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Post by jurinko on Nov 8, 2009 11:26:24 GMT
I think that blind attribution of the 15/33K temperature difference to back radiation of "GH" gases is similar to middle age theories, that planets fly around because being pushed by angels.
Angel theory has some elegancy, though.
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Post by steve on Nov 8, 2009 11:51:33 GMT
I have a question. Mars has 15x more CO2 in its atmosphere than Earth. It does not have water vapor and methane, so its effective concentration of "greenhouse gas" is cca equal to the earth. Why theoretical Mars temperature is 210K and actual temperature is... 210K? Where is the back ratiation heating the surface by 33K? Hint: Mars atmospheric pressure is 600 Pa, Earth atmospheric pressure is 101 300 Pa. Obviously, on earth a very significant greenhouse effect is water vapour, which Mars doesn't have. The thinner atmosphere has a lower heat capacity (and CO2 emission will cool it rapidly) which means more rapid cooling at night and near the poles. The rough Stephan-Boltzmann calculation works less well because of this.
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Post by steve on Nov 8, 2009 11:56:12 GMT
Kiwistonewall, A few questions. 1. I didn't see any mention of N2 in the plot, so why did you say N2. Also O2 is only referenced at less than 1 micron, where there isn't much radiation. 2. Your overlaying of outward radiation is problematical, because this is outward radiation *after* the effects of the transmittance. Eg. transmittance at 14-15 microns is zero - which is a measure of transmittance from the surface to space I assume. But because there is emission from the atmosphere as a whole, there is still outgoing emission of radiation at 14-15 microns. 3. When we talk about the forcing of a doubling of CO2, we are talking about a change in outgoing radiation of 3.7W/m^2 which is about 2% of the average. So throwing around figures like 65% or 70-80% leaves a *lot* of wiggle room even if I don't really accept that the figures are meaningful/accurate. In short, your plot basically dismisses the "saturation" argument that some people have, because despite 100% absorption of surface radiation at some wavelengths, the importance of emission and absorption of these same wavelengths is proven by the fact that there is significant outgoing radiation here. And it thereby leaves plenty of room for an increase in CO2 to have an influence as the emission around the CO2 wavelength is a significant fraction of the whole. Steve, you have failed (like most) by confusing thermal (ALL molecules) with spectral (discrete absorption at specific frequencies). Oxygen & Nitrogen account for the 20-30% absorption over the WHOLE spectrum - i.e. the difference between the curve & 100% - this is what we call a grey body system. No you are quite wrong. One of the things I learnt in my ding-dongs with Radiant was that water vapour has a continuum absorption between 6 and 13 microns. This probably accounts for the difference. Before you grab onto the "continuum" aspect, a lot of studies go into what mechanism results in this absorption. Nobody says, ah well yes it's just continuum emission from a grey body. The black-body grey body stuff is just theoretical thermodynamics. At the molecular/atomic level the photons have to be created by individual events. They don't just come out of the ether. Yes, I've noticed.
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Post by socold on Nov 8, 2009 14:17:45 GMT
I have a question. Mars has 15x more CO2 in its atmosphere than Earth. It does not have water vapor and methane, so its effective concentration of "greenhouse gas" is cca equal to the earth. Why theoretical Mars temperature is 210K and actual temperature is... 210K? Where is the back ratiation heating the surface by 33K? Hint: Mars atmospheric pressure is 600 Pa, Earth atmospheric pressure is 101 300 Pa. The greenhouse effect on Mars is about 10K. Which is to be expected because it does have a lower greenhouse effect than on Earth. 12 times the co2, but 2500 times less water vapor.
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Post by itsthesunstupid on Nov 8, 2009 16:35:37 GMT
Considering the differences in atmosphere composition between Earth and Mars, what is the common denominator for their similar temp fluctuation?
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Post by jurinko on Nov 8, 2009 17:28:55 GMT
The greenhouse effect on Mars is about 10K. Which is to be expected because it does have a lower greenhouse effect than on Earth. 12 times the co2, but 2500 times less water vapor. Not according to the NASA Planetary fact sheet. Blackbody and actual temperatures are both listed as 210K. If it is true that CO2 creates 5-20% of the earth "greenhouse effect", Martian 15x CO2 concentration should create effectively the same "GH" effect as on Earth.
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Post by spaceman on Nov 9, 2009 4:23:56 GMT
socold gave a very good description of how brownian motion of co2 keeps the heat here on earth from escaping. I guess the same laws don't apply on mars.
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Post by steve on Nov 9, 2009 10:16:50 GMT
Diurnal cycle on Mars at 19 degrees North: Radiation is proportional to T^4, so radiation at the warm part of the day is 3.5 times radiation at the cool part of the day. Measuring an average temperature here (plus at the poles) and attempting to equate it to a Boltzmann temperature is not a valid approximation.
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Post by kiwistonewall on Nov 9, 2009 10:22:52 GMT
Steve,Steve, PLEASE read up on thermal radiation. It is a property of ALL molecules related to the Boltzmann distribution & nothing to do with spectral absorption.
Why is it that real physics is "theoretical", but imaginary Physics a la IPCC isn't?
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Post by steve on Nov 9, 2009 11:23:54 GMT
Kiwistonewall, Kiwistonewall, I HAVE read up on thermal radiation, and brought up a number of papers in this thread.
See the references on emission and absorption in and around the 6-13 micron IR "window" that all the spectroscopers go on about and have been going on about long before the IPCC was invented and when Hansen was still an astrophysicist. They relate the absorption to states of water molecules in the atmosphere and not to oxygen or nitrogen.
Why can you not read these *real* physics papers based on *real* observations rather than believe your *theoretical* assumptions that the simple black-body grey-body approximations must be universally applied.
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Post by glc on Nov 9, 2009 13:26:56 GMT
I think that blind attribution of the 15/33K temperature difference to back radiation of "GH" gases is similar to middle age theories, that planets fly around because being pushed by angels.
Angel theory has some elegancy, though.
The surface (average temperature 288k) emits ~390 w/m2. Around 240 w/m2 is actually emitted to space from the atmosphere.
Can you explain what happens to the other ~150 w/m2?
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Post by icefisher on Nov 9, 2009 14:04:07 GMT
I have a question. Mars has 15x more CO2 in its atmosphere than Earth. It does not have water vapor and methane, so its effective concentration of "greenhouse gas" is cca equal to the earth. Why theoretical Mars temperature is 210K and actual temperature is... 210K? Where is the back ratiation heating the surface by 33K? Hint: Mars atmospheric pressure is 600 Pa, Earth atmospheric pressure is 101 300 Pa. The greenhouse effect on Mars is about 10K. Which is to be expected because it does have a lower greenhouse effect than on Earth. 12 times the co2, but 2500 times less water vapor. I thought water vapor was just feedback.
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Post by icefisher on Nov 9, 2009 14:05:32 GMT
Diurnal cycle on Mars at 19 degrees North: Radiation is proportional to T^4, so radiation at the warm part of the day is 3.5 times radiation at the cool part of the day. Measuring an average temperature here (plus at the poles) and attempting to equate it to a Boltzmann temperature is not a valid approximation. Since you are estimating the radiation rate of air Steve, you might want to consider its greybody characteristics.
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Post by steve on Nov 9, 2009 14:34:34 GMT
Icefisher
The *change* in the effects of water vapour is the feedback.
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Post by socold on Nov 9, 2009 19:20:27 GMT
The greenhouse effect on Mars is about 10K. Which is to be expected because it does have a lower greenhouse effect than on Earth. 12 times the co2, but 2500 times less water vapor. Not according to the NASA Planetary fact sheet. Blackbody and actual temperatures are both listed as 210K. If it is true that CO2 creates 5-20% of the earth "greenhouse effect", Martian 15x CO2 concentration should create effectively the same "GH" effect as on Earth. You are right, I was going by the Martian climate article on wikipedia which lists the observed temperature differently. I would expect Mars greenhouse effect to be weaker than on Earth because 15x co2 concentration is only 4 doublings above ours and there is no water vapor.
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