Numbers help tell stories. But numbers can also BE the story. The world’s population exists in numbers – billions of numbers. In 2022, human population reached 8 billion and that was the story, not just for the size of the number but for the short amount of time it took to reach. Just a hundred years prior, the world’s population had yet to reach 2 billion, less than a fourth of the number on Earth today. As we continue to add tens of millions of people to the world population each year, where are we headed? And when, if ever, will the world population stop growing?
Calculating Human Population Growth
Just like a historian assists in making sense of the past through the interpretation of records and events, a demographer acts in a similar capacity to make sense of human populations, both their present trends and future projections. And like historians, demographers use the best information available, beginning with a census. Most countries conduct a census – a count of the populace – every decade. In addition to census data, demographers consider fertility and life expectancy when making projections.
Fertility rate, the primary variable in making population projections, is defined as the number of children a woman will bear during her reproductive years (age 15-44). In order for a country to maintain the size of its current population, it must reach a fertility rate of 2.1 or what is called replacement level fertility. With a fertility rate of 2.1, a population is considered stable, which is a way of saying that the next generation of children born will equally replace the generation of adults who have passed. With the current global fertility rate at 2.3, our population increases. While the difference between a fertility rate of 2.1 and 2.3 may seem small, this difference propels population growth by tens of millions of people annually.
Most demographers expect global population growth to continue until the 2080s before it levels off. On the World Population History timeline, this growth is observed through the year 2050 when the global population is projected to be 9.7 billion. Because so many factors are at play in determining fertility rates, there are a range of potential outcomes for our projected global population. The United Nations developed a series of these projections for their report, World Population Prospects: 2022 Revision, based on possible changes to the global fertility rate, and provide estimates to the likelihood of three different scenarios unfolding.
Even small differences in the global fertility rate will have a significant impact on the trajectory of our global population. As demographers gain more accurate data from country reports, the projections are adjusted. For example, the 2017 Revision’s medium-variant projection had global population at an estimated 11.2 billion in 2100. The 2019 Revision decreased that medium-variant projection to 10.9 billion, and the 2022 Revision reduced the estimate further to 10.4 billion, following the analysis of recent health and demographic surveys. Because of the volatility of future projections, the United Nations utilizes probabilistic statistics to set the range of possible population outcomes rather than one exact number. Within each of the population projections there is an expected decline in fertility rates, but to what extent is still up for debate, as is the anticipated peak of our total global population.
Population of the world – UN Projections
The graph below is from the UN’s report, World Population Prospects: 2022 Revision.
Medium Variant
Under the assumption that the current global fertility rate of 2.3 will continue to decline and reach replacement level (2.1) by 2055, the United Nations projects the world’s population at 9.9 billion by then. Though the fertility rate will decrease, total population itself is not expected to decline until the end of the century because of a phenomenon known as “demographic momentum.” The medium, or median, variant outcome (seen as the solid red line on the graph above) has the highest statistical probability based on current census data and our understanding of fertility rate’s historical record.
95% Prediction Interval Projection
If the global fertility rate does not fall as quickly as expected, there is the possibility of our population reaching 12.4 billion by 2100. Alternatively, a much more rapidly declining fertility rate would produce a global population of 8.9 billion by 2100 – the lower limit of the 95% prediction interval. So, demographers are 95% certain that the world should prepare for a population somewhere between 8.9 billion and 12.4 billion by the end of the century.
The United Nations population projections is just one set of estimates as to future population growth, but it is the most widely used worldwide. This graph tracks fertility rate as a number but doesn’t necessarily explain why or how fertility rates change. Nor does it tell us where population growth is happening geographically. For that information, we need more help from demographers.
What Causes Changes in Fertility?
In trying to project how fertility rates might change in future years, we need to understand what could be behind those changes. A number of factors can affect how many children people choose to have, including economics, cultural norms and traditions, education, public and reproductive health care. Demographers analyze trends in these areas to determine how they might affect fertility. For example, with improved healthcare, infant mortality rates decline, and as a result of more children living on to their adolescent years, families are less likely to have additional children. Another factor influencing fertility rate is girls’ education. The higher the percentage of women within a country who have obtained at least a high school level of education, the lower the fertility rate. Because these and other factors (e.g. income, gender equity, traditions/cultures, health education, contraceptive use, personal and national security) have been linked to fertility trends, demographers track this information within countries to project what the future may hold.
Africa’s Growing Challenge
Up to this point the fertility rate has been discussed as a global average, but to really grasp population projections we need to explore that rate by country and region. One of the regions providing the greatest challenge to population projections is Africa. Since the 1950s fertility rates have dropped dramatically across most of the world, due in part to improved global health, education and income. Because fertility rates decreased so quickly in developing countries in Latin America and Asia, population projections were made based on a continuation of those trends holding true worldwide. But in many countries within Africa this rapid fertility rate decline has not happened. According to the UN, the population in sub-Saharan Africa could triple by 2100, nearing 3.5 billion people and becoming more densely populated than China.
So why have fertility rates remained so high? Of the 46 countries classified as “least-developed,” 34 of them are located in Africa. Lower levels of income, adult literacy (specifically the large gap in gender education equality), and lack of essential healthcare all have contributed to the current high fertility rates. The reason to highlight Africa in particular is because half of the world’s expected population growth will occur on the continent, and any economic and social improvements leading to lower fertility rates may have a dramatic impact on our larger global population projection as a whole. Population is expected to grow from 6.7 billion to 8.4 billion in less developed countries by 2050, yet remain largely unchanged in more developed countries.
Other Considerations
Although the fertility rate is a main determinant of future population size, it is by no means the only variable. Another key determinant is life expectancy. The UN forecasts increases in longevity through century’s end, with global life expectancy rising from 72 today to 82 in 2100. The greatest gains are expected in Africa, Asia and Latin America, as child mortality rates continue to fall. Over the past 50 years, international efforts and funds have helped to reduce fertility rates through commitments to family planning services and child survival.
Only time will tell as to what projection our global population will match. But one this is certain – the 8 billion people on Earth is a large number of people who have needs to be met, particularly if current consumption rates remain constant, or increase. Human population growth’s story isn’t a finished work. The decisions we make today as individuals and societies can affect the size of tomorrow’s global family.
