Following the boom in oil production from the hydraulic fracturing revolution, environmental protection outstripped energy independence as the major selling point of US biofuels policy. The ethanol mandate continues to grow and includes 15 billion gallons that can be met using ethanol made from corn. All of that corn ethanol, despite being a renewable fuel resource, does not deliver the environmental benefits hoped for by early biofuel advocates.

The production of billions of gallons of ethanol requires vast expanses of farmland, and with the introduction of the ethanol mandate, these areas have grown to encompass what were previously unimproved critical ecological areas. On top of degrading wildlife habitat, tilling previously unfarmed land releases long-term soil carbon stores. The mandate also competes with the Conservation Reserve Program, which pays farmers to keep environmentally sensitive land out of production. Together, these effects eat away at the possible environmental benefit of the ethanol mandate.

Expanding corn production into new areas exacerbates pre-existing environmental problems, particularly fertilizer runoff. This fertilizer eventually reaches the Gulf of Mexico dead zone, an area so heavily affected by runoff that marine life dies en masse. Environmental economists estimate that for every billion gallons of additional ethanol produced the dead zone expands by 30 square miles.

Finally, it must be noted that corn ethanol does little to help meet climate goals. The exact greenhouse gas reductions from ethanol relative to gasoline are a matter of heated academic debate, with some experts even concluding that corn ethanol has higher emissions. A recent meta-analysis in the American Journal of Agricultural Economics puts the greenhouse gas emissions reduction at less than a single percent — not a particularly strong tool in the fight against climate change.

It’s worth recognizing that many of corn ethanol’s worst environmental consequences are a direct result of its huge volumes of production. At lower production intensity, corn farmers might use less fertilizer and concentrate on areas that are better-suited for production. Eliminating the mandate would not come close to eradicating corn ethanol production, but cutting back the mandate may be all that’s necessary to mitigate the environmental damage.