World PopulationFSEC home page
(borrowed from Florida Solar Energy Centre)
 http://www.fsec.ucf.edu/ed/eie/population.htm

There are currently over 6 billion people living on our earth. That is more people than ever in the history of our planet. This is an enormous number of people for our planet to feed. In fact, 700 to 800 million people don't get enough food to support normal daily activities, and roughly 10 million people die each year from starvation. Moreover, today the world's birth rate is almost three times its death rate, meaning in representational terms, that the earth's population increases the equivalent of a New York City every month. And if the current rate continues, the world's population will double in 51 years.

How did we get here?
Approximately 12,000 years ago, several cultures shifted from hunting and gathering to farming. As humans learned to control their food supply, steady population growth began, just as would be expected--in the absence of limiting factors, all biological populations expand to the limit of their food supply. The development of agriculture led by turns to settlement, division of labor, mathematics, literacy and science. In the 1800s, advances in medicine, nutrition and infant mortality rates led to longer life spans. At the same time that life expectancy was rising, improvements in agricultural and food preservation techniques led to greater increases in food production and availability. Human numbers began increasing at an astonishing rate. It had taken humanity four million years to build a population of two billion people; the second two billion people took forty-six years, and the third two billion people were born in the next twenty-two years.

Earth's Carrying Capacity
Earth's basic carrying capacity refers to the greatest number of living species (including humans) that can be supported in an area given its environmental conditions. For example, to raise one cow requires one acre of rich pastureland or ten acres of scrub-land. Earth's human biophysical carrying capacity is the maximum human population size that the Earth can support in the long term using our technological capabilities, without degrading the environment.
 

Overpopulation occurs when people (or organisms) become so numerous that they degrade the ability of the environment to support their kind in the future. Symptoms of human overpopulation include such things as when soil is allowed to erode faster than new soil can be generated, draining aquifers faster than they can be recharged, or exterminating populations and species that are working parts of the ecosystems that support agriculture and fisheries. At the present time no nation on earth is supporting its present population on its own sustainable flow of renewable resources.

Demographic Momentum
In the United States there is a feeling that the population growth problem under control, since our fertility rate (the average number of children born to a woman in her lifetime) has decreased to 2.1. However, zero population growth can only be achieved when the percentage of elderly people is equal to the percentage at child bearing age, and even when that equilibrium occurs, it will take another 60 - 70 years for the population to stabilize, during which time the population will still continue to increase. Demographic momentum is the term used to describe this tendency of a previously growing population to keep expanding long after reproductive rates have been reduced. In the United States population will stabilize only when the numbers of births plus immigrants equals the number of deaths plus emigrants. It is not clear when, or even if, that will occur. Currently at 275 million, the United States is the third most populous country in the world and is growing by more than 2.5 million people each year. According to modest projections by the U.S. Bureau of the Census, the U.S. population could grow by 130 million Americans by 2050.

Population Timeline

Year
Event
World Population
10,000 BC End of the last Ice Age; humans lived as hunters and gatherers
4,000,000
 8000 Agricultural Revolution; domestication of plants and animals
4,500,000
 3000 Bronze Age begins; use of weapons and sailing ships
14,000,000
 1500 Iron Age begins
38,000,000
      1 AD
 Farmed land is producing 50 times more than unfarmed land
170,000,000
   700 Population explosion in China, first large urban developments
210,000,000
 1233 Coal mined in Newcastle, England
360,000,000
 1400 Bubonic Plague; in a period of about five years, one-fifth of the world's population (75 million) people are lost to this disease.
350,000,000
 1492 Europeans discover Americas
425,000,000
 1750 Industrial Revolution begins in Europe
760,000,000
 1800 Beginning of the Industrial Revolution in the United States
900,000,000
 1830 Advances in food production, water supply, sanitation,
transportation and disease control results in population expansion
1,000,000,000
 1930 Despite loses from World War I, population passes 2 billion
2,000,000,000
 1960 Medical advances contribute to population surpassing 3 billion
3,000,000,000
 1975 Population Explosion!
4,000,000,000
 1987  
5,000,000,000
 1999  
6,000,000,000

Resources

Demographic, Environmental & Security Issues Project - Animated map of world population, 1 A.D. to 2020 A.D.

Facing the Future Organization - Population Matters; site covers historical context of population growth, as well as environmental impact. Teacher materials available to download.

Museum of Natural History, France - Dozens of interactive questions covering population figures, fertility & death rates, and environmental resources, as well as a current population counter.

Population Action International - Student friendly site includes maps of major resource distribution.

Population Reference Bureau - Includes current reports, news and census data.

PBS - Paul Erlich and the Population Bomb - Site describes the current population growth problem.

World Book - People and the Planet - Discusses population growth and its effect on our environment.

Zero Population Growth - Site includes teacher and student resources.

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