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Post by northsphinx on Jan 28, 2010 20:27:36 GMT
The picture Steve is showing what I have trying to tell You: The NET radiation between surface and atmosphere is small. Compared to the other way of heating the atmosphere. And that is because the temperature difference between surface and absorbing part of the atmosphere is low. Because the atmosphere absorbs very well heat radiation except for the 40 w/m2 passing in the atmospheric window. Note: nearly twice as much as the radiative balance between earth surface and atmosphere. What limit net radiation is lack of temperature difference. With an atmosphere more capable to absorb/emitt heat radiation will that have a net cooling capacity Because the temp difference between heating surface is far less than to cooling space. And net radiation is a matter of temperature differences. Take a close look again: See? Net radiative heating is 26 of the atmosphere from the earth surface Because of small temperture difference Net radiative cooling is 235 from the atmosphere to space. Because of large temperture difference. Nearly ten times larger net neat transfered by radiation.. Make the atmosphere an even better absorber/emitter with for example CO2 and what You get? A cooling of the atmosphere.
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Post by glc on Jan 28, 2010 23:20:53 GMT
glc writes ". There you are, Jim, I've considered them. I've assumed the 3 processes will be unchanged. However the CO2 concentration WILL have changed and this will affect the radiative transfer. The main effect of additional CO2 will be in the higher, drier, colder upper troposphere." Now we are on the same page. Can you supply a reference which proves that what you say is true; that the 3 processes will be unchanged. Preferably one that has been peer reviewed. I didn't say they would be unchanged. I said we've assumed them to be unchanged (just as I assumed normal flat terrain when calculating the time taken to walk a mile). Actually I don't know how many times I've written this ..10?, 20?, 50 times. I've almost always qualified the ~3.7 w/m2 result with the phrase "all other factors remaining the same". So, Jim, do you have any reason to think they won't remain the same. Of course they might act in a way that increases the warming. Lots of scientists think they will. A warmer atmosphere can hold more water vapour.
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Post by Ratty on Jan 28, 2010 23:42:04 GMT
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Post by jimcripwell on Jan 29, 2010 2:10:42 GMT
glc writes "So, Jim, do you have any reason to think they won't remain the same."
What I am trying to point out, is that by considering only radiative transfer of energy, you are dealing with a purely hypothetical situation. The only way to calculate what is happening in the atmosphere is to take into account all ways in which energy is transferred in the atmosphere at the same time. If, in the end, global temperatures rise by somewhere between 1 and 5 C for a doubling of CO2, and humidity rises as well, it is inevitable that the other 3 modes of energy transfer will change. What your methodology neglects is the interaction between all modes on energy transfer.
You can argue as much as you like, but I will never be convinced that this purely hypothetical approach tells anything at all about the real world.
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Post by Ratty on Jan 29, 2010 3:44:37 GMT
[Snip] You can argue as much as you like, but I will never be convinced that this purely hypothetical approach tells anything at all about the real world. Well said, Jim. I repeat: " The more I hear and read, the more it seems that nobody understands the system in its entirety. " - Ratty
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Post by steve on Jan 29, 2010 8:57:56 GMT
Which agrees with what I said then! You've changed the argument and missed the point. But where is your evidence that CO2 will have nil effect? The MODTRAN calculations suggest that in a clear sky, the difference would be about 1.6W/m^2 in a tropical atmosphere, and 3W/m^2 in a mid-latitude winter for a doubling of CO2 leaving all other things the same. It's only a 1% difference spread across a lot of the spectrum, so it is likely undetectable in a real atmosphere. I have, though, already said that, while interesting, clear sky examples are not a good example for demonstrating the greenhouse effect per se, because typically they are not in radiation balance. Except at dusk and dawn, they are usually either rapidly cooling or rapidly warming.
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Post by steve on Jan 29, 2010 9:09:23 GMT
glc writes ". There you are, Jim, I've considered them. I've assumed the 3 processes will be unchanged. However the CO2 concentration WILL have changed and this will affect the radiative transfer. The main effect of additional CO2 will be in the higher, drier, colder upper troposphere." Now we are on the same page. Can you supply a reference which proves that what you say is true; that the 3 processes will be unchanged. Preferably one that has been peer reviewed. There is possibly a misunderstanding between what you are saying and what I and glc think you are saying. Are you looking for evidence of specific changes to conductivity, convection and evapotranspiration that are due to increase of CO2 alone? If so, I think it is generally understood that a change of 300ppm of a minor gas won't change these things much. Conductivity is very small anyway, and there is probably a reviewed paper on air conductivity somewhere that will demonstrate this. I bet that conductivity within the atmosphere has been ignored by climate models. Convection is hardly going to be affected by a 30-50% increase in the mass of 0.03% of the molecules (based on ration of the mass of CO2 to the mass of N2 and O2. Some of the carbon cycle models look at effects on transpiration rates (some plants use less water in high CO2 atmospheres). Other than that, I doubt there is much effect.
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Post by steve on Jan 29, 2010 9:15:46 GMT
ratty, That's one thing that everyone can agree on - we have a consensus at last.
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Post by northsphinx on Jan 29, 2010 10:10:29 GMT
But where is your evidence that CO2 will have nil effect? The MODTRAN calculations suggest that in a clear sky, the difference would be about 1.6W/m^2 in a tropical atmosphere, and 3W/m^2 in a mid-latitude winter for a doubling of CO2 leaving all other things the same. It's only a 1% difference spread across a lot of the spectrum, so it is likely undetectable in a real atmosphere. I have, though, already said that, while interesting, clear sky examples are not a good example for demonstrating the greenhouse effect per se, because typically they are not in radiation balance. Except at dusk and dawn, they are usually either rapidly cooling or rapidly warming. Just three things left I start from the end. Clear sky condition is, I argue, a perfect example to find the limit of radiation of any cause. With a clear sky is "other" source of heat transfer reduced as much as possible. If the earth was in constant clear sky would that be the maximum effect of CO2. This rapidly night cooling must be the best way to actually measure the radiation balance between surface and atmosphere. Real measurement that show that except of atmospheric window is already ALL outgoing radiation absorbed. It also show that net heat transfer is very low. That show that net heating of the atmosphere is NOT a radiative heating. In fact of net heating to atmosphere of total 67+24+78+26 = 195 w/m2 is only 26 from radiation. Or approx 13% The cooling of the atmosphere is 100% by radiation And modtran: How often is it clear sky conditions? Not 100% Have You run the number at say altitude 5 km looking up-wards? A increased cooling larger than increase in absorbing at low altitudes. The result is NET a cooling of the atmosphere. Especially because at ground level is clear sky condition far less common than at 5 k altitude. The proof that increased CO2 have a cooling effect is Your figure and Your modtran link.
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Post by steve on Jan 29, 2010 11:12:48 GMT
northsphinx That the "net heat transfer" is by your definition "low" is not telling us anything! Your figures show that the emissivity of the atmosphere at night is *usually* lower than the emissivity of the surface. That's why the surface cools quickly. During the day though, the surface warms due to direct solar radiation, and the higher emissivity of the surface combined with the higher temperature of the surface will likely lead to a net warming of the atmosphere through radiation. With the addition of 300ppm of CO2, though, we are talking about a change in net heat transfer of 1 or 2 Watts which doesn't significantly change any of the discussion above, because it is a relatively small effect. Try this: geoflop.uchicago.edu/forecast/docs/Projects/modtran.orig.htmlTropical atmosphere, no clouds or rain. Default settings for everthing else. Look at outgoing radiation viewing down from 70km. Look at radiation looking up from 0.01km (ie. radiation towards the surface. With 280ppm Outgoing is 289.2 up and 347.3 down - cooling rate is 336.5 With 560ppm Outgoing is 286.0 up and 348.5 down - cooling rate is 334.5 So the MODTRAN shows that the net cooling rate of the atmosphere in clear sky conditions *reduces* when you increase CO2. The extra downward radiation is less than the reduction in upward radiation. Furthermore, you have to remember that the extra downward radiation is quickly going to be recycled back into the system - it is not lost.
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Post by Ratty on Jan 29, 2010 12:04:54 GMT
ratty, That's one thing that everyone can agree on - we have a consensus at last. At last I have made my first meaningful contribution to the forum!
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Post by northsphinx on Jan 29, 2010 12:51:23 GMT
CO2 =280 PPM? Why not use 380 and 2 x 380?
Use std tropical values just alter CO2, Clear sky conditions.
First CO2=380ppm Altitude 0 looking up = Iout, W / m2 = 348.226
Now with 2 x CO2= 760 Altitude 0 looking up = Iout, W / m2 = 349.796
Increase of about 1.5 W/m2 in heat transfer. That is if You think of it a increased COOLING of the earth surface with 1,5 W/m2 to the atmosphere.
Let then use 5000 meters altitude ;D CO2 = 380 Up Iout, W / m2 = 152.164 Down Iout, W / m2 = 348.54 Net Balance between altitude 0 and 5K is less than 1W/m2 ==>IR Radiation is not the main heat source for the atmosphere.
And with 2x CO2 Up Iout, W / m2 = 156.529 Down Iout, W / m2 = 347.284 Net Balance between altitude 0 and 5K is increased with about 2.5 W/m2. An increased heat transfer from ground to 5k level. Then an even higher net tranfer from this level to space with 4,365 W/m2
You see? More going out and less going back to earth if You add CO2. A cooling!
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Post by steve on Jan 29, 2010 15:31:28 GMT
CO2 =280 PPM? Why not use 380 and 2 x 380? I expect the results are similar. I usually pick 280 and 560 because 280 is the estimated preindustrial level of CO2. If you are looking up then you are looking at radiation *from* the atmosphere incident on the earth's surface. You have it the wrong way around. Again. You have it the wrong way around. Looking up, you see 156 Watts. That means 156 Watts coming down from above. The doubling of CO2 is leading to an increase in downward LW radiation and a decrease in upward radiation. Both ways result in a warming below 5km. You should have realised this. There is no way that total LW radiation at 5km is more from above than from below.
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Post by Pooh on Jan 29, 2010 16:24:01 GMT
Steve in Re: FAO Jim Cripwell et al: 2xCO2=1 deg waming « Reply #54 Today at 6:12am » "So the MODTRAN shows that the net cooling rate of the atmosphere in clear sky conditions *reduces* when you increase CO2." Good news and Bad news: The Bad News is that it is yet another model with options and parameters. A computer "model" shows little except the results of the theory/assumptions built into the model and the initial state. The Good News is that it was developed under the auspices of the Air Force and has undergone Validation and Verification processes. www.kirtland.af.mil/library/factsheets/factsheet.asp?id=7915"MODTRAN 4 SOFTWARE" "MODTRAN - MODerate spectral resolution atmospheric TRANSsmittance algorithm and computer model, developed by AFRL/VSBT in collaboration with Spectral Sciences, Inc.
"MODTRAN4 has been available to the public since Jan 2000. It remains the state-of-the-art atmospheric band model radiation transport model." A Fortran 77 compiler is needed.
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