It is my understanding that increasing CO2 in the atmosphere reaches a saturation point, a point that after which you can add all the CO2 you like to the atmosphere and it will not increase temperatures any further. It is my understanding that the maximum warming that could occur with additional CO2 is about 1 degree celsius. You could take CO2 all the way to 6000ppm at which point it would become letahl to humans and you would still only have the one degree of warming.
Correct me if I am wrong, but I don't believe I am.
I've seen this aspect mentioned frequently, and this is a skeptical "talking point". My understanding is that this is a misapprehension of how CO2 energy absorption and re-radiation actually takes place. Below is the IPCC's short-and-simple statement:
"It has been suggested that the absorption by CO2 is already saturated so that an increase would have no effect. This, however, is not the case. Carbon dioxide absorbs infrared radiation in the middle of its 15 mm band to the extent that radiation in the middle of this band cannot escape unimpeded: this absorption is saturated. This, however, is not the case for the band’s wings. It is because of these effects of partial saturation that the radiative forcing is not proportional to the increase in the carbon dioxide concentration but shows a logarithmic dependence. Every further doubling adds an additional 4 Wm-2 to the radiative forcing."
http://motls.blogspot.com/2006/05/climate-sensitivity-and-editorial.html
An alternate view: http://www.realclimate.org/index.php/archives/2006/01/can-2c-warming-be-avoided/
Rather than discuss the physics, the authors imply that the CO2 itself will warm the air 2C. But their method obviously includes feedback, so it's not the CO2 doing the warming it's the water vapor in an uncertain and poorly modeled weather model.