When to replace a product to decrease environmental impact?—a consequential LCA framework and case study on car replacement

Many decisions are made during the life cycle of a product, e.g., whether to replace a product or to keep using it. To pinpoint the “greener” choice, the consequential environmental effects of each choice should be estimated. Hereto, only activities occurring after the decision should be considered and, thus, not necessarily the complete product life cycle. Decisions are taken at different levels in the economy, ranging from small scale (e.g., few individual purchases) to large scale (e.g., policies). In this article, we introduce a framework that mainly focuses on the small-scale decision of replacement of a product in usage, illustrated in case of a petrol versus an electric car.

For a fixed time span of usage (functional unit), the product system composition varies based on the selected time of replacement. Many market mechanisms occur within the cause-effect chain, for which argued presumptions are necessary. For example, the purchase of the alternative product is reasoned to possibly induce an additional product supply. Moreover, if the product is not obsolete after initial usage, it is sold in the secondhand market and will thus displace the average market mix. The developed framework for this small-scale replacement decision is different from the alternative consequential approach of ecoinvent that covers a different decision, namely, a marginal increase in demand, e.g., of car usage, at market level. In our framework, a ratio for the amount of newly car produced per purchase is introduced. For the case study, the global warming potential over 100 years is estimated, this using general data from databases and time-varying market mix (in composition), car technology, and electricity mix.

A set of equations is introduced that serves as a first simplified framework. Bearing in mind limitations, if the petrol car is disposed of as waste after initial usage whereas the electric car resold, it is estimated that a replacement of the petrol car by the electric car at any time lowers the impact on climate change. A better characterization of impact over time and market and agent-based modeling should be at the core of further efforts, especially when upscaling to large-scale decisions.

Framework and insights are provided on the modeling of the environmental effects of a replacement decision. Finally, this article may serve as a stepping-stone towards an integrated consequential modeling of sustainability impact of product-related decisions, looking beyond a normative consideration of a fixed product life cycle.