A Demand-Centered, Hybrid Life-Cycle Methodology for City-Scale Greenhouse Gas Inventories

Department of Civil Engineering, University of Colorado Denver, Denver, Colorado, USA.
Environmental Science and Technology (Impact Factor: 5.33). 10/2008; 42(17):6455-61. DOI: 10.1021/es702992q
Source: PubMed


Greenhouse gas (GHG) accounting for individual cities is confounded by spatial scale and boundary effects that impact the allocation of regional material and energy flows. This paper develops a demand-centered, hybrid life-cycle-based methodology for conducting city-scale GHG inventories that incorporates (1) spatial allocation of surface and airline travel across colocated cities in larger metropolitan regions, and, (2) life-cycle assessment (LCA) to quantify the embodied energy of key urban materials--food, water, fuel, and concrete. The hybrid methodology enables cities to separately report the GHG impact associated with direct end-use of energy by cities (consistent with EPA and IPCC methods), as well as the impact of extra-boundary activities such as air travel and production of key urban materials (consistent with Scope 3 protocols recommended by the World Resources Institute). Application of this hybrid methodology to Denver, Colorado, yielded a more holistic GHG inventory that approaches a GHG footprint computation, with consistency of inclusions across spatial scale as well as convergence of city-scale per capita GHG emissions (approximately 25 mt CO2e/person/year) with state and national data. The method is shown to have significant policy impacts, and also demonstrates the utility of benchmarks in understanding energy use in various city sectors.

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    • "Based on the functionality of cities, indirect energy use and associated GHG emissions were computed for the critical urban imported materials mainly including water, fuel, food, and cement (Ramaswami et al., 2008). For Xiamen City, only the materials which produced outside the city area are calculated, so they have no significant overlap with carbon emissions by urban end-use sectors (Section 2.1). "
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