JEFFREY BROWN: Hari Sreenivasan takes the story from there.
HARI SREENIVASAN: Just what are the consequences of such explosive growth?
The PBS NewsHour, in partnership with the Pulitzer Center and National Geographic, has been covering that for the past year. We have explored how the composition of our society is changing. We are becoming a more urban population. Mega-cities, those with more than 10 million residents, are booming.
In 1975, there were only three such places. Now there are more than 21.
Fred de Sam Lazaro reported from New Delhi last December.
FRED DE SAM LAZARO: Jyoti Sharma, a conservation activist who runs a small aid agency, says the city is simply overwhelmed.
JYOTI SHARMA, water activist: Every year, we get an additional .5 to .7 million people. That's the net addition to the city.
FRED DE SAM LAZARO: Seven hundred thousand people every year?
JYOTI SHARMA: Seven hundred thousand people, yes.
A majority of this growth is of people who are poor. And they typically come and settle in these kind of settlements. Only 27 percent of the city is actually a planned city. The rest of it has just grown like this. And you cannot stop them from coming, because that's the only place they will get some livelihood from.
HARI SREENIVASAN: Babies born today enter a world where 13 percent of the population doesn't have access to clean drinking water.
That was the subject of Steve Sapienza's report in march from Dhaka, Bangladesh.
STEVE SAPIENZA: If you want to see the human toll exacted by unsafe water and poor sanitation in Dhaka, you come here. This is the overflow tent at the short-stay unit at Dhaka's main cholera and diarrhea hospital.
This man arrived at the hospital with no vital signs. After 15 minutes of trying to revive him, his wife is given the news. The staff reports cholera as the cause of death.
HARI SREENIVASAN: But while the overall number continues to rise, in places like Brazil, family sizes are shrinking. In August, Fred de Sam Lazaro outlined some of the forces changing fertility rates there.
FRED DE SAM LAZARO: Eighty percent of women of childbearing age use contraception. At the same time, a robust economy has needed their labor. Today, women make up 40 percent of the country's work force up and down the economic ladder. The majority of college graduates in Brazil are women.
HARI SREENIVASAN: To see many more images, you can download the National Geographic 7 Billion app for the iPad.
For more now on what a seven billion-person world might mean, we are joined by Azza Karam, a senior adviser at the U.N.'s Population Fund, and Dennis Dimick. He is the executive editor of environment at National Geographic magazine, our partner in world population coverage.
So, Dennis, let me start with you.
What are the implications of a 7 billion-person world? You have been looking at these stories all year.
DENNIS DIMICK, National Geographic magazine: Well, I think the idea that 7 billion is really just a spot on a trajectory that we're all on.
And if it's laid out, we were at 6 billion just a few years ago, and by 2025, we will be at 8 billion. So, really, what it is, it really gives us an opportunity not so much just to talk about 7 billion, but what does that mean and what are the kind of challenges that we all face as we go forward to try to fulfill the needs of everybody on the planet?
HARI SREENIVASAN: Now, Azza Karam, it's a nice round number that gets our attention. So now you have it. What should we be focused on?
AZZA KARAM, United Nations Population Fund: We should be focused both on the challenges that this represents, as well as on the opportunities, because there is no way that it is only a litany of challenges.
It certainly is a matter of access to resources. More people means more pressure on already rare resources, from the air we breathe, the water we drink, the food we eat. It literally is a great deal more demand than there may well be supply.
But at the same time, we have to balance that perspective by looking at the opportunities that 7 billion presents in terms of the most amazing amount of human power that this Earth has ever seen, and especially given the technology that is being evolving as we speak, especially communication technologies, but also the technologies of the better use of resources that we're all trying to harvest. The fact that there will be 1.8 billion of that 7 billion is young people, which is a remarkable potential, as we're seeing every day unfold in terms its of new strategies for seeking demand.
And one of the challenges and also an opportunity is the fact that we have a lot more women who will be hard-pressed as heads of households to make ends meet, but, at the same time, a lot more women in the labor force who are in positions of decision-making.
So I think we need to make sure we keep that balanced perspective all the time.
HARI SREENIVASAN: Dennis, as one of the stories we profiled showed, the rate of population growth isn't the same all over the world. In fact, the U.N. says that 42 percent of the population on Earth is not replacing itself generation after generation -- 40 percent is and maybe a little bit more. And then there is another 18 percent that's rapidly growing.
What are these disparities about?
DENNIS DIMICK: So, what we see in large measure is, in northern latitude countries -- in fact, we're seeing -- across Europe and Japan, we're actually seeing a fertility rate -- that's the number of children born per women that reach childbearing age -- is actually less than replacement.
And so we are seeing aging populations across Europe and in Japan. So we don't have the young people coming into the society that do things like work and pay the taxes and help pay for the pensions, for example. And then in, largely in southern countries, for example, most of the largest potential growth we're going to see is in Africa and in Southern Asia, where the populations are getting younger.
HARI SREENIVASAN: Ms. Karam, what does it mean when we have these sort of lopsided societies, when certain countries are going to have much older populations without the young to support them?
AZZA KARAM: Well, it basically means what we're seeing evolve right now, which is migration patterns from the areas where there seems to be too many people, if one can say that, to areas where there is obviously a need for labor, because there is a serious shortage of that labor.
That is only one of many implications, which is this migration trend. You are also going to see different kinds of pressures being exerted by governments, unfortunately, on women to either try to encourage them to have more children.
But what is infinitely more effective, I think -- and that's one of the reasons why the United Nations Population Fund has been leading a 7 Billion Actions campaign globally -- what is a great deal more effective is to show how women can become very important agents of change in their societies.
But in order to do so, they need access to good health care, access to education, equitable access to all kinds of resources. But we also know that investing in health care, especially maternal health and education about sexuality and reproductive health, can be -- can save lives and it can save a great deal of money.
So it's very cost-effective to do this.
HARI SREENIVASAN: Dennis, on your site, there's a story that says a baby born today in the U.S. or perhaps in a Western nation has a 50/50 chance of living to be 100 years old.
What sorts of resource strains -- or what sorts of resources do we have to have to sustain a population that can live that long?
DENNIS DIMICK: Well, I think that's one point that we have tried to make in our series, also, is that this discussion of population is really not just about numbers of people, but it's also the resources that each of us use.
And if you look in the United States, for example, we use many, many times much more resources per person than say a person in Bangladesh or other country that doesn't have advantage of, say, things like electricity. A quarter of the world's population doesn't even have electricity, like we take advantage of every day.
HARI SREENIVASAN: Ms. Karam, what are those correlations that you're seeing between the levels of education for a woman and the population growth in those countries?
AZZA KARAM: Well, we know for a fact that the statistics indicate that women who have more access to population and who are better educated are actually women who choose to have smaller families, certainly smaller compared to generations before them.
So there is a very strong correlation between education and choosing or the ability to make choices about the size and the number of our families. But there's an even more important point I think that we have to make, which is that, effectively, there are over 200 million women who would want to have access to family planning facilities and care and who cannot have that access.
And one of the things that the United Nations Population Fund and many partners around the world is engaging in is trying to ensure that there is an awareness that we have to make sure that not only knowledge and education, but also access and information about family planning and reproductive health care and access to services, all manner of reproductive health services, needs to be made available for women around the world and for families.
HARI SREENIVASAN: All right.
Azza Karam from the United Nations Population Fund and Dennis Dimick from National Geographic magazine, thanks so much for your time.
DENNIS DIMICK: Thank you.
AZZA KARAM: Thank you.