Materials are at the basis of human society [1]. Urbanization, industrialization and growing consumption drive the demand for wood, concrete, steel, plastics, chemicals, and various technologoy materials. Providing adequate access to modern and low-carbon energy services and the need to adapt to climate change further increase resource consumption, as new energy infrastructure and protective measures such as dams and dikes need to be built.
The global use of natural resources has grown at an unprecedented rate and the number of chemical elements and their combinations used in modern technologies have multiplied. As a consequence, the natural resource endowment and the quality of the environment keeps on declining in most country, especially in the Global South, which in turn fuels economic, social, and geopolitical conflicts.
Currently, material production accounts for about 23% of global greenhouse gase emissions [2]. This major contribution to global warming, plus the large impacts of mining on land use change [3] and water consumption [4], highlight the need for research on how materials are linked to and can be decoupled from environmental impacts and service provision to people by establishing a circular economy of materials [5]. Resilient and sustained supply of so-called critical materials [6,7,8,9] as well as the large material requirements of the transition to low-carbon energy [10] are major global concerns that involve materials. On the social side, material extraction is often connected to struggles for environmental justice [11].
The SEM approach
Socio-economic metabolism (SEM) is a research paradigm that looks at material and energy turnover and processing at the society level [12]. SEM researchers study human-controlled stocks and flows of energy and materials and their links to social outcomes and environmental impacts. Under the SEM paradigm, researchers have developed methods and established accounting approaches to measure material use in the economy, model scenarios for the transformation of material cycles, and provide policy advice regarding resource use constraints of policy interventions [12a]. Material flow analysis (MFA), often combined with energy flow analysis (MEFA), is the basic accounting and modelling method of scientific analysis of socio-economic metabolism [13, 14]. In-use stocks, the material stocks in the built environment, are a key component of society’s metabolism, as they provide services such as shelter and mobility and also provide the resources for future recycling [15].
Applied at the national level, economy-wide MFA [16] gives insights into material use of national and global economies. In recent years, the research community, together with statistical offices and government departments, has established methodological guidelines for material flow and stock accounts at a national level. Today, this core material use accounting method complements the System of National Accounts by adding the material layer. It is used by Eurostat, or the International Resoure Panel, amongst others, to monitor resource use across and within countries.
Economy-wide MFA: Global material flows, waste and emissions, 2019, billion tonnes. Source: Figure 2.8 in United Nations Environment Programme (2024). [17] The first iteration of this figure appeared in Haas et al. (2015), published in the Journal of Industrial Ecology. [5] The accounting scheme used here, Material Flow Accounting, was devleoped and standardized by members of our community [16].
Socio-economic metabolism is complex and includes many delays, like the lifetime of products in use, and couplings, such as the different materials contained in a single vehicle. For another example, many green technologies to reduce greenhouse gas emissions use critical minerals, making these industries potentially vulnerable to supply disruptions. To deepen the understanding of how materials flow through the economy, where losses occur and where efficiency can be improved, more detailed accounts of resource use and waste are needed. Such detailed material flow accounts form the basis for assessing efficiency and circular economy improvements for businesses and governments at company, city [18,19,20], regional, and national scales [21,22,23], and global scales [24]. The analysis may also focus on certain materials of concern because of their availability or toxic capacity and will identify the impact of regulatory and engineering solutions to metabolic problems. The process-flow diagram below is a good example for an explicit system definition and description of material flows of interest.
Typical examle of an MFA system diagram, from Han et al. (2014) [25]. Chlorine-containing material flows in 2011. The dashed arrow represents non-chlorine flow; the dashed box represents plant that is under construction. When quantifying the system, the regional and temporal scope of the stocks and flows is indicated as well.
The results of a material flow analysis are commonly visualized in Sankey diagrams like the one below for the cumulative flows in the global steel cycle.
Material flow analyis: the global historical steel cycle in a Sankey diagram, where the numbers represent the accumulated annual flows over the past 115 years. Source: Fig. 3a in Wang et al. (2021) [26]. The flows trace steel from mining, through iron aking, steel making, fabrication, the different end uses to the end-of-life stage and recycling. For an explanation of all technologies and end uses, please check the original publication.
Another research stream is the compilation of in-use stock accounts at high spatial resolution, which enables to estimate the exact locatin of future waste flows. More importantly, the high resolution maps can be compared against other high resolution maps of population density, socio-demographic factors, and travel behaviour to deepen our understanding of how material stocks are linked to service provision and wellbeing outcomes.
Country-wide spatial distribution of the material stocked in buildings for Japan, 2009. Cell size is 1 km² using the geographical information systems data set. Source: Japan map of material stocks, Tanikawa et al. (2015) [27].
Dynamic MFA studies show how in-use stocks and material cycles [28, 29, 29a] evolve over time. They quantify the accumulation of stocks in our economy [30] such as the material demand of the energy transition [31, 32]. A main focus of dynamic MFA is on industrial countries, such as Japan [21] and China [22, 23], which often depend on imports and have large production industries and consumption levels. Dynamic MFA helps identify future ‘urban mines’ (recycling potential) and allows us to estimate the decline of ore grades as reponse to growing demand [33]. Thus, such studies provide necessary information for assessing the potential of circular economy strategies, e.g., in the global building sector [24] (see figure below) or for cement [34].
Circular Economy Potentials: Life-cycle emissions from homes with and without Material Efficiency strategies in 2050 in G7 countries, China and India. Source: UNEP International Resource Panel (IRP) (2020) [24].
Practical applications, current trends and new research avenues in SEM research
Numerous industry and policy implementations of MFA exist, see the examples on the industry and policy applications side: https://is4ie.org/sections/metabolism/pages/41
On the research side, the high-resolution mapping of in-use stocks continues as new data sources become assessible to the research community (see the figure below for an example).
Global maps of mobility infrastructure stocks for the year 2021 at 5 arcmin resolution, showing total materials in mobility infrastructure networks per square kilometer. Source: World map of infrastructure stocks, Wiedenhofer et al. (2024) [35].
MFA studies are now linked to supply chain assessment, e.g., via MFA-LCA combinations [36], and to assessments of the economic implications of changed consumption and circular economy measures, e.g., to estimate rebound effects [37]. Increasingly, MFA studies are linked to social and environmental impacts [38]. To study the social and environmental aspects of material use more systematically, the energy and material service cascade [39] (figure below) offers a framework that combines the key elements of socio-economic metabolism (material services, stocks, and flows) to human wellbeing on the one hand and materials and to environmental impacts on the other hand. Different social and environmental links of material can be studied, as well as different decoupling options along the cascade. The framework allows for coupling MFA studies to the assessment of legal instruments and economic incentives at the different stages of the cascade, as well as to explore the link between material stocks, product stocks, product functioning, service provision, and wellbeing.
Different stages of coupling between human well-being and climate impacts in the energy and material service cascade. Each stage of the cascade offers the possibility of decoupling, i.e., ‘more with less’. In the technical stages (products, energy technologies), decoupling is achieved through new technologies that are more efficient or based on other energy sources (e.g., sunlight). The cascade shown here is based on the energy service cascade proposed by Kalt et al. [39]. Image source: [40]
The multi-stage cascade and its link to culture, lifestyle, regulations, and economics enables us to systematically expand the traditional set of economic indicators to include well-being indicators beyond GDP that measure how effectively basic human needs are being met, alongside high-level information on material use, waste, energy use, emissions, and water use. This refined understanding of human material use in the energy and material service cascade leads to an expanded set of indicators that is critical to redesigning our provisioning systems to achieve a good life for all within planetary limits.
This text was written in October 2024 with input from the ISIE-SEM section board with the purpose of updating the section’s homepage.
References:
The references below show the spectrum of SEM research. Many more colleagues have contributed to an enormous body of research on understanding the links between society, materials, and the environment.
[1] On the materials basis of modern society. T. E. Graedel, E. M. Harper, N. T. Nassar, and Barbara K. Reck. PNAS 112 (20) 6295-6300, 2013. https://doi.org/10.1073/pnas.1312752110
[2] Increased carbon footprint of materials production driven by rise in investments. By Edgar G Hertwich. Nat. Geosci. 14, 151–155 (2021). https://doi.org/10.1038/s41561-021-00690-8
[3] A pantropical assessment of deforestation caused by industrial mining, by Stefan Giljum, Victor Maus, Nikolas Kuschnig, and Anthony J. Bebbington. PNAS 119 (38), 2022. https://doi.org/10.1073/pnas.2118273119
[4] Water footprinting and mining: Where are the limitations and opportunities? By Stephen A. Northey, Gavin M. Mudd, Elina Saarivuori, Helena Wessman-Jääskeläinen, and Nawshad Haque. Journal of Cleaner Production Volume 135, 1 November 2016, Pages 1098-1116. https://doi.org/10.1016/j.jclepro.2016.07.024
[5] How Circular is the Global Economy?: An Assessment of Material Flows, Waste Production, and Recycling in the European Union and the World in 2005. By Willi Haas, Fridolin Krausmann, Dominik Wiedenhofer, and Markus Heinz. Journal of Industrial Ecology, 2015. https://doi.org/10.1111/jiec.12244.
[6] Six Years of Criticality Assessments: What Have We Learned So Far? T. E. Graedel, Barbara K. Reck. Journal of Industrial Ecology, Volume 20, Issue 4, Pages 692-699, 2016. https://doi.org/10.1111/jiec.12305
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[12] https://en.wikipedia.org/wiki/Social_metabolism
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[37] Integrating Dynamic Material Flow Analysis and Computable General Equilibrium Models for Both Mass and Monetary Balances in Prospective Modeling: A Case for the Chinese Building Sector. Zhi Cao, Gang Liu, Shuai Zhong, Hancheng Dai, and Stefan Pauliuk. Environ. Sci. Technol. 2019, 53, 1, 224–233. https://doi.org/10.1021/acs.est.8b03633
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