A Review of the Environmental Effects of the Renewable Fuel Standard’s Corn Ethanol Mandate

September 26, 2018

Project Summary

The Renewable Fuel Standard (RFS) mandates the use of ethanol in domestic gasoline supplies. The law, which was originally created chiefly to help secure energy independence, is now typically justified by its purported environmental benefits. Ongoing academic research, however, indicates that the RFS has numerous unintended environmental consequences and may not reduce emissions relative to gasoline. This paper reviews that literature and details the broad environmental impact of the corn ethanol mandate.

Many of corn ethanol’s environmental consequences stem from the expansion of unsustainable corn farming practices that are necessary to produce feedstock. The RFS drove corn demand sharply upward, with corn grown for fuel use increasing by 4.1 billion bushels between 2004 and 2016. To meet that new demand, corn farms replaced other farm land, unfarmed habitats, and lands previously set aside to prevent erosion or species loss. Sustainability practices like crop rotations and anti-erosive land management were foregone to make room for yet more corn. These changes collectively jeopardize vast swaths of habitat and soil.

The expansion of corn farming consumes significant quantities of water and fertilizer that exacerbate existing environmental problems. For example, midwestern aquifers are already overdrawn and waterways are heavily polluted with fertilizer runoff. Adding even more corn to the landscape amplifies those existing problems.

If ethanol were a highly productive energy source, these environmental impacts may be a worthwhile tradeoff, but ethanol is less scalable than is often assumed. Producing a gallon of ethanol yields little net energy, and the carbon emissions savings relative to gasoline are negligible at best. Burning ethanol also emits other pollutants, like ozone and nitrogen oxides, at higher levels than ethanol-free gasoline.

While some of ethanol’s problems are unavoidable at any level of production, many could be mitigated simply by decreasing ethanol production. Since ethanol is useful in bolstering fuel octane, ethanol demand would not disappear without the mandate. Ethanol sales would, however, drop significantly, mitigating the issues associated with current production levels. An unmandated market for ethanol could produce enough to enhance the octane of the nation’s fuels while avoiding the harshest impacts of cropland expansion and other unsustainable farming practices.

This research explores the environmental consequences of mandating ethanol in greater detail and makes recommendations for how to mitigate these impacts

Project Authors
Arthur R. Wardle
Download