The amount of carbon dioxide in the atmosphere has been increasing for many decades now, mostly due to the burning of fossil fuels by mankind. In this exercise, students will track their daily activities, and and estimate how much carbon dioxide they are responsible for emitting with the use of an online Personal Greenhouse Gas Calculator developed by the U.S. Environmental Protection Agency (EPA). The calculator sums the carbon dioxide produced by driving, electricity use, and waste disposal, and provides an estimate of annual carbon dioxide emissions. It also allows users to see how changes in lifestyle could reduce carbon dioxide emissions. Links to websites with additional information are also provided.