Q: When could world population stop growing?

A: World population will stop growing when the birth rate equals the death rate; no one knows whether this will happen.

The birth rate and the death rate would eventually reach equilibrium several decades after couples average two children each. This two-child average is called replacement level fertility, because each couple simply replaces themselves, not increasing the size of each generation. The total fertility rate (TFR) refers to the average number of children women are having. When the total fertility rate is at replacement (2.1 children per family), the two children born essentially replace the parents when they die. The replacement level TFR is 2.1, not 2.0, since not all females survive to their childbearing years. In countries with high mortality rates, such as certain African countries with high HIV/AIDS prevalence rates, replacement level fertility can be 3 or more.

When might it be possible for world population growth to come to an end? The United Nations has projected that growth could end in the latter part of this century if the use of family planning were essentially universal and couples limited themselves to fewer than two children. Under such a scenario, world population would be about 9 billion by the end of the century and in slow decline. There is certainly no guarantee that this will happen. If couples average more than 2.1 children in the long term, world population could pass 14 billion by century's end.

We do know that world population growth is inevitable in the near term. But there is a wide range of possible world population scenarios. Three plausible projections published by the United Nations in 2006 lead to outcomes ranging from 7.8 billion people to 10.8 billion people in 2050.

Terms

Birth rate (or crude birth rate:) The annual number of births per 1,000 total population.

Death rate (or crude death rate:) The annual number of deaths per 1,000 total population.

Mortality: Deaths as a component of population change.

Total fertility rate (TFR): The average number of children a women would have assuming that current age-specific birth rates remain constant throughout her childbearing years (usually considered to be ages 15 to 49).