Paved with Green Intentions

Biofuels are touted as a planet-friendly substitute for coal and oil. While ethanol (made from corn or sugarcane) and biodiesel (made from soybean or palm oil) burn cleaner and produce less greenhouse gas than fossil fuels do, critics warn that biofuels have their own dark side. Cuba's Fidel Castro even called powering cars with food "sinister" policy, but here's a more level-headed breakdown of the impact and limitations of farming for fuel.

Corn. One-fifth of the U.S. corn crop is now turned into ethanol at 114 biorefineries, located primarily in the Midwest. To meet Bush's 2017 target of producing 35 billion gallons of ethanol, the entire current U.S. crop would need to be turned into fuel. So long, cornflakes?

Soybean. A dietary staple in Asia for 2,000 years, soybeans today are increasingly grown for oil and animal feed. The U.S. leads the world in soybean and corn production, but it would have to turn 100% of both crops into fuel in order to offset just 11% of U.S. on-road fuel consumption.

Palm. Plantations of oil palms have been held responsible for 87% of the deforestation in Malaysia already. Growing demand for biofuels is expected to only increase the pace of destruction of rain forests on the biologically rich islands of Borneo and Sumatra.

Sugarcane. Boosters see Brazil, which meets 40% of its transportation fuel needs through ethanol, as a model to emulate. But critics warn that sugarcane encroaches on wildlife habitat, degrades soils and causes pollution when fields are burned.