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174    Cha pte r  Ni ne

                   A more challenging task is quantifying the environmental foot-
               print of a company or other entity in terms of the ecosystem goods
               and services that are required to support its operations. For example,
               one technique below uses land area as an indicator, but it is difficult
               to capture the many important ecosystem services that we depend
               upon, such as climate regulation, water purification, and pollination
               (see Chapter 2).  As discussed later in this chapter, new scientific
               methods based on life-cycle exergy consumption make it possible to
               quantify all of the indicators shown in Figure 9.1 within a common
               framework.
                   To complicate matters further, the scope of a footprint analysis
               can vary enormously based on the chosen life-cycle boundary.  As
               illustrated in Chapter 1, Figure 1.1, a materials or energy footprint
               may be confined to the direct operations of a company or facility, it
               may extend to indirect activities associated with purchased goods or
               services, or it may encompass the full breadth of ecosystem goods
               and services. In published environmental reports, most companies are
               satisfied to quantify their environmental footprint in terms of direct
               consumption and direct generation of waste and emissions. As noted
               in Chapter 3, efforts have begun to include the full supply chain foot-
               print in GHG inventories. While actual use of indicators to measure
               ecosystem service consumption is rare, many companies are begin-
               ning to track their water footprints.
                   The following briefly describes a number of methods for calcu-
               lating different types of environmental footprints—carbon, materials,
               land area, and water.

               Carbon Footprint
               A carbon footprint can be calculated by taking an inventory of the
               total greenhouse gas emissions for a company, facility, product, com-
               munity, family, or any other entity. The Kyoto Protocol identifies
               six greenhouse gases: carbon dioxide (CO ), methane (CH ), nitrous
                                                   2             4
               oxide (N O), sulfur hexafluoride (SF ), perfluorocarbons (PFCs),
                       2                        6
               and hydrofluorocarbons (HFCs). Each greenhouse gas has a global
               warming potential that can be expressed in terms of equivalent
               CO  [4]. Carbon footprints are typically organized in terms of three
                  2
               successively broader scopes, covering the following GHG sources:
                    • Scope 1: Fuel combustion in vehicles or facilities that are
                      directly owned and/or controlled
                    • Scope 2: Purchased electricity from fossil fuel combustion
                      (e.g., coal, oil, natural gas)
                    • Scope 3: Other indirect sources of GHG emissions (e.g., waste
                      disposal, business travel)
                   The methodology for Scope 1 and Scope 2 assessment is straight-
               forward—it involves enumerating emission sources and estimating
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