Keith Smith, of the University of Edinburgh, criticizes LCAs of biofuels from crops

Life cycle analyses [LCAs] are designed to measure factors relating to the production, usage, and disposal of a fuel, to determine how use of a given fuel impacts the environment. Within a post titled Study: Environmental benefit of biofuels is overestimated, Dr. Keith Smith, from the University of Edinburgh criticizes some LCAs for biofuels. He observes: "Emissions of N2O from the soil make a large contribution to the global warming associated with crop production because each kilogram of N2O emitted to the atmosphere has about the same effect as 300kg of CO2."

See also Environmental Benefit of Biofuels is Overestimated, New Study Reveals