With governments and consumers scrambling for alternatives to fossil fuel, worldwide demand for biofuels has gone through the roof; in Europe, where more than half of all automobiles run on diesel, consumption of biodiesel is set to triple by 2010. US subsidies for biofuels, mostly ethanol, will add up to $92 billion between 2006 and 2012, and producers in developing countries like Indonesia are often eligible for millions of dollars in development money from the World Bank.

But amid the hype, problems have emerged. Biodiesel emits less than one-quarter the carbon of regular diesel once it's burned. But when production—and the destruction of ecosystems in the developing countries where most biofuel crops are grown—is factored in, many biofuels may actually emit more carbon than does petroleum, the journal Science reported last year. Because oil palms don't absorb as much CO2 as the rainforest or peatlands they replace, palm oil can generate as much as 10 times more carbon than petroleum, according to the advocacy group Food First. Thanks in large part to oil palm plantations, Indonesia is now the world's third-largest emitter of CO2, trailing only the US and China.