The use of substitution in attributional life cycle assessment

Substitution is used within attributional life cycle assessments (LCAs) as a means of avoiding allocation between co-products, and a number of existing standards and guidance documents permit its use in this way. This article discusses the appropriateness of substitution for attributional LCA, and suggests that the use of substitution introduces consequential elements into attributional analysis and that attributional assessments that use substitution will not be appropriate for consumption-based carbon accounting or corporate greenhouse gas reporting. This article suggests that, as a methodological principle, attributional LCA should only include actual physical burdens and should not include values for burdens that are avoided (i.e. do not physically occur). We also suggest that existing standards and guidance should be amended so that substitution is not permitted as a method within attributional LCA and that substitution should be clearly distinguished from expanding the function studied by an assessment. This article focuses on greenhouse gas LCA, but the discussion and conclusions apply to attributional LCA generally.