Using a colorful infographic handout and a guide sheet, hold a class discussion about how a bathtub can serve as a model for the greenhouse effect created by Earth's atmosphere. Participants will understand that as energy or matter is put in, an equal amount must be removed in order to maintain balance. After the class discussion, learners pair up and draw flow rate curves for the amount of carbon dioxide gas leaving the atmosphere over a period of time. It's not necessarily an exciting lesson, but it is to-the-point, and the included infographic is an illuminating visual aid.