Page 142 - Biofuels for a More Sustainable Future

128 Biofuels for a More Sustainable Future

biomass cultivation followed by an equal, positive flow later in the life cycle.
The latter, more explicit approach is supported by standards such as PAS
2050 (BSI, 2011) and ISO 14067 (ISO, 2013b)
However, this is a topic of ongoing debate, particularly for long-lived
feedstocks such as wood from forestry, where rapid deforestation can
indeed create a net contribution to the environment depending on the
extent and speed of reforestation. The issue is also complicated by the
potential production of methane, which is a more potent GHG than
CO 2 , under anaerobic conditions
Biogenic carbon accounting approaches are discussed in more depth in
the literature, including carbon payback time, carbon discounting, and
time-integrated accounting techniques (Cherubini et al., 2011; ICCT,
2014), but these are beyond the scope of this chapter
Land use change
Soil and vegetation contains large amounts of carbon that may be disturbed
as a result of land use change (LUC). Part of this stored carbon is then
oxidized and released to the atmosphere as CO 2 . In the energy sector,
LUC can occur as a direct result of conversion of grasslands or forests to
biomass cultivation (direct LUC), or via the displacement of other crop
cultivation activities to previously uncultivated land (indirect LUC). This
is a major driver of climate change: from 1750 to 2011 it is estimated
that LUC accounted for 32% (16%–55%) of cumulative anthropogenic
CO 2 emissions (IPCC, 2014)
Direct LUC is often incorporated into LCA modeling, with the simplest
method being that proposed by the European Commission (European
Commission, 2010) which involves estimating the carbon stored in two
carbon pools: carbon stock (i.e., living and dead organic biomass) and
soil carbon stock. Indirect LUC is more difficult to account for due to
the challenges of consequential analysis, that is, producing an accurate
economic model to determine how much crop cultivation activity would
be displaced by the additional demand for energy/feedstock crops. This
topic is a subject of ongoing research and debate at the time of writing,
the depth of which is beyond the scope of this chapter. Readers should
note that the majority of many LCA impact assessment methods already
include some form of land use accounting in the calculation of climate
change impacts