In this activity, students plot data on the concentrations of various greenhouse gases in Earth's atmosphere and look for trends. They will learn that greenhouse gases allow the Sun's light to pass through them to the surface of Earth, but also absorb some of the infrared radiation from Earth's surface. Students will discover that constructing graphs allows them to more easily spot trends in the data and also makes it easier to project what might occur in the future. They will also see that the quantities of several greenhouse gases are increasing in our atmosphere even though the production of chlorofluorocarbons (CFCs) is now decreasing.