Resolving the Biofuels Dilemma
Biofuels Increases Greenhouse Gases Through Emissions from Land
Use Change.” Originally published in Science Express online Feb. 7;
Science Feb. 29 DOI: 10.1126/science/1151861.) Because agricultural
commodity markets are relatively inelastic (i.e., demand changes little in response to reduced supply), new farmland is likely to be
brought into productivity somewhere else to compensate. The emissions created as a result of the land clearing at the end of this domino chain are referred to as indirect emissions. While the logic is sound,
the effect is tough to quantify. The difficulties arise from the subtleties
of determining just how elastic agricultural markets are. Even in the
most inelastic markets, demand will decline to some degree in
response to high prices caused by reduced supply. In the case of agricultural commodities, this effect will likely be most pronounced in the
demand for meat and other “luxury” foods.
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In addition to accurately estimating elasticity, calculating indirect
emissions depends on all the factors that affect direct emissions —
assumptions regarding where new farmland will be broken out, what
ecosystems will be cleared in the process, what crops will be grown,
what yields can be achieved and what timeframe is being considered.
Searchinger et al. describes a comprehensive model for calculating the
indirect emissions of using farmland to produce corn for ethanol in
the United States. The model is based on a core of established econom-
Given the incalculable values provided by rainforests, it should be a
global priority to conserve them rather than destroy them for short-
term economic gains.
storage in the land being cleared, the larger the carbon debt. The greater the
annual yield of biofuels, the faster the carbon debt can be repaid. Clearing tropical peatland rainforest to grow oil palm would result in a carbon debt that would take 840 years to repay. On the other hand,
ethanol produced from fast-growing sugarcane in the Brazilian cerrado becomes carbon-neutral after only 17 years, according to this study.
These payback periods become meaningful only in the larger context of agreed-upon global emissions targets. For example, should the
global community aim to reduce emissions 80 percent by 2050, then
ethanol produced on former cerrado could play a role in that strategy, whereas biodiesel from tropical peatlands could not. It is important to keep in mind, however, that natural ecosystems provide many
benefits that are critical to sustaining our societies, including clean
water, wildlife habitat, biodiversity, foods and medicines, wood products, flood protection, recreation and other cultural values and ecosystem services. In many (if not most) natural ecosystems, avoiding the
loss of these values would outweigh the benefits that would be gained
from clearing land and producing biofuels. Globally, about one-fifth
of carbon emissions come from deforestation. Given the enormous
and incalculable values provided to the earth by rainforests (the
Amazon is often referred to as the “lungs of the planet”), it should be
a global priority to conserve them rather than destroy them for short-term economic gains.
The second Science study (Searchinger et al.), by a group of
researchers from Princeton University, Woods Hole Research Center
and Iowa State University, takes a step beyond direct emissions to
investigate the indirect emissions resulting from market-driven land-use change. Indirect emissions are caused when existing agricultural
land is diverted from producing food to producing biofuel feedstocks.
(See Searchinger, T., R. Heimlich, R.A. Houghton, F. Dong, A. Elobeid,
J. Fabiosa, S. Tokgoz, D. Hayes and T. Yu. “Use of U.S. Croplands for
A key value of the Science studies is in identifying land-use effects, an
important element in determining the overall impacts of biofuels.
ic, agricultural and engineering models and includes interactions
among all of the aforementioned key factors. The study concludes that
increased use of farmland for corn ethanol will double total emissions
relative to petroleum fuels over a 30-year period.
Both Science papers are important steps forward in our understanding of the climate impacts of biofuels, but they are among the very first
attempts to quantify these impacts. As we continue to try to understand