Measuring material efficiency: A review of the historical evolution of indicators, methodologies and findings

Increasing material efficiency, or material productivity, is essential for decoupling resource depletion and associated environmental pressures from economic development. This paper reviews the historical evolution of indicators monitoring material efficiency, their underpinning methodologies and major findings in the past three decades. Early studies investigated the material-economy relationship through intensity of use (IU) of some selected single materials. Economy-wide material flow accounting (EW-MFA) established a standardized framework for aggregating overall material inputs into an economy. Consumption-based material footprint (MF) analysis extended the system boundary to cover global resource extraction along supply chains to satisfy final consumption. Studies on material cycles (MC), especially metal cycles, further helped trace all major life cycle stages of anthropogenic material use, with the capability to account for in-use stocks of materials and products. Impact-based indicators investigate the opportunities to reduce negative environmental, social and economic impacts of material use, which is the ultimate purpose of improving material efficiency. Monitoring material efficiency with different indicators might lead to very different conclusions regarding a society's dependence on material and its dematerialization trend. We present a generalized framework for constructing all kinds of material efficiency/productivity indicators and make the case that election of indicators should be problem-oriented and policy-relevant.