Some background on Greenhouse Gases
The sun is a giant thermonuclear fire ball that is held together by gravity. Because of its mass and composition, the sun emits light mostly centered around the visible spectrum but with a great deal of IR.
Solar spectra have been directly measured. The sun puts out a ton of IR and we even know why it does this.
Energy is conserved. As an immediate consequence, if something takes on energy from another source it must manifest it in some way.
CO2, absorbs IR radiation very well. This has been known since 1896.
If matter interacts with light, several things can happen.
The light can be absorbed. This causes the molecules of the matter to vibrate and do various mechanical motions. This is what heat is. If you doubt heating occurs in this way, sit outside on a sunny day. It is cooler in the shade, because you are not absorbing as much light and warming up.
If light gets reflected, energy is still conserved. The thing doing the reflection does not heat as a result. The energy comes in and then it goes out.
If the bonds of the molecule are just rightly tuned to the frequency of the incident light, as is the case with CO2 and IR, is that the light is absorbed and then re-radiated out some time later in all directions.
That means that IR that was reflected by the Earth’s surface can get caught by CO2 in the atmosphere and re-radiated back down where it has another shot of getting absorbed and heating something.
This is called the greenhouse effect.
This is a property of the material. If you have more of it, you have more energy trapped in the Earth system and the Earth gets hotter because energy as always, is still conserved. The re-radiated light has a second chance to get absorbed and turned into heat. The more re-radiation you have, the hotter you get. The Earth cools by radiation ultimately also. The real issue is that this alters the rate of heat flow in compared to the rate of heat flow out.
Past this point, there is NO debate. There is none. if you get this basic science, then you must conclude that adding more CO2 means trapping more IR.
To believe that adding more CO2 to the atmosphere would not cause warming is like believing that adding three table spoons of salt to your coffee would not alter the taste. These are properties of the materials. They do what they do.