Strategies toward ambitious climate targets usually rely on the concept of 'decoupling'; that is, they aim at promoting economic growth while reducing the use of natural resources and GHG emissions. GDP growth coinciding with absolute reductions in emissions or resource use is denoted as 'absolute decoupling' , as opposed to 'relative decoupling' , where resource use or emissions increase less so than does GDP. Based on the bibliometric mapping in part I (Wiedenhofer et al, 2020 Environ. Res. Lett. 15 063002), we synthesize the evidence emerging from the selected 835 peer-reviewed articles. We evaluate empirical studies of decoupling related to final/useful energy, exergy, use of material resources, as well as CO 2 and total GHG emissions. We find that relative decoupling is frequent for material use as well as GHG and CO 2 emissions but not for useful exergy, a quality-based measure of energy use. Primary energy can be decoupled from GDP largely to the extent to which the conversion of primary energy to useful exergy is improved. Examples of absolute long-term decoupling are rare, but recently some industrialized countries have decoupled GDP from both production-and, weaklier, consumption-based CO 2 emissions. We analyze policies or strategies in the decoupling literature by classifying them into three groups:(1) Green growth, if sufficient reductions of resource use or emissions were deemed possible without altering the growth trajectory.(2) Degrowth, if reductions of resource use or emissions were given priority over GDP growth. (3) Others, e.g. if the role of energy for GDP growth was analyzed without reference to climate change mitigation. We conclude that large rapid absolute reductions of resource use and GHG emissions cannot be achieved through observed decoupling rates, hence decoupling needs to be complemented by sufficiency-oriented strategies and strict enforcement of absolute reduction targets. More research is needed on interdependencies between wellbeing, resources and emissions.

As long as economic growth is a major political goal, decoupling growth from resource use and emissions is a prerequisite for a sustainable net-zero emissions future. However, empirical evidence for absolute decoupling, i.e. decreasing resource use and emissions at the required scale despite continued economic growth, is scarce and scattered across different research streams. In this two-part systematic review, we assess how and to what extent decoupling has been observed and what can be learnt for addressing the sustainability and climate crisis. Based on a transparent approach, we systematically identify and screen more than 11 500 scientific papers, eventually analyzing full texts of 835 empirical studies on the relationship between economic growth (GDP), resource use (materials and energy) and greenhouse gas emissions. Part I of the review examines how decoupling has been investigated across three research streams: energy, materials and energy, and emissions. Part II synthesizes the empirical evidence and policy implications (Haberl et al 2020 Environ. Res. Lett. 15 065003). In part I, we examine the topical, temporal and geographical scopes, methods of analysis, institutional networks and prevalent conceptual angles. We find that in this rapidly growing literature, the vast majority of studies-decomposition, 'causality' and Environmental Kuznets Curve analysis-approach the topic from a statistical-econometric point of view, while hardly acknowledging thermodynamic principles on the role of energy and materials for socio-economic activities. A potentially fundamental incompatibility between economic growth and systemic societal changes to address the climate crisis is rarely considered. We conclude that the existing wealth of empirical evidence merits braver conceptual advances than we have seen thus far. Future work should focus on comprehensive multi-indicator long-term analyses, conceptually grounded on the fundamental biophysical basis of socio-economic activities, incorporating the role of global supply chains as well as the wider societal role and preconditions of economic growth.

Dynamic material flow analysis (dMFA) is widely used to model stock‐flow dynamics. To appropriately represent material lifetimes, recycling potentials, and service provision, dMFA requires data about the allocation of economy‐wide material consumption to different end‐use products or sectors, that is, the different product stocks, in which material consumption accumulates. Previous estimates of this allocation only cover few years, countries, and product groups. Recently, several new methods for estimating end‐use product allocation in dMFA were proposed, which so far lack systematic comparison. We review and systematize five methods for tracing material consumption into end‐use products in inflow‐driven dMFA and discuss their strengths and limitations. Widely used data on industry shipments in physical units have low spatio‐temporal coverage, which limits their applicability across countries and years. Monetary input–output tables (MIOTs) are widely available and their economy‐wide coverage makes them a valuable source to approximate material end‐uses. We find four distinct MIOT‐based methods: consumption‐based, waste input–output MFA (WIO‐MFA), Ghosh absorbing Markov chain, and partial Ghosh. We show that when applied to a given MIOT, the methods’ underlying input–output models yield the same results, with the exception of the partial Ghosh method, which involves simplifications. For practical applications, the MIOT system boundary must be aligned to those of dMFA, which involves the removal of service flows, sector (dis)aggregation, and re‐defining specific intermediate outputs as final demand. Theoretically, WIO‐MFA, applied to a modified MIOT, produces the most accurate results as it excludes massless and waste transactions. In part 2 of this work, we compare methods empirically and suggest improvements for aligning MIOT‐dMFA system boundaries.

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Herein, a techno-economic and environmental performance evaluation (i.e. Life Cycle Assessment (LCA)) of a 45 kW Microbial Electrolysis Cell system is presented in the context of industrial wastewater conversion.

Modeling pathways toward sustainable production and consumption requires improved spatio‐temporal and material coverage of end‐use product stocks. Momentarily, studies on inflow‐driven, dynamic material flow analysis (dMFA) extrapolate scarce information on material end‐use shares (i.e., ratios that split economy‐wide material consumption to different end‐use products) for single countries and years across longer time periods and global regions. Therefore, in part 1 of this work, we reviewed five methods to derive material end‐use shares which use industry shipment data in physical units and monetary input–output tables (MIOTs). Herein, we comparatively apply these methods to the United States, drawing on detailed national data, as well as the multi‐regional input–output model EXIOBASE3. To better match MIOT and dMFA system definitions, we propose the end‐use transfer method, which re‐routes specific intermediate outputs to final demand in MIOTs. In closing, we conclude on 12 points for improved end‐use shares. We find mixed results regarding the fit between end‐use shares derived from industry shipments and MIOTs: for detailed national data, we find good fit for some materials (e.g., aluminum), while others deviate strongly (e.g., steel). In many cases, the temporal trend of MIOT‐derived end‐use shares roughly agrees with industry shipments. For EXIOBASE3, we find good fit for some countries and materials, but substantial mismatches for others. Despite mixed results, combining MIOT‐based end‐use shares with industry shipments and auxiliary country‐level data could enable improved temporal, geographical, and end‐use resolution. However, the scarcity, documentation, and quality of input data are key limitations for more accurate and detailed end‐use shares. This article met the requirements for a gold‐gold data openness badge described at http://jie.click/badges.

Globally, more than half of all extracted materials are used to build and maintain material stocks. The United States of America (USA) is one of the largest global consumers of these materials. To assess the role of stocks for long‐term material use in an affluent industrialized economy, we present an analysis of material use and stock accumulation for the USA from 1870 to 2100. On the basis of the dynamics of stocks and resulting end‐of‐life (EoL) outflows, we investigate stock‐building material demand, waste management, and circular economy potentials and present two prospective scenarios until 2100 to highlight the long‐term effect of stock‐flow dynamics. From 1870 to 2017, we found continuous stock growth, which strongly decelerated after the 2007 crisis. Overall, 40% of historical domestic material consumption was used to build and maintain stocks. EoL outflows from stocks increased until 2017, about half of which were discarded as final waste. In both prospective scenarios to 2100, stock build‐up and maintenance require material inputs larger than those used over the whole historical period. Stabilizing stocks near the current level could mitigate 23% of material demand compared to a return to pre‐2007 stock growth. Stabilized stocks also result in stable EoL outflows after 2050, whereas ongoing stock growth makes outflows grow until 2080. Increased recycling of these EoL outflows could potentially cover for large parts of material requirements for maintaining stable future stocks. Limiting demand for stocks and increasing recycling will require targeted demand‐side policies, adjustments to EoL management, and the establishment of recycling industries within the USA. This article met the requirements for a gold–gold JIE data openness badge described at http://jie.click/badges.

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