Social scientists who study population dynamics (demographers) estimate that at the time of Christ there were no more than 250 million people in the world, about 57 million fewer individuals than reside in the United States today.
It took approximately 1,650 years for global population to double to 500 million and only another 150 years to reach one billion in 1800. The second billion was added in 130 years (1930), the third billion in 30 years (1960), the fourth billion in 15 years (1975), the fifth billion in 12 years (1987), the sixth billion in 12 more years (1999). With a mid-2010 global population estimate of 6.8 billion, world population will reach 7 billion by late 2011.
This incredible growth in global population invariably triggers two related questions. Why was population growth so slow for almost all of human history? And second, what forces are responsible for the unprecedented population growth that began in the early 20th century and escalated dramatically in the post-World War II era?
The demographic transition
The Demographic Transition Theory (DTT) was proposed in 1929 by the American demographer Warren Thompson, who witnessed the early stages of rapidly increasing global population, and later modified by Frank Notesien in 1945. According to these demographers, a nation's birth and death rates will change as it passes through the following stages:
Stage One lasted for almost all of human history and was characterized by high birth rates and almost equally high death rates. Birth rates were high because labor was a necessary and valued commodity in hunting-gathering and agricultural societies. Death rates (including high infant-mortality rates) were also high because of an overall low standard of living and lack of medical knowledge. Population growth during this period was low and extremely slow. However, because of high birth rates, Notesein referred to this stage as one of "high growth potential."
Stage Two was a period of "transitional growth" that began with the Industrial Revolution and had high birth rates and rapidly declining death rates. With advances in medicine, sanitation and nutrition, mortality rates (especially infant mortality) fell dramatically. It's imperative to understand that this period of explosive population growth is not a consequence of rising birth rates but of a sharp and unprecedented decline in death rates. Developing nations whose populations are still growing rapidly are "stuck" in this stage of the demographic transition.
In the latter part of the this second stage, fertility rates in the developed nations begin to "catch down" with mortality rates and rapid population growth slows as people gain both the desire and ability (effective methods of contraception) to control fertility. Demographer John Caldwell notes that in traditional, agrarian societies, "The flow of wealth is upward from children to parents and even grandparents, and high fertility is profitable, at least in the long run to parents." However, as nations begin to modernize and children become non-working, full time students, they are much more of an economic liability, and fertility begins to decline.
Stage Three is one of "incipient decline," with both low fertility and low mortality and, therefore, low/slow population growth. Contraceptive use is extensive, effective and increasingly acceptable. As women gain economic and political rights, their work and careers outside of the home complicates child rearing. Couples delay starting a family, often well into their 30s, and have fewer children as the cost of raising sons and daughters escalates. According to a recent U.S. Department of Agriculture Report, it costs $286,500 to raise the average American child today. And this figure does not include the cost of college or university training. Divorce rates increase dramatically as marital dissolution also functions to depress birth rates. According to the DTT, developed nations are in this "final," long-lasting stage of the demographic transition.
Although global population growth has declined from the post-World War II peak years of increase, there is a common misconception that the rapid expansion of the human species is over. This observation (or conclusion) is at odds with demographic reality. The highly regarded Population Reference Bureau (PRB) in Washington, D.C. estimates that world population will expand from 6.89 billion in 2010 to approximately 9.5 billion people in 2050. This projection assumes that the fertility level in the developing world of 2.7 children per woman (currently 4.8 children in Africa) will drop to the 1.7 fertility rate of women in the developed world. If this fertility decline in the world's poorest countries does not occur, global population will exceed 9.5 billion people in 2050 by tens of millions if not hundreds of millions of people.
Consider Africa, a continent of 1 billion people in 2010 (up from 133 million in 1900). The PRB estimates that Africa's population will double to just over 2 billion by the year 2050. (While the AIDS virus has slowed population growth in Africa, it has hardly stopped it.) The implications for this rate of growth are staggering as virtually the entire infrastructure of poor African nations will have to double over the next 40 years just to maintain the current level of widespread poverty. Today, almost 50 percent of the world's population lives on less than $2 a day, with a disproportionate number of these impoverished individuals residing in Sub-Saharan Africa. One can only imagine what percentage of Africa's 2 billion people in 2050 will live in poverty.
While China's population is expected to increase from 1.34 billion people in 2010 to 1.437 billion in 2050, India will add 560 million people during this period (the present-day equivalent of the United States, France, Germany, the United Kingdom, Portugal and Canada) and far outdistance China as the world's most populous nation.
Keep in mind that this growth will occur in an era when fertility rates in the less-developed world are projected to decline. However, as a result of modern medicine and the control of numerous infectious diseases, death rates are declining even faster than birth rates. India's annual death rate is seven per 1,000 population; the comparable statistic in the United States is eight deaths annually per 1,000 population.
A major reason why India's death rate is so low is that it has a very young population (32 percent under age 15) and younger people have significantly lower death rates than older people. This very young population is also the key to understanding India's continuing high rate of population increase. In 15 years, India's current under-15 population, about 375 million people, will be between 15 and 30 years of age, the peak years of reproduction. If these individuals as a group have only 2.1 children per couple ("replacement level") they will contribute another 375 million people to India's population during that 15-year period. If India's current fertility rate of 2.6 children per woman does not decline, population growth in that nation will be even higher than current projections.
Rapid growth, big problems
Adding 2.6 billion people to the global population over the next 40 years can only exacerbate a host of existing global problems, including access to clean water. At 9.5 billion people in 2050, the world will have 38 times as many individuals as inhabited the planet at the time of Christ. While water is a renewable resource, it's not an expanding one. According to Food & Water Watch, 2 billion people currently live in "water stressed" areas, and 3 billion individuals have no running water within 1 kilometer of their homes.
As fresh water becomes increasingly scarce, tens of millions of people will be forced to migrate in search of this most precious resource. Numerous observers have noted that "water wars" will erupt in the more arid parts of the world. A United Nations Report states that by 2020, between 75 and 250 million people in Africa may be exposed to increased water stress as a consequence of global warming and that "conflicts will likely increase."
The Times of India reports that China and India currently face "massive water shortages," a situation that will grow more severe as the populations of these countries (especially India) increase. Quoting a study by an Indian research institute, the Times states that "in the next 20 years, the four countries in the Himalayan sub-region (India, Nepal, China, and Bangladesh) will face the depletion of almost 275 billion cubic meters of annual renewable water." This is more than the total amount of water now available in Nepal.
George J. Bryjak lives in Bloomingdale after teaching sociology for 24 years at the University of San Diego.