Population: 7 Billion

World Population Milestones
1 billion 1804 200,000 years
2 billion 1927 123 years
3 billion 1960 33 years
4 billion 1974 14 years
5 billion 1987 13 years
6 billion 1999 12 years
7 billion 2011 12 years
8 billion ????

On October 31, 2011, according to demographers, the earth’s human population crossed the 7 billion mark. It took only 12 years for the global population to increase from 6 billion in 1999—and only 12 years before that to increase from 5 billion. Compare that with the length of time it took for human population to jump from 1 billion in 1804 to 2 billion in 1927 (123 years). It is clear that we are experiencing a period of rapid population growth like the world has never before seen.

Because of population growth and the growing number of people joining the middle class, demanding more resource-intensive lifestyles, the natural systems that are necessary to our survival are being swiftly and severely disrupted. Rains that replenish lakes and aquifers and water crops are no longer reliable. Trees that once shielded us from flood waters and strong winds are gone, replaced by barren, dusty landscapes incapable of supporting life. Peak oil is in our past, threatening the agricultural systems that feed us and our livestock, not to mention our highly motorized way of life. Fish stocks are disappearing and the Great Pacific Garbage Patch is growing each day as our discarded waste is sucked in by the swirling gyre. And the challenges faced by wildlife around the world are even graver than those facing humans.

Many social problems are exacerbated by rapid population growth as well. It is very difficult for families to climb out of poverty when couples begin childbearing early and have more children than they can afford to educate. And to complete the cycle, less educated children tend to grow up and have their own large families. For example, in Angola, women with no education have 7.8 children on average, compared with 2.5 children for women with at least some secondary education.

Demographers project that world population will reach 8 billion between 2025 and 2040. The range is due to the unknown fertility rate of women over the next 15-30 years. If the current fertility rate continues, we’ll cross the 8 billion mark before 2025. If the fertility rate declines markedly and starting now, the population will stabilize and then begin to decline around mid-century.

To illustrate the dependability of population projections on fertility (the most important independent variable), let’s take this year’s milestone as an example. In 1999, when the world population reached 6 billion, the UN Population Division projected that world population would reach 7 billion in 2013. In reality, we’re getting there a full two years earlier. This means that fertility rates did not decline as quickly or as significantly as demographers projected they would.

The world total fertility rate (TFR) is currently 2.6. This is the average number of children a woman will have in her lifetime if current age-specific fertility rates hold steady. (Of course, TFR varies considerably from country to country, and even within countries. For example, the TFR in South Korea is 1.2; in Niger, it’s 7.4.) In the middle of the last century, the global TFR was nearly 5. By the middle of the 21st century, demographers project that the TFR could be anywhere from 1.54 to 3.24, accounting for the very wide range in population projections.

Researchers1 did a series of population projections based on three scenarios of fertility decline to replacement level (replacement level fertility is the number of children a woman must have in order to replace herself and her partner). In Niger, for example, the population is currently about 17 million. If the country were to reach replacement level fertility in 2020, the population would stabilize around 33 million in 2070. If replacement fertility weren’t reached until 2060, the population wouldn’t stabilize until 2110 and the peak figure would be 74 million. In other words, a delay in reaching replacement fertility could cause the eventual population of Niger to be more than twice what it would be if the fertility rate declined sooner.

Of course, for the TFR in places like Niger to drop toward replacement level, greater investments must be made toward universal access to family planning education, information, and services—including access to modern methods of contraception. The United States should meet its commitment stated at the 1994 Cairo International Conference on Population and Development, and “Double the Money” invested in voluntary family planning programs overseas. With a commitment of $1 billion, we would be well on our way to eliminating the “unmet need” for contraception that an estimated 215 million women around the world still face.

The bottom line: Family planning programs must be scaled up, and soon. There is no more time to waste. In population projections and outcomes, timing is everything.

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