A group of students from the Massachusetts Institute of Technology (MIT) has estimated the carbon footprint of Americans, ranging from the homeless to multimillionaires. The students found that anyone who lives in the United States contributes more than two times as much greenhouse gas to the atmosphere as the global average and that individual emissions rise steadily as their income increases.

The average annual carbon dioxide emissions per person, they found, was 20 metric tons, compared to a world average of 4 tons. The lowest anyone in the U.S. could reach was 8.5 tons for a homeless person eating in a soup kitchen and sleeping at a homeless shelter.

The students conducted detailed interviews or made detailed estimates of the energy usage of 18 lifestyles, spanning the gamut from a vegetarian college student and a 5-year-old up to the ultrarich--Oprah Winfrey and Bill Gates, according to the ScienceDaily article

In general, spending money on travel or on goods that have substantial energy costs in their manufacture and delivery adds to a person's carbon footprint

But the biggest factors in most people's lives were the obvious energy-users: housing, transportation and food. "The simple way you get people's carbon use down is to tax it," Professor Timothy Gutowski says.

You can use the carbon footprint calculator, courtesy of The Nature Conservancy to figure out how many tons of CO2 and other greenhouse gases your choices create each year. Feel free to post your number in the comment section. It will be fun to compare.

According to the Nature Conservancy the average amount of CO2 emissions per year for an individual in the U.S. is 27 tons. Their world average is 5.5 tons. My number was 19 tons.