Biofuels, by recycling atmospheric carbon, are a potential boon to the
world's ailing climate. But efforts in the tropics to significantly expand
biofuel production by replacing tropical forests with oil palm, sugarcane and
other agricultural biofuels could speed climate change, a new study warns.
In Wednesday's issue of the journal Environmental Research Letters, a team of
researchers from the UW-Madison and other universities cautions that expanding
biofuel crop production in natural tropical ecosystems will lead to a
significant increase in carbon emissions for decades and possibly hundreds of
years.
"Cutting down rainforests to grow biofuel crops will likely never be a winning
proposition for climate change or the environment, even considering projected
improvements in agricultural and energy technology," said Holly Gibbs, a
University of Wisconsin-Madison graduate student who is the lead author of the
study.
Based on powerful new geographic databases of the world's existing agricultural
lands and their yields as well as carbon stored in tropical ecosystems such as
forests and savannas, the study confirms and expands upon earlier reports that
replacing tropical forests with crops for biofuels will increase carbon
emissions to the atmosphere, the primary cause of global warming.
Such tropical ecosystems store much of the world's carbon, harboring an
estimated 340 billion tons, about 40 times the amount released into the
atmosphere each year, primarily through the burning of fossil fuels. When
forests are cleared, the future storehouse is eliminated and the carbon
sequestered in the forest is also released to the atmosphere, as fire remains a
primary method for clearing tropical forests.
The result, said Gibbs and her colleagues, is increased "carbon debt" because
the carbon savings from using biofuels in place of petroleum fuels is generally
much less than the carbon stored in tropical forests.
The new study, say its authors, gives renewed urgency to developing policies and
economic incentives to protect tropical forests. The world's last large tracts
of undeveloped land exist in the world's tropical zones and are viewed by many,
including governments, as ripe for transformation into biofuel croplands.
Earlier studies suggesting that the transformation of tropical ecosystems to
biofuel crops would increase the world's carbon debt were controversial because
anticipated advances in agricultural and energy technologies were not taken into
account. The new study, said Gibbs, does consider future scenarios of biofuel
production and supports previous conclusions.
However, the authors of the study funded by the U.S. Department of Energy and
NASA say that there are potential carbon gains to be had by directing new
biofuel crop production to other non-forested lands. "Sustainable production of
agricultural biofuels on degraded lands that are unsuitable for food production
could provide immediate environmental benefits," Gibbs said.
Jonathan Foley, a co-author of the study and a professor in UW-Madison's Nelson
Institute for Environmental Studies, also stresses that the study is not an
argument against biofuels.
"This study just indicates that biofuel production should not be occurring at
the expense of tropical forests. Other ways of producing biofuels in the tropics
-- on degraded lands, former agricultural areas and so on -- are clearly
possible, and could have tremendous environmental, economic and social
benefits," Foley said.
In addition to Gibbs and Foley, authors of the new study include Matt Johnston,
Tracey Holloway and David Zaks, all of the Center for Sustainability and the
Global Environment, part of UW-Madison's Nelson Institute for Environmental
Studies. Additional authors are Chad Monfreda of Arizona State University's
Consortium for Science Policy and Outcomes and Navin Ramankutty of McGill
University.