No subject appears to divide as many people in the climate change arena as biofuels. Their potential to positively impact greenhouse gas emissions is undoubtedly enormous.

But the pursuit of such non-fossil fuel energy replacements has raised concerns over the impact on the global food supply — and the environment itself.

When people talk about biofuels they are essentially referring to ethanol or biodiesel, the former favored by the Americas (Brazil and the U.S. produce 90 percent of the world’s ethanol between them); the latter preferred by Europe (accounting for 89 percent of global biodiesel production in 2005).

Biofuels can be produced from any number of plant crops; most ethanol in the world today being derived from corn, with sugar cane increasingly gaining favor (the latter providing double the yield per acre of the former).

Biodiesel emanates mainly from vegetable oils or animal fats, and waste cooking oil from China’s restaurants has been to thank for supplying China’s growing biodiesel industry.

Cellulosic ethanol, also fast becoming the darling of the biofuel movement, is produced by breaking down plant cell walls. And as cellulose is the most common organic compound around, it can be sourced from many more places and has the added bonus of turning things that used to be regarded as waste — corn stalks, wood chips, grasses — into incredibly useful sources of energy.

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