Limits to growth – synthesis

Sources, sinks and services are all interrelated. Several methods exist for integrating them. Three considered in this chapter are system dynamics, the human appropriation of the net products of photosynthesis (HANPP), and the ecological footprint. System dynamics is most helpful for examining the behaviour of systems over time. It was used in the Limits to Growth published in 1972, which explored the behaviour of the world system and projected it would collapse in the 21st century if trends continued. Retrospective assessments by Graham Turner 40 years later suggest the trends have not fundamentally changed. By some estimates, humans are using about a quarter of the global net products of photosynthesis and maybe as much as a half. This comes at the expense of other species with whom we share the planet and HANPP is increasing with economic growth. The ecological footprint conveys the same message of the link between economic growth and the loss of biocapacity.