Factors driving previous population growth

The broad outlines of the history of global population growth are by now familiar. At the dawn of the agricultural revolution (8000 years before present), total population was about 250 000 (Cook 1962). It took all of human history (until 1800) for global population to reach one billion – roughly today's population of Europe and North America combined. It took 130 years (until 1930) to reach two billion. It took only 60 more years (1960) to reach three billion. The fourth billion was reached between 1960 and 1975, the five billion mark was passed in 1987 and the six billion mark was reached in 1999.

Less well appreciated are the facts that both the annual growth rate and the annual absolute increment of world population have passed their peaks and are expected to continue to decline. The growth rate peaked at 2.1% per year in the late 1960s and fell to 1.35% by 2000 (see table 6.1), and the annual absolute increment to population peaked at about 87 million per year in the late 1980s and was about 81 million at the end of the 20th century. This does not mean, of course, that little further population growth is to be expected; most mid-range population projections foresee future population rising to 8–10 billion by the end of the 21st century.

As shown in table 6.1, the TFR (average number of children per woman under a period perspective) declined modestly in most parts of the world from 1950–1955 to 1970–1975, then declined over the following 25 years with a rapidity that was unimaginable in the 1960s.