The Environmental Impact of 300 Million

"The U.S. is the only industrialized nation in the world experiencing significant population growth," says Vicky Markham of the Center for Environment and Population. "That, combined with America's high rates of resource consumption, results in the largest ... environmental impact [of any nation] in the world."

Ecologists point out that at current consumption rates, the long-term "carrying capacity" of the U.S. wouldn't sustain even half of the nation's current population. Baby boomers, with their relative wealth and preference for big homes and vehicles, are doing more than their part as the highest resource consumers in the nation's -- and the world's -- history.

The U.S. population doesn't look likely to stabilize anytime soon; it's expected to hit 400 million by mid-century. And the world population hit 6.5 billion earlier this year.