Some readers insist on denying the obvious fact that Venus temperatures are due to high atmospheric pressure. The latest argument being that the lapse rate is dependent on GHG levels. This is trivial to demonstrate as incorrect.
The first problem with that argument is that the lapse rate on Earth is very similar to Venus, despite very different atmospheres.
The second problem is that on Earth, water vapor is the most important GHG – yet the dry adiabatic lapse rate is independent of humidity (for unsaturated air.)
For an adiabatic process, first law of thermodynamics can be written as
ncvdT − VdT / γ = 0
For adiabatic process:
PdV = − VdP / γ
Also since : α = V / n and : γ = cp / cv we can show that:
cpdT − αdP = 0
where cp is the specific heat at constant pressure and α is the specific volume.
Assuming an atmosphere in hydrostatic equilibrium: [ 8 ]
dP = − ρgdz
where g is the standard gravity and ρ is the density. Combining these two equations to eliminate the pressure, one arrives at the result for the DALR, [ 9 ]
In other words, the lapse rate is fixed on Earth – whether greenhouse gas levels are high or low.