Global Warming? It Just Ain’t So!
Written by Nick Schroeder, BSME, PE
Will Rogers (and Mark Twain) observed, “It’s not ignorance that is the problem, but that so much of what we know just ain’t so.” Adding to the “33C without an atmosphere” that is completely wrong is the case of Venus.
Venus, we are told, has an atmosphere that is almost pure carbon dioxide and an extremely high surface temperature, 750 K, and this is allegedly due to the radiative greenhouse effect, RGHE. But the only apparent defense is, “Well, WHAT else could it BE?!”
Well, this is what else it could be.
Venus is half the distance to the sun so its average solar constant/irradiance is twice as intense as that of earth, 2,615 W/m^2 as opposed to 1,368 W/m^2. But the albedo of Venus is 0.77 compared to 0.31 for the earth or 601.5 net ASR W/m^2 compared to 943.9 net ASR W/m^2.
The Venusian atmosphere is 250 km thick as opposed to earth at 100 km. Picture how hot you would get stacking 2.5 more blankets on your bed. RGHE’s got jack to do with it, it’s all Q = U A dT.
The thermal conductivity of carbon dioxide is about half that of air, 0.0146 W/m-K as opposed to 0.0240 W/m-K so it takes twice the dT/m to move the same kJ from surface to ToA. Put the higher irradiance, albedo, thickness and conductivity all together: 601.5/943.9 * 250/100 * 0.0240/0.0146 = 2.61.
So, Q = U A dT suggests that the Venusian dT would be 2.61 times greater than that of earth. If the surface of the earth is 15C/288K and ToA is effectively 0K then earth dT = 288K. Venus would be 2.61 * 288 K = 748.8 K, no S-B BB RGHE hocus pocus need apply.