Sustaining life on the earth.

Abstract

At the time of the toolmaking revolution around 1 million years ago human numbers rose to 5 million. As humans invented agriculture and animal husbandry the population grew to about 500 million. In 1994 the number was 5.6 billion; it may double or triple before leveling off again 300 years after the industrial revolution began. If the transition to a warmer more crowded more diverse world can be managed there may be promise of an environmentally sustainable future. The reconstructed population series for 4 ancient regions the Nile Valley (6000 years) the Tigris-Euphrates lowlands of Iraq (6000 years) the basin of Mexico (3000 years) and the central Maya lowlands of Mexico and Guatemala (2200 years) all show waves in which population doubled over the previous base and then fell by at least half. This raises questions about human life on the earth: perhaps even regions that are world leaders can collapse in modern times. Among likely threats are 3 areas of concern: 1) pollutants: acid rain in the atmosphere heavy metals in the soils and chemicals in the groundwater 2) global atmospheric dangers of nuclear fallout stratospheric ozone depletion and climatic warming 3) deforestation desertification and species extinction. 10 billion people would require a 4-fold increase in agricultural production a 6-fold rise in energy use and an 8-fold increase in the global economy. 2.1 births per woman is required for zero-population growth while the current birth rate is 3.2. In developing countries after World War II the life expectancy at birth was 40 years now it has increased to 65 years. The slowing of the rate of population growth everywhere is encouraging for sustaining life on the earth which requires cohabitation with the natural world; limits to human activity; and wider distribution of the benefits of human activity.