In 1993, fifty-six of the world’s scientific academies (including the U.S. National Academy) came together in a “Scientific Summit” on world population. The conference was an out growth of two earlier meetings, one by the Royal Swedish Academy of Sciences, the other by the Royal Society of London and the U.S. National Academy of Sciences. At both meetings, urgent concern was expressed for the expanding world population and a commitment was made to continue discourse on matters related to population growth. The resulting 1993 Science Summit—the first large-scale collaborative activity ever undertaken by the world’s scientific academies—set as its primary goal the formulation of a statement to be presented at the International Conference on Population and Development in 1994. The statement, reprinted below, underscores the need for government policies and initiatives that will help achieve “zero population growth within the lifetime of our children.” 

The Growing World Population

The world is in the midst of an unprecedented expansion of human numbers. It took hundreds of thousands of years for our species to reach a population level of 10 million, only 10,000 years ago. This number grew to 100 million people about 2,000 years ago and to 2.5 billion by 1950. Within less than the span of a single lifetime, it has more than doubled to 5.5 billion in 1993.

This accelerated population growth resulted from rapidly lowered death rates (particularly infant and child mortality rates), combined with sustained high birth rates. Success in reducing death rates is attributable to several factors: increases in food production and distribution, improvements in public health (water and sanitation) and in medical technology (vaccines and antibiotics), along with gains in education and standards of living within many developing nations.

Over the past 30 years, many regions of the world have also dramatically reduced birth rates. Some have already achieved family sizes small enough, if maintained, to result eventually in a halt to population growth. Theses successes have led to a slowing of the world’s rate of population increase. The shift from high to low death and birth rates has been called the “demographic transition.”

The rate at which the demographic transition progresses worldwide will determine the ultimate level of the human population. The lag between downward shifts of death and birth rates may be many decades or even several generations, and during these periods population growth will continue inexorably. We face the prospect of a further doubling of the population within the next half century. Most of this growth will take place in developing countries.

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 twenty-first 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 twenty-first 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.

Read the entire Appendix here.