This is another time I don't really have great answers, but a question over at the question place has me thinking about it. Namely, what makes for a good experiment? As far as the science goes, I'm comfortable about knowing the answer. Or at least knowing enough of an answer.
But for the purposes of you readers -- what makes for a good experiment that you could do yourself? How big or small could it be? How long should it take to run? How much expense is ok? Is following a circuit diagram to assemble test equipment something you're comfortable with? Carpentry? And so on.
For the original question -- a tabletop demonstration of the greenhouse effect -- I might actually have an answer of sorts. I went running shortly after first reading the question. That's often a good time for ideas to come to me, and a few did. But at the moment, they'd take a pretty big table (like, say, 10 feet), you'd have to get hold of a dry ice supply (for the CO2), and you'd have to assemble a fairly simple circuit. A several Watt laser would also be a plus, but I'm going to try to make sure that the experiment will work without it.