This is where the oversimplified argument gets in trouble: if it’s already opaque, adding more won’t make a difference, right? The science is something like: C

This is where the oversimplified argument gets in trouble: if it’s already opaque, adding more won’t make a difference, right? The science is something like: CO2 is so opaque to IR that the determining factor for warming is the part of the spectrum where it isn’t so opaque. However the thermal transport still goes through several bounces as it goes up through the layers of the atmosphere. At the higher layers the frequencies shift down and the absorption spectrum changes in complicated ways. This all interacts nonlinearly with water at the lower layers and ionised gases in the higher layers. Actually simulating something that won’t just give you gibberish answers is decidedly nontrivial. It’s not a question of precision — I’m not talking about +2C instead of +1.5C! An overly simplistic model will predict -50C or +100C!