Small-scale greenhouse effect demonstration

I was wondering whether it would be possible to demonstrate the greenhouse gas property of CO2 at a small scale. For example, if we took two rooms that were identical in every other way except for the fact that one of the rooms had a CO2 concentration that was, say, twice as high as the other, with this higher concentration being maintained continuously for the duration of the experiment, would the temperature of the room with the higher CO2 level have a distinctly higher average temperature? Or is the greenhouse effect a phenomena that only becomes significant at much larger scales?

If this effect is noticeable, would it be feasible to heat a room by raising its CO2 content relative to the normal atmospheric content rather than using heaters (which I am assuming requires more energy than just changing the mixture of gases and letting the greenhouse effect “do its work”)

I cannot see any mechanism by which a room with a higher CO2 concentration would retain more heat. Unlike the earth as a whole, the heat is not predominantly being lost by radiation through the air - or at least not through the air inside the room.

As to the second part, the greenhouse effect isn’t a source of heat. Just a source of insulation, if you like.

This. CO2 by itself won’t much a noticeably different heat capacity than normal air. In fact, CO2 has a lower heat capacity than air, so a room filled with CO2 would cool faster (assuming it was heated up to start with), with the heat loss being affected by the thermal conductance of the walls and windows.

However, you can demonstrate that CO2 absorbs infrared radiation and thus can behave as a greenhouse gas, as in this simple experiment which uses two bottles, one with CO2 enriched air (the CO2 can come from seltzer water, baking soda and vinegar, etc). Or, if you have an IR camera, you can do this experiment, in which a candle flame becomes invisible when CO2 is passed in front of it. Actually, this isn’t much different from the two rooms, except light is being shone into the bottles, which contain a black absorber which in turn emits IR, but the room won’t get warmer by itself.