Ten fundamentals about bioenergy: Part 4 biofuels
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Fundamental #4: Biofuels are better for the environment than fossil fuels.
This is the fourth in a series of articles on bioenergy. Today’s
installment addresses the environmental benefits associated with
biofuels, particularly in reducing our carbon footprint. In the mass
media lately, we have been hearing a lot about “carbon footprints,”
“greenhouse gases,” “climate change” and “global warming.”
Unfortunately, some of the information is non-defensible, inaccurate, or
misrepresented. This muddling of the facts has been especially
prevalent when assessing the environmental impact of biofuels. Further
complicating the issue are non-scientifically valid efforts to assess
and assign indirect carbon costs such as land use changes occurring on
other continents. Land use change in foreign countries is as old as
history itself and the multiplicity of factors that drive it are far too
complex to attribute solely to biofuel production in the United States.
Furthermore, serious errors have been uncovered in the methodology used
in these indirect land use change assessments such as ignoring the fact
that approximately half of the feed value of corn grain is maintained
in co-products such as distillers grain when corn is converted to
ethanol.
However, it is fairly straight forward to compare the direct carbon
footprint of gasoline relative to a biofuel such as corn ethanol.
According to the USEPA, for each gallon of gasoline burned in an
automobile, 19.4 lb of CO2 are emitted to the atmosphere. This is just
from the carbon actually contained in the gasoline and does not include
the carbon from extracting the crude oil, transporting the crude oil,
refining the crude oil, and transporting the gasoline. Furthermore,
prior to refining, the carbon from gasoline was safely sequestered below
the earth’s surface for hundreds of millions of years. It is basically
new carbon added to the atmosphere – 2.7 trillion pounds of new CO2
annually from cars in the United States alone.
By comparison, the net global warming potential of an equivalent amount
of ethanol (1.4 gallons of ethanol per gallon of gasoline) is
significantly lower. This is because the carbon contained in biofuel
ethanol is autotrophically derived, meaning it came from the atmosphere
in the first place (through photosynthesis of the corn plant from which
the ethanol was made). When burned, the ethanol carbon is simply
recycled back to the atmosphere from where it came. It is not new carbon
added to the atmosphere. However, using international carbon accounting
practices established by the International Panel on Climate Change
(IPCC), we should consider the fossil fuel carbon used in producing
ethanol. Using typical corn production inputs, a 150 bushel per acre
corn crop will require approximately 28,000 seeds; 150 lb of N, 55 lb of
P2O5, and 85 lb of K2O fertilizers; two quarts of herbicide, and five
gallons of fuel/lub/oil. On a per acre basis, these inputs would run up a
carbon debt of about 1250 lb CO2 per acre. The same acre would produce
about 420 gallons of ethanol, giving a carbon footprint of only 2.9 lb.
of CO2 per gallon of ethanol. Or, on a gasoline equivalent basis, 4.2 lb
of CO2 emitted for each 1.4 gallons of ethanol burned which represents a
78 percent reduction in net global warming potential simply by using
ethanol instead of gasoline (see Figure 1). Even more promising, the
carbon footprint of second generation biofuels made from perennial
grasses will be substantially lower yet – estimated at a 94 percent
reduction from gasoline.
Figure 1. Relative carbon footprint from direct effects of
combusting A = gasoline; B = grain ethanol; and C =
cellulosic ethanol. A =19.4 lb CO2/gal., and B and C
represent a 78 and 94% respective reduction (on an
energy equivalent basis) in carbon footprint relative to A.
Read part 1, part 2, part 3, part 5, part 6, part 7, part 8, part 9, part 10 of this series.