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A survey of unresolved problems in life cycle assessment

Part 1: goal and scope and inventory analysis

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Abstract

Background, aims, and scope

Life cycle assessment (LCA) stands as the pre-eminent tool for estimating environmental effects caused by products and processes from ‘cradle to grave’ or ‘cradle to cradle.’ It exists in multiple forms, claims a growing list of practitioners, and remains a focus of continuing research. Despite its popularity and codification by organizations such as the International Organization for Standards and the Society of Environmental Toxicology and Chemistry, life cycle assessment is a tool in need of improvement. Multiple authors have written about its individual problems, but a unified treatment of the subject is lacking. The following literature survey gathers and explains issues, problems and problematic decisions currently limiting LCA’s goal and scope definition and life cycle inventory phases.

Main features

The review identifies 15 major problem areas and organizes them by the LCA phases in which each appears. This part of the review focuses on the first 7 of these problems occurring during the goal and scope definition and life cycle inventory phases. It is meant as a concise summary for practitioners interested in methodological limitations which might degrade the accuracy of their assessments. For new researchers, it provides an overview of pertinent problem areas toward which they might wish to direct their research efforts.

Results and discussion

Multiple problems occur in each of LCA’s four phases and reduce the accuracy of this tool. Considering problem severity and the adequacy of current solutions, six of the 15 discussed problems are of paramount importance. In LCA’s first two phases, functional unit definition, boundary selection, and allocation are critical problems requiring particular attention.

Conclusions and recommendations

Problems encountered during goal and scope definition arise from decisions about inclusion and exclusion while those in inventory analysis involve flows and transformations. Foundational decisions about the basis of comparison (functional unit), bounds of the study, and physical relationships between included processes largely dictate the representativeness and, therefore, the value of an LCA. It is for this reason that problems in functional unit definition, boundary selection, and allocation are the most critical examined in the first part of this review.

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Notes

  1. Calculated from the difference in the energy multiplier to assemble (4 MJ/$) and produce vehicle and parts (12 MJ/$) (Lenzen 2000, p. 137).

  2. Examples of multi-functional processes requiring allocation include: incinerators, landfills, sawmills, dairies, oil refineries, metal smelting, transportation, etc. (Ekvall and Finnveden 2001).

  3. Heijungs and Frischknecht have suggested that the allocation problem arises from the fact that when one models the unit processes used in the LCI assessment as a technology matrix, many times the matrix cannot be inverted and its pseudo-inverse does not yield an exact solution to the problem. From this perspective, which seems to apply only to descriptive closed-loop recycling cases where the technology matrix is square (i.e., the number of unit processes equals the number of balances), “…it is the database itself, the collection of process data that is used for finding the inventory table for any functional unit, that can create the allocation problem…independent of the case study at hand.” (Heijungs and Frischknecht 1998).

  4. Exported functions refer to functions or co-products that are exported internally or externally of the product system studied.

  5. Indirect effects refer to the effects that decisions in the product system of interest will have on other product systems.

  6. The determining co-product is the product that has the single most influence regarding the inputs and outputs of the process. This influence may be due to the fact that it provides the most revenue, has a large market demand, is the only avenue of processing the co-product, etc.

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Acknowledgements

The presented material is based on work supported in part by NSF grants DMI-0600243 and DMI-0522116. We also gratefully acknowledge support from Georgia Tech’s Manufacturing Research Center and Woodruff School of Mechanical Engineering. John Reap and Scott Duncan gratefully acknowledge financial support provided by NSF grants DMI-0600243 and DMI-0522116, respectively. Felipe Roman acknowledges financial support given by Georgia Tech’s President’s Fellowship and the Goizueta Fellowship Program. All authors thank Valerie Thomas of Georgia Tech’s School of Industrial and Systems Engineering as well as IJLCA’s anonymous reviewers for their thoughtful comments and criticisms. Any opinions, finding, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the US government and/or the authors’ parent institutions.

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Authors and Affiliations

  1. Sustainable Design and Manufacturing Program, Systems Realization Laboratory, The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, 30332-0405, USA

    John Reap, Felipe Roman, Scott Duncan & Bert Bras

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  1. John Reap
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  2. Felipe Roman
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Correspondence to Bert Bras.

Additional information

Preamble This series of two papers reviews unresolved problems in life cycle assessment (LCA). Part 1 focuses upon problems in the goal and scope definition and life cycle inventory analysis phases. Part 2 (Reap et al. 2008) discusses problems in the life cycle impact assessment and interpretation phases. Having probed LCA’s main weaknesses, Part 2 identifies critical problems and suggests research agendas meant to ameliorate them. Additionally, the second paper in the series brings closure to the review with a unifying summary.

Part 2 ‘Impact assessment and interpretation’ follows in the subsequent issue.

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Reap, J., Roman, F., Duncan, S. et al. A survey of unresolved problems in life cycle assessment. Int J Life Cycle Assess 13, 290–300 (2008). https://doi.org/10.1007/s11367-008-0008-x

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