Letter to Science (Original…

                                       Letter to Science
    (Original version submitted to Science on Feb. 14th, 2008; revised on March 14th, 2008)

                                         Michael Wang
                               Center for Transportation Research
                                 Argonne National Laboratory

                                            Zia Haq
                                  Office of Biomass Program
                      Office of Energy Efficiency and Renewable Energy
                                  U.S. Department of Energy


The article by Searchinger et al. in Sciencexpress ("Use of U.S. Croplands for Biofuels Increases
Greenhouse Gases through Emissions from Land Use Change," February 7, 2008) provides a
timely discussion of fuel ethanol's effects on greenhouse gas (GHG) emissions when taking into
account GHG emissions from potential land use changes induced by ethanol production.

Land use change issues associated with biofuels were explored in life-cycle analyses beginning
in early 1990s (Delucchi 1991). In general, the land use changes that occur as a result of biofuel
production can be separated into two categories: direct and indirect. Direct land use changes
involve direct displacement of land for farming of the feedstocks needed for biofuel production.
Indirect land use changes are those made to accommodate farming of food commodities in other
places in order to maintain the global food supply and demand balance.

Searchinger et al. used the GREET model developed by one of us at Argonne National
Laboratory in their study (see Wang 1999). They correctly stated that the GREET model
includes GHG emissions from direct land use changes associated with corn ethanol production;
the emissions estimates in GREET are based on land use changes modeled by the U.S.
Department of Agriculture (USDA) in 1999 for an annual production of 4 billion gallons of corn
ethanol in the United States by 2010. Needless to say, the ethanol production level simulated by
USDA in 1999 has been far exceeded by actual ethanol production -- about 6 billion gallons in
2007 (Renewable Fuels Association 2008). Thus, the resultant GHG emissions from land use
changes provided in the current GREET version need to be updated. Argonne, and several other
organizations, recently began to address both direct and indirect land use changes associated with
future, much-expanded U.S. biofuel production. Such an effort requires expansion and use of
general equilibrium models at the global scale.

Many critical factors determine GHG emission outcomes of land use changes. First, we need to
clearly define a baseline for global food supply and demand and cropland availability without the
U.S. biofuel program. It is not clear to us what baseline Searchinger et al. defined in their
modeling study.

Searchinger et al. modeled a case in which U.S. corn ethanol production increased from 15
billion gallons a year to 30 billion gallons a year by 2015. However, in the 2007 Energy
Independence and Security Act (EISA), Congress established an annual corn ethanol production



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cap of 15 billion gallons by 2015. Congress established the cap -- based on its awareness of the
resource limitations for corn ethanol production -- to help prevent dramatic land use changes.
Thus, Searchinger et al. examined a corn ethanol production case that is not directly relevant to
U.S. corn ethanol production in the next seven years.

Corn yield per acre is a key factor in determining the total amount of land needed for a given
level of corn ethanol production. It is worth noting that U.S. corn yield per acre has steadily
increased -- nearly 800% in the past 100 years (Perlack et al. 2005). Between 1980 (the
beginning of the U.S. corn ethanol program) and 2006, per-acre corn yield in the United States
has increased at an annual rate of 1.6% (Wang et al. 2007). Seed companies are developing
better corn seeds that resist drought and pests and use nitrogen more efficiently. Corn yield could
increase at an annual rate of 2% between now and 2020 and beyond (Korves 2007). The
statement "We assume that these positive and negative effects on yield balance each other out
although we test an alternative scenario in our sensitivity analysis" (p.6 of the supporting online
material) may lead readers to interpret that Searchinger et al. used a constant corn yield in their
simulations. After direct communications with us, the authors clarified that the historical trend of
corn yield growth in the U.S. was assumed in their study.

Searchinger et al. also assumed that distillers' grains and solubles (DGS) from corn ethanol
plants would displace corn on a pound-for-pound basis. The one-to-one displacement ratio
between DGS and corn fails to recognize that the protein content of DGS is much higher than
that of corn (28% vs. 9%). The actual displacement value of DGS is estimated to be at least 23%
higher than that assumed by Searchinger et al. (Klopfenstein et al. 2008).

Searchinger et al. estimated that U.S. corn ethanol production (between 15 billion and 30 billion
gallons) would result in an additional 10.8 million hectares of crop land worldwide: 2.8 million
hectares in Brazil, 2.3 million hectares in China and India, and 2.2 million hectares in the United
States, and the remaining hectares in other countries. The researchers maintain that with their
simulated corn ethanol production scale, the United States will experience export reductions of
62% for corn, 31% for wheat, 28% for soybeans, 18% for pork, and 12% for chicken.

Historically, U.S. corn exports have fluctuated around the 2-billion-bushel-a-year level since
1980. In 2007, when U.S. corn ethanol production increased dramatically, its corn exports
increased to 2.45 billion bushels -- a 14% increase from the 2006 level. This increase was
accompanied by a significant increase in DGS exports by the United States -- from 0.6 million
metric tons in 1997 to 3 million metric tons in 2007. Some researchers anticipate that with corn
ethanol production of around 15 billion gallons by 2015, U.S. will be able to maintain its corn
export at the present level or at a moderately increased level (Korves, 2007). One of the factors
that cause dramatic U.S. export reductions in agricultural commodities in Searchinger et al. study
is the arbitrarily high corn ethanol production of 30 billion gallons by 2016.

Searchinger et al. had to decide what land use changes would be needed in Brazil, the United
States, China, and India to meet their simulated requirement for 10.8 million hectares of new
crop land. With no data or modeling, Searchinger et al. used the historical land use changes that
occurred in the 1990s in individual countries to predict future land use changes in those countries
(2015 and beyond). This assumption is seriously flawed by predicting deforestation in the
Amazon and conversion of grassland into crop land in China, India, and the United States. The


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fact is, deforestation rates have already declined through legislation in Brazil and elsewhere. In
China, contrary to the Searchinger et al. assumptions, efforts have been made in the past ten
years to convert marginal crop land into grassland and forest land in order to prevent soil erosion
and other environmental problems.

In estimating the GHG emissions payback period for corn ethanol, Searchinger et al. relied on
the 20% reduction in GHG emissions that is provided in the GREET model for the current
ethanol industry. Future corn ethanol plants could improve their energy efficiency by avoiding
DGS drying (in some ethanol plants) or switching to energy sources other than natural gas or
coal, either of which would result in greater GHG emissions reductions for corn ethanol (Wang
et al. 2007). Searchinger et al. failed to address this potential for increased efficiency in ethanol
production.

In one of the sensitivity cases, Searchinger et al. examined cellulosic ethanol production from
switchgrass grown on land converted from corn farms. Cellulosic biomass feedstocks for ethanol
production could come from a variety of sources. Oak Ridge National Laboratory completed an
extensive assessment of biomass feedstock availability for biofuel production (Perlack et al.
2005). With no conversion of crop land in the United States, the study concludes that more than
1 billion tons of biomass resources are available each year from forest growth and by-products,
crop residues, and perennial energy crops on marginal land. In fact, in the same issue of
Sciencexpress as the Searchinger et al. study is published, Fargione et al. (2008) show beneficial
GHG results for cellulosic ethanol.

On the basis of our own analyses, production of corn-based ethanol in the United States so far
results in moderate GHG emissions reductions. There has also been no indication that U.S. corn
ethanol production has so far caused indirect land use changes in other countries because U.S.
corn exports have been maintained at about 2 billion bushels a year and because U.S. DGS
exports have steadily increased in the past ten years. U.S. corn ethanol production is expected to
expand rapidly over the next few years -- to 15 billion gallons a year by 2015. It remains to be
seen whether and how much direct and indirect land use changes will occur as a result of U.S.
corn ethanol production.

The Searchinger et al. study demonstrated that indirect land use changes are much more difficult
to model than direct land use changes. To do so adequately, researchers must use general
equilibrium models that take into account the supply and demand of agricultural commodities,
land use patterns, and land availability (all at the global scale), among many other factors. Efforts
have only recently begun to address both direct and indirect land use changes (see Birur et al.
2007). At this time, it is not clear what land use changes could occur globally as a result of U.S.
corn ethanol production. While scientific assessment of land use change issues is urgently
needed in order to design policies that prevent unintended consequences from biofuel production,
conclusions regarding the GHG emissions effects of biofuels based on speculative, limited land
use change modeling may misguide biofuel policy development.




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References

Birur, D.K., T.W. Hertel, and W.E. Tyner, 2007, The Biofuel Boom: The Implications for the
World Food Markets, presented at the Food Economy Conference, the Hague, the Netherlands,
Oct. 18­19.

Delucchi, M.A., 1991, Emissions of Greenhouse Gases from the Use of Transportation Fuels
and Electricity, ANL/ESD/TM-22, Volume 1, Center for Transportation Research, Argonne
National Laboratory, Argonne, Ill., Nov.

Fargione, J., J. Hill, D. Tilman, S. Polasky, and P. Hawthorne, 2008, "Land Cleaning and Biofuel
Carbon Debt," Sciencexpress, available at www.sciencexpress.org, Feb. 7.

Klopfenstein, T. J., G.E. Erickson, and V.R. Bremer, 2008, "Use of Distillers' By-Products in the
Beef Cattle Feeding Industry," forthcoming in Journal of Animal Science.

Korves, R., 2007, The Potential Role of Corn Ethanol in Meeting the Energy Needs of the United
States in 2016­2030, prepared for the Illinois Corn Marketing Board, Pro-Exporter Network,
Dec.

Perlack, R.D., L.L. Wright, A. Turhollow, R.L. Graham, B. Stokes, and D.C. Urbach, 2005,
Biomass as Feedstock for Bioenergy and Bioproducts Industry: the Technical Feasibility of a
Billion-Ton Annual Supply, prepared for the U.S. Department of Energy and the U.S. Department
of Agriculture, ORNL/TM-2005/66, Oak Ridge National Laboratory, Oak Ridge, Tenn., April.

RFA (Renewable Fuels Association), 2008, Industry Statistics, available at http://www.
ethanolrfa.org/industry/statistics/, accessed Feb. 13, 2008.

Searchinger, T., R. Heimlich, R.A. Houghton, F. Dong, A. Elobeid, J. Fabiosa, S. Tokgoz, D.
Hayes, and T.H. Yu, 2008, "Use of U.S. Croplands for Biofuels Increases Greenhouse Gases
through Emissions from Land Use Change," Sciencexpress, available at www.sciencexpress.org,
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Wang, M., 1999, GREET 1.5 ­ Transportation Fuel-Cycle Model, Volume 1: Methodology,
Development, Use, and Results, ANL/ESD-39, Volume 1, Center for Transportation Research,
Argonne National Laboratory, Argonne, Ill., Aug.

Wang, M, M. Wu, and H. Hong, 2007, "Life-Cycle Energy and Greenhouse Gas Emission
Impacts of Different Corn Ethanol Plant Types," Environmental Research Letter, 2: 024001 (13
pages).




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