Population

Extra facts

• Global population estimates for 2050 range between 8.1 billion and 10.6 billion.
• Asia will remain the world’s most populous region in the 21^st century, but Africa will gain ground as its population grows from 1 billion in 2011 to 3.6 billion in 2100—even as its fertility is projected to drop from 4.6 children per woman in 2005 to 2010 to 3.0 children per woman in 2040 to 2045.
• The world population is expected to rise throughout the 21^st century, although this growth is projected to decelerate markedly in 2050 to 2100. Currently, the world population’s annual growth rate is 1.1 percent.
• Among the least developed countries (LDC), average fertility per woman was estimated at 4.4 children in 2005 to 2010; it is not expected to decline to the replacement level (the total number of babies adults must produce to replace themselves; 2.1 children per woman) before the end of the century. This implies that the LDC population will rise up to 2100.
• In high-income countries (Europe, Northern America, Australia/New Zealand and Japan), the estimated average fertility in 2005 to 2010 is 1.66 children per woman, well below replacement level.

Source: UN-DESA, 2011

Methods, caveats and issues

Methods

The United Nations Department of Economic and Social Affairs (UN-DESA)’s latest fertility projections are based on two probabilistic models (mathematical models used to analyze vast amounts of data), which are applied in the following order. The Bayesian Hierarchical Model is used for countries with high and medium fertility in 2005 to 2010. This model does not apply a target value or asymptote.

1. It only uses information about the distributions of the rates of decline from all countries that have already experienced fertility declines. This model projects fertility declines for the high- and medium-fertility countries that reach their lowest levels (often far below 2.1 children per women) at some point in the future.
2. The first-order autoregressive time series model (AR1) is used for countries that have already reached their lowest fertility levels. For these countries, the distributions in the rates of change are calculated from all low-fertility countries that have already experienced slight increases in fertility. In the long-term, the total fertility is assumed to converge toward and fluctuate around replacement-level fertility of 2.1 children per woman.

There is no empirical evidence to suggest that countries would have fertility below replacement levels for very long periods. According to UN-DESA, it is more plausible that low fertility countries are “stabilized” in the long run with a fertility fluctuating around 2.1. (http://esa.un.org/wpp/Other-Information/faq.htm#q6).

Definitions

• High-fertility countries: Countries that up to 2010 had no fertility reduction or only an initial decline.
• Medium-fertility countries: Countries where fertility has been declining but whose estimated level was still above 2.1 children per woman in 2005 to 2010.
• Low-fertility countries: Countries with total fertility at or below 2.1 children per woman in 2005 to 2010.

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Sources

• [UN-DESA] United Nations Department of Economic and Social Affairs. 2011. World population prospects: the 2010 revision. Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat. New York. (Available from http://esa.un.org/unpd/wpp/index.htm)
• [UN-DESA] United Nations Department of Economic and Social Affairs. 2011. World Population prospects, the 2010 revision, highlights and advance tables. Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat. New York. (Available from http://esa.un.org/unpd/wpp/Documentation/pdf/WPP2010_Highlights.pdf)
• [UN-DESA]United Nations Department of Economic and Social Affairs. 2011. World Population Prospects, the 2010 Revision, Frequently asked questions. Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat. New York. (Available from http://esa.un.org/wpp/Other-Information/faq.htm)
• [UN-DESA] United Nations Department of Economic and Social Affairs. 2011. Assumptions underlying the 2010 revision. Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat. New York. (Available from http://esa.un.org/wpp/Documentation/pdf/WPP2010_Highlights-Chapter%20V.%20Assumptions_19-May-2011.pdf)
• [UN-DESA] United Nations Department of Economic and Social Affairs. 2011. World Population Prospects: The 2010 Revision. CD-ROM Edition - Extended Dataset in Excel and ASCII Formats. New York. (Available from http://esa.un.org/wpp/Excel-Data/WPP2010_F02_METAINFO.xls)
• [UN-DESA] United Nations Department of Economic and Social Affairs. World population, all variants, 2000-2050. New York. (Available from http://esa.un.org/wpp/)