Page 110 - Materials Chemistry, Second Edition

8 Scope Definition 95

be “what environmental impact can be attributed to product X?” or “what envi-
ronmental impact is product X responsible for?” As hinted by these questions, there
is an element of subjectivity involved in attributing impacts to a product system or
deciding the impact responsibility of a product system. This subjectivity arises in
the act of artificially separating the studied product system from the rest of the
economy. This separation is artificial because many, if not most, product systems
interact with other products systems through multifunctional processes, meaning
that they, as explained in the previous section, cannot be described as physical
entities in isolation. For example, from a strict physical perspective, the product
system of a bottle of milk cannot be described in isolation and the assignment of
processes that the product system is seen as “responsible for” therefore involves
choices. Before the ILCD guidelines came into place attributional modelling was
generally associated with allocation as the approach to solving the issue of multi-
functional processes, provided that subdivision (the preferred solution of the ISO
hierarchy) was not possible. By contrast, ILCD in some cases recommends solving
multifunctionality by system expansion within an attributional modelling frame-
work (see below).
Besides the issue of multifunctionality, attributional LCA is also associated with
the use of average processes in the background system, which reflects the modelling
of an average supply chain. In practice, this means that a market mix is used. This
could be for the global aluminium market or the electricitymarket of a nation. The
former is composed of a range of bauxite mines with different ore grades and
processing facilities that employ different production technologies, while the latter
is composed of different energy conversion technologies, such as the combustion of
coal, natural gas, oil and biomass, the harvesting of wind and solar power and the
use of nuclear power. As an example, Fig. 8.8 shows the Danish electricity con-
sumption mix in 2014.
Consequential LCI modelling was developed around the year 2000 to eliminate
the weakness inherent in the attributional LCA modelling framework due to the
attempt to artificially separate a product from the rest of the economy. Its overall
aim is to describe the changes to the economy caused by the introduction of the
studied product system, i.e. the product system’s consequence. Consequential LCI
modelling thus aims to answer the question “What are the environmental conse-
quences of consuming X?” For example, a consequential LCA of a bottle of milk
would attempt to model how the market responds to the change in demand for milk
represented by the functional unit of the study (e.g. involving a milk volume of 1 L
or a specified nutritional value). This is a very different approach than attributional
modelling because the change in the economy can look very different than the
representation of the isolated bottle of milk system. For example, the increased
demand for milk may lead to an increase in the capacity for milk production (i.e. the
numbers of cows giving milk), which in turn may lead to a reduction in the
production of some meat (e.g. beef from raising cattle) due to the increasing supply
of meat from dairy cows. This corresponds to handling the multifunctional process
of milk production by system expansion. A consequence of increased consumption
of milk may therefore be a reduction in environmental impacts from the avoided