Bongaarts: 7 billion and counting . . .

John Bongaarts is vice president and distinguished scholar at the Population Council, an international nonprofit research organization based in Manhattan.

The arrival of the 7 billionth human on the planet -- projected to happen sometime on Oct. 31 -- presents a rare moment to reflect on the slow but relentless demographic trends that shape our lives and environment. The fact that we've managed to add 4 billion people to the world since 1960 without a complete breakdown of our natural environment is a tribute to human ingenuity.

World population is expected to rise to 9.3 billion by 2050, and nearly all this growth will occur in the poorest regions of the world. Nearly half the world's population still lives on less than $2 a day. Inequality between the poor and rich has reached unprecedented levels.

Prospects are grimmest for those poor countries that have limited natural resources and extremely rapid population growth. Over the next four decades, sub-Saharan Africa is expected to add more than a billion to its current population of 856 million. Consider Niger. Even the small amount of arable land remaining there is threatened by desertification. The country's current population lives on the edge of famine.

Yet by 2050, Niger's population is projected to more than triple in size -- from 16 million now to 58 million. If left unaided, Niger and many of the other poorest countries like it face a dismal future.

Signs of environmental stress from population growth and the consumption of the world's resources are becoming more and more evident. Food prices worldwide are increasing. People fear that expanding human numbers are outstripping the planet's ability to sustain us. Although the recent price spikes are partially the result of short-term factors -- droughts, floods, speculative investing, low reserves and hoarding -- prices are likely to remain high. And while higher food prices will have a negative effects everywhere, they will have a particularly severe impact on the poor, who already spend a large part of their incomes on sustenance and will be forced to spend even more.

The ability to grow more food worldwide is limited by our natural environment. On much of the planet, the most productive land is already being used for agriculture or it's covered by artificial structures. The best river sites have been dammed, and technological advances in agricultural production have already been heavily exploited. Energy prices are rising.

Energy is an integral part of every step in the food production system -- cultivation, harvesting, transportation, refrigeration, packaging and distribution. Food production can be increased by cultivating more land, investing in agricultural technology, and subsidizing fertilizer, pesticides and water. But these approaches come with high environmental costs: deforestation, exhaustion of fresh water resources, soil erosion and pollution. Agriculture is among the most destructive of human activities, and its impact will become more severe over time.

What can be done to prevent a such a bleak future? Fortunately, there are solutions that are both desirable and attainable. Family planning programs that provide women with a choice of contraceptive methods, information about their use and good-quality care are one solution.

Of the 186 million annual pregnancies in Asia, Latin America and Africa combined, 75 million are unintended. With those comes a greater incidence of detrimental health and economic effects for women and their families. Not only can unintended pregnancy and birth be harmful to mother and child, they often trap women in a cycle of poverty in which they are unable to educate or support themselves or provide for their children.

More than 100 million women around the world do not want to get pregnant, yet they are not using contraception -- they either lack knowledge of the methods available, have limited access to supplies and services, fear the side effects of contraception, or have husbands who oppose it. Poor and uneducated women are the most affected by these obstacles, which is why they have more unplanned pregnancies than their wealthier and educated counterparts.

Family planning programs -- which can alleviate these obstacles, reduce unintended pregnancies and save women's lives -- are most effective where socioeconomic conditions and education levels are improving. In fact, educating girls is a powerful way to reduce birthrates.

Educated women are more valued, desire a lower-than-average-sized family (in part because the costs of childbearing, in terms of economic opportunity and advancement, are higher for these women), and are more capable of overcoming the obstacles to using family planning. They also can better understand family-planning literature, and have better chances of getting wage-paying jobs.

Governments and international organizations recognize the multiple benefits of family planning and girls' education for health, poverty reduction and the environment. The Obama administration has sharply increased funding for international family planning activities, and the World Bank is implementing a major new Reproductive Health Action Plan. These efforts can substantially increase access to quality family planning services. Few decisions are more personal or important than choosing when and how many children to have.

Smaller families have a beneficial impact on human welfare and the environment. The birth of the world's 7 billionth person is a stark reminder that powerful demographic forces threaten our future. Prompt, substantial investments in family planning and education for girls offer an opportunity to work toward a brighter tomorrow for the Earth's poorest populations.