By Carol Werner
Biofuels have been touted in recent years as a
leading solution to many of our nation’s challenges. In December the president signed into law
the Energy Independence and Security Act of 2007,
including a substantially increased renewable fuels
standard. This standard calls for biofuels production to reach 36 billion gallons by 2022, with 21
billion gallons of that amount to be advanced biofuels — those derived from biomass other than corn starch and emitting at least 50 percent less greenhouse gases compared to gasoline or
diesel. Congress has strongly supported expanded development of
biofuels for energy security and economic benefits and to reduce
greenhouse emissions. Not even concerns about biofuels’ effect on global food prices have been a stopper; proponents argued that they could
be addressed by advancing nonfood feedstocks like switch grass. Then,
in February, Science published two articles that call into question the
carbon-neutrality of biofuels. The articles have generated considerable
doubt and controversy regarding the true benefits of biofuels.
Specifically, the studies identify situations in which certain biofuels may produce greater greenhouse gas emissions than conventional petroleum fuels if, for example, producing them has resulted in rainforest deforestation or destruction of other ecosystems that store vast
amounts of carbon. To a large extent, the shift in public opinion following publication of these articles is understandable. When produced
using unsustainable practices, biofuels have the inherent potential to
negatively affect soils, water resources, biodiversity and additional
social and environmental factors. Furthermore, as the Science papers
illustrate, direct and indirect emissions from certain biofuels have the
potential to rival or even exceed emissions from equivalent petroleum fuels during a given timeframe.
Unfortunately, the media have cited these studies frequently and
erroneously as evidence that these problems are universal for all types
of biofuels in all locations. On the contrary, both papers support a very
different conclusion: that direct and indirect emissions from biofuels vary
considerably depending on where they are produced and what feedstocks are
used. In fact, the authors of both papers identify several feedstocks (as
well as the most appropriate lands to produce them) that can be used
to produce climate-beneficial biofuels.
Avoiding Unintended Consequences
In Fargione et al., scientists from the Nature Conservancy and the
University of Minnesota investigated the climate impacts of clearing
forests and other ecosystems for the production of biofuels. (See Fargione, J., J. Hill, D. Tilman, S. Polasky and P. Hawthorne, “Land Clearing and the Biofuel Carbon Debt.” Originally published in Science
Feedstocks most likely to help counter climate change are those
having little effect on agricultural commodity markets, primarily
agricultural wastes and feedstocks from nonagricultural lands, like
algae. Facing page, Solix Biofuels and Colorado State University are
developing technology to convert algae into biodiesel.
PAT CORKERY, NREL
A key measure is the total energy yield per unit area. Doubling the
amount of usable energy produced from a bushel of corn has the
same effect as doubling the bushels produced per acre.
Express online Feb. 7; Science Feb. 29 DOI: 10.1126/science.1152747.)
Although the use of biofuels reduces global emissions by substituting
for conventional petroleum fuels, these savings are offset by any
emissions that result from producing the biofuels. In this study, the
authors began by calculating the total emissions from land clearing;
this number constitutes the “carbon debt.” Based on the size of the
carbon debt, as well as the annual yield of fuels, the authors were able
to calculate the number of years it would take for the landscape to
repay the carbon debt through the effect of petroleum substitution.
After the carbon debt is repaid, further production of biofuels will
effectively reduce global emissions.
For instance, clearing lowland tropical forest in Southeast Asia to
create oil palm plantations would result in an immediate spike of
610 megagrams (610 metric tons) of carbon dioxide per hectare. Based
on the average annual yield of oil palm for this region, it would take
86 years to produce enough biodiesel to repay this carbon debt. For
other biofuels, this figure varies quite a lot; the greater the carbon
