CO2 absorbs solar radiation only at a specific wavelength (14.77 microns). The first 50 ppm of atmospheric CO2 absorb most of the radiation at this frequency. he next 50 ppm absorb half as much, and so on. At 380 ppm (current level), there are no solar photons left to absorb at this frequency. Tripling the level to 1000 ppm would have no measurable impact on absorption of solar radiation (and, hence, on warming).