My grandparents have seen the number of people in the world more than triple over their lifetime. When they were born in 1937, there were 2.2 billion people in the world; now, in their 80s, there are around 7.7 billion.

My parents, born during the “baby boomer” period of the mid-1960s, have already seen the population more than double. Yet, a doubling is something I will never see. Population growth is likely to level off before it crosses 11 billion.

My grandparents have lived through the most remarkable period of human history. They’ve experienced the steep rise and peak, and most of the fall, in global population growth. The problem is that they—like many—still think we’re on the upward slope of the curve.

Who can blame them? Fueled by Paul Ehrlich’s book The Population Bomb, they were inundated throughout the 1970s and 1980s with predictions of overpopulation, mass famine, and humanitarian crisis. Yet agricultural innovation and the Green Revolution meant that such dire predictions did not come true. In fact, when we look at reconstructions of historical data on famine deaths—which can be done in detail only to around 1860—we see that famine deaths have been at their lowest levels post-1970. Not quite what everyone was expecting.

The idea of uncontrolled population growth nevertheless lives on. Many people believe that exponential population growth is not only happening but is destined to continue. Not only is this untrue, it simply cannot be true. The population growth rate is falling steeply. It peaked half a century ago—reaching a high of 2.1 percent in the 1960s. Since then it has been halved to just over one percent per year.

This does not mean that the population is not growing fast. We add 82 million people every year: 140 million babies are born and 58 million people die. But growth is slowing, and by the end of the century we expect population to have leveled off—at around 10.8 billion, based on the latest United Nations projections.

One thing that studying demography has taught us is that population “explosions” are temporary. They are finite periods of change between stable equilibriums. Why is this the case?

It comes down to the simple balance of the things that matter for population growth: the number of children born and the number of people who die.

For most of human history, population growth was close to zero: women had many children but also lost many. When we look at historical evidence of child mortality, we find that irrespective of culture and geographical location, around one-quarter of newborns died before their first birthday; at least half died before reaching adolescence. Parents would have six children but would tragically lose three or four of them. Population was kept in check by the heartbreak of human loss.

Population began to increase rapidly in recent centuries because child mortality fell before fertility rates did. Better health and improved living standards meant that if a woman had six children, she would instead lose “only” two of them. Every couple would have four surviving children, which would naturally cause the population to double. Population increased because we stopped children from dying. For me, this is humanity’s greatest achievement to date. How odd that this is often framed in a negative light.

Today, women are having far fewer children, and very few of those children are dying. This is where we reach an equilibrium again—and population growth comes to an end. As the late Hans Rosling once put it: “The balance of population in the past was controlled by death: it was ugly and unacceptable. The new balance is controlled by love.”

In short, we are now arriving at a historical moment in demographic history: soon the number of children in the world will reach its peak.

Over the past 50 years, the global fertility rate has been halved. Some countries reduced fertility rates extremely quickly: it took Iran only 10 years to halve fertility rates, from six to three children per woman. (It took the United Kingdom 95 years to achieve this; in the US, it took 82 years.) Currently, the average woman in Bangladesh or Nepal has only two children—a fact that my grandparents would scarcely believe. Fertility rates in Brazil are now lower than in the US, the UK, and Sweden.

But this is not true in all countries. Fertility rates remain high in many low-income countries—predominantly in sub-Saharan Africa. The average woman in Niger still has seven children. And that disparity—the different rates at which countries move through a demographic transition—is shifting the human population curve along two other key axes: location and age.

The past 50 years have revealed the story of the rise in population in Asia and its decline in Europe. In 1950, more than one person in five lived in Europe; today, it’s around one in ten; and by 2100, it will be one in 20. The next 50 years will witness the story of African growth: by the end of the century, this continent’s share of the world population is expected to rise from 17 percent to 40 percent. It will grow from 1.3 billion to around 4 billion people.

At the same time, populations—especially in rich countries—are ageing fast. Japan is a prime example: in 1950s Japan, every twentieth person was over 65 years old; today, it’s one person in four. By the 2030s, it will be one in three.

This is true of many other countries. In 1950, eight percent of the US population were older than 65. By end of the century, it will be 28 percent.

Economically, population ageing generates a new challenge for many countries. It’s a problem for which—after decades of fearing overpopulation—we are ill-prepared.

For the poorest countries, ageing could be a major economic plus: their large populations will grow from children into working-age adults. In present-day Nigeria, 44 percent of the population are younger than 15 years old: this either creates a large number of dependents or forces young children out of school and into work. By the end of the century, the share younger than 15 will fall to 23 percent. And if Nigeria (and similar countries) can get these populations into work, it could be an economic boom for them.

Globally we’re shifting to a new equilibrium, one of smaller families and older societies. What this shift of the human population curve means for environmental sustainability remains an open question.

Will ageing populations result in lower economic output, and therefore lower levels of consumption? Will the shrinking of young, working-age populations result in slower technological innovation—a factor which will be crucial to decoupling prosperity from environmental degradation? Or will the emergence of large working-age populations in Africa and Asia simply shift the source of this technological advancement?

These are questions that have been masked by continued fears of overpopulation. When the data points shift, so too must the conversation.

________________

Hannah Ritchie is a senior researcher and Head of Research at Our World In Data, based in Oxford.