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 21st 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.