The goal of the circular economy (CE) is to transition from today's take-make-waste linear pattern of production and consumption to a circular system in which the societal value of products, materials, and resources is maximized over time. Yet circularity in and of itself does not ensure social, economic, and environmental performance (i.e., sustainability). Sustainability of CE strategies needs to be measured against their linear counterparts to identify and avoid strategies that increase circularity yet lead to unintended externalities. The state of the practice in quantitatively comparing sustainability impacts of circular to linear systems is one of experimentation with various extant methods developed in other fields and now applied here. While the proliferation of circularity metrics has received considerable attention, to-date, there is no critical review of the methods and combinations of methods that underlie those metrics and that specifically quantify sustainability impacts of circular strategies. Our critical review herein analyzes identified methods according to six criteria: temporal resolution, scope, data requirements, data granularity, capacity for measuring material efficiency potentials, and sustainability completeness. Results suggest that the industrial ecology and complex systems science fields could prove complementary when assessing the sustainability of the transition to a CE. Both fields include quantitative methods differing primarily with regard to their inclusion of temporal aspects and material efficiency potentials. Moreover, operations research methods such as multiple-criteria decision-making (MCDM) may alleviate the common contradictions which often exist between circularity metrics. This review concludes by suggesting guidelines for selecting quantitative methods most appropriate to a particular research question and making the argument that while there are a variety of existing methods, additional research is needed to combine existing methods and develop a more holistic approach for assessing sustainability impacts of CE strategies.
Although circular initiatives emerge around the world, the process of decoupling the economic activity from resource consumption and environmental impacts is far of being achieved. The concept of circular economy embodies the opportunity to reconcile an improved resource use while reducing the environmental footprint. Appropriate assessment metrics and methodologies are needed to identify potential trade-off between these 2 sides of a single coin. In this paper, we apply the Material Circularity Indicator (MCI) and Life Cycle Assessment (LCA) to analyse tires end-of-life strategies aiming at improving the circular flow of all tire materials. Results reveal re-treading is interesting to produce trade-offs on environmental impacts while re-grooving offers a fully decoupled strategy that improves material circularity avoiding environmental burdens. Further improvements should integrate environmental assessment as well as economic factors to link micro scale to macro scale contributions to sustainable development.
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