Since you mentioned the mythbusters, that episode is really wrong, though I really love it because it is the only one of its kind I know of that uses more than

Since you mentioned the mythbusters, that episode is really wrong, though I really love it because it is the only one of its kind I know of that uses more than two gases. There is a real flaw there, which is the same in all those kind of experiments actually. And it is a real scientific flaw. If it were to be done properly, that would be interesting and I would bet it would reveal surprising results. As you mentioned, a structure is required. The CO2 is useless. By the way, on a greenhouse, CO2 has no function regarding temperature.