The 2009 TIME 100

Amory Lovins had the solution to the energy problem in 1976. It's taken the rest of us 33 years to catch up. In the wake of the 1973 Arab oil embargo, Lovins wrote his seminal piece in Foreign Affairs comparing what he called "the hard" and "the soft" energy paths.

The hard path, which most people advocated, involved securing more and more fossil fuel at any price. The soft path involved looking for new and renewable energy sources. In 1982, Lovins, who had studied physics and the arts at Harvard and Oxford, founded the Rocky Mountain Institute, where he kept his green drumbeat going, calling for cars that hacked away at the inefficiencies of the postwar era. Now 61, he is watching as his arguments become accepted wisdom and is even helping in the transition away from fossil fuels, as when he taught Wal-Mart how to make its trucks more efficient. It's been a long wait — more than three decades — but Lovins' patience has clearly paid off.

Pope is executive director of the Sierra Club