Venus vs Earth: Atmospheric Mass, Pressure and Temperature

To help Lennart Bengtsson (as discussed in the previous post) to come up with his computation of the temperatures on Earth and Venus with switched atmospheric composition (with mass conserved), I suggest to take a look at the above picture comparing temperature and pressure through the atmospheres of Venus and Earth. We see that for pressure between 10 and 1000 bar the temperatures are pretty much the same (the difference can probably be explained from the fact that Venus is closer to the Sun), indicating that the composition of the atmosphere has little influence at the same pressure, and that it is the large mass and resulting high pressure that makes the surface of Venus about 450 C warmer than that of the Earth.

From the picture we can estimate an Earth-temperature of 15 C with Venus-atmosphere composition (2400 times as much CO2), and a Venus-temperature of 450 C with Earth-atmosphere composition. That is, no difference!