Ethanol's Broken Promise

Using Less Corn Ethanol Reduces Greenhouse Gas Emissions

May 29, 2014

Ethanol's Broken Promise: EPA’s Emissions Assessment

The Energy Independence and Security Act of 2007 specified that in order to comply with the Renewable Fuel Standard, biofuels must meet greenhouse gas emissions reduction thresholds. EPA set these thresholds in March 2010 with its final rule, which ensures that an increasing volume of biofuels would be blended into fuels and those biofuels would meet emission reduction thresholds. Under the final rule corn ethanol must reduce emissions by 20 percent, and advanced biofuels must cut emissions by 50 percent. 7

Also as part of the final rule, EPA released a Regulatory Impact Analysis that projected the greenhouse gas emission performance of various biofuels. This Analysis compared the projected lifecycle greenhouse gas emissions of corn ethanol and gasoline over three 30-year time periods with different starting points – 2012 to 2042, 2017 to 2047 and 2022 to 2052. The Analysis included lifecycle emissions of biofuels produced in plants using different power sources and milling processes. Corn ethanol production results in a solid co-product called distiller’s grains that is used as animal feed. These distiller’s grains are produced either wet or dry, but dried distiller’s grains require more energy for drying. Another factor that determines the life-cycle emissions of producing a biofuel is the power source. Most ethanol plants in 2014 use natural gas as the power source, but some still use coal. The life cycle greenhouse gas emissions projected for corn ethanol produced using natural gas, for wet and dry distiller’s grains, are shown in Table 2.

Because of the expected amount of land use change, EPA’s analysis predicted that corn ethanol’s emissions would be 33 percent higher than gasoline’s in 2012 but would be 17 percent lower by 2022. However, in its Regulatory Impact Analysis, EPA projected that overall corn ethanol would reduce emissions by 21 percent based on the assumption that by 2022 biomass would power ethanol plants, which would reduce overall ethanol emissions.

The assumption is questionable given the recent increase in natural gas production in the U.S. and consistently low natural gas prices. Unless ethanol plants are given financial incentives to use biomass, switching away from natural gas is unlikely. Moreover, EPA’s projection for 2022 ignored emissions from land use conversion between 2007 and 2022, even though the climate damage from those emissions will continue for years to come. Carbon dioxide stays in the atmosphere for 30 to 95 years.8


In its Regulatory Impact Analysis, the EPA essentially ignored all land use change emissions before 2022 and evaluated corn ethanol based on emissions from 2022 to 2052 only. In other words, the EPA’s accounting disregards the legacy of increased emissions from earlier land conversion. The agency started its analysis of projected emissions at 2022 because this is the year when the Renewable Fuel Standard requires the blending of the ultimate goal of 36 billion gallons of biofuels.

The agency’s calculation was challenged in 2013 in a white paper by the Clean Air Task Force, an independent non-profit environmental organization, using EPA’s own numbers. It found that if the EPA had taken into account emissions from the start of the Renewable Fuel Standard’s implementation, corn ethanol’s emissions would be much higher than those from an energyequivalent amount of gasoline (Figure 1).



Clean Air Task Force’s white paper points out that if the EPA had done its emissions accounting for RFSmandated corn ethanol starting in 2010 and ending in 2044 (30 years after the corn ethanol mandate ramped up to 15 billion gallons), it would have found greenhouse gas emissions from corn ethanol were 28 percent higher than from an energy-equivalent amount of gasoline.13