The great hope for the future is “cellulosic” ethanol, which can be made from a wide variety of biological matter. Cellulosic ethanol is an exciting development because it’s much more energy efficient than corn ethanol and emits less pollutants. It can also be made out of waste materials such as wood chips or cornstalks, though the fuel source considered to have the most potential is switchgrass — a native plant that once blanketed the American prairie.Yet even cellulosic ethanol has production limits. Making it out of plant materials gathered from forest floors, as some have proposed, would reduce the health of forests.

Farmers intentionally leave cornstalks and other crop waste in their fields in order to till them into the soil; removing it would reduce soil quality and thus require more fertilizers. And widespread switchgrass cultivation once again raises worries that conservation lands would be dedicated to farming.The other thing about cellulosic ethanol is that it doesn’t actually exist — no one has yet figured out how to make it economically in commercial quantities. The result is that farmers will plant more corn to meet federal mandates, even as the number of corn-based ethanol refineries skyrockets. There are 124 in the United States, with 76 more being built, according to the Renewable Fuels Assn. Their investors are operating on the assumption that use of corn-based ethanol will expand for years to come. If the economic and environmental effects of this practice are bad now, they’ll soon get far worse.The ethanol craze, like so much of U.S. energy policy, is designed more to please small but politically powerful constituencies such as corn growers and Detroit automakers than to solve the nation’s energy problems.

There is no other way to explain the flip-flops by presidential candidates Hillary Rodham Clinton and John McCain, who as senators were critical of ethanol but, desperate to the win the primary in corn-growing Iowa, have more recently become ethanol boosters.Likewise, there’s no other way to explain the country’s 54-cent-a-gallon tariff on Brazilian ethanol, which, because it’s made of sugar, is dramatically more energy efficient (as well as being much cheaper to produce) than U.S corn ethanol. The tariff protects corn growers while guaranteeing higher prices for consumers.Meanwhile, our fuel-economy rules allow automakers to build lower-mileage cars than they could otherwise if they also make flex-fuel vehicles capable of running on E85. Yet E85 requires an expensive, separate fueling infrastructure, which is why it’s available at just 1% of gas stations nationwide and at only four in California. Thus, Detroit gets to build bigger gas-guzzlers in order to boost an inefficient, highly polluting fuel that almost no one uses.There are much better ways to cut greenhouse gas emissions and decrease our reliance on foreign oil. They start with improving fuel economy standards, as the Senate proposes to do in its energy bill.

There’s no compelling reason to make E85, let alone for the government to promote it. Instead, Congress could mandate a national fuel blend containing a minimal percentage of ethanol, with the quantity rising over time as cellulosic comes on line. The tariff on Brazilian ethanol has to go, though some sort of import cap may still be needed to avoid encouraging Brazilian farmers to clear the Amazon rain forest to grow more sugar cane.Henry Ford, whose Model T ran on ethanol, made the mistake of thinking alcohol for motor fuel could be made in limitless supply. He didn’t count on how widespread his invention would become, nor the fact that the world’s population would grow so large that there wouldn’t be enough agricultural land or fresh water on Earth to feed us all.