Metrics (potentials, potency factors, equivalency factors or characterization factors) are available to support the environmental comparison of alternatives in application domains like process design and product life-cycle assessment (LCA). These metrics typically provide relative insights into the implicit concern associated with chemicals, emissions and resource consumption in the context of human health, ecological health and resource depletion. The approaches used to derive the metrics range in their site-specificity, complexity, comprehensiveness, sophistication and uncertainty. It is therefore often necessary to consider the use of more than one approach within the context of a given impact category to help support a decision. In this paper we outline some of the strengths and weaknesses of available approaches in the commonly considered categories of global warming, stratospheric ozone depletion, tropospheric ozone (smog) creation, eutrophication/nutrification, acidification, toxicological impacts and resource depletion.
The article explains that environmental metrics help compare alternatives in process design and product life cycle assessment. They express the relative concern associated with chemicals, emissions and resource use in relation to human health, ecological health and resource depletion. The metrics are not interchangeable: the approaches available for an impact category can differ in how site-specific, complex, comprehensive and uncertain they are. These differences affect what a comparison can show and how confidently it can support a decision.
Rather than assuming that one method is best for every purpose, the authors recommend considering more than one approach within an impact category when this helps inform a decision. Their review discusses strengths and weaknesses across global warming, stratospheric ozone depletion, ground-level ozone formation, eutrophication, acidification, toxicological impacts and resource depletion. The paper therefore offers a framework for understanding the choices behind environmental comparisons, while emphasizing that the suitable metric depends on the assessment context.
