[cbacba]

for amusement, here is a quick very rough back of the envelope calculation of co2 in the atmosphere for earth, venus and mars

earth - about 0.056 moles/ square inch surface to space column. 1 mole is avagadro's number of molecules (6.023E+22).

venus - about 10330 moles/ sqr in or 184000 x the amount of earth

mars - about 2.24 moles / sqr in. or 40 x the amount of earth.

typical venus surface temperature 735k

typical earth surface temperature 288k

mean mars surface temperature 227K

Typical venus TOA insolation based on 0.72 AU = 2636 w/m^2

Typical earth TOA insolation based on 1.0 AU = 1367 w/m^2

Typical mars TOA insolation based on about 1.5 AU = 607 w/m^2

net result - the absolute temperature on venus is about 2.5 x that of earth with 184000 times the co2 level and twice the incoming energy at TOA. (note that clouds block the vast majority of incoming energy and outgoing energy anyway).

The absolute temperature of mars

the absolute temperature is about 3/4 that of earth with about 1/2 the incoming solar insolation and 40 x the co2 levels.

note that the 40x is actually the number of molecules of co2 in the path which is directly proportional to the optical pathlength tau and the amount of attenuation of the absorption is exp(-tau*pathlength) where tau is a function of density (molecules/ (Area * distance) in path).

for mars to balance radiatively, the outbound LW over 4*pi*r^2 needs to balance with the I*pi*r^2 of the SW incoming. or the output LW needs to be I/4 = 607 = 151.75 w/m^2

using stefan's law with sigma = 5.67E-8 J/s*m^2*k^4

determining T comes out to be 227K - assuming emissivity of 1.0.

for the nominal temperature observed of 227K this is exactly what is expected for a blackbody radiator and calculated using stefan's law and ignoring the atmosphere.

Note that the 0.15 albedo is for sunlight and is probably the Bond Albedo which is visible only. Emissivities for rocks and sand tend to shoot up into the > 0.96 realm for LW radiation even when the typical visible light emissivity is in the range of 0.85 (corresponding to 0.15 albedo).

Hence with 40 times the amount of co2 in the atmosphere, there is no obvious observable greenhouse effect where the atmosphere is moderating the climate there in excess of 1 deg K or so.

Note that the only other difference is going to be less line broadening due to lower pressure which spreads out the tails of the absorption lines while reducing the peaks somewhat. Trying to put that in is well beyond the scope of a back of the envelope calculation.

Perhaps this will put a bit more perspective on interpretting and understanding what is involved in the GHG based GW and it's comparison to other examples.