Alternative fuels and green aviation - Biomass as Energy Source: Resources, Systems and Applications - page 215

while others are proprietary (such as ecoinvent 2 ). With such databases, one can drill down to the
smallest details and quantify the environmental impact of using material A versus material B for
a pipeline of length L .
LCAs are relatively new methodology, so that a literature survey of aviation fuel LCAs can
be somewhat confusing due to conflicting results and methodologies. In 2006, ISO 14040 (ISO,
2006a) and 14044 (ISO, 2006b) were established to provide a uniform approach to environmental
LCAs. By 2012, the field has matured considerably. GREET (Greenhouse Gases, Regulated
Emissions, and Energy Use in Transportation) is a software package developed by Argonne
National Laboratories in the US to perform LCAs for vehicular fuels. This code is also commonly
used in LCAs for aviation fuels. Another option is the evolving OpenLCA, which is freeware
developed for generalized LCAs.
Startup costs, or capital expenditures, are often ignored in economics-focused LCAs, but they
can make all the difference in predicting whether a specific venture will be profitable or not, or
that a particular fuel will be environmentally friendly or not. If the extraction of the petroleum
fuel is at a remote location and requires a road to be built to get there, this can be a significant
cost. Not only is there the direct material cost due to asphalt and other building materials, and the
energy cost associated with road-building equipment, there may also be indirect costs associated
with land use change, such as deforestation if that is needed to build the road. If we slash and
burn forest to create farmland on which to grow biofuel feedstocks, the economic cost could be
significant, but the environmental impact could be even worse.
In the process of photosynthesis, plants turn CO 2 , a greenhouse gas, into O 2 . As such, forests
are living, breathing systems that store, or sequester, carbon in their limbs and roots. When trees
die, fall to the forest floor and decompose, the sequestered carbon in the wood becomes nutritious
soil for the next generation of plants. When we clear forestland to create farmland, not only do
we lose the benefit of this natural process, but also the carbon that was stored in the plant matter
may be released into the atmosphere, typically by burning. The upfront greenhouse gas emissions
due to clearing a hectare (ha, with 1 ha = 10,000 square meters) of forest can result in the release
of 604-1146 megatons of greenhouse gases (MT) into the atmosphere (Searchinger et al. , 2008).
Clearing a savannah or grassland can release 74-305MT/ha into the atmosphere. Since the net
environmental benefit of growing corn for ethanol is measured in at best a couple of megatons
per hectare per year (MT/ha/y), it can take decades to recover the environmental cost of preparing
untouched land for farming (Searchinger et al. , 2008). In fact, some have argued that land-use
issues end up being the dominant issue in sustainability (Melillo et al. , 2009; Righelato and
Spracklen, 2007).
More subtly, the effect of land use change can be indirect. Suppose that a farmer in Iowa
decides to sell the corn harvest to an ethanol refinery rather than a grocery store chain in order
to benefit from agricultural subsidies provided in the US. This corn will no longer be available
to feed human beings or animals, and the price of corn rises. The globally rising price of corn
encourages another farmer in Mexico to clear virgin land to produce corn. The net effect on the
environment is to increase the amount of greenhouse gas pumped into the atmosphere due to land
use change. Some LCAs do not attempt to quantify indirect land use change, since it is difficult to
formulate a meaningful model of the process that adequately describes the socioeconomic factors
that are involved. Nevertheless, this is a real phenomenon, and this is an active area of research,
particularly for LCAs geared towards analysis of global issues in sustainability.
Other land-use concerns revolve around the use of nutrients to more efficiently grow crops.
Nitrogen fertilizers tend to outgas nitrous oxide, which can lead to smog formation when com-
bined with hydrocarbons and sunlight. Nitrogen and phosphorous fertilizer are also responsible
for eutrophication as nutrient-rich runoff from farmland escapes into a lake or ocean and create
algal blooms. As the algae die off, their decomposition robs the water of dissolved oxygen that fish
and other marine life depend on for survival. Not only are we creating unnecessary problems for
2 See http://www.ecoinvent.ch