The world population is 8 billion in 2022. It was only 1800 billion in XNUMX and has therefore increased eightfold since then. (see Figure 1 opposite).
It should continue to grow and could reach almost 10 billion in 2050. Why should the growth continue? Is stabilization possible in the long term? Wouldn't degrowth right away be preferable?
If the world population continues to increase, it is due to the excess of births over deaths – the first are twice as many than the latter. This surplus appeared two centuries ago in Europe and North America when mortality began to decline in these regions, marking the beginnings of what scientists called the demographic transition. It then extends to the rest of the planet, when advances in hygiene and medicine and socio-economic progress reach other continents.
A growing African population
Population growth slows down though. It reached a maximum rate of over 2% per year sixty years ago and has since halved, reaching 1% in 2022 (see Figure 2 opposite).
It should continue to fall in the coming decades due to the decline in fertility: 2,3 children on average per woman today in the world, compared to double (five children) in 1950. Among the regions of the world where fertility is still high (greater than 2,5 children), we find in 2022 almost all of Africa, part of the Middle East and a strip in Asia ranging from Kazakhstan to Pakistan via Afghanistan (see the map below). This is where most of the world's future population growth will be located.
One of the great changes to come is the tremendous growth in the population of Africa which, including North Africa, could triple by the end of the century, rising from 1,4 billion inhabitants in 2022 to probably 2,5 .2050 billion in 1,2. While one in six humans live in Africa today, it will probably be more than one in three in a century. The increase should be particularly significant in Africa south of the Sahara where the population would increase from 2022 billion inhabitants in 3,4 to 2100 billion in XNUMX according to the medium scenario of the United Nations.
What to expect in the decades to come
These numbers are projections and the future is obviously not written down.
It remains that demographic projections are relatively reliable when it comes to announcing the size of the population in the short term; that is to say for a demographer, the next ten, twenty or thirty years. The majority of men and women who will live in 2050 have already been born, we know their number and we can estimate without too much error the proportion of humans today who will no longer be alive. Concerning the newborns who will be added, their number can also be estimated, because the women who will give birth to children in the next 20 years have already been born, we know their number and we can also make an assumption on their number. of children, again without too many errors.
It is illusory to think of being able to act on the number of men in the short term. Decreasing the population is not an option. Because how to get it? By an increase in mortality? Nobody wants it. By massive emigration to the planet Mars? Unrealistic. By a drastic drop in fertility and its maintenance at a level well below replacement level (2,1 children) for a long time. This is already happening in a large part of the world, humans having chosen to have few children while ensuring them a long and quality life.
But this does not immediately result in a decrease in population due to demographic inertia: even if world fertility was only 1,5 children per woman right away like in europe, the population would continue to increase for a few more decades. The latter still includes many adults of childbearing age, born when fertility was still high, resulting in a high number of births. On the other hand, the elderly or very elderly are few in number on a global scale and the number of deaths is low.
The question of fertility decline
Forty years ago, demographers were surprised when surveys revealed that fertility had started to decline very rapidly in many countries in Asia and Latin America in the 1960s and 1970s. the decrease in their demographic projection for these continents.
Another, more recent surprise came from Africa. Its fertility was expected to decline later than in Asia and Latin America, in relation to its lag in socio-economic development. But we imagined a simple shift in time, with a rate of decline similar to other regions of the South once this one started. This is indeed what happened in North Africa and Southern Africa, but not in intertropical Africa where the decline in fertility, although begun today, is taking place there. slower. Hence an increase in projections for Africa which could bring together more than one inhabitant of the planet in three in 2100.
Fertility is decreasing in intertropical Africa, but in educated circles and in towns more than in the countryside where the majority of the population still lives. If the decline in fertility there is currently slower than that observed a few decades ago in Asia and Latin America (see Figure 4 opposite), this is not due to a refusal of contraception.
Most rural families have certainly not yet converted to the two-child model, but they wish to have fewer children and in particular more spaced apart. They are ready for this to use contraception but do not benefit from the appropriate services to do so. National birth control programs exist but are not very effective, lack the means, and above all suffer from a lack of motivation of their managers and the staff responsible for implementing them in the field. Many are not convinced of the value of limiting births including at the highest state level, even if this is not the official discourse given to international organizations.
This is one of the differences with Asia and Latin America in the 1960s and 1970s and one of the obstacles to be overcome if fertility is to decline more rapidly in sub-Saharan Africa.
Long term: explosion, implosion or equilibrium?
Beyond the next fifty years, however, the future is full of questions, without a model on which to rely.
That of the demographic transition, which has proved its worth for the evolutions of the last two centuries, is of little use to us for the future. One of the great uncertainties concerns fertility. If the very small family becomes a dominant model in a sustainable way, with an average fertility of less than two children per woman, the world population, after having reached the maximum level of ten billion inhabitants, would inexorably decrease until the term extinction.
But another scenario is possible in which fertility would rise in countries where it is very low to stabilize on a global scale above two children. The consequence would be uninterrupted growth, and once again the disappearance of the species in the long term, but this time in excess. If we do not resolve the catastrophic scenarios of the end of humanity, by implosion or explosion, we must imagine a scenario of a return to equilibrium in the long term.
It's the lifestyles that matter
Humans must of course now think about the balance to be found in the long term, but the urgency is the short term, that is to say the next few decades.
Humanity will not escape an increase of 2 billion inhabitants by 2050, due to the demographic inertia that no one can prevent. On the other hand, it is possible to act on lifestyles, and this without delay, in order to make them more respectful of the environment and more economical in resources. The real question, the one on which the long-term survival of the human species depends, is ultimately less that of numbers than that of lifestyles.