One of the most influential writers on the topic of balance of population and resources was Thomas Malthus. Malthus believed that throughout history a segment of every human population seemed doomed to poverty. He explains in his An Essay on the Principle of Population, that population growth generally preceded expansion of the population’s resources, in particular the primary resource of food because population, if unchecked, increases at a geometric rate (i.e. 1, 2, 4, 8, 16, etc.), whereas the food-supply grows at an arithmetic rate (i.e. 1, 2, 3, 4, 5 etc.). Fortunately, most of Malthus’s predictions have been proven wrong by the world’s ingenuity (Wikipedia, 2008).
Historical World Population
When viewed against human history, population growth is a fairly recent phenomenon (see Figure 1). Prior to 1 AD, the world’s population growth was very slow with most estimates showing population in 1 AD around 300 million. From 1 AD it took about 1600 years for the world’s population to double to 600 million. By 1750, estimates show the population had grown to about 800 million people. In 1800 the estimated population grew to 1 billion people resulting in a doubling rate of approximately 200 years. Since 1750, the world’s population has grown at an unprecedented rate. In 1900 the world’s population estimate was 1.7 billion people, nearly doubling the population just 100 years earlier (Raleigh, 1999).
Prior to 1750 high birth rates were tempered by relatively high death rates with occasional catastrophic death rates from war, famines, and infectious diseases. Infectious diseases such as bubonic plague and tuberculosis took a serious toll on Europe’s population between the 6th and 14th centuries. When the bubonic plague struck England in 1348, the countries population dropped 20 percent in just three years. During this period England’s life expectancy of over 30 years dropped to just 18 years. Population growth in Europe was also controlled through self imposed social restrictions on procreation as a response to the availability of economic resources (Raleigh, 1999).
Europe finally broke the demographic stalemate in the mid 18th century when they ended the near equilibrium birth and death rates. The disappearance of some of the great killer diseases resulted in greater longevity and thus higher populations. Improved health measures, medical advances, improved sanitation, personal hygiene, and living standards throughout the 9th century brought even greater longevity. Improved longevity was countered by a desire for smaller families and the growing use of abortion and contraception (Raleigh, 1999).
Although the demographic transition to what is typical in developed countries (long-living family with limited number of children) took nearly two centuries, the transition in developing countries has occurred over just the last 50 years as advanced public health and prevention technologies have been shared world-wide. Although fertility declines have occurred in developing countries they have been slower than the population gains through greater longevity, resulting in tremendous population growth over the past two centuries. By 1900 the world’s population took 65 years to double; by 1930 the doubling rate was 45 years; and by 1960, the doubling rate was 40 years. In the year 2000, there were an estimated 6 billion people on the earth, the last 50 years of which saw more population added to the earth than in the whole known history of the world to that point (Raleigh, 1999).
Current World Population
According to the United Nations, the world’s population growth peaked in the 1980’s with small declines in growth occurring throughout the 1990’s. But even with those declines, the world adds approximately 78 million people to the population every year. Until the 1970’s the fertility rate was fairly constant at 5 births per woman. The fertility rate has fallen drastically since then with the current fertility rate of approximately 3 births per woman. Although all high fertility countries fertility rates are declining they still vary from 1.2 births per woman in some European countries to over 6 for some African women (United Nations, 2007).
Globally, 132 million babies are born each year and 52 million people die, approximately 20 percent of which are ages 5 and younger. According to the World Health Organization, about one-third of deaths are due to infectious and parasitic diseases, one-third are due to circulatory diseases, and 12% are due to cancer (Raleigh, 1999).
Projected World Growth
Although fertility rates have declined over prior decades, the high fertility rates of the past have resulted in a large population that has entered the reproductive years of their lives. Because of this large population, the number of births world-wide is not expected to decline until approximately 2025 resulting in unavoidable growth throughout the next 50 years. The future fertility rate will then determine the world’s population growth (Raleigh, 1999).
There are five main sources of projected world population growth. The United Nations Population Division produces the most widely used compilation of current and past estimates of population size, age structure, and birth and death rates. The United States Census Bureau produces its own baseline data, although its estimates are not completely independent from those of the UN. A third source, the International Institute for Applied Systems Analysis (IIASA) uses baseline data on population size, total fertility rates, and life expectancies from the Population Reference Bureau. The fourth source, the Population Reference Bureau bases its estimates on the work of the UN, and independent consideration of other sources including official country statistics, the Council of Europe, and the U.S. Census Bureau. The fifth source is the World Bank, whose projections are generally used for planning and managing projects. Even though each of these organizations uses slightly different methodologies, makes different assumptions about future demographic trends, and begins with slightly different estimates of current population size their population projections fall within a relatively small band for the next 50 years (see FigureÂ 2) (Population Reference Bureau, 2001)
Figure 3 shows a summary of global population projections from three of the major sources. The middle or “most likely” scenarios from the UN, IIASA, and the U.S. Census Bureau are similar that they differ by about 10% in 2050 and 9% in 2100. The UN projects the least amount of growth, reaching approximately 8.9 billion in 2050. IIASA projects the most growth, reaching approximately 9.9 billion in the same year. The USCB projects a population of approximately 9.3 billion in 2050. The 2100 population projections follow a similar pattern with IIASA projecting a global population declining 10.4 billion in 2100 after peaking in 2080. The UN projects a smaller population of approximately 9.5 billion in 2100, but one that is still growing slowly (O’Neill, 2001).
It is obvious from looking at Figure 3 that each of these organizations uses different assumptions in their scenarios. Primary assumptions that are used in each of these organizations’ projections include birth rate, death rate, and demographic transition (migration) scenarios. In developing countries, the primary driver of the projections is the fertility or birth rate. Since fertility rates are currently higher in developing countries than they are in developed countries a big decline in fertility rates in developing countries can have a drastic impact on the resulting population estimate. Migration is a primary driver in scenarios with more developed countries since birth and death rates nearly cancel each other out (O’Neill, 2001).
Projections of global population growth differ less between the different institutions than do projections at the country level. Differences in assumptions and results at the country and region level often cancel each other when aggregated to global levels. In some cases, agreement in projections of population size masks large differences in underlying assumptions with offsetting effects, such as a scenario in a region with high fertility rate and high death rate and a competing scenario with a low fertility rate and a low death rate (O’Neill, 2001).
One of the major diseases that will likely impact population growth models over the next several decades is HIV/AIDS. Although the disease isn’t of the same scale as some of the pre-industrial age diseases, it is having a huge impact on mortality in some regions of the world. Of the 52 million deaths that occur each year, approximately 2.1 million are from AIDS. USAIDS estimates that 33.2 million people with HIV and 2.5 million new cases every year. Since the disease impacts people in the prime of their reproductive life and has such a large impact in some regions of the world most models attempt to account for this disease (UNAIDS, 2007).
One of the biggest results of the population growth is simply that there will be a larger population that needs a place to live and food to eat.
Another result is the continued trend toward increasing urbanization. The UN projects that nearly all of the population growth will occur in urban areas with the number of urban dwellers expecting to pass rural dwellers in 2008. In the next couple of decades the number of rural dwellers is expecting to start declining (United Nations, 2007).
There will also be a higher concentration of people in less developed countries. Nearly half of the babies born into the world are born in only six countries India (22%), China (11%), Pakistan (4%), Nigeria (4%), Indonesia (4%) and Bangladesh (3%) (Chamie, 2005).
By 2050, the populations of over 50 countries are expected to decline, including some well developed countries. The three largest countries projected to loose people (Russian Federation, Ukraine, and Japan) are expected to decline by a combined 67 million people (Chamie, 2005).
It is projected that by 2050, every major region of the world, except Africa, will be at or below replacement fertility rate of 2.1 children per woman. Today, 65 countries, accounting for 43% of world population, have fertility rates at or below the replacement level. As a result, many countries are concerned about population decline and ageing, as well as the social, economic and cultural consequences of very low fertility (Chamie, 2005).
With the exception of sub-Saharan Africa mortality rates and longevity are expected to continue to increase with global life expectancy for those born in 2050 to be about 76 years (Chamie, 2005).
As people live longer the population will include more people over the age of 65. It is estimated that by 2050 the percentage of the population over will 65 will double from the present 7 percent to about 15 percent. Population ageing raises serious questions about the financial viability of pension and health care systems for the elderly (Chamie, 2005).
The more developed countries will continue to be net receivers of international immigrants with an estimated 2 million immigrants per year for the next 50 years. This brain drain of the most educated people in the less developed countries will increase the challenges of developmental efforts in the less developed countries (Chamie, 2005).
As the changing world population continues to increase so will the demand for food. As less developed countries become more developed and peoples’ incomes increase either in their country of birth or the country they have migrated to they will demand more food and more calories forcing our world’s resources to be spread among an additional 2 to 3 billion people. As this occurs, the topic of food security will once again be at the forefront of many conversations.
Chamie, J. 2005. 21st century demographics: highs and lows. The globalist, Jul 14, 2005. [Online]. Available at http://www.theglobalist.com/DBWeb/StoryId.aspx?StoryId=4629
O’Neill, B.C, D. Balk, M. Brickman, and M. Ezra. 2001. A guide to global population projections. Demographic research, Vol. 4. Art. 8. [Online]. Available at http://www.demographic-research.org/volumes/vol4/8/.
Population Reference Bureau. 2001. Understanding and using population projections. [Online]. Available at http://www.prb.org/pdf/UnderStndPopProj_Eng.pdf.
Raleigh, V.S. 1999. Trends in world population: how will the millennium compare with the past? Human reproduction update 1999, Vol. 5, No.5p. 500-505. [Online]. Available at http://humupd.oxfordjournals.org/cgi/reprint/5/5/500.pdf.
UNAIDS. 2007. Aids epidemic update: December 2007. New York. [Online]. Available at http://data.unaids.org/pub/EPISlides/2007/2007_epiupdate_en.pdf
United Nations. 2007. World population prospects: The 2006 revision. United Nations Secretariat, Department of Economic and Social Affairs, Population Division, New York. [Online]. Available at http://www.un.org/esa/population/publications/wpp2006/English.pdf
Wikipedia contributors. 2008. “Thomas Malthus,” Wikipedia, the free encyclopedia. [Online]. Available at http://en.wikipedia.org/w/index.php?title=Thomas_Malthus&oldid=194307261.