He mentions the role of international migrations in controlling strong population growth (like the massive flows from Europe to the Americas in the 19th century) and the differences in periods and in the speed of national transitions, across time and space (Chesnais 1986b, p. 1061).
Since the publication of Chesnais’ book (Chesnais 1986a), empirical observations have called into question these postulates: in Europe fertility may have declined at the same time or before mortality (Coale and Cotts Watkins 1986; Vallin 2003). However, in Africa, Asia and Latin America, the differences are even greater in the timing and speed of demographic changes, as well as in the underlying factors (Guzmán et al. 2006; Attané and Barbieri 2009; Koba et al. 2019). In Latin America, the three-phase reproductive transition pattern did not occur in the same form, in that order, or at the same speed (Cosio Zavala 2011).
Below, we will present the various changes in world population, which have been determined by the history of demographic transitions.
1.3. World population changes and trends (2019–2100)
According to the United Nations Population Division, the world population is expected to continue to grow for several decades (United Nations 2019a)4. The population might increase from 7.7 billion inhabitants in 2019 to 9.7 billion in 2050 and 10.9 billion by 2100 (medium-variant projection). Between 2019 and 2050, projections predict a near doubling of the population in Africa, whereas the European population might decrease during this period (Table 1.1). Leridon confirms the likelihood of the population exceeding 9 billion by 2050, “unless one considers catastrophes of unprecedented magnitude at a global scale” (Leridon 2020)5.
On the basis of the theory of demographic transition, the perspectives of the United Nations foresee a reduction and a convergence in mortality and fertility levels6: by 2060, fertility might reach 1.75 children per woman in developed countries and 2.15 children per woman in developing countries (United Nations 2019a, Fert/4). Table 1.2 shows the populations of different regions in the world, between 2019 and 2100, classified into six groups, according to the stages of their demographic transitions. We consider the demographic transition to be complete when life expectancy is over 70 years old (average for both sexes) and when fertility is equal to or lower than 2.1 children per woman.
Table 1.1. Estimates and projections of the population of the world’s geographic regions in 2019, 2050 and 2100 (thousands of inhabitants)
(source: Population Prospects 2019; United Nations 2019a)
| Region | Population | ||
| 2019 | 2051 | 2100 | |
| Africa | 1,308,064 | 2,489,275 | 4,280,127 |
| Asia | 4,601,371 | 5 290,263 | 4,719,907 |
| Europe | 747,183 | 710,486 | 629,563 |
| North America | 366,601 | 425,200 | 490,889 |
| Latin America and the Caribbean | 648,121 | 762,432 | 679,993 |
| Oceania | 42,128 | 57,376 | 74,916 |
| Total | 7 713,468 | 9,735,034 | 10,875,394 |
The composition of the six demographic transition groups is as follows:
– For 2019, group 1 brought together the countries of Europe, North America and Oceania (1.1 billion inhabitants), which completed their demographic transition before 1970. In 2019, they represented 14% of the world population. The European population is expected to decline (with the exception of Northern Europe) and that of North America and Oceania is expected to increase. This first group could reach a total of 1.2 billion inhabitants by 2100, with low growth between 2019 and 2100, around 10% (according to estimates and medium-variant) (United Nations 2019a).
– Group 2 brings together countries whose demographic transition was completed at the end of 20th century. Japan joined this group in 1970, the Republic of Korea in 1985, China in 1990 and the Democratic Republic of Korea in 1995. These East Asian countries had nearly 1.7 billion inhabitants in 2019 (21% of world population). By adding all the countries whose fertility is lower than or equal to 2.1 children per woman – such as Chile, Brazil, Colombia and Uruguay, many small island countries, a large part of the Middle East’s countries, Bangladesh, Iran and Sri Lanka – there are a total of 2.4 billion inhabitants (31% of the world population). However, this population should decrease to approximately 2 billion inhabitants by 2100 (18% of the world population). The population of East Asia, including China, might start to decline in 2050, reaching 1.2 billion people in 2100, half a billion less than in 2019 (according to estimates and medium-variant) (United Nations 2019a).
– Group 3 includes countries that will have completed their fertility transition by 2030. During the second half of the 20th century, they experienced a sharp decline in mortality, a rapid reduction in fertility as well as exceptional population growth. In 2019, these countries narrowly exceeded those of the second group, with 2.5 billion inhabitants (33% of the world population). These are large countries in Southern Asia (India) and countries in Southeast Asia (except Cambodia, Laos and the Philippines). The majority of Latin American and Caribbean countries are in group 3 (except Bolivia, Guatemala, Haiti, Panama and Paraguay). In Africa, this group brings together a few North African countries (Libya and Tunisia) as well as small island countries (Mauritius, Reunion and Cape Verde). By 2100, this set of populations will have grown to 2.1 billion, a fifth instead of a third of the world population (according to estimates and medium-variant) (United Nations 2019a).
– For group 4, the fertility transition will be completed in around 2050. These are Pakistan, Cambodia, Laos and the Philippines in Asia; Algeria and Morocco in North Africa; some Latin American countries (Bolivia, Guatemala, Haiti, Panama and Paraguay) and some sub-Saharan African countries (Botswana, small island countries and South Africa). Group 4 had around 550 million inhabitants in 2019 (7% of the world population), and will count 860 million by 2100, 8% of the world population (according to estimates and medium-variant) (United Nations 2019a).
– Group 5 consists of countries in sub-Saharan Africa (Benin, Burkina Faso, Cameroon, Nigeria, Chad, Togo and Senegal), which will be close to completing their fertility transition by 2100 (between 2.1 and 2.3 children per woman). In 2019, this group brought together