The U.S. Environmental Protection Agency has just released a report showing that carbon dioxide emissions from light trucks, cars, and SUVs have fallen dramatically since 1975 even as the proportion of SUVs and trucks sold has increased to nearly half of all sales. Grams of carbon per mile have fallen from 579 in 1975 to 422 in 2009. Fuel economy has increased from 13.1 miles per gallon to 21.1.