These days, Jason Clay walks around with an eerie sense of déjà vu.

For instance, Clay watched as biofuels, once hailed as the savior of the climate, became an environmental sinner almost overnight—blamed for everything from food riots to trashed tropical forests. "The backlash has been pretty ferocious—ethanol and biodiesel have lost a lot of their green image," he says.

The dream of cellulosic ethanol, however, is causing nightmares for many ecologists. They fear that growing demand for cheap, ample supplies of cellulose will create powerful incentives to convert diverse, native grasslands into sterile "energy lawns" and to simply chop down vast swaths of wild forests.

can the pursuit of clean, "green" fuels lead to a true ecological solution