Since the beginning of the 19th century, the world population has exploded. According to a summary of US Census Bureau estimates, the world population was approximately 970 million in 1800 (midpoint of high and low estimate). The Census Bureau site indicates that the population has generally increased in previous centuries, although it peaked in 1800.
During the 19th century, the world’s population is said to have increased by around 70%, reaching almost 1.7 billion. During the 20th century, the world’s population grew by 4.5 billion to reach 6.5 billion, an increase of more than 270%. Current United Nations projections predict a growth of 4.2 billion in the 21st century, reaching 10.4 billion, an increase of almost 70%. According to the UN Low Variant projection, the population would increase by 900 million, to a total of 7.0 billion, an increase of 114% (Figure 1).
The acceleration of growth after 1800 was based on various factors, all of which were facilitated by the unprecedented economic growth since that time. Medical advances have led to substantial reductions in infant mortality and greater longevity. There has been unprecedented urbanization since 1800, when only 5% of the population was urban; the share of the urban population has now reached over 55 percent.
At the same time, fertility rates (the number of live births to an average woman of childbearing age) have fallen dramatically over the past few decades, as living standards have risen. Economists have identified an association between lower fertility rates and greater wealth.
From now to 2100
Today, the world’s population is nearly 7.9 billion, according to the United Nations World Population Prospects 2022. This is more than three times the population of 1950 (2.5 billion), the first year for which United Nations population data is available. The population is expected to exceed eight billion by the end of 2022 (See: Note: UN Population Projection Accuracy).
World Population Prospects 2022proposes three population projection scenarios to 2100. The “middle variant” projections receive the most attention, but there are also the “low variant” and “high variant” projections (Figure 2).
According to the middle variant, the 21st century could add another four billion, with an increase to 10.349 billion in 2100, but by then the planet’s population would be in decline. The world’s population is expected to peak at 10.431 billion in 2086. Over the last year (2099-2100), the population would decline by 11 million, equivalent to the population of North Carolina.
According to the low variant, the world population would fall to 7.043 billion in 2100, about one third (32%) less than the projection of the medium variant. In one year between 2099 and 2100, the world population would fall by around 65 million, or around the population of France. The population peak would be reached in 2053, at 8.939 billion, 33 years before the medium variant. From 2022 to 2100, the population is expected to drop by 1.9 billion. Under the low variant, the world is already a billion above its projected population peak for 2053.
The high variant presents a much different picture. In 2100, the world population would reach 14.8 billion, an increase of about 85%. The population would not have peaked at this time, as from 2099 to 2100 the population would increase by nearly 90 million, equivalent to the current population of Iran.
Total fertility rate
Clearly, fertility is the main driver of population growth, along with longer lifespans. In 1950, the global synthetic fertility index (ISF) was 4.9. An ISF of around 2.1 is needed to maintain the population level. However, from 1950 to 2022 there has been a substantial decline in the TFR, to 2.3, barely above the replacement rate. Projections predict that ISFs in all three variants will continue to decline, which is why the population peaks before in the 2080s under the middle variant and in the 2050s under the low variant. In 2100, the medium variant estimates the global TFR to be below the replacement level of 1.84, with a TFR of 1.36 below the low variant. In the high variant, the TFR would remain above the replacement rate, at 2.32 (Chart 3).
More and less developed regions
Population growth in the highest income countries has long been much lower than in the rest of the world. The United Nations classifies North America (Canada, the United States and some Caribbean countries), Europe, Japan, Australia and New Zealand as “more developed regions”. The rest of the world is considered “less developed regions”. In 1950, the most developed regions had around 800 million inhabitants. The least developed regions have 1.7 billion, representing more than two-thirds of the world’s population.
Over the next 70 years (until 2022), the population of the most developed regions grew by 500 million, reaching almost 1.3 billion. At the same time, the less developed regions experienced a population explosion nearly 10 times greater, adding almost 5 million to reach 6.7 billion. Over the past seven decades, about 90% of population growth has occurred outside the most developed regions.
Projections of medium variants: By 2100, the most developed regions would lose almost 125 million inhabitants according to the projection of the medium variant. The most developed nations would drop from 1.275 billion to 1.15 million in 2100. This loss relates to the current population of Japan. All of the population growth would be in the less developed regions, at 2.5 billion, with the population increasing from 6.7 billion to 9.2 billion (Figure 4).
Low Variant Projections: According to the projection of the low variant, the most developed regions would lose 470 million, against 1.275 billion currently at 800 million. This one-third loss is equivalent to the current population of the United States (330 million) and the Russian Federation (145 million). At the same time, less-developed regions would suffer an almost equally large loss, at 430 million, rising from 6.7 billion in 2022 to 6.2 billion in 2100 (Chart 5).
With total fertility rates falling, it seems likely that the world’s population will peak by the end of this century, as predicted by the United Nations, or possibly much sooner. Already, populations have stabilized or are declining in countries like Japan. South Korea and China and will soon lose population. Future population growth will be driven by FSIs in the less developed world, particularly in sub-Saharan Africa, where rates remain high. Critically, they could also follow the pattern seen in some of the world’s poorest countries that have fallen to replacement level or below, including India and Bangladesh. The future is far from settled, but it looks like the once terrifying demographic tsunami may soon be replaced by less extreme waves.
Note on United Nations population projections: A quick look at the UN’s World Population Prospects: 1980 indicates considerable accuracy when it comes to world population in 2020. In 1980, the UN projected world population to be between 7,376 (low variant) and 8,063 billion (medium variant) in 2020. In 2022, the UN estimated the world population at 7.894 billion, about 2.5% less than forecast. The 2020 population was about three-quarters of the way between the low and medium variants as projected in 1980.
Wendell Cox is director of Demography, an international public policy firm located in the St. Louis metropolitan area. He is a founding senior fellow at the Urban Reform Institute in Houston, a senior fellow at the Frontier Center for Public Policy in Winnipeg, and a member of the advisory board of the Center for Demographics and Policy at Chapman University in Orange, California. He was a visiting professor at the National Conservatory of Arts and Crafts in Paris. His main interests are economics, the fight against poverty, demography, urban policy and transport. He is co-author of the annual Demographia International Housing Affordability Survey and author of Demographia World Urban Areas.
Mayor Tom Bradley appointed him to three terms on the Los Angeles County Transportation Commission (1977-1985) and Speaker of the House Newt Gingrich appointed him to the Amtrak Reform Board, completing the term unexpired of New Jersey Governor Christine Todd Whitman (1999-2002). He is the author of War on the Dream: How Anti-Sprawl Policy Threatens the Quality of Life and Toward More Prosperous Cities: A Framing Essay on Urban Areas, Transport, Planning and the Dimensions of Sustainability.
Photo: Dhaka, Bangladesh (by author)