Introduction to Life-Cycle Assessment and Decision Making Applied to Forest Biomaterials 173
Single Score A single environmental score result is calculated using both the normalized
midpoint results and weighting methods as described by the following equation.
Communicating the single score results has the advantage of one data point that is
easy to compare across multiple scenario option; however, this one value is inherently
subjective and has more uncertainty than midpoint indicators. When communicating
results in a single score, it is necessary to also provide midpoint indicator score and
properly document the normalization and weighting factors used to determine the
single score. Study transparency is a critical to the integrity of any LCA study and
requires much documentation of these and other methods and data sources.
Single Score=
∑ Midpoint Indicator
Normilization Factor
×Weighting Value
5.3.2.14 Life Cycle Impact Assessment Interpretation
The impact assessment methods and impact categories selected in the goal and scope
can shape the study conclusions. Omitting or including different impact categories is
one way in which the study can be drastically altered. Additionally, there are times in
which the study set out to examine a wide list of impacts, but available data are not
sufficient to calculate one or several of the impact categories. It is important to again
interpret the results from each of the LCA steps and to realign new insights with the
goal and scope.
With regard to impact assessment, it is important to evaluate if the LCIA results
provide enough data to make decisions or to take action. At times, there can be two
options that present environmental trade-offs or where one options will have higher
values for some impacts and lower values for others. In these scenarios, LCIA left at a
midpoint indicator can do little to help a decision maker. Additional analysis such as
single scores or an SMAA can be performed to provide further guidance into the most
advisable action or decision (Prado-Lopezet al., 2014).
5.3.2.15 Problems Set –Life-Cycle Impact Assessment
Problem 1 Use the NREL US LCI database (discussed later) and determine the emis-
sions that contribute to GWP for 1 person*km and also for a transport scenario of 100
people transported 600 km. Then calculate the GWP using the characterization factors
shown in this chapter for the 100-year horizon and for the 100 people transported
600 km. Use the following transportation operations.
a. Transport, intercity bus, diesel powered, south
b. Transport, passenger car, gasoline powered
Transport, intercity bus, diesel powered, south
Flow Category Type Unit Amount
Outputs
Ammonia Air/unspecified ELEMENTARY_FLOW kg 5.49E− 07
Carbon dioxide, fossil Air/unspecified ELEMENTARY_FLOW kg 4.04E− 02
Carbon monoxide, fossil Air/unspecified ELEMENTARY_FLOW kg 9.37E− 05
