Population numbers from the UN by Hania Zlotnik

According to population numbers released by the United Nations in May of 2011, Earth’s human population will cross the seven billion mark on October 31 of this year. EarthSky spoke to U.N. Population Division Director Hania Zlotnik. She said:

It’s impossible to tell with absolute certainty when that’s happening, but, according to the data we have now, that’s when it is.

In other words, these numbers are projections, not actual census data – which would be difficult or impossible to obtain. Zlotnik told us more. She said that, according to the latest U.N. projections, Earth’s population will hit 9.3 billion in the year 2050 – and 10.1 billion in the year 2100. She explained that most of the growth is expected to occur in developing countries. She said:

Most of sub-Saharan Africa is included there, but there are also several countries in Asia – including Pakistan and Afghanistan, and several in Latin America including Haiti and Bolivia.

She said that the U.N. and its agencies use population projections such as these to develop and fund a range of programs to address global challenges – for example, how everyone on Earth will be fed. According to the Food and Agriculture Organization of the U.N., there are already over one billion people in the world today who don’t get enough food to be healthy and lead an active life.

The U.N.’s population projections highlight an urgent need for effective family planning in the developing world, said Zlotnik. If population in developing countries rises at faster rates than projected, she said, the world could have more like 16 billion people by the end of the 21st century.

Zlotnik offered a number of clarifications about the numbers she presented. First, she said that that the U.N. population projections for 2050 are far more accurate than the population projections for 2100. She told us:

There’s a lot of uncertainty around the 10 billion projected for 2100. What we have tried to emphasize is that, going to 2050, everyone that’s going to be 40 and over has already been born. We already have information. But when we look 90 years into the future, most people are not yet there, so the uncertainty grows. Usually everyone focuses on the central path. Because it’s the number that tells you around where the number is going to vary.

For 2100, the “central path” number is 10.1 billion – a projected population of 10.1 billion, that is. But the U.N. has also provided a possible population range that goes from a low of 6 billion to a high of almost 16 billion. Zlotnik said:

But no single path has a greater probability of happening in the future than another path. And that is why we have tried to provide a range. It is a range where the only difference between one projection and another is one-half a child in fertility terms. Both the high-range variant and the low-range variant represent only one-half a child difference in fertility from the medium variant [the 2100 population projection of 10.1 billion]. So the differences in fertility range are relatively narrow, but they can result in huge difference in population size.

Zlotnik also clarified that birth rates in most of the world are dropping.

Forty-two percent of the world’s population are from countries below replacement fertility, that is, their generations are not replacing themselves. They are balancing the population towards decline.

Those are places like Europe and China. Zlotnik continued:

Another 40 percent of the population is living in countries with above-replacement fertility but not too high. And the projection is that that fertility will continue to decrease, and towards the end of the century will be declining, too. Those might be okay, because they might not be putting too much pressure on resources if they stop growing.

These are places like India, the United States, and Egypt.

But then we have 18 percent of the population of the world which are living in countries which are still very poor. And those have very high fertility. And the projection reduces their fertility, but relatively slowly. And that’s where most of the population growth occurs in the future.

This 18 percent is spread throughout Africa, Asia, and Central and Latin America. It’s not geographically determined, she said. It’s about limited development. She said there are ways to address the growing population in these countries. Zlotnik continued:

Fertility has been reduced in almost every country of the world … in some countries really fast: Brazil, Iran, Thailand, and definitely China. These countries have had a combination of policies that have helped reduce fertility. The one that is essential is to provide the means by which people can plan their families. But together with that, you have to have communication campaigns to show them it is acceptable and possible to plan their families.

And these campaigns have to have an element to help empower women. It’s also very important that the mortality of children declines. Because if families are having children and watching them die, they are likely to want to have more children to make sure that some of them survive to adulthood.

Reduction in child mortality is happening successfully, she said, in many parts of the world, as a result of various health campaigns, some of them affiliated with the U.N.’s millenium goals.

Listen to EarthSky’s 90-second interview with Zlotnik on newest U.N. population numbers (at top of page).