The population of the world will reach 7 billion on Oct. 31, the United Nations estimates, bringing to the forefront longstanding concerns about the effects of overpopulation.

The U.N. has also estimated what the world population will be in 2100. The low estimate projects it will decline to 6.2 billion by 2100, while the high estimate projects adding 1 billion people to the planet each decade, reaching 15.8 billion at the close of the century.

One of the driving factors in population growth, which will affect whether we reach the high or low estimate, is the world's birth rate. Much of the population growth over the next century is expected to take place in Africa, and public health experts say the continent's birth rate would be lower if women there want more access to family planning resources and education.

"Africa, between now and the end of the century, will add another 2.55 billion people and that is if we assume that the [birth rate] goes down," said Gerhard Heilig, a section chief in the United Nations Population Division.

In comparison, Asia, whose growth is driven in part by an already large population, is expected to increase by only 432 million over this century.

"Certainly, Africa should be a focal point of attention, because many countries still have very high rates of population growth," Heilig said.

Heilig said the U.N. revises its population growth estimates every two years, and one of the primary reasons its most recent estimate went up slightly is because the birth rate in Africa has not declined as much as expected.

Pregnancy & contraception

To be sure, its birth rate is not necessarily the only reason for Africa's surging population Heilig said some of the increase may be due to retroviral treatments extending the lives of people with HIV and AIDS (an estimated 22.5 million people in sub-Saharan Africa are HIV positive, according to U.N. statistics). But the birth rate concerns some, because many of the births may be unwanted.

"The area with the highest unmet need for family planning is in Africa," said Dr. Yves Bergevin, senior maternal health adviser for the United Nations Population Fund. "A third to a fifth of women of reproductive age would like to use family planning, but don't access it. That shows a gap, clearly, in the services of family planning."

Those services should focus on providing information, said Emily Frazier of the Population Media Center, a nonprofit organization that focuses on health education, including reproductive health.

"It's definitely not about telling people not to have more than one child," Frazier said. "Ultimately, people are going to do what they want to do." One educational program Frazier is involved in creates soap operas where characters benefit from better family planning.

With education, and available contraception, many of the world's women would choose to have fewer children, Frazier said. She pointed to a 2009 report from the Guttmacher Institute and the United Nations Population Fund, showing 215 million women worldwide say they would like to use contraception but are not able to do so. Education and access would likely alter the trend.

But Frazier said she is not optimistic. The Guttmacher report called for an increase in international funding of education and women's health services to $24.6 billion, from current levels of $11.8 billion. That amount would result in 53 million fewer unintended pregnancies globally, a drop of more than two-thirds, the report said. It would also reduce maternal deaths by two-thirds, from 356,000 to 105,000; cut newborn deaths in half, from 3.2 million to 1.5 million.

Bergevin said any aid would only be needed temporarily African countries, with growing economies, could likely provide the funding themselves after 10 to 20 years. Sustaining their current economic growth while reducing their population growth would heighten the economic benefits they see.

But the increased funding hasn't come.

"I think it's unlikely right now," Frazier said. "We've seen developed nations continue to reduce their funding for contraception and access to contraception and services."

The U.S. birth rate

While the United States does not have the same rate of unintended pregnancies as many developing nations (the projected U.S. population growth is fueled mostly by immigration both actual immigration and a higher birth rate in that population), people here consume much more in terms of goods and energy, so avoiding unintended pregnancies here is a concern as well, Frazier said.

A 2009 Oregon State University study found, for example, that the resources used by a baby born in the U.S. generate seven times the carbon emissions of a baby born in China.

In part for those reasons, Bergevin said, health and education need to go hand-in-hand.

"Health and education, as we have seen in Asia, [are the] key to sustainable human development."

Family planning programs need to be aimed at all socioeconomic classes, he said, as the poorest tend to be those with the most children.

Still, while the increasing population has worried some, it's unclear whether the growth will truly prove to be a negative for the world's poorest countries.

"We cannot say if this is a problem or not," Heilig said. "If you have a functioning economy, if you have a stable political system, if you have a good health system for the population, many countries can probably cope with the increase in population. If you don't have that...then of course these population numbers will be challenging for some of the countries."

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