Biofuels were initially championed by environmental campaigners as a silver bullet against global warming. They started to change their minds as a stream of research showed that biofuels from most food crops did not significantly reduce greenhouse gas emissions – and in many cases, caused forests to be destroyed to grow more food, creating more net carbon-dioxide emissions than fossil fuels. Some green activists supported mandates for biofuel, hoping they would pave the way for next-generation ethanol, which would use non-food plants. That has not happened. Today, it is difficult to find a single environmentalist who still backs the policy.

