ABSTRACT
Sustainability is achieved when the supply of social, economic, and environmental capital exceeds the demand. This chapter introduces a simple approach to estimating the impact of human activities on environmental resources. It uses the ImPACT identity to calculate carbon footprints and water footprints. The chapter provides an application of the ImPACT identity, one that aggregates many different environmental impacts to estimate total environmental impact of individuals and society: the ecological footprint (EF). The EF is an estimate of the amount of land required to provide adequate resources and absorb wastes. In 1798 Thomas Malthus published a paper titled "An Essay on the Principle of Population". Malthus argued that agricultural production would limit human population growth. Unchecked population growth could lead to a Malthusian catastrophe in which widespread starvation would reduce the population to a level that could be supported at a subsistence level. In developed countries, the demographic transition has greatly slowed the rate of increase of the human population.
