Population Bulletin: The World at 7 Billion

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This article is the introduction to Population Bulletin: The World At 7 Billion

(July 2011) Even though the world population growth rate has slowed from 2.1 percent per year in the late 1960s to 1.2 percent today, the size of the world's population has continued to increase—from 5 billion in 1987 to 6 billion in 1999, and to 7 billion in 2011.

The sixth billion and seventh billion were each added in record time—only 12 years. If the 2.1 percent growth rate from the 1960s had held steady, world population would be 8.7 billion today. It is entirely possible that the 8th billion will be added in 12 years as well, placing us squarely in the middle of history's most rapid population expansion.

This prospect seems to run counter to the prevailing belief that concern over population growth is a thing of the past, and that today's "population problem" is that birth rates are too low, not too high. In fact, there is some truth to that notion, depending on the region or country one is talking about. Today, most population growth is concentrated in the world's poorest countries—and within the poorest regions of those countries.

Figure 1
World Population Growth

Source: United Nations Population Division, World Population Prospects: The 2010 Revision, medium variant (2011).

The decrease in the world growth rate since the 1960s resulted from the realization on the part of some developing country governments and donors about unprecedented rates of population growth. It took all of human history to reach a world population of 1.6 billion at the beginning of the 20th century. Just one hundred years later, in 2000, the population total had reached 6.1 billion. How did this sudden, momentous change come about? To understand this change, we must first consider the demographic transition—the shifts in birth and death rates that historically have occurred over long periods of time. And then we must look at how very differently the transition has taken place in the world's developed and developing countries.

The transition describes two trends: the decline in birth rates as the need or desire for larger numbers of children diminished, and the decline in death rates as public health initiatives and modern medicine lengthened life.

In today's developed countries, this transition took many centuries, but in today's developing countries the changes are taking place in mere decades. In developed countries, birth and death rates tended to decline in parallel. Economies and societies changed during that time: Fewer families stayed on farms and the Industrial Revolution changed the way people lived and worked. But the transition's pace was still slow. In Sweden, for example, the slowly declining death and birth rates produced a population growth rate that has remained fairly stable over the past 250 years, rarely exceeding 1 percent per year.

In developing countries during the 20th century, major improvements in public health, the practice of modern medicine, and immunization campaigns spread quickly, particularly after World War II. Death rates dropped while birth rates stayed high. In Sri Lanka, infant mortality (under age 1) in the early 1950s is estimated to have been about 105 deaths per 1,000 live births. By the 1990s, the rate had dropped dramatically to below 20, due in large part to basic public health interventions such as immunizations, oral rehydration therapy, and birth spacing—all of which have contributed to lower rates of infant and child mortality.

With health conditions improving so rapidly, birth rates in developing countries did not have time to change as they did in Europe. This lag between the drop in death rates and the drop in birth rates produced unprecedented levels of population growth. In Kenya, infant mortality declined first—contributing to a rise in life expectancy at birth from about 42 years in the early 1950s to 56 years in the late 1970s—before fertility began a decline from the then-prevalent eight children per woman. During that same period, Kenya's annual population growth rate approached an unheard-of 4 percent. In the early 1950s, Pakistan had a life expectancy of 41 years and an average fertility rate of 6.6 children per woman. It was not until the early 1980s, when life expectancy had reached 59 years—due in large part to reductions in infant and child deaths—that Pakistan's fertility began to decrease and its population growth rate began to slow. These lengthy growth spurts resulted in the relatively new phenomenon of government policies aimed at lowering birth rates. Some governments, such as Indonesia and Thailand, were quite successful in lowering birth rates; many other governments have not been.

In addition to policies, social norms also contribute to how a country moves through the demographic transition. Although at times these norms conflict with public policies and programs, cultural factors such as age at marriage, desired family size, and gender roles all have a strong influence on fertility behavior.

Figure 2
The Classic Phases of the Demographic Transition

Notes: Natural increase or decrease is the difference between the numbers of births and deaths. The birth rate is the number of live births per 1,000 population in a given year. The death rate is the number of deaths per 1,000 population in a given year.

What might the future look like? It is fundamental to remember that all population projections, whether performed by a national statistical office, the United Nations, or the U.S. Census Bureau, are based on assumptions. Demographers make assumptions on the future course of the factors that determine population growth or decline: the birth rate and the death rate. When looking at projections, one needs to consider the assumptions before the results. In the case of developing countries, a typical assumption is that birth and death rates will follow the path of demographic transition from high birth and death rates to low ones—mirroring the transition as it played out in developed countries. But when, how, and whether that actually happens cannot be known. When considering a population projection for a developing country, several questions need to be posed. If fertility has not yet begun to decline significantly, when will it begin and why? This question would be appropriate for Niger and Uganda, whose fertility rates are still very high at 7.0 and 6.4, respectively. If fertility is declining, will it continue to do so or "stall" for a time at some lower level as it has in Jordan and Kenya? Finally, will a country's fertility really fall to as little as two children per woman or fewer, as is commonly expected?

This Population Bulletin looks at the four phases of the demographic transition as descriptive of past and future population growth. We highlight four countries to illustrate each phase and its implications for human well-being:

• Uganda (high birth rate, fluctuating death rate).
• Guatemala (declining birth and death rates).
• India (approaching replacement-level fertility).
• Germany (low or very low birth and death rates).