A review on the quantification of life cycle greenhouse gas emissions at urban scale

Cities are responsible for 75%-80% of emissions worldwide, and policies that target emissions reductions are often implemented at an urban scale. This paper reviews studies using life cycle assessment (LCA) methods, specifically input-output and hybrid analysis, which used a consumption based accounting system to quantify direct (Scope 1) emissions and indirect (Scope 2 and Scope 3) emissions at the urban scale. Life cycle greenhouse gas emissions for case studies are scaled toward three metrics: nominal Gross Domestic Product, population, and population density; as these factors are known to be influential in life cycle assessment results at these scales. However, this work illustrates that, for the cities and countries considered in these case studies, the similarity between cities within the same country is more pronounced than any effects of Gross Domestic Product (economy) or population/population density (city size) across cities in different countries. Accounting for greenhouse gas emissions at city scale using LCA methods presents difficulties in three LCA phases: In Phase 1, there is no agreement available on a concisely defined city boundary and the extent to which indirect emissions are included; In Phase 2, there is a lack of publicly available data from governments for a wide range of locations; In Phase 3, there are few studies among those reviewed that provided a thorough analysis of greenhouse gas emissions using life cycle impact assessment at urban scale. Because of these issues with LCA Phases 1-3, Phase 4 (interpretation of results) cannot be performed effectively to assist with emissions reduction policy-making and planning. (C) 2020 Elsevier Ltd. All rights reserved.