Renewable energy, by contrast, is certainly plentiful. In any given hour, more energy from the sun reaches Earth than is used by the whole human population in any given year. The trouble, of course, is that it's the very opposite of coal or oil. Instead of being concentrated, it's diffused. There's a little bit everywhere, except at night, when there isn't any at all. The same with wind and with many other alternatives. This doesn't necessarily make them impractical. We may be out of silver bullets, but perhaps we've got enough silver buckshot. Still, it's very hard to see quite how we'll power the world we're used to living in. Look at the whole apparatus of our society as you head to work or school today: the thrumming of the engine in your car, the whir of the machine that makes your coffee (not to mention the ship that carries the coffee to our shores and the roaster that makes it taste good and the machine that washes your cup). All of them depend primarily on the burning of the barrels and lumps of ancient biology now running short and threatening to wreck our climate.

We've somehow got to transform all that so that the ultimate power comes from somewhere else—and we have to do it without breaking the planet's economy. Money, in fact, becomes almost as important as Btu in these calculations. If we can't do it at a reasonable cost, it's unlikely that we'll do it at all, both because we'll run out of cash and because we'll run out of politicians willing to vote for expensive projects.

There are, happily, some real possibilities. To start with, we waste a lot of energy: The average American uses twice as much as the average western European, even though our standard of living is no higher. The Belgians don't have a secret technology; they merely have a region that, because fuel prices have been high for 50 years, learned how to economize. Some of the difference is technological—building codes call for more insulation, and cars are held to higher mileage standards. But much of it is behavioral—people have learned to take the train instead of drive, to travel on the sched­ule of their community, not just their own whim. Some of that will be hard to translate back onto our shores; our suburban sprawl is a machine for burning energy. But there's plenty we can do, beginning with replacing those incandescent lightbulbs. Why not buy a hybrid car or, better yet, one of the new plug-in hybrids soon to be on the market? Efficient appliances pay back in no time. If you take the commuter train, you can read a book on your way to work. In a strange way, the good news is that we're so energy obese that cutting the first, say, 20 percent won't be tough at all. It'll be like losing weight by cutting your hair.