Cars

The United States has 4.6% of the world's population, 30% of the world's cars, and emits 45% of the world's automotive CO2 emissions.

In 2004 U.S. cars emitted 314 MMT CO2. That's 6% of global energy-related CO2 emissions. It equals the amount of carbon in a coal train 50,000 miles long, says the report from Environmental Defense.

Vehicles per capita have risen from about 0.3 in 1950 to about 0.8 today. The cars per capita in my household exceed even this number by 25%.

(Via Past Peak and Environmental Defense)