We live in an energy-dependent world.

When we start the engines of our cars or turn on the heat in our homes, we are using fossil fuels such as petroleum (crude oil), 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 great deal of electricity – and the production of electricity also creates a great deal of carbon dioxide by much the same process

Each year, estimates show that all the things every American does produces 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? Find out by exploring the objects in each street scene. One scene shows a typical town in 1930. The other shows a town of today.