Mercury is closer to the Sun than Venus but with no atmosphere, and it's slightly cooler than Venus. Explain that one Galileo.

How about this experiment? Build several greenhouses but use partially-reflecting glass that allows as much radiation out as it does in, so that just the glass alone won't change the temperature. Fill one with CO2, a few others with other greenhouse gases, and leave the last one with a normal atmosphere. See which ones get hotter than the others.

Or just read the fucking textbook that explains what a greenhouse gas does. I'm sure somewhere in there it describes the experiment that proves it.