Something like 90% of all the radiation from the ground is already stopped leaving 40 left available for additional IR active gases. Lets take a wild guess (based on seeing spectra) that CO2 is active in 10% of all IR bands. That suggests massive increases in CO2 might cause an addition 4 increase in captured radiation. Lets assume this were to happen and this is called catastrophic doomsday alarmists were right sceptics are deniers warming .
Fallacy: oversimplification