MR. GREEN.

Amory Lovins's home, which also serves as his office and "bioshelter," is open for self-guided tours weekdays from nine o'clock in the morning until four in the afternoon. Built into a mountainside above Snowmass, Colorado, it has curved stone walls, a flat roof, and several sets of solar panels, some of which rotate to track the angle of the sun. The building's double-paned windows are lined with a polyester film that allows visible light to pass in but prevents thermal radiation from getting out, and the space between the panes has been filled with krypton. Although wintertime temperatures on the mountain routinely drop below zero, the building has no furnace; it is warmed by sunlight and by heat that has been collected in, among other places, a pond that lies between the Xerox machine and the dining room. The first time I visited, Lovins had just finished doing some laundry in his front-loaded, energy-saving washing machine. He took the damp clothes out of the washer and hung them in a little glass-ceilinged room. It was a bright blue morning, and Lovins predicted that the clothes would be ready to wear by nightfall. In the winter, if the sky is overcast, it can take up to two days for items like bluejeans to dry completely, but this is no problem, he assured me, provided one is capable of thinking more than twenty-four hours in advance.

Lovins is a short man with a salt-and-pepper mustache, a fringe of tousled black hair, and droopy brown eyes that give him a passing resemblance to Einstein. He wears Coke-bottle eyeglasses, a necklace of turquoise beads, and a watch that is supposed to prevent jet lag by sending out an electromagnetic signal exactly the same frequency as the earth's. He is routinely described, even by people who don't particularly like or admire him, as a "genius."

Lovins first came to national attention in 1976, when he was twenty-eight. In an essay published in Foreign Affairs, he asserted that the United States could completely phase out its use of fossil fuels and do so not at a cost but at a profit. "We stand here confronted," he wrote, quoting Pogo, "by insurmountable opportunities." At the time, the country was in the midst of what might now be called the first energy crisis, and the article created a stir; testifying on Capitol Hill, Lovins emerged as the demand-side management version of a rock star. Symposia were held to debate his ideas, and critiques were published by, among others, the physicist and Nobel Laureate Hans Bethe. (Lovins, in turn, wrote a response twice as long as Bethe's critique, and Bethe conceded several points.)

Thirty years later, the world faces another energy crisis, and Lovins still sees limitless opportunity. He maintains that the U.S. can eliminate its use of oil by 2050, even while reducing its coal and natural-gas consumption, enjoying unprecedented prosperity, and preserving the Arctic National Wildlife Refuge. Although Lovins was one of the first to appreciate the dangers of global warming, he believes that the problem seems so daunting only because those studying it have got the math wrong. "Climate protection, like the Hubble space telescope, has been spoiled by a sign error," he told me.

Lovins is a prolific writer--of books, of articles, and of technical treatises. During my first visit with him, he informed me that he had picked out a few of the most important ones for me to take home: papers on topics like microgeneration, "super-efficient" building practices, and data-center design were arranged in stacks that covered nearly the entire surface of a large dining-room table. That day, we ended up talking for several hours, and as I was packing up my things to go Lovins went to check on his laundry. It was nearly dry, he reported cheerfully. As I was driving back down the mountain in my rental car, it occurred to me that Lovins might be the most impractical person I had ever met. Then it occurred to me that he might be the only truly practical one.

This year, Americans will consume close to four trillion kilowatt hours of electricity. In addition, we will burn through a hundred and forty-three billion gallons of gasoline, which at current retail prices will cost us some three hundred and sixty billion dollars, and twenty-six billion gallons of jet fuel, worth fifty billion dollars. To heat our homes and businesses this winter, we will purchase sixty-two billion dollars' worth of natural gas and heating oil, and just to grill our weenies we will buy some seven hundred and seventy-one million dollars' worth of charcoal briquettes. In 2007, total energy expenditures in the U.S. will come to more than a quadrillion dollars, or roughly a tenth of the country's gross domestic product.

With so much at stake, basic economics suggests that any significant inefficiencies should have been wrung out of the system long ago. It follows that further efforts will cost more than they will return. This reasoning is pervasive in the U.S., its most prominent spokesman being Vice-President Dick Cheney, who once dismissed energy conservation as a "sign of personal virtue." Lovins's fundamental premise is that this fundamental premise is wrong.