Content area
Full Text
Scientific uncertainty about whether and how Earth will support its projected human population has led to public controversy: will humankind live amid scarcity or abundance or a mixture of both (1, 2)! This article surveys the past, the present, and some possible futures of the global human population; compares plausible United Nations population projections with numerical estimates of how many people Earth can support; presents simplified models of the interaction of human population size and human carrying capacity; and identifies some issues for the future.
The Past and Some Possible Futures
Over the last 2000 years, the annual rate of increase of global population grew about 50-fold from the average of 0.04% per year between A.D. 1 and 1650 to its all-time peak of 2.1% per year around 1965 to 1970 (3). The growth rate has since declined haltingly to about 1.6% per year (4) (Fig. 1).(Fig. 1 omitted) Human influence on the planet has increased faster than the human population. For example, while the human population more than quadrupled from 1860 to 1991, human use of inanimate energy increased from 10 sup 9 (1 billion) megawatt x hours/year (MW x hours/year) to 93 billion MW x hours/year (Fig. 2).(Fig. 2 omitted) For many people, human action is linked to an unprecedented litany of environmental problems (5), some of which affect human well-being directly. As more humans contact the viruses and other pathogens of previously remote forests and grasslands, dense urban populations and global travel increase opportunities for infections to spread (6): The wild beasts of this century and the next are microbial, not carnivorous.
Along with human population, the inequality in the distribution of global income has grown in recent decades (7). In 1992, 15% of people in the world's richest countries enjoyed 79% of the world's income (8). In every continent, in giant city systems, people increasingly come into direct contact with others who vary in culture, language, religion, vales, ethnicity, and socially defined race and who share the same space for social, political, and economic activities (9). The resulting frictions are evident in all parts of the world.
Today, the world has about 5.7 billion people. The population would double in 43 years if it continued to grow at its present rate...