Page 32 - Materials Chemistry, Second Edition

18 E. I. Wiloso and R. Heijungs

(Finnveden et al. 2009). Other distinctive characteristics of CLCA are that unit
processes within a system boundary are included to the extent of their expected
change caused by a demand and that co-products are handled by system expansion
(Weidema 2003). To summarize the main characteristics of these approaches, a
comparison between ALCA and CLCA is given in Table 1.
CLCA is, in principle, only preferable within certain limits since the uncer-
tainties in the modeling stage may outweigh the insight gained from it (Cherubini
and Strømman 2011). This is related to the fact that the reference system should
always refer to the scope and context of the study. For example, the bioenergy
system is typically compared with a fossil reference system producing the same
amount of products and services. In most cases, however, studies use conventional
extraction of crude oil as a benchmark, thereby ignoring the increasing carbon
footprint arising from the extraction of non-conventional oil such as oil sands,
shale oil, and deep-ocean drilling (Harvey and Pilgrim 2011). Similarly, when the
bioenergy pathway delivers some co-products able to replace existing products, the
reference to the substituted products should also be defined in the fossil reference
system. The same applies to the case when the production of feedstock for biofuels
uses land that was previously storing carbon such as forests. In this case, the
previous land use should be taken into consideration for the determination of
carbon emissions due to land-use change (Singh et al. 2010). Also, when the same
feedstock is used for another function, the reference system should include the
alternative biomass use. In our view, this last example is the crucial aspect of
CLCA in the case of a bioenergy system. This requires a CLCA approach to
include the production of biomass feedstocks, resulting in a wider system
boundary. This feedstock, consequently, is no longer available for other purposes
(such as food, feed, or fiber), so new land to produce an extra feedstock may be
needed. The above requirements may increase the uncertainty of the assessment;
hence, the adoption of CLCA approach must be treated carefully.
A famous issue in CLCA is the coverage of indirect land use in a biofuel
system. Based on the study of Searchinger et al. (2008), Zamagni et al. (2012)

Table 1 Main characteristics of ALCA and CLCA (based on Thomassen et al. 2008)
Characteristics ALCA CLCA
Synonym Status quo, descriptive Change-oriented
Type of questions Accounting Assessing consequences on
changes
Type of required inventory data Average, historical Marginal, future
Knowledge on the cause–effect Physical mechanisms Physical and market mechanisms
chains
Functional unit Represents static situation Represents change in volume
System boundaries Static processes Affected processes by change in
demand
Treatment of multi-functional Co-product allocation System expansion
processes (partition)
Assessment quality Sensitive to uncertainty Higher sensitivity to uncertainty