"Behind all this advertising is the implication that we are going to consume our way to sustainability," he says on the phone from Cambridge, Mass.

"It's nonsense. It's so guilt-free. Heaven forbid we examine our lifestyle."

Which is one of the reasons he set a class of MIT students in 2007 an intriguing and enlightening assignment: Compare the energy consumption of a Buddhist monk, a homeless person and some of the wealthiest people in the country, among them Bill Gates and Oprah Winfrey.

They studied 18 lifestyles, including that of a vegetarian college student, a soccer mom, a pro golfer, a commercial artist, and a five-year-old.

Their conclusion: Even the most modest energy consumer in America far outpaces the world average.

By examining lifestyle, he says, it's easier to make recommendations on reducing the carbon footprint, a measure of carbon dioxide and other emissions produced in the course of daily life.

Americans on average have a massive carbon footprint – 20 tonnes compared to the world average of four.

While Gates's consumption was estimated from published reports, the students interviewed a local Buddhist monk. He lived off savings earned in the tech industry, and spent half the year sharing a friend's apartment and the other half, he claimed, living in a forest. His footprint: about 10.5 tonnes.

The homeless person, who used soup kitchens and slept in a city shelter, used about 8.5 tonnes, the "floor" for energy consumption in the U.S. In working out a formula to measure carbon footprint, Gutowski and his students took into account the services available to all Americans, including use of roads, police services, banks, schools, libraries and the judicial system.

"Goods and services are provided to all citizens, and certain amounts of energy are required and carbon is emitted for those services. At what point do you say you've got to fix the system?"

They also considered what Gutowski calls the rebound effect. If someone bought a hybrid car instead of an SUV, he had to account for how he spent the money he saved (from both the purchase price and the gas savings).

If he used the money to fly to Europe for a holiday, he would see a marked increase in his overall carbon emissions.

Gutowski suggests the savings should be spent in more environmentally friendly ways: taking art lessons, for example, getting a massage, or starting a fitness regime.

"A lot of things don't have to be the way they are," says Gutowski. "Ask people in urban areas whether they'd consider bicycling to work. They say they'd like to, but they'd like it to be safer, and we don't go out of our way to make it safer."

The study will be presented at the International Symposium on Electronics and the Environment, which begins tomorrow in San Francisco.

As a follow-up to last year's study, his students this semester are interviewing Americans, including a family of Amish farmers in Pennsylvania – "they're going to give a homeless person a run for his money" – about their energy use and what they could do to reduce their carbon footprint.

"This is painful stuff," he says. Driving less, heating only the rooms you're using, turning down the thermostat, eating less meat, seems easy enough, but people are still unwilling, says Gutowski. "A 30 per cent reduction is unlikely, 50 per cent is impossible."

Still, Gutowski is not without hope.

"On an individual basis, people say no, but with proper leadership and framing the problem, people as a group can do all kinds of things... they'd be willing to sacrifice and change their lifestyle if we do it as a community and with a sense of purpose."