Human population growth and the demographic transition

Abstract

The world and most regions and countries are experiencing unprecedentedly rapid demographic change. The most obvious example of this change is the huge expansion of human numbers: four billion have been added since 1950. Projections for the next half century expect a highly divergent world, with stagnation or potential decline in parts of the developed world and continued rapid growth in the least developed regions. Other demographic processes are also undergoing extraordinary change: women's fertility has dropped rapidly and life expectancy has risen to new highs. Past trends in fertility and mortality have led to very young populations in high fertility countries in the developing world and to increasingly older populations in the developed world. Contemporary societies are now at very different stages of their demographic transitions. This paper summarizes key trends in population size, fertility and mortality, and age structures during these transitions. The focus is on the century from 1950 to 2050, which covers the period of most rapid global demographic transformation.

Figure 1.

Population size estimates, 1900–2005 and projections 2005–2050. High, medium and low variants.

Figure 2.

Trends in the total fertility rate by region.

Figure 3.

Trends in LE by region.

Figure 4.

Distribution of population by age, by region, 2005.

Figure 5.

Dependency ratio estimates, 1950–2005.

Figure 6.

Percentage increase in population 2005–2050, by region, alternative projections. Black bars denote medium UN projection; grey bars denote instant replacement projection (hypothetical).