Quote:
Originally Posted by Bored Wombat
Mars' greenhouse effect is about 5K to 10K.
Much less than earth's of about 30K.
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Let's see, a calculation of mean temperature for an object at Mars' orbit with an albedo of about 12% is about 217 assuming no atmospheric absorption. Let's see, a recent textbook (Chaisson & McMillan) puts the average T for Mars at about 217 degrees. 217-217 = 5 to 10. Congrats on your new math wombat.
To clarify slightly, estimates for the mean T of mars range from 210 to 227 K. That places the atmospheric warming at between a cooling of 7 deg K and possibly a warming of up to 10K. Hence, the information available suggests that there is likely no warming occuring. Note that this is with 40 times the actual amount of co2 present in the atmospheric column of mars compareed to that of earth. This is equivalent to over 5 doublings over that of earth's approximately 10 doublings.
Considering that each doubling produces approximately an incremental value of around the same amount, one is stuck with the range for mars of a doubling producing anywhere from a -1/3 deg K up to possibly as much as just over +1/2 deg K, taking the 227K T which doesn't seem to be quite as popular as lower T values.
Comparing with earth, which does have higher atmospheric pressures that offer greater broadening from other sources, but not much self broadening or broadening by other co2 molecular pressure, your number of 30 K for a T increase can also be compared. The number 95% has been attributed to h2o and that is most likely quite valid when considering cloud effects. It's too high for just vapor. But then, around half of the earth's atmosphere contains clouds so a mean value of 30K rise due to our atmosphere would not be valid for clear sky only scenarios. Hence, I'm using 95% attributable to h2o, leaving 5% to others. That leaves 1.5 K available for other sources. If we assume co2 constitutes all of it (which is wrong) then for our 10 doublings worth of co2, we have the sum of 1.5K. Roughly being equal, that provides us with 0.15K rise per doubling.
Ignoring with line width variation, a 0.15k rise per doubling would offer about a 2.2k deg rise in mean martian temperature.
As a quick aside, the eccentricity of the mars orbit is significantly greater than that of earth's. A mean temperature measurement that doesn't take this into account could easily be off by a serious amount. Since mars spends more time further out, higher T values occur during less time than do lower and could explain the high reading 227k which is competing with 217 and even 210k measurements.
btw, none of this includes the dust factor warming. Atmospheric dust on mars can reach total coverage of the entire planet in massive dust storms.