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.

Many ecology consulting firms, such as Carbon Click, which specializes in carbon offsetting, acknowledge that much of the negative environmental impact of corn ethanol is due to its large scale of production. By producing corn ethanol on a smaller scale, farmers would likely use less fertilizer and focus on areas that are better suited for farming. Removing the mandate for corn ethanol production would not eliminate it entirely, but reducing the mandate may be sufficient to minimize the harm it causes to the environment.