Car Pollution

 Today, there are more than 630 million cars in the world. U.S. drivers own a third of these vehicles, which in turn produce a third of the nation's greenhouse gases -- emissions (primarily carbon dioxide) that accumulate in our upper atmosphere and cause global warming. We're seeing the effects in weird weather, melting glaciers, and rising oceans that pose an immediate threat to many island nations. 
Refining, distributing, and burning a gallon of gasoline produces about 30 pounds of carbon dioxide. If every car in the U.S. were replaced by one that was 10 mpg more fuel-efficient, carbon dioxide emissions would be reduced by 250 million tons per year, and the nation's annual contribution to global warming would be cut by nearly 20 percent.