We’re in search of a sustainable development trajectory for the planet. We want to help countries grow, especially the poorest countries, to break free of the poverty trap. We need to respect planetary boundaries, and we want growth to be fair, widely shared with a broad inclusive prosperity. We’ve seen how hard this is going to be, whether it’s the energy system, or the food production technologies that are going to have to change markedly. But a big part of the challenge, the extent of the challenge, the ability to meet sustainable development will depend on the future of population dynamics.
The more people there are on the planet, the more mouths to feed, the more challenges there will be to reconcile the economic objectives of rising living standards per person, multiplied by a larger number of people, and respecting the planetary boundaries. And so, facing the question of population is key. We also know it’s key for inclusiveness and breaking free of poverty. Because when poor families have large numbers of children, they are not able to provide the kind of investment in the human capital, as we call it. Meaning the health, the nutrition, the education, the skills of their own children. In order to ensure that they are productive and meet their their potential is, as adults. And so, reducing the fertility rates, voluntarily, respecting human rights and family desires to levels that are low enough to foresee a stabilization, even a gradual decline of today’s large population, or the one that we will have on the planet in the future, will make it easier to achieve the other aspects of sustainable development as well. Social inclusion, ending extreme poverty. And of course as I’m emphasizing, respecting the planetary boundaries. So where do we stand?
Well, if we go back to Thomas Robert Malthus in 1798, a world of 8 to 900 million people. And he warned us, be careful, populations will grow. They have grown maybe by a factor of nine or ten, since Malthus gave us that famous warning, to 7.2 billion today. And that 7.2 billion today is up from around 2.5 billion people in the middle of the 20th century. You’re looking at a very pertinent set of scenarios, four of them shown here, produced by the United Nations Population Division. Notice that the solid line shows the actual change in population from 2.5 billion to 7.2 billion between 1950 and 2010. And then the four lines diverge, depending essentially on alternative assumptions about fertility rates, out to the end of the 21st century, to the year 2100. What are these four scenarios? The medium scenario shown here, it’s the one that is third from the top on the right hand side, reaching about 10.8 billion people in the year 2100. It’s called the medium fertility scenario of the UN Population Division. It’s the one we tend to look to as something like a continuation of current trends. That scenario shows us having an increase of another 3.6 billion people between now and the end of the century. What an enormous increase. That’s the middle scenario. Now at the top is something unthinkable, unimaginable, but very interesting for us. Suppose fertility rates do not come down at all, and for each age and each country in the world, the age specific child bearing tendencies continue into the future without reduction. Well, simply running the clock forward, based on the current fertility rates, the world population would soar well past 20 billion, 25 billion. In fact, by 2100, it would be 28.6 billion, four times higher than now. Impossible.
The Earth couldn’t manage it, but it does tell us something. It tells us that the medium scenario of the United Nations isn’t exactly business as usual in a mere continuation of current trends. It builds in the assumption already of a significant decline of fertility rates in future years. Take that into account. Because if those fertility rates do not come down, then 10.8 billion is going to look awfully optimistic in terms of where the population would settle, where I’m using the term optimism to mean keeping it on the lower side, so that we can envision realistically sustainable development. A constant fertility rate continuing exactly what’s happening right now, 28 billion people.
The next line down is what’s called the high fertility rate. It’s a little bit more plausible, pretty frightening. It says, if, instead of that medium scenario, women were to have just, on average, one half child more. So that each woman, instead of having two children, would have two and a half children or, or to put it another way, every ten women would be having 25 children rather than 20 children. Would mean billions and billions of people more on the planet. That’s how sensitive the population forecasts are to the future dynamics of fertility. We could reach 16.6 billion that is more than 5 billion in addition to the forecast of 10.8 billion, obviously. Now if rather than the medium fertility forecast, which has a built in estimated decline of fertility gradually over time, the decline of fertility were a bit faster. So that women were having on average a half child fewer than in the medium forecast, or every ten women having five children fewer than in the medium forecast. Then the world population would actually peak around mid century, and gradually decline to about 6.8 billion at the end of the century. From my point of view, that’s most attractive if we aim for sustainable development, which we presumably are aiming for. Because if we can have a peak of the world population, then a gradual decline, it’s going to be much easier to meet the inclusiveness goals, the fairness. It’s going to be much easier to meet the environmental objectives and needs as well. What this shows is that small changes of fertility rates will have big changes of outcomes. And it suggests that if steps are taken to help facilitate a faster reduction of fertility by, for example, keeping young girls in school rather than having them married, as in traditional societies at the age of 14 or sometimes even younger. This could make a very big difference.
Now, the next graph shows the annual rate of change of population in the medium scenario, but for different groups of countries. This is also important. The solid line third from the top, is the world average. What you see is that the population growth of the world peaked at about 2%, around 1970. At that time, the world population was on the order of about 4 billion people, which means that at a 2% growth rate, the world was adding about 80 million people per year.
Now if you fast forward to the year 2010, the growth rate is a little over 1% per year, 1.1 to 1.2% per year. But now, the base on which that percentage growth is occurring is twice as large as back in 1970. It’s now 7.2 billion people, multiply 1.1% by 7.2 billion people, or 1.2% by 7.2 billion people. Lo and behold, you’re getting about the same 80 million increase as of 40 years ago. This says that the proportionate growth rate of population has slowed. But the absolute numbers, the arithmetic increase year by year remains around 75 to 80 million people added to the world’s population each year. In the medium scenario, that growth rate tends to decline. It declines to almost zero by the end of the century, because fertility rates basically come down to replacement. Replacement fertility rate means that each mother has two children, one is a daughter, one is a son. Each mother is replacing herself with a daughter who will become the mother of the next generation. And keeping the numbers, therefore, in the long-term stable.
So since the fertility rate is assumed by the United Nations to trend towards the replacement rate of around two, the population growth rate also tends to converge to around zero. But what you see on this graph is that the least developed countries ironically, but not unexpectedly, have the highest population growth rate. Those are the places where family planning is not used. Those are the places where girls drop out of school early. Those are the places where women face massive discrimination. They’re not in the labor market, and so the opportunity cost of their time is low. They’re supposed to be home having children, according to the prevailing social norms, or maybe the desires of their husbands. Maybe not their own desires in many places, but traditional societies impose, through cultural and other means, that kind of pressure for large numbers of children.
Well, to see where fertility rates are right now, we can look at the next graph, which measures the actual fertility rates up to the year 2010.
And then shows the projections of the United Nations in this medium fertility projection for different groups of countries out to the year 2100. What you see is that, as of 2010, the countries at the bottom of this curve, which are the more developed, or the developed regions of the world, are already below replacement rate. If they continue with that fertility rate for another couple of generations, the population size will begin to decline in the high income world. The highest fertility rates in the curve at the very top of this picture are the least developed countries. Whereas, in 2010, still the total fertility rate is above four. Each mother, on average, is having two daughters. That means the population is tending to double, generation by generation. because each mother is replacing herself statistically with two daughters, who will grow up to be two mothers of the next generation. That’s why the population growth remains so high. And one can see in this graph, is that for the less developed regions as a whole and for the world on average, the fertility rates are a bit above replacement, but not as high as in the least developed countries. And therefore, on average, the population growth rate is less than it is in the poorest countries, but higher than it is in the high income countries.
Well, what could lead to a faster transition to a stable population, and to a replacement fertility rate? We know through observation and careful study that there are many key determinants of the fertility rate, of the fertility choice. Let me mention some of them.
First, age of marriage. In traditional societies, girls are often not schooled at all, or pushed out of school early. And married very early, maybe by the command of their father, who marries the girl for economic reasons within the community, or traditional reasons at the age of 12 or 14. And then childbearing starts very soon thereafter. And these young girls, who remain illiterate throughout their lives without economic, political, or social empowerment, often end up with seven or eight or nine children. So that is one determinant.
A second, obviously, is access to contraceptions and family planning. Places where contraceptives are widely available, where clinical services work, where there is good culturally sensitive advising where women can discreetly gain access to their contraceptive desires, tend to have lower fertility rates. And family planning programs that are, again, culturally sensitive and aware, and operating effectively in low income countries, can dramatically lower, on a voluntary basis, the total fertility rates in those countries.
A third determinant is the woman’s role in the labor force. In some countries, women aren’t allowed to work, or they’re not allowed to work outside the home, or they’re not allowed to work in many occupations. They face massive legal and social discrimination, or cultural practices that basically keep them at home. Now, raising children takes a lot of time. And therefore, if a woman is earning a living in the labor market, the cost of raising children, in terms of the lost wage income, can be very, very high. That means women that are in the labor force and are working and have that opportunity tend to want to have fewer children, because the opportunity cost of raising children is really quite high in terms of lost income. Women who face massive discrimination and aren’t allowed in the labor force may end up with more children, in part because of the market value of their time is so low. Not because it couldn’t command a higher income, but it’s not allowed to because of gender discrimination.
Another major factor is the urban versus rural location of families. Children are often farm assets. They do work, they do chores, they milk the cows, they carry fuel wood, they carry water. They therefore are not seen as a high cost, but actually as part of the farm labor for a family farm. In the urban areas, the child, much more likely, is going to school, but not working in a formal way. Typically, not always. There are painful exceptions. But this means that, on average, families in rural areas see the cost of raising children to be lower, because they see even young children being economic inputs to the household production. Whereas that’s not the case in urban areas. When families move to urban areas, their fertility rates come down.
Child survival is another key determinant. If it’s with the good reliability that the children will survive, families choose to have fewer children. If there’s worry about whether children are going to survive, many risk-averse households will have many, many children to compensate for the expectation that some of the children will die. So one of the keys to a quick voluntary reduction of fertility is to help keep children alive. Good public health, good health facilities in the local community.
The legality of abortion also plays an evident, a quite significant role statistically, different societies have different views. But those that have legalized abortion tend to have lower observed fertility rates than those where abortion is illegal. Still often undertaken, sometimes in very, very dangerous conditions. But where abortion is legalized, fertility rates tend to be lower.
The public leadership plays a big difference, because these are culturally determined phenomenon. Some places in traditional societies when families were on the farm, when children were dying in large numbers, the cultural norms were, have as many children as possible. But when conditions change, children are surviving, families are in urban areas, children need to be educated. Farm sizes have already shrunk, ecological burdens are high. And you want a lower fertility rate as a result by giving the options and awareness to households. Then the political leadership’s saying, you know, for your good, your farm size has shrunk. You’re trying to help raise children with good education, have fewer children. The political leadership and the public awareness can play a huge role. As, of course, do the role models that people see. One of the things sociologists have found is that when television sets come into a poor rural area, fertility dmnaterates tend to come down. The hypothesis, at least, is that people are observing on their television shows, in their sitcoms and and in, in their soap operas, families with fewer children. And in the rural areas, that’s giving the idea that there’s only one son or daughter, maybe two children, not six or eight. And that changes the social norms as well. This is a big deal for us.
The dynamics of the world will look very different if the world population reaches 11 billion at the end of the century versus stabilizing, and even falling gradually below 7 billion. The latter would be much easier from the point of view of quality of life, income per capita, and environmental sustainability. And there’s good reason to believe it would be the preferred choice of households if they have access to family planning, education for their girls, child survival, jobs, and an absence of discrimination for women. Provide those conditions, most likely households will absolutely take the opportunity on a voluntary basis for a sharp reduction of fertility rates, helping to move the world more quickly to a peaking and stabilization, and then gradual decline of the world population thereafter.