The problem is that the coefficients come from interactions that are a question of biology, chemistry, solubility, etc. We know what CO2 does to sunlight transmission (physics) and to infrared transmission (physics). We do not know quantitatively how that effect relates to temperature change, other than it should produce some temperature change and there should be (mostly negative) feedback loops that suppress that change.
“We know what CO2 does to sunlight transmission (physics) and to infrared transmission (physics).”
Knowing such thing is trivial and doesn’t mean that “the physics is clear” and even less that more “CO2 means more warming”.
1) CO2 has much less absorbing bands than H2O, thus is a much less powerfull the greenhouse gas than H20 (physics). 2) More CO2 means less H20 because the sum is supposed to be constant and set by pressure which is set by gravity (physics).
So more CO2 means more weak GHG as a whole (physics), means less “greenhouse” effect, means LESS warming.
Besides, CO2 absorbs the same bands that are already absorbed by H2O and since H20 is much more concentrated and more absorbant, there is not much left for CO2 (the “forcing” law of CO2 as a function of concentration is logarithmic and is out of the hat, not much physics in here, accept for window dressing).
So adding CO2 (and supposing it does not displace H20, which is an UNphysical hypothesis) to an already saturated medium should not change anything, like using black paint on an already black surface.
So no, the physics is NOT clear. It may be as well be that the “greenhouse” effect (which BTW has nothing to do with the real greehouse effect which involves convection, isn’t that telling us how bad climatism is?) has never existed, except in computers.