The adiabatic lapse rate is the key component of the GHE. Regrettably I do not seem to fully understand it and so I need to ask for help.
The average lapse rate on Earth is about 6.5K/1km. The "dry" lapse rate however is said to be 9.8K/km. So vapor (and the latent heat it transports) reduces the lapse rate significantly, in this way it also serves as a kind of anti-GHG. I mean if we understand the GHE as a combination of an elevated emission layer (photosphere) where we have 255K and the adiabatic lapse rate, which produces higher temperatures at the surface. Anyhow, the exact impact of vapor on the lapse rate is a key question.
Now I found this sightly confusion chart on the subject on wikipedia. There are some things I understand, and some things I don't. For instance we have lines for altitude (scale on the right) which are sloped. That is to be understood relative to the left scale of pressure, meaning with cold air pressure will decrease faster with altitude, as it has a higher density.
https://en.wikipedia.org/wiki/Lapse_rate#/media/File:Emagram.GIF
Now if I look at the bold line for the dry adiabat, for instance the one starting at 20°C, it intersects the 5km line at roughly -24°C. That are 44K for 5km, or 10.8K/km, significantly more than the 9.8K quoted before. Assuming the chart is right, what causes this difference? Is it because the troposphere is naturally unstable and heated at the surface, so to say?
Then the "wet" lapse rate starting at +15°C intersects the 5km line at about -14.5°C, meaning a delta of 29.5K or 5.9K/km. +15°C roughly corresponds to the actual surface temperatures on Earth, yet 5.9K/km is significantly less than the quoted 6.5K. Why is that? Is it representing a more theoretical perfectly wet atmosphere with a 100% H2O saturation??
