There's a link between wealth and footprint size. [Bill Gates]'s estimated consumption was about 10,000 times the American average. "When you're really wealthy, you have multiple houses, your own airplane and people working for you," says [Timothy Gutowski].

"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."

"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."