Does it? That's the old 'glass pane' greenhouse effect theory first postulated in the 1880's. But does our atmosphere actually act like a glass pane greenhouse? Does CO2 act like that? I've read papers from scientists that dispute that.
Dr. Roy Spencer, who is not a Warmista, does satellite measurements of IR radiation out into space by the planet and compares that to IR measurements at the surface. There is a significant difference between the two, but as I said before, the amount of heat trapped by greenhouse gasses is small and varies slightly by the total concentration of these gasses (all of them). Analyses show that after CO2 reaches a certain concentration, it no longer traps more heat, but allows it to pass on through. This little fact is what drives the warmistas nuts about Dr. Spencer, because he proves more CO2 WILL NOT result in more heat staying in the atmosphere.
Also, he has proven the correlation between CO2 concentration and "global average" temperature is very weak, orders of magnitude weaker than assumed by ALL the climate models. So weak in fact as to be statistically insignificant.