Spaceship earth's odyssey to a circular economy - a century long perspective

The circular economy is a rapidly emerging concept promoted as transformative approach towards sustainable resource use within Planetary Boundaries. It is gaining traction with policymakers, industry and academia worldwide. It promises to slow, narrow and close socioeconomic material cycles by retaining value as long as possible, thereby minimizing primary resource use, waste and emissions. Herein, we utilize a sociometabolic systems approach to investigate the global economy as embedded into a materially closed “spaceship earth” and to scrutinize the development of circularity during industrialization. We quantify primary material and energy inputs into the economy, as well as all outputs to the environment from 1900-2015. The assessment includes two fundamental cycles: a socioeconomic cycle of secondary materials from end-of-life waste and an ecological cycle in which resulting waste and emissions are assessed against regenerative capacities of biogeochemical systems. In a first approximation, we consider only the carbon-neutral fraction of biomass as renewable. We find that from 1900-2015, socioeconomic and ecological input cycling rates decreased from 43% (41-51%) to 27% (25-30%), while non-circular inputs increased 16-fold and non-circular outputs 10-fold. The contribution of ecological cycling to circularity declined from 91% to 76%. We conclude that realizing the transformative potential of the circular economy necessitates addressing four key challenges by research and policy: tackling the growth of material stocks, defining clear criteria for ecological cycling and eliminating unsustainable biomass production, integrating the decarbonization of the energy system with the circular economy and prioritizing absolute reductions of non-circular flows over maximizing (re)cyclingrates