At 35,000 feet, going 400 miles per hour, things can get cold. Really cold. For years skeptics argued that a biofuel could never withstand the subzero temperatures and requirements of modern aviation. In February, however, Sir Richard Branson flew his Virgin Atlantic Boeing 747 on a biofuel from coconut oil. Some environmentalists, unimpressed with this "stunt," accused Sir Branson of wiping out the rainforest.

At the epicenter of the deforestation debate is...