Will we one day be more than 10 billion human beings on Earth? By sticking to the latest United Nations projections unveiled in 2019, this threshold could be crossed during the second half of the 21st century. According to the UN, the world population would approach 11 billion in 2100, against 7.7 billion currently.
Is it a certainty? An article published on Tuesday by The Lancet reviews these demographic maps. According to this study by the Institute for Health Metrics and Evaluation (IHME), based in the United States, in Seattle, we will be “only” 8.8 billion on the planet in 2100, after a peak of 9.7 billion reached from 2064.
How to explain such a difference between these two projections?
About 2 billion people separate the IHME and UN projections for 2100, the equivalent of the current population of China added to those of the European Union and Brazil. For the UN, the number of inhabitants will continue to increase until 2100 at a less and less sustained pace whereas for Christopher Murray, director of the IHME, "the continuous growth of the population throughout the century n 'the more the more likely scenario'.
"The essential factor to explain these diverging views is the methodology used in relation to the fertility rate", explains Michel Guillot, director of research at the National Institute for Demographic Studies (INED). In this matter, the slightest deviation upsets the models. As the IHME underlines, a fertility rate higher than a tenth of a point translates into 500 million additional people in 2100!
The UN hypothesizes that this rate should go up in countries where it is very low, such as in East Asia or in the south of Europe. But for its part, the IHME makes projections based on the relationships between level of education, access to contraception and fertility rate. With this method, the Institute predicts a dizzying drop in the number of children per woman, from 2.37 to 1.66 in 2100, far from the 2.1 children needed to maintain the population without resorting to immigration. This threshold would no longer be reached in 183 out of 195 countries.
Which countries would experience the greatest upheavals?
The fertility rate is expected to drop across the world, including in sub-Saharan Africa, where it is highest. This would not prevent these countries from seeing their populations jump. Slightly more than 1 billion in 2017, it could triple by the end of the 21st century, Niger seeing its number of inhabitants sevenfold while its neighbor to the south, Nigeria, would have 584 million more people ( 790 million in 2100 against 206 million in 2017).
At the same time, other regions risk having their land depopulated. This would especially be the case for European and Asian countries. In 2100, the number of Chinese could be halved (732 million against 1.4 billion) and fall back to what it was in the 1960s. Japan or South Korea would follow this same trend. A fall of around 50% would also await Spain or Italy, countries where the fertility rate could collapse to 1.2.
What about France?
Unlike its neighbors, our country may not experience such great variation. In the space of 80 years, the number of French people would remain stable, going from 65 million in 2017 to 67 million in 2100. The 67 million mark was already reached in 2019, according to INSEE figures published last January .
Driven by a fertility rate of around 1.8 for much of the century, the French population would continue to grow very slightly until 2046, with a peak above 70 million inhabitants. A scenario departing a little from that drawn by INED and in which the French would be 76.4 million in 2070.
What effects would these demographic changes have?
The decline in the fertility rate, combined with the increase in life expectancy, should lead to a general aging of the population and redesign the age pyramid. One in ten human beings would be over 80 in 2100, while this age group represents only 2% of the world's population at this time. "Such an evolution poses vast questions about the system of financing pensions and health, even if the fact that people stay in good health longer mitigates this effect a little", underlines Michel Guillot.
Newsletter - The essentials of the news
Every morning, the news seen by Le ParisienI'm registering
Your email address is collected by Le Parisien to allow you to receive our news and commercial offers. Find out more
This aging of the population could also lead to a upheaval in the world economy due to the decrease in the number of people of working age. The IHME thus imagines the United States returning to China in the ranking of the largest GDP at the end of the 21st century, the number of Chinese workers rising from 950 to 357 million.
A reading that does not totally convince Michel Guillot: “It seems a little simplistic to me. The size of the population is one factor among many in the economy. We know, for example, that Germany has had very low fertility for a long time and that it succeeds in remaining among the great economic powers. "
What are the limits of this study?
Like all projections, those of the IHME are not to be taken literally. The figure of 8.8 billion inhabitants in 2100 comes with a fairly wide confidence interval - between 6.8 and 11.8 billion - to allow the American Institute not to get too wet and to be almost guaranteed to be right in 80 years.
Taking a 2100 horizon also seriously complicates the task of demographers, but this is not unique to IHME projections. “Until recently, the United Nations projected until 2050 but for several years, the horizon has been set at 2100. The further this horizon is, the more uncertainties there are. Beyond 30 years, all projections must be taken with great care, ”insists Michel Guillot, preferring to refer to the studies of the UN, which represents the consensus among demographers.
The other pitfall of this study is that it is based on the premise that countries like Italy will remain unresponsive to the free fall of their populations. There is nothing to say that they will not seek to raise their fertility rate, for example by allowing women to better reconcile work and family. The study authors also recognize that there is great uncertainty around the migration policies that will be implemented by each country to stem the decline in the number of workers.
