I've been asked to set up a table at a High school for earth day. I want to do something physics related, but I'm drawing a blank. I have access to all sorts of lab equipment. Any ideas? I think I might try the greenhouse effect with some 2L bottles, dry ice, and temperature probes. This is an outside event. Any suggestions? I doubt I'll have power, but I have battery powered probeware. I don't really want to make a sign or anything. I want to do some demonstration with standard equipment found in an educational science lab.