Consider three hypothetical scenarios* for the levels of human population in the century ahead:
Fertility declines within sixty years from the current rate of 3.3 to a global replacement average of 2.1 children per woman. The current population momentum would lead to at least 11 billion people before leveling off at the end of the 21st century.
Fertility reduces to an average of 1.7 children per woman early in the next century. Human population growth would peak at 7.8 billion persons in the middle of the 21st century and decline slowly thereafter.
Fertility declines to no lower than 2.5 children per woman. Global population would grow to 19 billion by the year 2100, and to 28 billion by 2150.
The actual outcome will have enormous implications for the human condition and for the natural environment on which all life depends.
KEY DETERMINANTS OF POPULATION GROWTH
igh fertility rates have historically been strongly correlated with poverty, high childhood mortality rates, low status and educational levels of women, deficiencies in reproductive health services, and inadequate availability and acceptance of contraceptives. Falling fertility rates and the demographic transition are generally associated with improved standards of living, such as increased per capita incomes, increased life expectancy, lowered infant mortality, increased adult literacy, and higher rates of female education and employment.
Even with improved economic conditions, nations, regions, and societies will experience different demographic patterns due to varying
Population Reference Bureau, The U.N. Long-Range Population Projections: What They Tell Us, Washington, D. C., 1992.
cultural influences. The value placed upon large families (especially among under-privileged rural populations in less developed countries who benefit least from the process of development), the assurance of security for the elderly, the ability of women to control reproduction, and the status and rights of women within families and within societies are significant cultural factors affecting family size and the demand for family planning services.
Even with a demand for family planning services, the adequate availability of and access to family planning and other reproductive health services are essential in facilitating slowing of the population growth rate. Also, access to education and the ability of women to determine their own economic security influence their reproductive decisions.
POPULATION GROWTH, RESOURCE CONSUMPTION, AND THE ENVIRONMENT
hroughout history, and especially during the twentieth century, environmental degradation has primarily been a product of our efforts to secure improved standards of food, clothing, shelter, comfort, and recreation for growing numbers of people. The magnitude of the threat to the ecosystem is linked to human population size and resource use per person. Resource use, waste production and environmental degradation are accelerated by population growth. They are further exacerbated by consumption habits, certain technological developments, and particular patterns of social organization and resource management.
As human numbers further increase, the potential for irreversible changes of far reaching magnitude also increases. Indicators of severe environmental stress include the growing loss of biodiversity, increasing greenhouse gas emissions, increasing deforestation worldwide, stratospheric ozone depletion, acid rain, loss of topsoil, and shortages of water, food, and fuel-wood in many parts of the world.