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Post by northsphinx on Aug 4, 2009 13:29:22 GMT
...increasing Atmospheric Carbon Dioxide" The document is here: pubs.giss.nasa.gov/docs/1981/1981_Hansen_etal.pdfAnd this is much the fundamentals Giss rely on. In fact this document is their first published result. And I do have problem with their assumptions. Basic radiation formulas, their (3), use the assumption that the lapse rate are LW radiative induces. It cant be in an Grey atmosphere. And this is the base for the entire document. And for the AGW hypothesis. (4) is also calculating with a significative radiative net flux which is close to zero due to small temperature differences available IN the atmosphere. To begin with. Now time for a cup of coffe.
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Post by northsphinx on Dec 13, 2009 11:01:13 GMT
Back from the coffee
Hansen et al is wrong.
What they miss is that CO2 absorb and emit equally. If the atmosphere should absorb Infrared radiation must there be a net heat transfer to the atmosphere. That is impossible within the atmosphere. To have a heat transfer within an absorbing atmosphere must there be a temperature gradient large enough to drive energy upward. Otherwise will there not be a net heat transfer by radiation.
Divide the atmosphere into multiple layer. Each layer absorbs and emits all IR energy in the CO2 band . Each layer absorb and emit energy equally well. The net energy transfered between each layer is depending on the temperature difference between these layer.
Our atmosphere lapse rate is 6.5 K/km.
The "problem" is that CO2 absorbs/emits 100% in less than 100 m. Each layer is then less than 100 m. A temperature difference between each absorbing/emitting layer of less than 100 meter will have a very low heat transfer capacity. With Stefan–Boltzmann law is the net heat transfer a function of temperature differences between each layer. But with a temperature difference of less than 0,6 K between each layer will the net transfer within each layer be in the range of nothing. CO2 cant trap energy in higher layer because there is no energy there to be trapped from under neat. Co2 absorption does not miss a lot of layer and then get trapped . Impossible.
Result? CO2 does only have an effect in the first layer between the earth surface and the atmosphere. There and only there is CO2 able to have an absorbing capacity = net heat transfer to to atmosphere. This depending of the temperature difference between the atmosphere and the surface.
In the atmosphere is the CO2 window not widening depending on more CO2. The window is already as wide as it can be due to CO2.
The CO2 heating capacity is in practice the first meter of atmosphere and have a very low impact in reality. Wind convection and evaporation have much larger impact in real life than CO2 absorption.
And with a higher level of CO2 will that just shorten the height of the first layer that have a impact. That is no difference in real world.
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Post by aj1983 on Dec 13, 2009 13:21:20 GMT
Your reasoning is very amusing, but incorrect. If you have actually studied (atmospheric) physics you should think again and be able to find your mistakes. I would suggest you start calculations with a few layers, and generalize your equations to see what will happen if the amount of layers go to infinity.
Good luck,
AJ
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Post by northsphinx on Dec 13, 2009 15:09:56 GMT
Funny You mentioned it aj1983. The result is that you cant transfer heat by radiation within CO2 absorbing/emitting bands inside a well CO2 mixed atmosphere. Not at all. Not now and not with double CO2. It is already blocked by CO2. An that is a mistake even now days "Sir" John Houghton does in his book "The physics of atmospheres" Read it with an open mind. It is interesting Oh, I forgot the literature references. Co2 absorption can be considered as a cloud from ground to space. Google "radiative heat transfer in clouds" as a start. Just an example: "The heat generation is almost zero inside the cloud because of the large optical thickness of the cloud droplets. On the other hand, radiative cooling or heating occurs in the thin layer beneath the cloud surface. The thickness of the radiation transfer layer is approximately 20–40 m. The lower surface of the cloud is heated by radiation from the ground, while strong radiative cooling occurs on the upper surfaces of the cloud.. " From ams.allenpress.com/perlserv/?request=get-abstract&doi=10.1175%2FJAS-3268.1The "cloud" itself block inside heat transfer. CO2 is a cloud from ground an to top of atmosphere. No radiative transfer inside that cloud either.
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Post by steve on Dec 13, 2009 16:25:32 GMT
Don't have long. But this:
is wrong.
100% of what?
Where in the atmosphere?
Spectral bands have a width, and their effectiveness tails off at the edges. So some bits of the spectrum may be 100%, but others will be 50%, 20%, 1% etc.
The higher you go in the atmosphere, the thinner the air. If it is 100m near the surface it will be 200m at 6km or so up.
A 0.6C difference surely cannot be dismissed as insignificant if we are talking about temperature rises of not much more than this.
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Post by aj1983 on Dec 13, 2009 17:40:08 GMT
Comparing CO2 (a gas) with a cloud (liquid and or frozen water droplets) is another mistake.
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Post by Purinoli on Dec 13, 2009 18:22:43 GMT
Comparing CO2 (a gas) with a cloud (liquid and or frozen water droplets) is another mistake. In fact, water has a significant greenhouse effect, CO2 minor one. After all, there is about 100 times more water vapour in the atmosfere than CO2. And cause of more or less clouds is an important key. Measuring this effects is not an easy or simple task. For example, clouds can cause greenhouse effect but also reflect sun's irradiation back to space =>cooling Earth and vice versa...And amount of water vapour is also much more important than CO2... A very good explanation about CO2 story can be found in an excellent work of German scientists : icecap.us/images/uploads/Falsification_of_CO2.pdf
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Post by northsphinx on Dec 13, 2009 21:21:13 GMT
Ok Maybe You get it if it from another source landshape.org/enm/optical-depth-of-co2-explained/"his follows from the fact that the mean free path of the photons that interact with atmospheric components is so short that there are no appreciable temperature differences along this path [order of meters]. Not even higher up in the stratosphere. So almost all heat transfer [save direct IR radiation through the atmospheric window] from surface upwards is by vertical convection, with or without water condensation. This means a very efficient negative feedback of water vapor on surface temperature."
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Post by steve on Dec 14, 2009 9:28:33 GMT
The atmospheric window to IR is 6-13 microns - right in the main part of the surface radiation spectrum. So they are ignoring a main part of the emission spectrum. At the edge of this window (13 microns) is the CO2 absorption. Add more CO2 and this gets a bit wider.
For reasons similar to the above, this bit is wrong wrong wrong:
The fact that IR telescopes can see different layers of clouds at different temperatures ought to be a clue that this might be wrong.
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Post by poitsplace on Dec 14, 2009 10:17:24 GMT
I think a bigger problem is ignoring the percentage of the contribution from water vapor. Energy emissions from the atmosphere are pretty much only within the spectrum of the greenhouse gases. Due to the abrupt drop-off in atmospheric concentration of water vapor at about the temperature at which water freezes, water vapor emits almost all the energy of its spectrum at levels along the line of about a 0C black body emission curve. About 2/3 of that energy just goes straight out into space.
The rest of water vapor's spectrum overlaps CO2's spectrum. For some stupid reason everyone treats the so-called "back radiation" as if it was doled out to CO2 and ONLY CO2 could ever deal with it. However...with concentrations approaching 1% (as opposed to .04% for CO2) you can be sure that any "back radiation" from CO2 is insignificant near the surface...but once it's near the surface 2/3 of it gets tossed straight out of water vapor's window and at over twice the emission rate.
Obviously some balance has long since been struck between CO2 and water vapor...and water vapor has been spewing the bulk of CO2's radiation. With water vapor spewing about five or six times the energy of CO2...CO2 just doesn't have enough energy to emit in the first place.
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Post by northsphinx on Dec 14, 2009 11:03:43 GMT
But Steve;
The fact that IR telescope see different layer of clouds is the proof. What the IR measurement see is the boundary of the cloud for that spectrum. Check any IR satellite measurement of a cloud. IR does not see through a cloud that absorb/emit in the same spectrum.
And guess what the You see in the CO2 spectrum from the space. Yes. Top of the atmosphere temperature. Or as I would say: temperature of the CO2 cloud top.
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Post by steve on Dec 14, 2009 11:29:54 GMT
Who are these people problematically ignoring water vapour? I have to say that the 2/3 going to space statement must be taken with a pinch of salt since half of the emission goes downwards, and a large percentage goes sideways at a not very large angle.
Also, Kirchoff's theorem would tell you that bald statements that 2/3 of energy go straight to space sounds a bit dodgy given that gases emit and absorb at the same frequencies.
And water vapour can and does exist in the atmosphere at well below 0C.
Obviously at heights of 4-5km and above, where emitted radiation does seem to stand a better chance of getting to space, the relative proportion of CO2 is more significant. Anyone like to find out what typical water vapour levels at 5km up are (ie. not when there is a great big cumulonimbus).
The arguments about "overlapping spectra" and so fortth misses the fact that most of the energy transfer between molecules is by collision, not by transfer of photons. The average number of photons emitted by a CO2 molecule is almost entirely dependent on the temperature and pressure of the gas, and is virtually unaffected by the relative proportions of H2O, CO2 etc. (The same arguments don't quite apply to H2O as water molecules can temporarily combine with each other which changes the spectral lines they emit and absorb - the level of humidity will change the proportion of this sort of emission).
No doubt someone will be along shortly to further confuse things by claiming we are ignoring convection and conduction...
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Post by icefisher on Dec 14, 2009 15:11:16 GMT
A 0.6C difference surely cannot be dismissed as insignificant if we are talking about temperature rises of not much more than this. LOL! OK its a significant amount of an insignificant temperature rise. You can have that point!
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Post by poitsplace on Dec 14, 2009 18:32:43 GMT
Who are these people problematically ignoring water vapour? I have to say that the 2/3 going to space statement must be taken with a pinch of salt since half of the emission goes downwards, and a large percentage goes sideways at a not very large angle. I can see where that would be misleading. Let me rephrase. About 1/3 of water vapor's spectrum overlaps with CO2. Of the 2/3 of these frequencies that are NOT covered by CO2...they're allowed to radiate straight out into space at energy levels just a bit below the 0C black body curve...because there's just no water vapor up there to stop it. The remaining 1/3 has to traverse CO2's spectrum above. But if CO2 increases caused any rise in the amount of "back radiation" it would still have to go back through that layer of water vapor. Guess what happens to much of the "back radiation" as it passes through the layers with more water vapor? Yep, 2/3 of the forward radiation that comes off the water vapor is radiated outside of CO2's spectrum.
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Post by steve on Dec 14, 2009 20:31:40 GMT
Who are these people problematically ignoring water vapour? I have to say that the 2/3 going to space statement must be taken with a pinch of salt since half of the emission goes downwards, and a large percentage goes sideways at a not very large angle. I can see where that would be misleading. Let me rephrase. About 1/3 of water vapor's spectrum overlaps with CO2. Of the 2/3 of these frequencies that are NOT covered by CO2...they're allowed to radiate straight out into space at energy levels just a bit below the 0C black body curve...because there's just no water vapor up there to stop it. The remaining 1/3 has to traverse CO2's spectrum above. But if CO2 increases caused any rise in the amount of "back radiation" it would still have to go back through that layer of water vapor. Guess what happens to much of the "back radiation" as it passes through the layers with more water vapor? Yep, 2/3 of the forward radiation that comes off the water vapor is radiated outside of CO2's spectrum. You make it sound like a tennis match.
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