NOVA

Many people find it hard to believe that humans are acting as a geologic force, outstripping even volcanoes as a contributor to global climate change. (dramatic music) Have you ever thought about how much carbon is in a gallon of gasoline? Let's weigh it and find out. (dramatic music) A gallon of gasoline weighs about 6.3 pounds, 87% of that is carbon, and that means there's five pounds of carbon in a gallon of gasoline. Think of that like a five-pound bag of charcoal briquets. (car engine revs) (dramatic music) When you burn gasoline, you create carbon dioxide and water. Carbon dioxide's an odorless, invisible gas, but think about this. What if the carbon came out of your tailpipe, not as carbon dioxide, but as solid chunks of carbon. (dramatic music) Kinda like car turds. So if the average American car gets around 25 miles to the gallon, that means that every 25 miles you're dumping five pounds of car turds out your tailpipe. The average mileage for each car is about 12,000 miles a year, so that releases over a ton of carbon. In the U.S., there are a total of about 100 million cars on the road, releasing about 330 thousand tons of carbon per day. (dramatic music) When we include the rest of the world's one billion cars, we reach three million tons of car turds every day and that's just cars. When we add in power plants, factories, aviation and agriculture, and multiply it by 365, the total carbon released by human activities in a year, is a massive 12.5 billion tons, enough to leave a pile of car turds four miles across and over a mile high. (dramatic music)