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.
Highlights
After centuries of very slow and uneven growth, the world population reached one billion in 1800
The UN relies on empirical regularities in past trends in countries that have completed their transitions, mostly in the North, where fertility declined to approximately the replacement level, and increases in life expectancy (LE) became smaller over time
This implies that momentum and declining mortality are responsible for nearly half of the projected future population growth in Africa and for the large majority of growth in Latin America, and South and West Asia
Summary
After centuries of very slow and uneven growth, the world population reached one billion in 1800. World population more than doubled to 6.5 billion in 2005 (United Nations 1962, 1973, 2007). Over the course of this transition, declines in birth rates followed by declines in death rates bring about an era of rapid population growth. This transition usually accompanies the development process that transforms an agricultural society into an industrial one. Population growth is again near zero after the completion of the transition as birth and death rates both reach low levels in the most developed societies. The main source of data is the United Nation’s 2006 world population assessment, which provides estimates for 1950 –2005 and projections from 2005 to 2050 (United Nations 2007)
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