Human-made material stocks accumulating in buildings, infrastructure, and machinery play a crucial but underappreciated role in shaping the use of material and energy resources. Building, maintaining, and in particular operating in-use stocks of materials require raw materials and energy. Material stocks create long-term pathdependencies because of their longevity. Fostering a transition toward environmentally sustainable patterns of resource use requires a more complete understanding of stock-flow relations. Here we show that about half of all materials extracted globally by humans each year are used to build up or renew in-use stocks of materials. Based on a dynamic stock-flow model, we analyze stocks, inflows, and outflows of all materials and their relation to economic growth, energy use, and CO 2 emissions from 1900 to 2010. Over this period, global material stocks increased 23-fold, reaching 792 Pg (±5%) in 2010. Despite efforts to improve recycling rates, continuous stock growth precludes closing material loops; recycling still only contributes 12% of inflows to stocks. Stocks are likely to continue to grow, driven by large infrastructure and building requirements in emerging economies. A convergence of material stocks at the level of industrial countries would lead to a fourfold increase in global stocks, and CO 2 emissions exceeding climate change goals. Reducing expected future increases of material and energy demand and greenhouse gas emissions will require decoupling of services from the stocks and flows of materials through, for example, more intensive utilization of existing stocks, longer service lifetimes, and more efficient design. material flow accounting | socioeconomic metabolism | circular economy | carbon emission intensity | manufactured capital T he growing extraction of natural resources, and the waste and emissions resulting from their use, are directly or indirectly responsible for humanity approaching or even surpassing critical planetary boundaries (1). Both decoupling of resource use from economic development and absolute reductions in the use of certain materials and energy sources are imperative for sustainable development (2). The demand for materials and energy is to a large extent driven by constructing, maintaining, and operating inuse stocks of materials (hereafter "material stocks"), or what economists call manufactured capital (buildings, infrastructure, artifacts). These stocks transform material and energy flows into services, such as shelter or mobility (3, 4). The significance of longlived stocks of infrastructure and buildings for determining and potentially reducing future material and energy use and greenhouse gas emissions is increasingly recognized (5, 6). This study investigates the dynamics of global stocks and flows of materials by using and expanding a material flow accounting (MFA) approach. MFA is used in industrial ecology to study the biophysical domain of society, comprising in-use stocks and the processes and flows that maintain and operate these stocks, ...

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.

Summary The international industrial ecology (IE) research community and United Nations (UN) Environment have, for the first time, agreed on an authoritative and comprehensive data set for global material extraction and trade covering 40 years of global economic activity and natural resource use. This new data set is becoming the standard information source for decision making at the UN in the context of the post‐2015 development agenda, which acknowledges the strong links between sustainable natural resource management, economic prosperity, and human well‐being. Only if economic growth and human development can become substantially decoupled from accelerating material use, waste, and emissions can the tensions inherent in the Sustainable Development Goals be resolved and inclusive human development be achieved. In this paper, we summarize the key findings of the assessment study to make the IE research community aware of this new global research resource. The global results show a massive increase in materials extraction from 22 billion tonnes (Bt) in 1970 to 70 Bt in 2010, and an acceleration in material extraction since 2000. This acceleration has occurred at a time when global population growth has slowed and global economic growth has stalled. The global surge in material extraction has been driven by growing wealth and consumption and accelerating trade. A material footprint perspective shows that demand for materials has grown even in the wealthiest parts of the world. Low‐income countries have benefited least from growing global resource availability and have continued to deliver primary materials to high‐income countries while experiencing few improvements in their domestic material living standards. Material efficiency, the amount of primary materials required per unit of economic activity, has declined since around 2000 because of a shift of global production from very material‐efficient economies to less‐efficient ones. This global trend of recoupling economic activity with material use, driven by industrialization and urbanization in the global South, most notably Asia, has negative impacts on a suite of environmental and social issues, including natural resource depletion, climate change, loss of biodiversity, and uneven economic development. This research is a good example of the IE research community providing information for evidence‐based policy making on the global stage and testament to the growing importance of IE research in achieving global sustainable development.

Summary In order to fully comprehend the socioeconomic metabolic (SEM) dynamics and material balance of nations, long‐term accounting of economy‐wide material stock is necessary in parallel to material flow accounts. Nevertheless, material stock accounts have been scarce, isolated, and mostly focused either on single materials, short time spans, or small regions. This study has two objectives: (1) review the state of the art of material stock research in the SEM discourse and (2) present a project to map, in a high level of detail, the in‐use construction material stocks of Japan and its 47 prefectures from the 1940s until the present era. This project documents the two major depositories of material stock: buildings and infrastructure. We describe the challenges and benefits of utilizing a bottom‐up approach, in order to promote its usage in material stock studies. The resulting database presents the accumulation of stock over time, as well as visually displaying the spatial distribution of the stock using geographical information systems (GIS), which, we argue, is an essential aspect of material stock analysis in the context of socioeconomic metabolism research.

As one quarter of global energy use serves the production of materials, the more efficient use of these materials presents a significant opportunity for the mitigation of greenhouse gas (GHG) emissions. With the renewed interest of policy makers in the circular economy, material efficiency (ME) strategies such as light-weighting and downsizing of and lifetime extension for products, reuse and recycling of materials, and appropriate material choice are being promoted. Yet, the emissions savings from ME remain poorly understood, owing in part to the multitude of material uses and diversity of circumstances and in part to a lack of analytical effort. We have reviewed emissions reductions from ME strategies applied to buildings, cars, and electronics. We find that there can be a systematic trade-off between material use in the production of buildings, vehicles, and appliances and energy use in their operation, requiring a careful life cycle assessment of ME strategies. We find that the largest potential emission reductions quantified in the literature result from more intensive use of and lifetime extension for buildings and the light-weighting and reduced size of vehicles. Replacing metals and concrete with timber in construction can result in significant GHG benefits, but trade-offs and limitations to the potential supply of timber need to be recognized. Repair and remanufacturing of products can also result in emission reductions, which have been quantified only on a case-by-case basis and are difficult to generalize. The recovery of steel, aluminum, and copper from building demolition waste and the end-of-life vehicles and appliances already results in the recycling of base metals, which achieves significant emission reductions. Higher collection rates, sorting efficiencies, and the alloy-specific sorting of metals to preserve the function of alloying elements while avoiding the contamination of base metals are important steps to further reduce emissions.

National material stock (MS) accounts have been a neglected field of analysis in industrial ecology, possibly because of the difficulty in establishing such accounts. In this research, we propose a novel method to model national MS based on historical material flow data. This enables us to avoid the laborious data work involved with bottom-up accounts for stocks and to arrive at plausible levels of stock accumulation for nations. We apply the method for the United States and Japan to establish a proof of concept for two very different cases of industrial development. Looking at a period of 75 years (1930–2005), we find that per capita MS has been much higher in the United States for the entire period, but that Japan has experienced much higher growth rates throughout, in line with Japan's late industrial development. By 2005, however, both Japan and the United States arrive at a very similar level of national MS of 310 to 375 tonnes per capita, respectively. This research provides new insight into the relationship between MS and flows in national economies and enables us to extend the debate about material efficiency from a narrow perspective of throughput to a broader perspective of stocks.

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The data record contains Material Intensity data for buildings (MI). MI coefficients are often used for different types of analysis of socio-economic systems and in particular for environmental assessments. Until now, MI values were compiled and reported ad-hoc with few cross-study comparisons. We extracted and converted more than 300 material intensity data points from 33 studies and provide the results in a comprehensive and harmonized database. Material intensity is reported as kilograms per gross floor area for 32 materials as primary data points. Furthermore, we augmented the data with secondary attributes for regional information, such as climate and socioeconomic indicators. The data are hosted on the version control platform GitHub using accessible data formats and providing detailed contribution guidelines. This “database seed” facilitates data analysis, accessibility, and future data contributions by the research community. In the Technical Validation we illustrate that consistency of the data and opportunities for further analysis. This database can serve scientists from various disciplines as a benchmark to determine typical ranges and identify outliers.