Mongabay: Biofuels meant to help alleviate greenhouse gas emissions may be in fact contributing to climate change when grown on converted tropical forest lands, warns a comprehensive study published earlier this month in the journal Environmental Research Letters. The new research looks at the “carbon payback time” or “carbon debt” of various biofuel feedstocks including oil palm, sugar cane, and soy. Carbon payback time refers to the number of years it takes for the …