If you write an Assessment Report for the IPCC about greenhouse effect on Earth, with much uncertanties, you would certainly want to compare it with other cases like planet Mars to validate assumptions. That's Science and the scientific method, assuming that the same physical laws are correct on Mars as well. There isn't any of that in the Third Assessment Report. Not a single study. Hans Erren calculates the CO2 forcing like this: http://members.lycos.nl/ErrenWijlens/co2/howmuch.htm Now if you would really want to calculate greenhouse gas forcing, there is a splendid object for that. Mars and its CO2 atmosphere. So let’s do an attempt. Mars fact sheet: http://quest.nasa.gov/mars/background/vitals.html Median value is not necessarily the average value so let’s peek some more for an average temperature: http://science.howstuffworks.com/terraforming1.htm On the other hand it’s -55C in several other sources like: http://www.nineplanets.org/mars.html So let's use both values, then the average Mars temperature is about 210K/218K; 6 degrees lower or 2 degrees warmer than Black body but Mars albedo is 0.16. Suppose that relationship was linear (it probably isn’t), then the basic temp of a 16% reflecting body could be (273-217)*0.16= 9 degrees lower, hence 208K. So, if that’s to be correct, then the greenhouse gas effect on Mars is 2K or 10K degrees. But I’m sure that this linear relationship that I assumed is wrong. Who can help? Now, 95% of the 7 millibar atmosphere is CO2, let's say: 7 millibar CO2. Earths atmosphere contains 380 ppmv CO2 (0.38 pptv) in a one bar atmosphere, this is equivalent to 0.38 millibar that's 17-18 times less than Mars. So, You’d need a little more than 4 times doubling (0.38 -> 0.76 -> 1.52 -> 3.04 -> 6.08) to get to the Mars CO2 concentration. So Mars greenhouse effect of CO2 is over 4 times as strong as on Earth. But the greenhouse effect appears to be only 2K or 10K degrees, hence Earths greenhouse effect in total for CO2 should be one fourth of that: 0,5K or 2,5K? But then again, is there greenhouse effect on Mars? http://www.deccanherald.com/deccanherald/feb282005/snt2.asp Conclusion. There is no chapter in the Third Assessment Report of the IPCC about greenhouse effect of CO2 on Mars, to validate Earth greenhouse effect because the greenhouse effect on Mars is negliglible, despite the strong CO2 concentration (~17-18 times stronger than on Earth). So if it doesn't work on Mars, why not write it down in an objective assessment report? Because we are not dealing with science but ideology and politics?
I think you have a good point. Mars is an interesting test case for CO2 calculations. I am too lazy to do more than suggest some things: (1) Use the mean (twice), max and min positions to calculate the solar heating (inverse square with range to sun) but average of these four "quarterly positions" and Mar's thermal inertial should give reasonable estimate of energy that needs to be re-radiated into space, to keep surface temperature constant. (It will be lower at the poles and higher at equator, but I would ignore this at least in first pass at answer.) (2) If one - same albedo is used (1 - 0.16 = 0.84) as emissivity (probably can find more accurate value of emissivity in the IR) then initially assume no atmosphere and calculate temperature of "gray body" (.084 times black body) required to get rid of the solar energy absorbed. (Again ignoring pole to equator variations) (3) Now with that spectral distribution of IR (from temperature of step 2 gray body) add up all "out bound" IR that cannot make it thru the actual atmosphere. (4) Return to step (1) but add as if fully absorbed this "blocked IR energy" to the gray body solar absorbed. - continue in this cycle until it stabilizes with only modest change for prior pass thru the cycle. (You do know that the total radiation is proportional to T^4 of black body - quick skim of your post made me wonder.) Hope you are less lazy than I am and provide us with some results. Again you point is well taken, but I bet the effect of CO2 will turn out to be much more than 2 degrees warming you estimated. To make procedure more accurate improve step (3) - learn about "optical thickness" and get IR emissivity at the peak wavelength of step (2) temperature. (This will change with each pass thru the loop but not much with the 2nd to 3d pass.) I have neglected the atmospheric radiation, when assuming you should add all the "blocked IR" back to the sun's input. This will make your CO2 heating too large. (An "upper bound", but knowing your bias, I assume that is what you want to claim / show CO2 is not that big a deal. I.e. error to the "advantage of your adversary" and still show you point.)
