Analysis of the CO2 Emissions from Land Use Changes Caused by U.S. Corn Ethanol Production

AgMRC Renewable Energy & Climate Change Newsletter
June 2010

Don HofstrandDon Hofstrand
Agricultural Marketing Resource Center

A recent research report from the Agricultural Economics Department of Purdue University sheds new light on the hotly debated issue of carbon dioxide emissions from the land use changes caused by the U.S. corn ethanol industry.  

The passage of the Energy Independence and Security Act (EISA) of 2007 mandated certain levels of U.S. corn-starch ethanol production under the Renewable Fuels Standard (RFS).  As shown in Table 1, the EISA requires the minimum amount of corn-starch ethanol blended in gasoline to gradually increase annually until 15 billion gallons are reached in 2015.  The industry can blend more than mandated amounts if economic conditions encourage it.

Table 1.  Ethanol Production Mandates of the Renewable Fuels Standard

Year Renewable Fuel Corn-Starch Ethanol
2006 4,000 4,000
2007 4,700 4,700
2008 9,000 9,000
2009 11,100 10,500
2010 12,950 12,000
2011 13,950 12,600
2012 15,200 13,200
2013 16,550 13,800
2014 18,150 14,400
2015 20,500 15,000
2016 22,250 15,000
2017 24,000 15,000
2018 26,000 15,000
2019 28,000 15,000
2020 30,000 15,000
2021 33,000 15,000
2022 36,000 15,000

The RFS has triggered concerns about the large shift away from corn for food and feed use to ethanol.  The discussion centers around the concern that the reduction in food and feed availability will stimulate corn production around the world on land not currently used for crop production (forests and grasslands).  Converting this land to crop production will release carbon that was previously sequestered in the timber, grasses and soils.  The land use argument concludes that these emissions should be assigned to U.S. corn ethanol production.

While it is likely that corn ethanol production of the magnitude mandated by the RFS will result in significant land use changes, measuring the amount of land use change and subsequent carbon dioxide emissions from this shift is difficult.  Previous research on this topic estimated a sizable level of carbon dioxide emissions (AgMRC Newsletter, Climate Change – Are Biofuels Good or Bad).   The Purdue study provides new insight into the magnitude of land use changes and subsequent carbon dioxide emissions caused by corn ethanol production.  Our summary below draws heavily upon the study report.

Economic model

The basic objective of this research was to estimate land use changes associated with U.S. corn-starch ethanol production up to the 15 billion gallon by 2015 mandated by the Renewable Fuel Standard. Greenhouse gas emissions associated with corn ethanol production were computed based on these land use changes.

The economic model used in the analysis is a special version of the Global Trade Analysis Project (GTAP) model. Although analysis of this type is very complex with substantial uncertainty, the basic GTAP model has withstood the test of time and peer review.  It is a computable general equilibrium model that is global in scope. The version used for this analysis has up to 87 world regions and 57 economic sectors plus the biofuel sectors that were added for this analysis. It is widely used for analysis of trade, energy, climate change, and environmental policy issues. The version used in this analysis contains energy, GHG emissions and land use, and encompasses many changes to the GTAP model to improve the analysis of corn ethanol.

Improvements in the model include the following

  • The three major biofuels have been incorporated into the model: corn ethanol, sugarcane ethanol, and biodiesel.
  • Cropland pasture in the U.S. and Brazil and Conservation Reserve Program lands have been added to the model.
  • The energy sector demand and supply elasticities have been re-estimated and calibrated to the 2006 reality. Current demand responses are more inelastic than previously.
  • Corn ethanol co-product (DDGS) has been added to the model. The treatment of production, consumption, and trade of DDGS is significantly improved.
  • The structure of the livestock sector has been modified to better reflect the functioning of this important sector.
  • Corn yield response to higher corn prices has been estimated econometrically and included in the model.
  • The method of treating the productivity of marginal cropland has been changed so that it is now based on the ratio of net primary productivity of new cropland to existing cropland in each country and agro-ecological zone (AEZ). 

Three groups of simulations were developed to evaluate the land use implications of U.S. ethanol production.

  1. The first group of simulations calculated the land use implications of U.S. ethanol production using the 2001 database. This approach isolates the impacts of U.S. ethanol production from other changes which shape the world economy.
  2. The second group used a baseline that represents changes in the world economy during the time period of 2001-2006. Then the land use impact of U.S. ethanol production from the updated 2006 database was calculated, while following the principles of the first group of simulations for the time period of 2006-2015.
  3. The third group of simulations used the updated 2006 database obtained from the second group of simulations with the assumption that population and crop yields will continue to increase during the time period of 2006-2015.

The land use induced emissions from the GTAP model are then combined with the direct emission estimates associated with corn and ethanol production from the GREET life cycle model developed by the Argonne National Laboratory.  This is done to provide an estimate of the total greenhouse gas emissions from corn ethanol production and use.  


After two years of study by the authors, the results show that current and prospective future carbon dioxide emissions (including land use changes) from U.S. corn ethanol production are less than those of gasoline. As shown in Table 2, for the third group of simulations outlined above, greenhouse gas emissions from corn ethanol (column 4) are 83 percent of those of gasoline (17 percent reduction).  This is a significant reduction from the original estimates made in 2009 (92.4 percent of gasoline).

The original analysis by the authors occurred in January of 2009 (column 1 in Table 2) and is presented here as a point of reference.  Since that time the authors have made substantial improvements in the model (outlined above) to more accurately portray the land use changes and subsequent greenhouse gas emissions from corn ethanol production.  The impact of these improvements when applied to the 2001 data base (first group of simulations) is shown in column 2.  Column 3 shows the analysis when the baseline is updated to 2006 (second group of simulations).  Column 4 uses the 2006 baseline and assumes growth in demand and supply (third group of simulations). 

Table 2.  Summary of the Different Modeling Results

Items Units Original Jan. 09 estimates (1) Model improvements with 2001 database (2) Baseline updated to 2006 (3) Updated baseline & growth in demand & yield (4)
Land needed for ethanol hectares / 1000 gallons 0.27 ha 0.22 ha 0.15 ha 0.12 ha
Distribution of land use change between forest and pasture % forest / % pastures 23% / 77% 25% / 75% 35% / 65% 35% / 65%
Distribution of land use change between U.S. and rest of world % US / % others 35% / 65% 34% / 66% 25% / 75% 28% / 72%
Average emissions of 15 billion gallons program grams CO2 / gallon of ethanol 1,931 g 1,676 g 1,407 g 1,116 g
Emissions per gallon gasoline equivalent grams CO2 / gallon 10,564 g 10,342 g 9,933 g 9,490 g
Total ethanol emissions as % of gasoline percent 92.4% 90.5% 86.9% 83.0%

Some of the results are fairly stable over the three simulations.  For example, the distribution of land use change between forestland and cropland varies from 25% / 75%, and 35% / 65% among the three simulations.  Also the distribution of land use change between the U.S. and the rest of the world varies from 25% / 75% and 34% / 66%.

Other results of the three simulations tend to be more variable.  For example, the amount of additional land needed to produce 1,000 gallons of corn ethanol ranged from 0.12 hectares of (.30 acres) to 0.22 hectares (.54 acres) of land.  Also, the land use greenhouse gas emissions range from 1,116 grams (2.46 pounds) to 1,676 grams (3.69 pounds) per gallon of ethanol.

Emissions per gallon of gasoline equivalent represent total greenhouse gas emissions.  This is the summation of the direct emissions from producing ethanol (GREET model) and emissions from land use change (GTAP model).  This range is from 9,490 grams (20.9 pounds) to 10,342 grams (22.8 pounds) per gallon of gasoline equivalent.  These results appear to vary less because the same level of emissions from producing ethanol (GREET model) are used in all three simulations.


Although corn ethanol would meet a 10 percent greenhouse gas reduction standard, the study results suggest that it may not meet the 20 percent reduction standard required by the Renewable Fuel Standard of the Energy Independence and Security Act (EISA).  However, the authors believe that it cannot be concluded that corn ethanol would not meet the 20 percent reduction standard due to uncertainty of the analysis and the potential improvement in direct emissions associated with corn and ethanol production.  

For more information on the research analysis, go to the website below.

Land Use Changes and Consequent CO2 Emissions due to US Corn Ethanol Production: A Comprehensive Analysis

, Wallace E. Tyner, Farzad Taheripour, Qianlai Zhuang, Dileep Birur, Uris Baldos, April 2010, Department of Agricultural Economics, Purdue University.