Humankind is a ravenous organism, swallowing up all the resources provided by the earth, digesting it and processing it and excreting it again as garbage or exhaust gases – this metaphor roughly summarises what is behind the concept of social metabolism. In the project 'MAT_STOCKS', environmental researchers from the University of Natural Resources and Life Sciences in Vienna and the Humboldt University are examining the material and energy flows within this social metabolism with the aim of sustainably shaping the use of resources.

The building in which geographer and information scientists Franz Schug works is on the Humboldt-University's campus in Adlershof, a suburb in the south-east of Berlin which was still green countryside on the outskirts of the city at the beginning of the 20th century. If you have a look at the digital map of ground cover, which Schug calculated on the basis of satellite images, you see the area as solid red, i.e. as a densely built-up patch of earth. In Adlershof, especially since the end of the 1990s, a lot of buildings and infrastructure have been newly built and thereby a great deal of resources and materials used: minerals like sand and gravel for cement, concrete and brick, but also steel, copper, wood, plastics made from petroleum and bitumen for paving streets.

The developments in Adlershof reflect the global thirst for raw materials. According to data from the United Nations, the consumption of raw materials increased from 43 billion tonnes annually in 1990 to 92 billion tonnes annually in 2017 – the 'food' that the social organism ingests for its 'operation' has more than doubled in just over two and a half decades. The stock of buildings and infrastructure (research article) is growing much faster than humanity. "Within the last 120 years, the population of earth has grown fourfold," says Franz Schug. "But the extent of material stocks increased by a factor of 23 in the same period."

The satellite images of the earth, recorded by the earth observation satellites of the US space agency NASA and the European ESA, which Franz Schug uses as the basis for his 'material maps', depict 100 to 900 square meters of the earth's surface per pixel. But that is a comparatively low resolution, if, like Schug, you want to filter through individual buildings. That is why the doctoral student from the Integrative Research Institute on Transformations of Human-Environment Systems (IRI THESys) at HU, together with his colleague David Frantz from the Department of Geography, is developing automated methods. Not only do the algorithms they are using distinguish between paved urban areas and green areas, like forests and meadows, but they also provide information about the height of buildings (digital map)and the building's use. How densely built up is a residential area, which buildings are, in fact, residential, which are for leisure activities, and where are the commercial spaces? To identify streets, the data from the open access platform Open Street Map are also used.

"When we know what kind of building stands in which location, when it was built, its base area and height, then we can calculate how many tonnes of steel, copper, concrete and plastic (digital map of material use) have been used," says Schug. The specified quantities are not exact, rather they are approximations, though they do provide preliminary information about the spatial distribution of material stocks – to begin with for Germany, Austria and Japan, with India, the USA, Great Britain and other countries to follow.

Franz Schug‘s research is part of the research project Understanding the Role of Material Stock Patterns for the Transformation to a Sustainable Society (MAT_STOCKS), which is based at the University of Natural Resources and Life Sciences in Vienna. There, at the Institute for Social Ecology (SEC), global raw material flows have been studied over the past 20 years in order to determine the 'material footprint' of individual countries.

"We're not looking at individual environmental problems, but at their interdependencies," explains the social ecologist and project manager Dominik Wiedenhofer of the research approach. "To do this, we're analysing societal resource consumption in the system as a whole. From the extraction of raw materials to their consumption, for example through the construction and use of roads, buildings and various technologies, and their ecological consequences, from emissions and waste." To measure material flows and stocks, statistical data have been evaluated such as production statistics and trade balances, or regional planning documents in the form of land registers - a data base that is difficult to assemble and sometimes incomplete. "We want a systematic inventory for every country, and satellite data is very promising for this," believes Wiedenhofer.

In fact, when it comes to sand and gravel, the raw materials that are processed into concrete, cement and asphalt and are primarily used in buildings and infrastructure, gigantic quantities are involved. They make up most of the 47 to 59 billion tons of ores and minerals mined around the world every year. How much exactly, no one knows. It was only in 2019 that the UN Environment Programme pointed out that the demand for these common raw materials had tripled over the past two decades as a result of the global construction and real estate boom, and warned of the environmental consequences.

The maintenance of roads alone takes up a large portion of these building materials, especially in wealthy industrialised countries such as Germany and Austria, where the highway and road networks are quite dense. "One third to half of the total resource consumption in these countries is accounted for by building materials such as cement, sand, gravel and brick," says Wiedenhofer. "And the production of cement alone is responsible for four percent of global greenhouse gas emissions (research article)." The production of iron and steel, materials that are part of the supporting structures of almost every building and all infrastructure, make up a further five percent. When you also consider the climate-damaging emissions from heating these buildings and the army of petrol-powered vehicles on the streets, it becomes clear that many valuable insights can be ascertained using Franz Schug's maps. "We can make differences between countries and regions clear, map the spatial patterns of infrastructure and settlement areas and thus develop options to shape the use of materials," says Wiedenhofer.

According to Wiedenhofer, there is a wide scope to implement sustainable practices: "Improved social well-being assumes a certain level of resource consumption. Yet studies show that this can be achieved without resource consumption growing continuously. And that is fundamental for a sustainable future." Costa Rica, Brazil and New Zealand are examples of the fact that a comparatively high quality of life does not necessarily have to mean high resource consumption and material stocks. These countries only use a quarter to half as much concrete per capita as Germany, and energy and material consumption is also 50 percent lower.

Material stocks are a meaningful indicator on the path to a sustainable future, and, from a scientific point of view, a central starting point for its formation at the same time. Will the social metabolism be transformed by politics and society into something sustainable and therefore remain viable, or will it continue to exceed the limits of tolerance and at some point be consumed by itself? Thanks to the methods and mapping developed by Franz Schug, we can draw a more precise picture.

• Digital map of building heights in Germany
• Digital map of ground cover
• Digital map of resource usage in Germany and Austria
• United Nations report on 'Material Footprint' and the consumption of raw materials
  -Research article on the rise of material stocks globally pnas.org/content/114/8/1880
• Research article on greenhouse gas emissions in specific sectors, including the production of steel and cement