“Life-cycle assessment (LCA) is an environmental management tool for identifying (and comparing) the whole life cycle, or cradle-to-grave, environmental impacts of the creation, marketing, transport and distribution, operation, and disposal of specific human artifacts. The approach is intrinsically holistic in nature and considers direct and, ideally, related processes and hidden, nonmarket flows of raw materials and intermediate inputs, and waste and other material and energy outputs associated with the entire existence or “product chain” or “system” (Guinee et al. 1993). The LCA procedure often involves a comparison of a small number of substitutable products assumed to provide a similar consumption service.” (Daniels and Moore 2001)

This method is well-documented in the ISO 14040 and 14044 standards. The outcome of an LCA study generally provides insights into a number of different impact categories, which can for instance include climate change, acidification, eutrophication, and resource depletion. There is a significant use of LCA inside and outside of academia. There are many applications of this tool in industry, and the approach has been expanded with complementary methods like Life Cycle Costing (LCC) and Social Life Cycle Assessment (S-LCA), which focus on the economic and social aspects, respectively. The combination of LCA, LCC and S-LCA has been termed Life Cycle Sustainability Assessment (LCSA) (Kloepffer 2008).

Despite a clearly-defined guiding framework and unparalleled opportunities to understand the global impacts of material flows, LCA has not yet found wide uptake in urban metabolism assessments. Firstly, LCA faces data requirements that exceed those of other methods, and requires an understanding of production, distribution, disposal, and other operations outside of the city of study. Furthermore, a “functional unit” must be defined before being able to undertake an LCA. However, the city itself cannot be taken as a single functional unit. Instead, a particular product, material, or a service within the city should be defined as a functional unit.

A number of hybrid methods have been developed that take advantage of LCA but that can be combined with other assessment methods on an urban level. These methods are discussed in more detail in the Hybrid methods section.