As American farmers reap the corn-ethanol bonanza and new ventures chase more efficient ethanol feedstocks, two troubling studies reported in “Science” magazine say that all forms of biofuels will result in higher CO2 emissions
than petroleum.
Earlier analyses based comparative ratings on the full production cycle --
from growing a crop to its ethanol conversion to its final burning -- and
concluded that, while corn-ethanol might emit somewhat less than gasoline,
other plants such as sugar cane and switchgrass might cut emissions by as
much as 85%. But the “Science” studies factor in the carbon cost of land
conversion to raise those crops, and come up with the disturbing conclusion
that vastly more CO2 will be released into the atmosphere than were we to
continue to use gasoline.
The problem is this: the accelerating demand for raising crops for both
food and fuel worldwide will lead to millions of acres to be cleared, ranging
from grasses to mature forests. Whether suddenly from burning or gradually
from decomposition, the biomass on that land will release the stored CO2 that
funded its growth. Then comes the lost opportunity of how much CO2 that
biomass would have absorbed thereafter by its continued existence, especially
woodlands that are still growing.
The combined release of CO2 at the outset and the sacrificed “carbon
uptake” thereafter creates what the studies call a “carbon debt”. For a
biofuel crop to make sense, it must repay that debt in the course of its
repeated plantings by the CO2 emissions it saves compared to oil. Until that
payback, a biofuel will have led to the emission of more CO2 than the fossil
fuel it replaced.
Long Term Debt
The question: how long do different feedstocks on different types of
converted land take to cancel their debt?
The answer: the carbon debts incurred are enormous. The studies say that
scores of years and even centuries are needed to break even, depending on the
crop and the type of land put to the plow. When land use change is added on
the debit side of the ledger, most crops result in much higher emissions than
oil, especially across the next 30 years, the span during which the studies
assume we will be using biofuels before moving on to a non-agricultural-based
fuel.
One study found, for example, that even if it only displaced central U.S.
grassland, corn grown for ethanol would take 93 years before it overcame the
carbon debt of land use change with its lower carbon emissions compared to
gasoline.
The other study, which used globe-spanning agricultural models to assign
crops to land to meet projected demands, calculated that were corn to replace
forest, the sequestered carbon loss is about 330 to 630 times the amount the
field will pay back each year, the variance depending on the type of forest
and whether it is still growing.
Most findings are much worse when natural land cover is replaced by the
much reduced CO2 take-up of field crops. An insurmountable 319 year debt is
left behind when Brazil’s rain forests are leveled to produce soybeans for
biodiesel. The rain forests slashed in Indonesia in the race to produce palm
oil as fuel leave behind an astonishing 423 year debt.
There are few bright spots. One is Ethanol from Brazilian sugarcane. Its
extraordinary productivity could pay back its land use debt in only four
years, if tropical grazing land is used. Elsewhere, as in the United States,
the studies strongly advise that (1) only abandoned agricultural lands, or
land retired under U.S. programs, be planted, and with perennials, and (2)
otherwise, biofuels must be produced only from waste that would yield its CO2
anyway, and to no purpose, such as municipal waste, wood chips, and
agricultural discard.
- Stephen Wilson, PlanetWatch Editor
than petroleum.
Earlier analyses based comparative ratings on the full production cycle --
from growing a crop to its ethanol conversion to its final burning -- and
concluded that, while corn-ethanol might emit somewhat less than gasoline,
other plants such as sugar cane and switchgrass might cut emissions by as
much as 85%. But the “Science” studies factor in the carbon cost of land
conversion to raise those crops, and come up with the disturbing conclusion
that vastly more CO2 will be released into the atmosphere than were we to
continue to use gasoline.
The problem is this: the accelerating demand for raising crops for both
food and fuel worldwide will lead to millions of acres to be cleared, ranging
from grasses to mature forests. Whether suddenly from burning or gradually
from decomposition, the biomass on that land will release the stored CO2 that
funded its growth. Then comes the lost opportunity of how much CO2 that
biomass would have absorbed thereafter by its continued existence, especially
woodlands that are still growing.
The combined release of CO2 at the outset and the sacrificed “carbon
uptake” thereafter creates what the studies call a “carbon debt”. For a
biofuel crop to make sense, it must repay that debt in the course of its
repeated plantings by the CO2 emissions it saves compared to oil. Until that
payback, a biofuel will have led to the emission of more CO2 than the fossil
fuel it replaced.
Long Term Debt
The question: how long do different feedstocks on different types of
converted land take to cancel their debt?
The answer: the carbon debts incurred are enormous. The studies say that
scores of years and even centuries are needed to break even, depending on the
crop and the type of land put to the plow. When land use change is added on
the debit side of the ledger, most crops result in much higher emissions than
oil, especially across the next 30 years, the span during which the studies
assume we will be using biofuels before moving on to a non-agricultural-based
fuel.
One study found, for example, that even if it only displaced central U.S.
grassland, corn grown for ethanol would take 93 years before it overcame the
carbon debt of land use change with its lower carbon emissions compared to
gasoline.
The other study, which used globe-spanning agricultural models to assign
crops to land to meet projected demands, calculated that were corn to replace
forest, the sequestered carbon loss is about 330 to 630 times the amount the
field will pay back each year, the variance depending on the type of forest
and whether it is still growing.
Most findings are much worse when natural land cover is replaced by the
much reduced CO2 take-up of field crops. An insurmountable 319 year debt is
left behind when Brazil’s rain forests are leveled to produce soybeans for
biodiesel. The rain forests slashed in Indonesia in the race to produce palm
oil as fuel leave behind an astonishing 423 year debt.
There are few bright spots. One is Ethanol from Brazilian sugarcane. Its
extraordinary productivity could pay back its land use debt in only four
years, if tropical grazing land is used. Elsewhere, as in the United States,
the studies strongly advise that (1) only abandoned agricultural lands, or
land retired under U.S. programs, be planted, and with perennials, and (2)
otherwise, biofuels must be produced only from waste that would yield its CO2
anyway, and to no purpose, such as municipal waste, wood chips, and
agricultural discard.
- Stephen Wilson, PlanetWatch Editor
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