As a species, we're learning to be a mature adult
Joel Cohen explains 21st century population growth.
According to Joel Cohen, it’s possible humans have “finally outgrown our childhood and adolescence as a species.” He spoke to Earth & Sky’s Jorge Salazar shortly before the World Population Day of July 11, 2006, about the scientific prediction that Earth’s population may well stabilize sometime during the 21st century. Cohen knows a lot about population predictions. He’s the professor of populations at the Rockefeller University and Columbia University in New York City, and he heads the Laboratory of Populations at Rockefeller and Columbia.
Salazar: How many people will be on Earth by the year 2050?
Cohen: Population will probably grow from about 6.5 billion today to about 9.1 billion by 2050. Today, we have about 6.5billion people, more than twice as many people as we had in 1960, which was about 45 years ago. But a great revolution started inthe 1960s: the gradual decline of the population growth rate.
Since the 1960s, the population doubled. Meanwhile, the rate of increase dropped. In other words, population is still growing, but it’s growing more slowly. And we expect the rate of increase to continue to drop over the next 45 years. That means that the population will probably grow from about 6.5 billion today to about 9.1 billion by 2050. That’s an increase of roughly half, instead of a doubling as happened over the last 45 years.
We don’t know exactly what will happen. But some people think that population growth could actually come to an end in the 21st century.
Salazar: What will that look like? What will Earth’s population be like in 2050?
Cohen: People expect four things. As I said, they expect that there will be more people, maybe 2 billion more, maybe 3 billion more by 2050.
The second thing is that population growth will continue to slow. This year, we think that the population has increased by about 75 million. There are 75 million more people on the planet this year than last year. But by the time that we get to 2050, we expect the increase to be about half of that, maybe 34 million a year. So growth is slowing.
The third thing is that the population will be older. A much higher fraction of people on Earth will be age 60+. In fact, in the next couple of decades, we’re going to see a tsunami of aging unlike anything humanity has seen before. This will occur both in the rich countries and the poor countries.
And the fourth thing that will happen by 2050 is that most people will be living in cities. Actually, the date of transition from the majority of rural people to a majority of urban people is 2007, just next year. By 2050, at least two–thirds of the world’s population is expected be living in cities.
To summarize, the world’s population is going to be bigger, more slowly growing, older, and more urban. And there will be a tremendous shift in the proportion of the population from what are today, developing countries. All of the growth – an additional 2.6 billion – will be in the poor countries. So today’s poor countries will certainly dominate the world, demographically, by 2050.
Salazar: How do scientists know? What is the evidence?
Cohen: Well, demographers have an enlightened form of crystal ball gazing, but it’s crystal ball gazing nevertheless.
If you study the world’s population, you see that trends tend to continue for a while. So scientists have looked at birthrates – the number of children that each woman bears in her lifetime – which is called the “total fertility rate.” And they noticed that the total fertility rates have been dropping for the last 45 years.
And so if you just continue the trends, you can reasonably expect that total fertility of the world will continue to drop over the future.
As of today, the average number of children per woman per lifetime is around 2.6 or 2.7. Or you could say that 100 women have 260 children per lifetime. And that varies very widely from about 1.4 children per woman in Europe, to 5.1 in Africa today. There are demographers in the United Nations Population Division, in the Bureau of the Census, in the United States Census, and in other institutions such as the World Bank. Their projections are different in detail.
But they agree, in the large picture, that total fertility rates in the high–fertility countries and regions will probably drop.
Salazar: Why are fertility rates dropping?
Cohen: Let me give you some of the facts. In today’s rich countries, the average number of children expected for a newly–born woman, in a lifetime, given today’s fertility rates, is about 1.6 children. And in the poor countries of today, it’s about 3 children, roughly twice as many children.
There are a number of reasons for this difference. One is that the incentives for people to have children are higher if you’re living in an agrarian, rural setting, where you need hands to help you with the daily chores of bringing in water, for example. The water might be far away and girls are often assigned to do that, as well as gathering firewood and helping with the farm work.
So children are an asset if you’re in a rural environment, and 60% of the population in poor countries are in a rural environment as opposed to only 25% in the rich countries.
If you’re living in a city, children are a liability. It’s hard and expensive to find housing for them.
A second difference is that in the developing countries, access to modern means of contraception is much more limited. The more rural the community within the developing world, the more difficult it is to have access to modern contraception.
A third factor – and one that’s important – is that if you compare the infant mortality rates, they are much higher in the poor countries than in the rich countries. What is infant mortality rate? For every thousand babies, how many of them die before they reach the age of 1? In the rich countries, on the average, about six babies die out of 1,000 being born, before they reach the age of one. In the poor countries, 59 babies die out of 1,000 being born. That’s almost 10 times higher.
So there’s a much higher chance that one of those three children that women have, on the average in the poor countries, is going to be dead before it reaches the age of one.
And there’s much higher child mortality too: deaths before the age of five. So if women want to end up with one or two children, to protect them in their old age, in the developing countries, the poor countries today, women need to have more children because a child’s chance of survival is significantly lower than it is in the rich countries.
There are other factors. You asked a simple question and the answer is long and complicated.
The alternatives available to women in the poor countries for the use of their time are more limited. Often they are less educated, they don’t have access to jobs, they may have more limited access to schooling. So the alternative uses of women’s time, apart from childbearing, are more limited. And the level of education of women is lower in the developing countries, on the average. In every society, when women have more education, with one or two exceptions, they have lower fertility.
So it’s a mixture of incentives, roles for children, roles for women, education for women, alternative uses for their time, infant mortality, all of those contribute to higher fertility for the developing countries.
And as these countries develop, one can very reasonably expect fertility to decline. As women get more schooling, as they have more opportunities, as the countries urbanize, all of those things push fertility in a lower direction.
Salazar: What about death rates? Aren’t people living longer now?
Cohen: Death rates are the other side of the coin. Death rates have been dropping. Life expectancy rose from 30 or 40 years in 1900 to 66 years by the end of the 20th century.
That’s a colossal improvement in human well–being.
There’s some uncertainty as to what will happen to that trend in the future. But, overall, worldwide, demographers anticipate that life expectancy will continue to rise. There have recently been some dramatic and disastrous exceptions to the trend of rising life expectancy, most notably because of the epidemic of AIDS and, secondly, because of the breakdown of support systems in the former Soviet Union and some of the allied countries.
So, for example, male life expectancy in the former Soviet Union has fallen since about 1990. And in some AIDS–infected countries in sub–saharan Africa, life expectancy has fallen back to 30 years, which is just a colossal setback.
But, apart from those exceptional areas, we can expect that people will live longer.
Salazar: So what does it all mean, for Earth’s population, overall?
Cohen: It means we’ll be approaching a stationary population size, possibly during the 21st century. I don’t know any demographer who expects the world’s population to double again. So I think that we have finally outgrown our childhood and adolescence as a species. As a species, we’re learning to be a mature adult, with an older population that’s city–dwelling and not rapidly growing.
And I think that’s a wonderful achievement.
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