Comparing the material stock of seven cities
During the last century, global population increased by a factor of 4 while the global extraction of construction minerals rose by a factor of 34 (Krausmann et al., 2009). This considerable intensification in construction materials use illustrates an urbanisation of the global population leading to the creation and expansion of cities. Today, more than 50% of global population lives in urban areas and this share is likely to increase to 70 % by 2050 (United Nations-Department of Economic and Social Affairs, 2014). More specifically, 90 % of the people to be added to the world's urban population by 2050 (around 2.5 billion people), are expected to be concentrated in Asia and Africa where new cities will appear. As such, it is safe to expect that if current trends of urban material use are maintained, the future use of construction materials will follow a similar steep curve. Nevertheless, current levels of material use are unsustainable as they alter a number of ecosystems, put a significant pressure to their local and global environment, and lead to resource depletion. In anticipation of the future needs of construction materials for the creation and expansion of cities, it becomes necessary to better understand of what their material stock consists of. In fact, urban material stock analysis enables to inform about past, present and potentially future needs for construction materials (but also of construction and demolition waste). To gain insights about the quantity and the composition of materials present in urban material stock, this study proposed to briefly analyse and compare seven urban areas, namely Brussels, Melbourne, Paris, Vienna, Beijing, Geneva and Orleans. The methodology used, the materials as well as the built environment components considered will be discussed (Beijing, Geneva and Orléans' building stocks were not calculated by the authors but originate from (Emmenegger et al., 2003; Rouvreau et al., 2012; Serrand et al., 2013; Hu et al., 2010). Furthermore, this research will investigate the link between the quantity of materials with some urban and built environment characteristics such as population, density, number of buildings, average height, average dwelling area, etc. Finally, the results from this research will provide preliminary figures about average material requirements per capita in order to very roughly estimate future needs of construction materials. As a conclusion, this comparative research wishes to explore the urgent issue of construction materials use and waste generation through the lens of urban material stocks.