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Analysis Methods for Design Decisions      173

               Footprint Indicators
               The term “footprint” has become popular in the environmental lexi-
               con, but it is used so loosely as to be virtually meaningless. Most
               practitioners conceive of the environmental footprint of a company,
               a household, or a community as being an aggregate measure of the
               total burden that it places on the environment. However, some have
               interpreted this in terms of a single metric, such as a “carbon foot-
               print” while others have interpreted it as a collection of indicators
               representing different environmental burdens (e.g., energy use, solid
               waste, air emissions). In the latter case, plotting these indicators on
               a “radar chart” enables a company to track its progress over time as
               the footprint shrinks toward zero.
                   A variety of different boundaries commonly used for footprint
               analysis are depicted in Figure 9.1. For example, an energy con-
               sumption footprint may include only nonrenewable energy sources
               (e.g., petro-fuels, coal, nuclear) or may include renewable sources (e.g.,
               solar, wind, geothermal). A material footprint may analyze total mass
               throughput, may focus only on consumption of input materials, or
               may focus on wastes, which in turn may include solids, liquids,
               and/or airborne emissions. Note that a carbon footprint focuses on
               just one type of airborne emissions, greenhouse gases (GHG). Fur-
               thermore, a material footprint may include only products purchased
               within the economy, may include consumption of materials derived
               from ecological sources, such as biomass (e.g., grass, wood, fish), or
               may include ecological resources that are not consumed but can be
               degraded (e.g., water).



























               FIGURE 9.1  Alternative boundaries for scope of environmental footprint
               analysis.
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