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The current estimated world human population is 6,350,538,084 (July 2004 estimate is 6,379,157,361 *from the CIA World Fact Book 2004). This figure is deceptively precise, however, since there is no complete database on the world's population, and humans are constantly being born (at the rate of about 3 per second) and dying. However, it is clear that the world's population continues to grow, and at rates that are unprecedented prior to the 20th century.
By some estimates, there are now one billion young people in the world between the ages of 15 and 24.
The United Nations Population Fund designated
October 12, 1999 as the approximate day on which world population reached six billion. This was about 12 years after world population reached five billion, in 1987.(The term "billion" above is used to mean "thousand million", 109, rather than "million million" as used in some countries. See billion for details.)
The last 70 years of the 20th century saw the biggest increase in the world's population in human history. The following table shows when each billion milestone was met:
From the figures above, the world's population tripled in 72 years, and doubled in 38.
The UN estimated in 2000 that the world's population was then growing at the rate of 1.2 percent (or 77 million people) per year. This represents a decrease in the growth rate in 1990, mostly due to decreased birth rates.
Every year the world’s population gains about 75 million people, as of 2004.
The future growth of population is difficult to predict. Birth rates are declining slightly on average, but vary greatly between developed countries (where birth rates are often at or below replacement levels) and developing countries. Death rates can change unexpectedly due to disease, wars and catastrophes, or advances in medicine. The UN itself has issued multiple projections of future world population, based on different assumptions. Over the last 10 years, the UN has consistently revised its world population projections downward.
The current projections from the UN's Population Division, from their 2002 World Population Prospects database [1], are:
| Year | Population (billions) |
|---|---|
| 2010 | 6.8 |
| 2020 | 7.5 |
| 2030 | 8.1 |
| 2040 | 8.6 |
| 2050 | 8.9 |
Other projections of population growth predict that the world's population
will eventually crest, though it is uncertain exactly when or how. In some scenarios, the population will crest as early as the mid-21st century at under 10 billion, due to gradually decreasing birth rates.
In less optimistic scenarios, disasters triggered by a growing population's demand for scarce resources will cause a sudden population crash, or even a
Malthusian catastrophe. (See overpopulation for more details.)In 1798, Thomas Malthus predicted that population growth would eventually outrun food supply, resulting in catastrophe. In 1968 Paul R. EhrlichPaul Ralph Ehrlich (born May 29, 1932) is a Stanford University professor and a renowned entomologist specializing in Lepidoptera (butterflies). He is the author of the best-selling but controversial book The Population Bomb (published 1968) and other boo reignited this argument with his book The Population BombThe Population Bomb ( 1968) is a book written by Paul R. A best-selling work, it predicts disaster for humanity due to overpopulation and the "population explosion". In the 1970s and 1980s hundreds of millions of people will starve to death". See Malthusi, which helped give the issue significant mindshare throughout the 1960s and 1970s. The dire predictions of Ehrlich and other neo-Malthusians were vigourously challenged by a number of economists, notably Julian SimonJulian Lincoln Simon ( February 12, 1932 February 8, 1998) was professor of business administration at the University of Maryland and a Senior Fellow at the Cato Institute. He wrote many books and articles, mostly on economic subjects. He is best known fo.
More recently, some scholars have applied bayesian probabilityBayesianism is the philosophical tenet that the mathematical theory of probability applies to the degree of plausibility of statements, or to the degree of belief of rational agents in the truth of statements; when used with Bayes theorem, it then becomes to world population to argue that the end of humanity will come sooner than we usually think (see: Doomsday argumentThe Doomsday argument is a probabilistic argument that claims to predict the future lifetime of the human race given only an estimate of the total number of humans born so far. It was first proposed by the astrophysicist Brandon Carter in the 1980s and wa)