts will be due to a deepening and widening of the 15 micron bite in this spectrum. As the bite is already 20-25 Watts deep, we only require an increase in the bite size of less than 10%. In other words. The initial depth of the peak - due to the current 380ppm of CO2 is about 2W below the 255K black body line. With the addition of a further 180ppm (to reach the 560 doubling of CO2) it just needs to drop a further 0.2W to provide all the expected forcing. Does that sound so unrealistic? |
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Post by magellan on Apr 9, 2009 13:11:31 GMT
In a hypothetical situation where CO2 levels were to rise sharply in a geographical region on a seasonal basis, say a city, should there be a corresponding signature in temperature?
If the physics is cut and dried, that would be the case correct?
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Post by steve on Apr 9, 2009 13:33:23 GMT
In a hypothetical situation where CO2 levels were to rise sharply in a geographical region on a seasonal basis, say a city, should there be a corresponding signature in temperature? If the physics is cut and dried, that would be the case correct? The signal in the local temperature is far too small to be detected. Even if you assumed that the effect was the same as a doubling of CO2 as compared with the countryside, and assumed the extra heating of the extra CO2 stayed in the city and wasn't blown away by the weather, then the city would warm about 0.01C more than the countryside in a year, which is not at all significant. Not sure about the signature in the spectrum though. The levels of CO2 at above the clouds are probably more relevant for detecting a signature in the spectrum. These are less likely to be affected by local sources of CO2 at the surface. |
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Post by william on Apr 9, 2009 13:35:08 GMT
Two comments:
A) Positive Vs Negative Feedback
Figure 3 shows the affect of clear sky vs clouds.
A doubling of CO2 theoretically produces the 2 watts/m2 (ignoring the question of whether the troposphere is or is not saturated so additional CO2 does not result increased warming.) if there is a massive positive feedback response to a increase in forcing.
B) Other emission mechanisms in the troposphere
There is a significant delay before the CO2 molecule re-emits the infrared photon, as the emission is a quantum statistic process. During the period before re-emission the CO2 molecule transfers its kinetic energy to other molecules, atoms, or ions.
An ion unlike a molecule will radiate when it accelerates (change of direction.)
As one moves higher in the atmosphere there are more ions.
The portion of the energy that is re-emitted is then, if I understand the process set by the proportion of ions in the atmosphere at the height in question. Now if the radiation from the ion is at different frequency than the CO2 emission/absorption the photon continues on into space.
I would assume as there is direct evidence the troposphere is not warming the CO2 mechanism is saturated in the troposphere as well as in the stratosphere.
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Post by steve on Apr 9, 2009 13:47:31 GMT
William,
a) We don't have to ignore the question as to whether "the troposphere is or is not saturated". Clearly the plot shows emission of radiation into space between 14 and 16 microns of about 2W/m^2/steradian/micron. Clearly if you increase the CO2, some of this radiation will be affected in some way.
b) There are proportionally very few ions in the troposphere. And the troposphere *is* warming - check out the research by John Christy and Roy Spencer as well as others; and the stratosphere is cooling - another predicted effect of increasing CO2.
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Post by icefisher on Apr 9, 2009 15:48:50 GMT
The area above the earth's spectrum and below the 255K line represents a rough measure of CO2's contribution to the greenhouse gas (that keeps the planet 30 or so degrees warmer than it would otherwise be). I don't see a lot to dispute about this except your conclusion the entire 30 degrees is attributable to CO2. Most of it is attributable to water vapor as you can see in all the diagrams. I would suggest the lines are inverse to elevation. Water emitting lower in the atmosphere and the CO2 band higher. When the CO2 models were built I agree it was a feasible theory. But two problems. . . .one it is getting cooler despite increasing CO2 and it is not getting warmer in the realm of the atmosphere where CO2 dominates (upper half of the troposphere). Even the global warming theorists agreed that would need to happen. People are funny. Like rationalizing that it will get warmer over the next two years because of an expected transition to solar max. When the rationalization proves unsupportable historically seldom does the conclusion change. So you end up with theories in search of a rationalization when their original rationalization of the physical links in the process disappears. The bottom line is the basic greenhouse theory calls for first warming of the upper atmosphere, then warming of the surface, melting of glaciers, then warming of the oceans, then melting of sea ice. If the phase shifts you expect the first the cooling of the surface (no mention of upper atmosphere here because in this case we don't know the first cause as it could be clouds in the lower atmosphere), freezing of ice, cooling of oceans, and finally refreezing of sea ice. Now true all those will happen simultaneously but they won't be noticeable or substantial simultaneously. . . .but this year was the first year where you could see all the processes at work for cooling. Quite simply the above is the proof or disproof of the AGW theory. Right now its in a state of disproof. . . .all you have is how long it takes somebody to conclude its been disproven. So what you have is supposedly intelligent and educated physicists not talking about what at one time they admitted to as the primary mechanism and indicator. . . . namely warming of the upper troposhere, they are all running around talking about the most trailing of indicators like melting sea ice and ice shelves breaking off. . . .as if they never even picked up a newspaper this year and were ensconced in some air conditioned ivory tower all year. Last year it was reported the air exposed ice (glaciers) grew. . . .has anybody noticed the year of silence on that topic after several years of beating that drum? I am already hearing a rising cacophony of moderation on AGW next year I expect the sea ice to become far more silent also. Theory and models are fun stuff but first guess models and theory don't commonly pan out. The long period of warming seems to have provided a false validation that right now is not looking so strong. Ultimately nature wins. |
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Post by magellan on Apr 9, 2009 16:07:21 GMT
In a hypothetical situation where CO2 levels were to rise sharply in a geographical region on a seasonal basis, say a city, should there be a corresponding signature in temperature? If the physics is cut and dried, that would be the case correct? The signal in the local temperature is far too small to be detected. Even if you assumed that the effect was the same as a doubling of CO2 as compared with the countryside, and assumed the extra heating of the extra CO2 stayed in the city and wasn't blown away by the weather, then the city would warm about 0.01C more than the countryside in a year, which is not at all significant. Not sure about the signature in the spectrum though. The levels of CO2 at above the clouds are probably more relevant for detecting a signature in the spectrum. These are less likely to be affected by local sources of CO2 at the surface. So even if CO2 levels exceed 500 ppm it wouldn't be detectable? And the heat would blow away but the CO2 wouldn't? I am not referring to above the clouds. If CO2 captures heat it should do so in a real world environment as in a city should CO2 levels rise well above the current ~385 ppm. Do you have any evidence to support those statements? |
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Post by gettingchilly on Apr 9, 2009 21:28:13 GMT
If positive climate feedback was real then the planet would not still support life. We would have been alternately fried and frozen every few hundred years. Forget positive feedback as it's just nonsense, assume negative feedback as life has been around a while now despite the current generations best efforts. As it is, we have a warm spell (then a panic), a cool spell (then a panic) another warm spell (panic again) and now another cool spell (still panicking about the last warm spell). Why not just forget about the panic and enjoy the warm spells (nostalgia) and prepare for the cool.
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Post by jorgekafkazar on Apr 10, 2009 4:46:54 GMT
Does that sound so unrealistic? Yes. Sorry, but it's all handwaving, grabbing numbers here and there, no real science, no calculations. I suspect you're starting with the wrong paper to build your case. |
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Post by tallbloke on Apr 10, 2009 8:20:32 GMT
And the troposphere *is* warming - check out the research by John Christy and Roy Spencer as well as others But nowhere near enough to fit the model's predicitons via AGW theory. And other data shows an opposite trend, nothing very conclusive to be had. And if you hadn't noticed, the troposphere has been cooling again more recently. |
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Post by steve on Apr 10, 2009 10:56:28 GMT
The area above the earth's spectrum and below the 255K line represents a rough measure of CO2's contribution to the greenhouse gas (that keeps the planet 30 or so degrees warmer than it would otherwise be). I don't see a lot to dispute about this except your conclusion the entire 30 degrees is attributable to CO2. Most of it is attributable to water vapor as you can see in all the diagrams. I didn't say/mean that - I've clarified the initial post. The bite is a measure of CO2's *contribution* to the greenhouse effect, the whole of which keeps the planet 30 or so degrees warmer. I'm trying to focus this thread just on the CO2 contribution to the greenhouse effect, so I won't answer the rest of your points here. |
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numas
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Post by numas on Apr 10, 2009 11:11:11 GMT
I reproduce Fig 4 here: Note: The peak of the Earth radiation curve is at the OZONE absorption. This is going to be far more critical than any CO2 absorption outside the main radiation passing out from Earth. The other two big "bites" are water (5-9 microns) and Ozone again at 15 Microns - while CO2 also absorbs at 15 Microns, it is likely to be mainly Ozone, given the massive 9.5 Micron Bite. I don't see much room for CO2 to have any measurable effect at all.  "In fact, pound for pound, ozone is about 3000 times stronger as a greenhouse gas than CO2." |
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Post by poitsplace on Apr 10, 2009 11:14:40 GMT
Kiwistonewall has dug out this paper that I think is a good illustration of the greenhouse effect (that keeps the earth warm), and of the potential for the enhanced greenhouse effect (ie. AGW - the additional warming due to CO2 emissions). *big ol' snip* Does that sound so unrealistic? It doesn't sound unrealistic...except you missed the point about. The analogy is that currently the bands CO2 deals with are so saturated that almost all the energy is ALREADY being forced out the other frequencies. When you look at the spectrum of the observed output of the earth, it's already skewed to have more radiation in other bands than it would. A good example of this would be...many parallel resistors. For most of the spectrum the energy has almost no resistance. Then we've got CO2 which already has a substantial amount of resistance. Adding more CO2 so it resists more has almost no affect on the overall resistance because there's very little energy going out there anyway. |
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Post by steve on Apr 10, 2009 11:35:32 GMT
The signal in the local temperature is far too small to be detected. Even if you assumed that the effect was the same as a doubling of CO2 as compared with the countryside, and assumed the extra heating of the extra CO2 stayed in the city and wasn't blown away by the weather, then the city would warm about 0.01C more than the countryside in a year, which is not at all significant. Not sure about the signature in the spectrum though. The levels of CO2 at above the clouds are probably more relevant for detecting a signature in the spectrum. These are less likely to be affected by local sources of CO2 at the surface. So even if CO2 levels exceed 500 ppm it wouldn't be detectable? And the heat would blow away but the CO2 wouldn't? If a 10km^2 city had emissions that kept local CO2 at 500ppm all the way to the top of the atmosphere as compared with 380 everywhere else, it would be equivalent to a heating of 150 megawatts. But obviously the CO2 will blow away as it rises in the atmosphere - see below. But if the city has a population of 1 million, their power consumption would be about 10 times this amount. Also, a variation of 1% in albedo would give a similar amount of heating or cooling. So the heating from the CO2 is relatively small. You are missing a key point about the greenhouse effect. Near the surface, the absorption is pretty much saturated such that the CO2 emits as much as it absorbs. The important effect of the greenhouse is high up in the atmosphere where the temperatures are 250 or so Kelvin. The CO2 in the cold high layers gives you an absorption line because it is absorbing parts of the spectrum from the warmer gas below it. Because the high layers are colder, the CO2 is emitting less than it is absorbing - the chance of a CO2 absorbing a photon then passing it to a N2 or O2 molecule in a collision is higher than the chance of the reverse process, where an unexcited CO2 molecule is excited by collision with an N2 or O2 molecule and then subsequently emitting a photon. You can see a similar effect with the Ozone. The ozone produces an absorption line for the same reasons, because it is a greenhouse gas. But if you look at higher resolution, there is a narrower emission line superimposed on the absorption line. This is due to emission from the stratosphere - the stratosphere is warmer than 250K (which is why you get an emission line), and the line is narrower because the pressure is lower. |
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Post by steve on Apr 10, 2009 11:51:10 GMT
I reproduce Fig 4 here: Note: The peak of the Earth radiation curve is at the OZONE absorption. This is going to be far more critical than any CO2 absorption outside the main radiation passing out from Earth. The other two big "bites" are water (5-9 microns) and Ozone again at 15 Microns - while CO2 also absorbs at 15 Microns, it is likely to be mainly Ozone, given the massive 9.5 Micron Bite. I don't see much room for CO2 to have any measurable effect at all. "In fact, pound for pound, ozone is about 3000 times stronger as a greenhouse gas than CO2." Welcome numas! The greenhouse effect is caused by water vapour, CO2, methane, ozone and other gases. It keeps earth approximately 30C warmer than it would be if the atmosphere were pure O2, N2 or argon. The *enhanced* greenhouse effect is the effect caused by *increasing* one or other of the greenhouse gases. The main concerns are the tropospheric *increase* in CO2, methane, N20, halocarbons *and* ozone. Normally debates get stuck on CO2 because the CO2 increase currently is having the biggest effect. Ozone is a stronger greenhouse effect, and it is increasing. But the the increase is less than for CO2 such that the effect is thought to be no more than 1/6 to 1/3 of the total enhanced greenhouse effect. This is the current IPCC assessment:  |
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