Minneapolis/St. Paul, Minnesota
February 7, 2008
Findings have major
implications for climate change policy
Turning native ecosystems into
“farms” for biofuel crops causes major carbon emissions that
worsen the global warming that biofuels are meant to mitigate,
according to a new study by the
University of Minnesota and the Nature Conservancy.
The work will be published in
Science later this month and will be posted online Thursday,
Feb. 7.
The carbon lost by converting rainforests, peatlands, savannas,
or grasslands outweighs the carbon savings from biofuels. Such
conversions for corn or sugarcane (ethanol), or palms or
soybeans (biodiesel) release 17 to 420 times more carbon than
the annual savings from replacing fossil fuels, the researchers
said. The carbon, which is stored in the original plants and
soil, is released as carbon dioxide, a process that may take
decades. This “carbon debt” must be paid before the biofuels
produced on the land can begin to lower greenhouse gas levels
and ameliorate global warming.
The conversion of peatlands for palm oil plantations in
Indonesia ran up the greatest carbon debt, one that would
require 423 years to pay off. The next worst case was the
production of soybeans in the Amazon, which would not “pay for
itself” in renewable soy biodiesel for 319 years.
“We don't have proper incentives in place because landowners are
rewarded for producing palm oil and other products but not
rewarded for carbon management,” said University of Minnesota
Applied Economics professor Stephen Polasky, an author of the
study. “This creates incentives for excessive land clearing and
can result in large increases in carbon emissions.
“This research examines the conversion of land for biofuels and
asks the question ‘Is it worth it"’,” said lead author Joe
Fargione, a scientist for The Nature Conservancy. “And
surprisingly, the answer is no.”
Fargione began the work as a University of Minnesota
postdoctoral researcher with Polasky, Regents Professor of
Ecology David Tilman; he completed it after joining the Nature
Conservancy. They, along with university researchers Jason Hill
and Peter Hawthorne, also contributed to the work.
“If you’re trying to mitigate global warming, it simply does not
make sense to convert land for biofuels production,” said
Fargione. “All the biofuels we use now cause habitat
destruction, either directly or indirectly. Global agriculture
is already producing food for six billion people. Producing
food-based biofuel, too, will require that still more land be
converted to agriculture.”
These findings coincide with observations that increased demand
for ethanol corn crops in the United States is likely
contributing to conversion of the Brazilian Amazon and Cerrado
(tropical savanna). American farmers traditionally rotated corn
crops with soybeans, but now they are planting corn every year
to meet the ethanol demand and Brazilian farmers are planting
more of the world’s soybeans. And they’re deforesting the Amazon
to do it.
The researchers also found significant carbon debt in the
conversion of grasslands in the United States and rainforests in
Indonesia.
Researchers did note that some biofuels do not contribute to
global warming because they do not require the conversion of
native habitat. These include waste from agriculture and forest
lands and native grasses and woody biomass grown on marginal
lands unsuitable for crop production. The researchers urge that
all fuels be fully evaluated for their impacts on global
warming, including impacts on habitat conversion.
“Biofuels made on perennial crops grown on degraded land that is
no longer useful for growing food crops may actually help us
fight global warming,” said Hill. “One example is ethanol made
from diverse mixtures of native prairie plants. Minnesota is
well poised in this respect.”
“Creating some sort of incentive for carbon sequestration, or
penalty for carbon emissions, from land use is vital if we are
serious about addressing this problem,” Polasky said.
“We will need to implement many approaches simultaneously to
solve climate change. There is no silver bullet, but there are
many silver BBs,” said Fargione. “Some biofuels may be one
silver BB, but only if produced without requiring additional
land to be converted from native habitats to agriculture.”
The work was supported by the University of Minesota’s
Initiative for Renewable Energy and the Environment and the
National Science Foundation. |
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