Long-Run Global Population Forecasts: A Critical Appraisal

Abstract

MAJOR FORECASTS OF DEMOGRAPHIC TRENDS in the twenty-first century are in reassuringly close agreement': growth rates will decline steadily throughout the century, leading to a nearly stationary world population of 10 to 11 billion people, or roughly twice the current number.2 Thus the next and final doubling of world population will take three times as long as the previous, and the population explosion will recede into history as a brief aberration. This scenario may be comforting or appalling, depending on one's views of the economic and environmental consequences of population size and growth. But in any event, one might well wonder about how such a forecast is made, the nature of its conceptual underpinnings, and the degree of confidence it merits. This article considers standard demographic forecasts in the broader intellectual context of theoretical and empirical studies of population dynamics. The article has four parts. First, I consider the insights to be gained from demographic analysis, with an emphasis on the declining influence of mortality change on growth rates. Second, I consider at some length the different approaches to forecasting: those that hypothesize levels and changes in the vital rates without reference to the implied changes in population size, and those that reason in terms of the Earth's carrying capacity and the responsiveness of population growth rates to feedback. Third, I consider the degree of uncertainty in population forecasts. Fourth, I review some recent long-run forecasts of global population.