In an effort to help persuade federal regulators to raise fuel efficiency standards for automobiles, Environmental Defense released a report entitled ' Global Warming on the Road'. Their findings suggest that cars driven in the U.S. are responsible for roughly half of the global greenhouse gas emissions from automobiles. This is true, despite the fact that the nation's vehicles account for 30% of the roughly 700 million cars operating worldwide. Environmental Defense attributes this to more miles driven, lower fuel economy standards, and the use of more carbon intensive fuels. According to the report, "U.S. cars and light trucks were driven 2.6 trillion miles in 2004, equal to driving back and forth to Pluto more than 470 times". Surprisingly, small cars were found to emit more carbon dioxide than SUVs. The lead author of the report suggests that this is due to the fact that there is a greater number of older small vehicles with higher emissions still on the road. See also ::Biobutonal: A Superior, Renewable Substitute for Gasoline and ::Who Killed the Electric Car?, ::THTV: Who Killed the Electric Car?