(third post in a series dedicated to the planet Venus as “example” of runaway greenhouse warming)
Venus post #1: Venus: Cool Greenhouse?
Venus post #2: Venus Warming Revisited
Venus post #3: Venus Missing Greenhouse Warming
Venus post #4: Venus and a Thicker-Atmosphere Earth
Let’s compute (in a simplified manner!) what would happen were Earth suddenly equipped with an atmosphere as massive as Venus’ (ie 90 times more than ours).
Given the similarities in mass and diameter of the two planets, we can assume this new atmosphere would behave similarly to Venus’, and in particular, purely adiabatically below 60km (instead of below 12km as at present).
For another simplification, let’s also imagine the new atmosphere to be just as our current one but without any water.
The lapse rate for dry Earth atmosphere is known and is 9.760 K/km.
How higher would the surface temperature be, with a dry atmosphere and a 60-km-thick troposphere?
9.760 * (60-12) = 468K higher than at present (288K)
The total for Earth is then 756K. Compare that to Venus’ surface temperature of 735K.
For an amazing coincidence, that’s 97% of the above, whilst the ratio of absorbed Solar radiation at Venus compared to Earth is… 96%.
Note how the increase in temperature doesn’t depend on any greenhouse gas.
And so do we really need to believe in greenhouse warming when mere mass can explain the observations?