IOWA is the nation’s top producer of corn, and nearly half of it ends up as ethanol, thanks to a government mandate that requires ethanol to be mixed into gasoline. The mandate is worth hundreds of millions of dollars to farmers there.

No wonder most Iowans talk it up, as do most of the presidential candidates campaigning there in the lead up to the caucuses.

Ethanol thrives because of the volume-based approach of the mandate, which specifies that a growing percentage of various renewable fuels must be mixed into gasoline every year until 2022.

But that approach has stifled innovation and, if its track record to date is any indication, biofuels will not be a major player in meeting our 2050 targets for reducing greenhouse gas emissions from cars and trucks.