Cool...but what about the IR coming from the sun and stars? Wouldn’t an excess of CO2 prevent what you are explaining by increasing absorption in the mid/thermal IR bands which I know absorb less energy than the rest of the spectrum?
The atmosphere blocks most radiation coming from space, except in the visible spectrum. The surface of the earth reflects some of the light back into space, which is why the earth is visible to a camera in space. Some of the visible radiation is absorbed by the objects on the surface of the earth. Black absorbs strongly, snow not so much. Regardless, the surface of the earth converts the absorbed sunlight to heat. The surface then glows at infrared, depending on its temperature. This glow radiates away the heat. Air is warmed by contact with the surface, via convection.
The infrared glow of the sunlight-warmed earth is only partially absorbed by the CO2 in the atmosphere - only certain wavelengths. Just as absorbing sunlight warms the surface, so absorbing IR “heats” the CO2. The CO2 will re-reradiate the IR, unless it interacts with (”collides”) with another molecule first. The heating is dependent on the mean time between collision with another molecule being short compared to the mean time before it reradiates. Effectively all the IR that is in the bands that CO2 absorbs is converted to heat. The denser the CO2 the closer to surface the conversion occurs.