Review of GHG Emissions of Corn Ethanol under the EPA RFS2

Twelve years of experience and improved analysis methods have provided new insight into the life cycle greenhouse gas (GHG) emissions from corn ethanol. This study reviews the key factors that affect the life cycle emissions from corn ethanol production as well as the most recent agricultural data. Some of the key factors affecting corn ethanol have evolved as predicted in EPA’s 2010 Regulatory
Impact Analysis (2010 RIA), while other factors point towards substantially lower life cycle GHG emissions.

EPA developed a consequential LCA approach that estimated the emissions associated with the incremental ethanol capacity induced by the RFS policy as well as the incremental crop production required to make up for the net effect of corn crops diverted to ethanol production and distiller’s grains sold as animal feed. The modeling approach involved a combination of the FASOM model that has been used to develop the U.S. inventory for agricultural emissions, the FAPRI model, which estimates the effect of the use of agricultural products on global agricultural production, and the GREET model, which estimates life cycle GHG emissions from the fuel used in ethanol plants. EPA’s analysis aligned the economic modeling of the FASOM and FAPRI modeling and calculated emission impacts that are tied to the model predictions including changes in rice and beef consumption as well as deforestation associated with new crop production.

The 2010 RIA overestimated the GHG impact of corn ethanol due largely to overestimating indirect land use conversion (ILUC) emissions as well as numerous small details associated with the life cycle of corn ethanol. EPA’s agro-economic models rely on economic projections to attribute land use change to crop production without considering factors such as changes in farming and cattle production practices. Recent data on deforestation has shown that land ownership is much more important in affecting deforesting than the macro-economic pressure or crop prices. Burning in the Amazon has declined and increased due to policies associated with land ownership. A more accurate representation of the effect of crops on pasture conversion is represented in more recent publications based on the GTAP model and EPA would generate similar results if its ILUC modeling tools included an accurate representation of factors such as flexibility in changing cattle stocking rates. The analysis inputs to GTAP modeling would yield similar results in the FASOM/FAPRI modeling system. If EPA continues to use the FAPRI results for its international LUC analysis, the results could be scaled to reflect the values from GTAP that more accurately represent the interaction between pasture and cropland.

Several other factors affecting corn ethanol have also changed since the publication or the 2010 RIA. Corn ethanol uses about 0.7 kWh to produce one gallon of ethanol and the GHG intensity of electric power has declined substantially with increased natural gas production, a reduction in coal-based power, and growth in renewable power. The RIA also underestimated the adoption of low emission technologies that have resulted in lower emissions from ethanol plants and many small details associated with each step of the ethanol life cycle.