Hi, @
Nyx.
The mechanism for planetary heating by CO2 is pretty simple, but I've never seen it explained in the popular press.
First, think of a red filter. Red light goes straight through it, but blue light is blocked, usually by being absorbed by compounds which have been mixed into the glass when it was molten. CO2 gas has the same kind of properties as those compounds, in that it lets visible light through, but blocks light that is in the Infrared part of the spectrum. If your eyes could see those wavelengths, the air would look as black as soot. There usually isn't a lot of CO2 in the atmosphere, so the air at those wavelengths is merely really, really foggy and dark looking. Infrared cameras and imagers are designed to not look at those wavelengths, because there is nothing to see there. Everything is dark.
The temperature of the earth is a balance of the heat coming in from the sun, and the heat being radiated back into space. Space is cold, and like an icebox, if you have something at room temperature (like your face) and place it in front of an open icebox, the heat from your face will flow out into the cold and your face will get colder. You face is shining out heat in the infrared, just like a light bulb, just like the ground, and can lose heat that way.
Most of the heating energy from the sun arrives in the visible part of the spectrum, where the air is usually transparent. Sunlight streams straight down to the earth, and heats the ground.
As the ground heats up, it begins to radiate that heat back out into space in the form of infrared light, just like an iron heated by a fire begins to glow dull red (infrared), then red, then yellow, then white. The color of the heated rod depends on its temperature, and the "color" of the earth's dirt and water is infrared, because it is not that hot. The temperature of the earth results from the balance of the incoming sunlight and the outgoing thermal infrared light.
Unfortunately, adding more CO2 turns the air pitch black, and the heat (the infrared light) can't get through it to get back out into space. So, just like piling blankets onto a bed keeps your body heat in and keeps you warmer, the planet just warms up under the CO2 blanket and gets hotter and hotter.
The things that clear this CO2 from the air are its absorption into the oceans (like soda pop with fizzy CO2 dissolved in it, it dissolves your teeth and marine shells), the conversion of CO2 into plant material, and the weathering of rocks. But these processes are very, very slow to correct the damage CO2 does by heating the planet. Better to just not add more of it.
Planetary scientists can calculate the expected temperature of a planet, based on its size, distance from the sun, rotation rate, atmospheric composition, etc. If the earth didn't have its carbon-dioxide blanket at all, the average temperature would not be 58 degrees F, but would be slightly below freezing. Add a few more blankets, and it is not hard to figure out what will happen.