World population grew by almost 300% during the twentieth century; over the same time period, world per capita incomes grew by about 400%. This association of sizable increases in world population with large increases in per capita incomes should continue to the end of this century.
Forecasts of the world’s population only a few years in the future are generally quite accurate because the number of births and deaths during the next few years are largely determined by the existing distribution of the number of people at different ages. At the same time, forecasts of the population 50 or more years into the future are notoriously inaccurate because of difficulties in predicting changes over a long time period in birth rates, and to a much lesser extent, also in death rates.
In particular, one cannot take seriously the UN’s median forecast of 10 billion persons by the end of the century. For this forecast assumes that birth rates in high fertility countries will not decline during the next half-century. Since it is highly likely that these countries will raise significantly their per capita incomes and education of their women, their fertility rates will fall, probably drastically. If so, world population in 2100 would be well below 10 billion people.
(photo credit: Anirudh Koul)