“US biofuel policy is intended to reduce net greenhouse gas emissions by the US transportation sector. However, the extent of cropland expansion found by Lark et al. suggests that measures like RFS2 are actually accruing an unintended, but substantial, carbon debt.”
-Christopher K Wright, Environmental Research Letters, Volume 10, Number 5
http://iopscience.iop.org/article/10.1088/1748-9326/10/5/051001