We live in an energy-dependent world. When we start our cars or heat our homes, we are using fossil fuels such as petroleum, natural gas, or coal. As the fuel burns, cars move and our houses warm. The carbon compounds in the fuels break down and carbon dioxide is released. We also use a lot of electricity – and the production creates a lot of carbon dioxide by much the same process. Each year, estimates show that Americans produce almost 19 metric tons of carbon dioxide. That's about 41,900 pounds of carbon dioxide. Sixty years ago (in 1950), the total for every American was about 4 metric tons, or just under 9,000 pounds. What has changed?