Without carbon dioxide mean global temperature would be something like 18 F. Thank God for CO2.
“Greenhouse effect” is a misleading term. Greenhouses act by reducing convective cooling. “Greenhouse” gases convert normal IR radiation emitted by the surface of the earth to heat, and thereby shift the equilibrium temperature of the troposphere higher. Most of the absorption takes place in the upper troposphere. With or without additional “anthropogenic” CO2 effectively all of the IR emitted by the surface will be absorbed. More CO2 means it is absorbed closer to the surface.
The important questions are how much of a shift in the surface equilibrium temperature will occur, and what the consequences are.
A first order answer to the first question is simple physics, and it indicates that a doubling of CO2 will result in approximately 0.5 degree F of surface warming. In order to get a bigger number, +1 C, +5 C, +yourguessisasgoodasanybodies, alarmists posit amplification through positive feedback mechanisms. These feedbacks have not been observed and some (Roy Spence) believe that the evidence indicates that the feedbacks are slightly negative, reducing the first order effects. YMMV.
The answer to the second question, “what are the consequences?” is not easy to answer. There are likely to be winners and losers, but on net, a warmer world is probably a happier world. IOW, the current mean world temperatures are sub-optimal.
An often overlooked side benefit of enriched CO2 is more and better plant growth. The earth is becoming more verdant.
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?