MISO Material Inputs, Stocks and Outputs: A model of global material stocks and flows

Global resource use is growing at high rates and is moving society beyond planetary boundaries within which it may safely operate. Understanding global patterns and trajectories of socio-economic metabolism is of key importance to develop effective policies to reduce societys resource demand and for the transition towards a more sustainable industrial metabolism. Research on socio-economic metabolism has made considerable progress in the last two decades, but so far has largely focused on material flows, in particular on patterns and trends of extraction, trade and consumption of materials. Much less research has been devoted to socio-economic stocks of materials, the interrelation of stocks and flows and the role of stocks in the metabolic transition. This project fills some of the existing knowledge gaps in the field. It develops a dynamic integrated model of material inputs, stocks and outputs (MISO). Using an existing database of global material use we provide a comprehensive estimate of historic stocks and stock related flows and calculate resource use scenarios for 2050. In its retrospective part, the project develops an encompassing estimate of the evolution of global socio-economic material stocks and flows since 1900, applying a dynamic top-down modelling approach and taking uncertainties into account. The results serve as basis for an analysis of global patterns of stocks and flows and their development during the metabolic transition. In the prospective part of the project we use the developed model and the insights from the analysis of historical stock-flow dynamics to calculate scenarios for the future development of material demand, stocks and waste production. This yields insights how changes in inflows, in average lifetimes of stocks and in recycling rates interact and how they determine future demand for virgin materials and waste production. The outcomes of the project contribute to the advancement of the understanding of the global metabolic system and the ongoing metabolic transition. The project provides new insights into potentials and limitations for a circular economy of high significance for policy makers: Achieving targets to reduce resource flows and to close material loops strongly depends on the size and structure of stocks. Vice versa, reducing flows will have an impact on future stocks and the services they can provide. Synthesizing these findings we will be able to draw conclusions for the development of strategies of sustainable resource use and we provide the basis for physical models of social metabolism and more reliable, physically based projections of future resource demand than currently available.

The MISO project investigates the long term development of the global socio-economic metabolism from 1900 to 2015 and tracks material resources through the economic system. In the focus of the research are in-use stocks of materials, i.e., the materials that accumulate in infrastructures, buildings and long living goods and what this accumulation of physical capital implies for sustainable resource use and Circular Economy. Stocks are of crucial importance for strategies towards a more sustainable resource use, because they provide services like shelter, mobility or supply and discharge which are key for human well-being, while building and maintaining these stocks as well as using them is a major driver for material and energy use. We find that the size of metabolism of the global economy not only has multiplied by a factor of 12 since 1900, it also changed from a throughput system based on renewable biomass to a stock-piling system based on fossil and mineral materials. The share of materials that are used to build and maintain long-living artefacts has more than doubled from 20% to over 50% of the yearly inflow of materials. These materials remain in the system for decades and sometimes centuries before they become outflows of wastes at the end of their service live time. Consequently, the size of in-use stocks has increased from 35 to 960 bio. tons. We find that global stocks have grown at roughly the same pace as GDP and have reached a size similar to that of the stock of biomass in terrestrial ecosystems. Differences in per capita stocks across world regions are large. Many countries in the Global South have just begun to expand their infrastructures and built environment, but also in the industrialized countries stocks continue to grow. This expansion of stock will drive growth in global resource use in the next decades. According to our scenarios a global convergence at the current level of per capita stocks in the industrialized countries until 2050 would increase the annual material demand by a factor 2.5 and result in the emission of 600 bio. tons of carbon to the atmosphere, even if substantial gains in resource efficiency are assumed. Our results further show that the degree of circularity of the global economy has declined from 50% in 1900 to 25% in 2015. Rather than reflecting changes in recycling patterns, this is due to far reaching structural changes in societies metabolism in the last century, particularly, the rapid growth of the overall size of material flows, massive stock building and the high share of fossil materials in input. We also expect that large amounts of materials will become available as secondary resources from retired stocks in the next decades. Our findings contribute to the development of strategies towards a Circular Economy and a more sustainable use of natural resources and they indicate the importance of a better understanding of the interrelation between resource flows, in-use stocks and well-being for sustainable development.