Challenging the planetary boundaries I: Basic principles of an integrated model for phosphorous supply dynamics and global population size

A simple mass balance model has been developed to assess the planetary boundary for P supply in relation to use by human society. Phosphorus sources used by humans are from fossil reserves. The model takes into account resource use rate and reserves, consumption, phosphate to food production, environmental degradation, waste and recycling. Various policy scenarios are tested from current end of pipe solutions to clean production and pollution prevention, sustainable consumption and production polices and sustainable population policy. In order to get an overview of possible future scenarios it is necessary to close nutrient cycles and formulate a sustainable population policy. The outcome of systems dynamics based modeling for four scenarios are given in a sister paper in this issue. Results show that effective population and P recycling policies are crucial to avoid world hunger.