I just discussed in class about the controversy about biofuels. An excellent example is the article titled Palm oil is a major driver of peatlands destruction in Indonesian Borneo.
First, if you want to know what a peatland is see the wikipedia article, Peatlands.
Palm oil has many uses, including as a biofuel, but much of palm oil is planted either in tropical rainforest or on peatlands, both causing damage to the ecosystems.
But in addition, destruction of peatlands causes release of methane, a greenhouse gas with an effect greater than that of carbon dioxide.