Page 31 - Materials Chemistry, Second Edition

Key Issues in Conducting Life Cycle Assessment 17

Goal and scope definition is an important initial step since the choice of meth-
odology used depends on the purpose of the individual study. These methodo-
logical choices include system boundary, treatment of multi-functional processes,
types of required inventory data, and functional unit. The first three topics are
described in the following section (attributional and consequential LCA), while the
last one is described separately.

2.1 Attributional and Consequential LCA

A clear definition of the goal and scope should specify the types of LCA needed.
They can be attributional or consequential (ALCA and CLCA for short). In gen-
eral, the goal of ALCA is to assess the environmental burden of a product,
assuming a status quo situation, while the goal of CLCA is to assess environmental
consequences of a change in demand (Thomassen et al. 2008). These different
LCA principles require a systematic approach to reduce uncertainty due to free-
dom of choosing the methodology (Finnveden et al. 2009).
ALCA describes the environmentally relevant flows to and from a life cycle and
its subsystems (Finnveden et al. 2009). The attributional method is less important
for policy decisions as its purpose is not to support changes. ALCA, however, is
useful in obtaining insight into the main environmental impacts related to existing
bioenergy products. This is done to better describe the effect of changing feed-
stocks, changing production processes, or improving efficiency. Another type of
application with a more direct relevance to a bioenergy system is the use of ALCA
to identify main hot spots in the life cycle chain, the share of certain emissions, or
flows to an impact category. This can be a first step in realizing process
improvements from a sustainability point of view. An example of this is the LCA
study of a generic life cycle of bioenergy with a boundary system as shown in
Fig. 1 but without involving the indirect effects. This is in contrast with a CLCA
concept, which also includes the indirect effects.
CLCA describes how relevant environmental flows (resource use and emis-
sions) will change in response to possible decisions (Finnveden et al. 2009).
Referring to this definition, Cherubini and Strømman (2011) concluded that the
CLCA appears as the most broadly applied in bioenergy systems as compared to
ALCA. They revealed that almost three-fourths of the reviewed studies compare
the environmental impacts with those of a fossil reference system. This is done to
address the needs of policy makers in order to decide on relevant bioenergy
options. The assessment, however, needs further clarification since not all com-
parison studies necessarily qualify as consequential.
A distinction between foreground and background systems is especially useful
in the CLCA approach. Background systems are often based on databases repre-
senting average data of aggregated industrial processes, such as electricity. When a
chain of processes are being considered as a foreground system, the proposed
technology needs to be specifically known and marginal data are required