The Material Stock–Flow–Service Nexus: A New Approach for Tackling the Decoupling Conundrum

Material Requirements of Decent Living Standards

Decent living standards (DLS) provide a framework to estimate a practical threshold for the energy, GHG, and material consumption required to alleviate poverty. Currently, most research has focused on estimating the energy required to provide the DLS. However, no attempt has been made to estimate the material consumption needed to provide the DLS. Thus, we ask the following questions: First, what is the amount of materials in stocks and flows needed to provide a DLS? Second, which lifestyle and technology choices are effective in providing a DLS without creating an excessive demand for additional materials? To provide a DLS, a material footprint (MF) of 6 t/(cap*yr) with a lower and upper bound between 3 and 14 t/(cap*yr) is required. The direct and indirect in-use stocks required are estimated at 32 t/cap and 11 t/cap, respectively. Nutrition (39%) and mobility (26%) contribute the most to total MF. Buildings account for 98% of direct stocks, while the construction sector accounts for 61% of indirect stocks. We extend the coverage of the DLS by including the collective service dimension and link the material stock-flow-service nexus and life cycle assessment to compute the MF and in-use stocks needed to provide the DLS.

Understanding material and energy use in the processes of decoupling CO2 emissions from economic growth

The share of emissions from materials has dramatically increased over the last decades and is projected to rise in the coming years. Therefore, understanding the environmental effect of materials becomes highly crucial, especially from the climate mitigation perspective. However, its effect on emissions is often overlooked and more attention is heavily paid to the energy-related policies. In this study, to address this shortcoming, we investigate the role of materials on the decoupling of carbon-dioxide emissions (CO2) from economic growth and compare it with the role of energy use in the world's top-19 emitting countries for the 1990-2019 period. Methodologically, using the logarithmic mean divisia index (LMDI) approach, we first decompose CO2 emissions into four effects based on the two different model specifications (materials and energy models). We secondly determine the impact decoupling status and efforts of countries with two different approaches: Tapio-based decoupling elasticity (TAPIO) and decoupling effort index (DEI). Our LMDI and TAPIO results show that material and energy-related efficiency effects have an inhibitory factor. However, the carbon intensity of materials has not contributed to CO2 emissions reduction and impact decoupling as much as the carbon intensity of energy has. DEI results indicate that while developed countries make relatively good progress towards decoupling, particularly after the Paris Agreement, developing countries need to further improve their mitigation efforts. Designing and implementing some policies only centering energy/material intensity or carbon intensity of energy might not be sufficient to achieve the decoupling. Both energy- and material-related strategies should be considered in harmony.

Perspectives on the material dynamic efficiency transition in decelerating the material stock accumulation

The golden rule of material accumulation can be defined as the ability of society to process materials as the benefit of capital, with physical investments as the expense of the process. Societies are incentivized to accumulate resources while disregarding resource restrictions. Since they earn more on such a path, despite how unsustainable it is. We propose the material dynamic efficiency transition as a policy tool for sustainability, with the goal of slowing down material accumulation as an alternative sustainable path. The material dynamic efficiency transition is characterized by a simultaneous drop in savings and depreciation rates. In this paper, we first examine a sample of 15 countries -using dynamic efficiency measures-in terms of their economies' responses to declining depreciation and saving tendencies. We then construct a large sample of material stock estimation and economic characteristics for 120 countries to examine the socioeconomic and long-term developmental implications of such a policy. We found that investment in the productive sector withstood the scarcity of available savings, whereas residential building and civil engineering investments reacted intensely to the changes. We also reported on the continuous rise in developed countries' material stock, accentuating the civil engineering infrastructure as a focal point of the related policies. The material dynamic efficiency transition shows a substantial reduction effect of 7.7%-10%, depending on the stock type and development stage. Therefore, it can be a potent tool for slowing material accumulation and mitigating the environmental implications of this process without causing significant disruptions in economic processes.

How Can Material Stock Studies Assist the Implementation of the Circular Economy in Cities?

City and regional planners have recently started exploring a circular approach to urban development. Meanwhile, industrial ecologists have been designing and refining methodologies to quantify and locate material flows and stocks within systems. This Perspective explores to which extent material stock studies can contribute to urban circularity, focusing on the built environment. We conducted a critical literature review of material stock studies that claim they contribute to circular cities. We classified each article according to a matrix we developed leveraging existing circular built environment frameworks of urban planning, architecture, and civil engineering and included the terminology of material stock studies. We found that, out of 271 studies, only 132 provided information that could be relevant to the implementation of circular cities, albeit to vastly different degrees of effectiveness. Of these 132, only 26 reported their results in a spatially explicit manner, which is fundamental to the effective actuation of circular city strategies. We argue that future research should strive to provide spatial data, avoid being siloed, and increase engagement with other sociopolitical fields to address the different needs of the relevant stakeholders for urban circularity.

Improved Copper Circularity as a Result of Increased Material Efficiency in the U.S. Housing Stock

Material efficiency (ME) can support rapid climate change mitigation and circular economy. Here, we comprehensively assess the circularity of ME strategies for copper use in the U.S. housing services (including residential buildings and major household appliances) by integrating use-phase material and energy demand. Although the ME strategies of more intensive floor space use and extended lifetime of appliances and buildings reduce the primary copper demand, employing these strategies increases the commonly neglected use-phase share of total copper requirements during the century from 23-28 to 22-42%. Use-phase copper requirements for home improvements have remained larger than the demand gap (copper demand minus scrap availability) for much of the century, limiting copper circularity in the U.S. housing services. Further, use-phase energy consumption can negate the benefits of ME strategies. For instance, the lifetime extension of lower-efficiency refrigerators increases the copper use and net environmental impact by increased electricity use despite reductions from less production. This suggests a need for more attention to the use phase when assessing circularity, especially for products that are material and energy intensive during use. To avoid burden shifting, policymakers should consider the entire life cycle of products supporting services when pursuing circular economy goals.

The urbanisation-environment conflict: Insights from material stock and productivity of transport infrastructure in Hanoi, Vietnam

Developing regions experience rapid population growth and urbanisation, which require large quantities of materials for civil infrastructure. The production of construction materials, especially for urban transport systems, however, contributes to local and global environmental change. Political agendas may overlook the environmental implications of urban expansion, as economic growth tends to be prioritised. While elevating the standard of living is imperative, decision-making without careful environmental assessments can undermine the overall welfare of society. In this study, we evaluate the material demand and in-use stock productivity for the large-scale development plan for transport infrastructure in the city of Hanoi, Vietnam, from 2010 to 2030, combining geospatial and socioeconomic data with statistics on roads and railways. The results show that the total material stock could rise threefold from 66 Tg in 2010 to 269 Tg in 2030, which roughly translates to an addition of 30 Empire State Buildings per year by mass. The materials we account are required for construction exceed the availability of local sand and will need to be gathered farther away. Furthermore, the material stock productivity of the transport infrastructure appears to have been declining overall since 2010, and this trend may continue to 2030. These findings demonstrate the importance of informing urban planning with a comprehensive assessment of construction materials demand, supply capacity, and environmental impacts. Policy priorities for improving the in-use stock productivity are also recommended towards achieving a more efficient utilisation of natural resources.

Mining the Built Environment: Telling the Story of Urban Mining

Materials are continuously accumulating in the human-built environment since massive amounts of materials are required for building, developing, and maintaining cities. At the end of their life cycles, these materials are considered valuable sources of secondary materials. The increasing construction and demolition waste released from aging stock each year make up the heaviest, most voluminous waste outflow, presenting challenges and opportunities. These material stocks should be utilized and exploited since the reuse and recycling of construction materials would positively impact the natural environment and resource efficiency, leading to sustainable cities within a grander scheme of a circular economy. The exploitation of material stock is known as urban mining. In order to make these materials accessible for future mining, material quantities need to be estimated and extrapolated to regional levels. This demanding task requires a vast knowledge of the existing building stock, which can only be obtained through labor-intensive, time-consuming methodologies or new technologies, such as building information modeling (BIM), geographic information systems (GISs), artificial intelligence (AI), and machine learning. This review paper gives a general overview of the literature body and tracks the evolution of this research field.

Global scenarios of resource and emission savings from material efficiency in residential buildings and cars

Material production accounts for a quarter of global greenhouse gas (GHG) emissions. Resource-efficiency and circular-economy strategies, both industry and demand-focused, promise emission reductions through reducing material use, but detailed assessments of their GHG reduction potential are lacking. We present a global-scale analysis of material efficiency for passenger vehicles and residential buildings. We estimate future changes in material flows and energy use due to increased yields, light design, material substitution, extended service life, and increased service efficiency, reuse, and recycling. Together, these strategies can reduce cumulative global GHG emissions until 2050 by 20–52 Gt CO₂-eq (residential buildings) and 13–26 Gt CO₂e-eq (passenger vehicles), depending on policy assumptions. Next to energy efficiency and low-carbon energy supply, material efficiency is the third pillar of deep decarbonization for these sectors. For residential buildings, wood construction and reduced floorspace show the highest potential. For passenger vehicles, it is ride sharing and car sharing.

Material production accounts for a quarter of global greenhouse gas emissions. Here, the authors show that resource efficiency and circular-economy strategies can allow for cumulative emission reductions of 20–52 Gt CO2-eq from residential buildings and 13–26 Gt CO2e-eq from cars by 2050.

Open and Consistent Geospatial Data on Population Density, Built-Up and Settlements to Analyse Human Presence, Societal Impact and Sustainability: A Review of GHSL Applications

This review analyses peer-reviewed scientific publications and policy documents that use built-up density, population density and settlement typology spatial grids from the Global Human Settlement Layer (GHSL) project to quantify human presence and processes for sustainability. Such open and free grids provide detailed time series spanning 1975–2015 developed with consistent approaches. Improving our knowledge of cities and settlements by measuring their size extent, as well as the societal processes occurring within settlements, is key to understanding their impact on the local, regional and global environment for addressing global sustainability and the integrity of planet Earth. The reviewed papers are grouped around five main topics: Quantifying human presence; assessing settlement growth over time; estimating societal impact, assessing natural hazard risk and impact, and generating indicators for international framework agreements and policy documents. This review calls for continuing to refine and expand the work on societal variables that, when combined with essential variables including those for climate, biodiversity and ocean, can improve our understanding of the societal impact on the biosphere and help to monitor progress towards local, regional and planetary sustainability.

Do material efficiency improvements backfire?: Insights from an index decomposition analysis about the link between CO2 emissions and material use for Austria

To keep global heating and other negative consequences of socioeconomic activities within manageable boundaries, industrialized countries must undergo substantial decarbonization, requiring the exploitation of synergies with other environmental endeavors. Improving resource efficiency-that is, reducing the resources required to generate a unit of economic output-is a prominent goal pursued across levels of scale. How does resource efficiency relate to decarbonization? Do economies decrease their emissions as they become more efficient? We examine this relationship for Austria from 2000 to 2015 by conducting an index decomposition analysis at the sectoral level by using consumption-based indicators from the multi-regional input-output model Exiobase. Our analysis shows that for Austria, the currently popular pursuit of material efficiency appears to run the risk of coinciding with higher emissions, suggesting that the opportunities to achieve both decarbonization and dematerialization are limited. The Austrian service sectors could contribute to a reduction of the CO2 footprint via material efficiency improvements, but strong economic growth foils this possibility coming to fruition. The Austrian economy would do well to either curb demand for goods and services driving global CO2 emissions or to produce imported goods and services domestically in an environmentally more benign manner.

High-Resolution Maps of Material Stocks in Buildings and Infrastructures in Austria and Germany

The dynamics of societal material stocks such as buildings and infrastructures and their spatial patterns drive surging resource use and emissions. Two main types of data are currently used to map stocks, night-time lights (NTL) from Earth-observing (EO) satellites and cadastral information. We present an alternative approach for broad-scale material stock mapping based on freely available high-resolution EO imagery and OpenStreetMap data. Maps of built-up surface area, building height, and building types were derived from optical Sentinel-2 and radar Sentinel-1 satellite data to map patterns of material stocks for Austria and Germany. Using material intensity factors, we calculated the mass of different types of buildings and infrastructures, distinguishing eight types of materials, at 10 m spatial resolution. The total mass of buildings and infrastructures in 2018 amounted to ∼5 Gt in Austria and ∼38 Gt in Germany (AT: ∼540 t/cap, DE: ∼450 t/cap). Cross-checks with independent data sources at various scales suggested that the method may yield more complete results than other data sources but could not rule out possible overestimations. The method yields thematic differentiations not possible with NTL, avoids the use of costly cadastral data, and is suitable for mapping larger areas and tracing trends over time.

Introduction: The Metabolism of Islands

This editorial introduces the Special Issue “Metabolism of Islands”. It makes a case why we should care about islands and their sustainability. Islands are hotspots of biocultural diversity, and home to 600 million people that depend on one-sixth of the earth’s total area, including the surrounding oceans, for their subsistence. Today, they are on the frontlines of climate change and face an existential crisis. Islands are, however, potential “hubs of innovation” and are uniquely positioned to be leaders in sustainability and climate action. We argue that a full-fledged program on “island industrial ecology” is urgently needed with the aim to offer policy-relevant insights and strategies to sustain small islands in an era of global environmental change. We introduce key industrial ecology concepts, and the state-of-the-art in applying them to islands. Nine contributions in this Special Issue are briefly reviewed to highlight the metabolic risks inherent in the island cases. The contributors explore how reconfiguring patterns of resource use will allow island governments to build resilience and adapt to the challenges of climate change.

Regional disparities in decoupling economic growth and steel stocks: Forty years of provincial evidence in China

Human-made material stocks promote the economic prosperity, while the consumption, maintenance, and operation of them have led to adverse environmental impacts. Decoupling materials stocks from economic growth is a key strategy for relieving environmental pressures and achieving sustainable development. China's unprecedented development offers a unique opportunity for uncovering the relationship between in-use stocks and economic growth. In this study, we analyzed the regional disparity of in-use steel stocks estimated by bottom-up accounting method during 1978-2018 in 31 provinces in mainland China, explored the stocks productivity on provincial and regional scale, and conducted a decoupling analysis of in-use steel stocks with economic growth. The results showed that there was a huge disparity among the provincial total steel stocks, per-capita steel stocks, and stocks density. Some provinces, e.g. Beijing, Tianjin, and Shanghai, that had the highest stocks density had comparatively lower per-capita steel stocks and total steel stocks, indicating higher share of in-use steel stocks and lower material intensive economic structure. In-use steel stocks in China showed no clear signs of saturation or flatten off pattern although their growth rate declined recently. An increase in steel stocks productivity was found during 1978-2018, which means relative decoupling of in-use steel stocks from economic growth, but still far away from absolute decoupling. The dematerialization pattern revealed in this study deepens our understanding of material-economy interactions. Policy implications for dematerialization transition should focus on developing compact cities, prolonging the lifespan of products, and advancing technological development.

GIS-Based Material Stock Analysis (MSA) of Climate Vulnerabilities to the Tourism Industry in Antigua and Barbuda

In the past decades, the Caribbean economy has transformed to rely primarily on tourism with a vast amount of infrastructure dedicated to this sector. At the same time, the region is subject to repeated crises in the form of extreme weather events that are becoming more frequent, deadly, and costly. Damages to buildings and infrastructure (or the material stocks) from storms disrupt the local economy by an immediate decline in tourists and loss of critical services. In Antigua and Barbuda (A&B), tourism contributes 80% to the GDP and is a major driver for adding new material stocks to support the industry. This research analyzes A&B’s material stocks (MSs) in buildings (aggregates, timber, concrete, and steel) using geographic information systems (GIS) with physical parameters such as building size and footprint, material intensity, and the number of floors. In 2004, the total MSs of buildings was estimated at 4.7 million tonnes (mt), equivalent to 58.5 tonnes per capita, with the share of non-metallic minerals to be highest (2.9 mt), followed by aggregates (1.2 mt), steel (0.44 mt), and timber (0.18 mt). Under the National Oceanic and Atmospheric Administration’s (NOAA’s) 2 meter (m) sea level rise scenario, an estimated 4% of the island’s total MSs would be exposed. The tourism sector would disproportionately experience the greatest exposure of 19% of its MSs. By linking stocks to services, our research contributes to the understanding of the complexities between the environmental and economic vulnerability of island systems, and the need for better infrastructure planning as part of resilience building.

The Social Metabolism of Quiet Sustainability in the Faroe Islands

This paper investigates the interrelations between social metabolism and socio-ecological sustainability in the Faroe Islands in a long-term perspective. It traces the trajectory and changes in socio-metabolic configurations from the time of settlement until today and shows how social metabolism has increased to very high per capita levels during the past century. The analysis departs from the recognition that a decrease in social metabolism, i.e., a net reduction in throughput of natural resources in human economies, is necessary in order to curb the impending ecological crisis. It is argued that parallel to the growth oriented formal Faroese economy, economic food-provisioning practices rooted in the traditional, and ecologically sustainable, land management system continue to be practiced by Faroese people. These practices can be conceptualized as practices of so-called “quiet sustainability” and their contribution is estimated in bio-physical metrics of weight. The analysis shows that practices of “quiet sustainability” contribute significant quantities of certain food items to the local population thereby enhancing food security and food sovereignty. Moreover, these practices are an integral element in the biocultural diversity, which has constituted the Faroe Islands for close to two millennia. Therefore, they should be considered real alternatives to import-based consumption and taken into account in sustainability discourse and policy to a higher degree than is currently the case.

Time Matters: The Carbon Footprint of Everyday Activities in Austria

Mitigating climate change to achieve the goal of staying below 2 °C of warming requires urgent reductions of emissions. Demand-side measures mostly focus on the footprints of consumption. Analysing time use can add to understand the carbon implications of everyday life and the potentials and limitations for decarbonising consumption better. We investigate the carbon footprints of everyday activities in Austria. We linked data from the Austrian Time-use Survey and the Austrian Household Budget Survey with the Eora-MRIO for 2009-2010 in order to estimate the household carbon footprints of all time-use activities. We introduce a functional time-use perspective differentiating personal, committed, contracted and free time to investigate the average carbon intensity of activities per hour, for an average day and for the average woman and man. We find that personal time is relatively low-carbon, while household as well as leisure activities show large variation in terms of CO2e footprint/h. The traditional gendered division of labour shapes the time-use patterns of women and men, with implications for their carbon footprints. Further research analysing differences in household size, income, location and availability of infrastructure in their relation to time use is crucial to be able to assess possible pathways towards low carbon everyday life.

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

Integrated Assessment Models based on Computable General Equilibrium (IAM/CGE) and dynamic Material Flow Analysis (dynamic MFA) are two most widely used prospective model families to assess large-scale and long-term socioeconomic metabolism (SEM) and inform sustainable SEM transition. The latter approach could complement the former by a more explicit understanding of service provision, in-use stocks, and material cycles in a mass balanced framework. In this paper, we demonstrated this by integrating the dynamic MFA and CGE model approaches for the Chinese building sector from 2012 to 2030. Our results revealed the impacts of building stock dynamics on sectoral and economy-wide CO₂ emissions: lower service saturation levels and later saturation time of building stock development could free up investment on buildings and accumulatively save up to 25.4 Gt in embodied CO₂ emissions of the building construction sector, representing a 2.7-fold of 2012 countrywide CO₂ emissions. However, the save-ups are partly compensated by an increase of embodied CO₂ emissions in the other sectors due to economy-wide rebound effect (ca. 18.8 Gt or about 74%). The integrated model we developed could help ensure both mass and monetary balances, explore rebound effects in prospective modeling, and thus better understand the economy-wide consequences of infrastructure development.

Describing and Visualizing a Water–Energy–Food Nexus System

The objective of this study is to describe a target water–energy–food (WEF) nexus domain world including causal linkages and trade-off relationships between WEF resources and their stakeholders, and to develop a WEF nexus system map as an interdisciplinary tool used for understanding the subsequent complexity of WEF nexus systems. An ontology engineering method, which is a qualitative method, was applied for the replicability of the WEF nexus domain ontology and the map, because ontology engineering is a method of semantic web development for enhancing the compatibility of qualitative descriptions logically or objectively. The WEF nexus system map has three underlying concepts: (1) systems thinking, (2) holistic thinking, and (3) an integrated approach at an operational level, according to the hypothesis that the chains of changes in linkages between water, energy, and food resources holistically and systemically affect the WEF nexus system, including natural and social systems, both temporally and spatially. This study is significant because it allows us to (1) develop the WEF nexus domain ontology database, including defining the concepts and sub-concepts of trade-offs relating to WEF for the replicability of this study; (2) integrate the qualitative ontology method and quantitative network analysis method to identify key concepts serving as linkage hubs in the WEF nexus domain ontology; and (3) visualize human–nature interactions such as linkages between water, energy, and food resources and their stakeholders in social and natural systems. This paper also discusses future challenges in the application of the map for a science–policy–society interface.

From resource extraction to outflows of wastes and emissions: The socioeconomic metabolism of the global economy, 1900-2015

The size and structure of the socioeconomic metabolism are key for the planet's sustainability. In this article, we provide a consistent assessment of the development of material flows through the global economy in the period 1900-2015 using material flow accounting in combination with results from dynamic stock-flow modelling. Based on this approach, we can trace materials from extraction to their use, their accumulation in in-use stocks and finally to outflows of wastes and emissions and provide a comprehensive picture of the evolution of societies metabolism during global industrialization. This enables outlooks on inflows and outflows, which environmental policy makers require for pursuing strategies towards a more sustainable resource use. Over the whole time period, we observe a growth in global material extraction by a factor of 12 to 89 Gt/yr. A shift from materials for dissipative use to stock building materials resulted in a massive increase of in-use stocks of materials to 961 Gt in 2015. Since materials increasingly accumulate in stocks, outflows of wastes are growing at a slower pace than inputs. In 2015, outflows amounted to 58 Gt/yr, of which 35% were solid wastes and 25% emissions, the reminder being excrements, dissipative use and water vapor. Our results indicate a significant acceleration of global material flows since the beginning of the 21^st century. We show that this acceleration, which took off in 2002, was not a short-term phenomenon but continues since more than a decade. Between 2002 and 2015, global material extraction increased by 53% in spite of the 2008 economic crisis. Based on detailed data on material stocks and flows and information on their long-term historic development, we make a rough estimate of what a global convergence of metabolic patterns at the current level in industrialized countries paired with a continuation of past efficiency gains might imply for global material demand. We find that in such a scenario until 2050 average global metabolic rates double to 22 t/cap/yr and material extraction increases to around 218 Gt/yr. Overall the analysis indicates a grand challenge calling for urgent action, fostering a continuous and considerable reduction of material flows to acceptable levels.

Carbon dynamics and GHG implications of increasing wood construction: long-term scenarios for residential buildings in Austria

Wooden construction elements often exhibit lower life cycle greenhouse gas (GHG) emissions than conventional counterparts ('material substitution effect'). Moreover, the building stock represents a carbon (C) sink if timber inflows (construction) surpass outflows (demolition) ('C-stock effect'). A dynamic stock model incorporating these effects is applied to quantify potential climate benefits of wood construction in Austria's residential building sector. If present trends are maintained, culminating in a wood construction share (WCS) of 50% during 2050-2100, building shells could contain three times as much C in 2100 as today. Annual timber demand for residential construction could double, but would remain well below Austria's current net exports. Compared to a baseline scenario with constant WCS (22%), cumulated GHG savings from material substitution until 2050 are estimated 2 to 4.2 Tg CO₂-equivalent - clearly less than savings from C-stock expansion (9.2 Tg). Savings from both effects would double in a highly ambitious scenario (WCS=80% during 2050-2100). The applied 'Stock Change Approach' is consistent with IPCC Guidelines, but the above-mentioned savings from C-stock changes would not materialize under the current default GHG inventory accounting approach. Moreover, savings from C-stock effects must eventually be weighed against forest C-stock changes, as growing domestic demand might stimulate wood harvesting.