Here is an example of science on the other side of the discussion. It represents for me though an example of a place where interpretation means everything. There is a chart on this page showing the IR absorption in the atmosphere. It shows it for 100ppm and for 1000ppm.
If I read correctly, he is saying "See at 1000 ppm, the band of absorption is wider".
I look at it an say, "See, at a 10X increase in concentration, you get a slightly larger absorption window. It ain't even 10% wider" (Excuse my eyeballs, I didn't get the ruler out to measure.)
--- OR ---
Wife says -- "He wants sex all the time, we have it like twice a week!"
Husband says -- "She never wants sex, we only have it like twice a week!"
Yes, I suppose I should have logged on to that site to comment, but couldn't be bothered. The childishly simple question to ask is "How does the concentration of a fairly rarefied gas affect its ability to absorb radiation?"
Note also how this (quite useful) thought experiment takes place on a waterless planet. I suspect that on a water world the trivial effects of CO2 will be totally overwhelmed by vertical mass transport and latent heat effects, aka clouds.
Normally, if two curves were that close to each other, you would assume that they were identical and that any apparent difference was an artefact caused by rounding or approximation. One needs the Eye of Faith to see any widening.
As all can see, I am a professional engineer and not a scientist.
The amount of CO2 is, so it is said, 385 parts per million.
(385/1,000.000) X 25,000 (gallons of water) = 9.625 gallons
So then, round it up to 10. It is not difficult to find a swimming pool with a capacity of 25,000 gallons.
So I propose a physical experiment. Measure the temperature in a swimming pool of 25,000 gallon size. Pour in 10 gallons of boiling water. Mix by running the filter pump for 1/2 hour. Then measure the temperature again. I would predict that there would be no discernable difference in temperature.
Since sunlight is a 1/2 day cycle, repeat daily.
That CO2 has any significant effect on the temperature of the atmosphere is obviously absurd.