World population

Map of countries by population —showing the population of the People's Republic of China and India, the only two countries to have a Population greater than a billion. (See List of countries by population.)

The world population is the total number of humans alive on the planet Earth at a given time. According to estimates published by the United States Census BureauUnited States Census Bureau, the Earth's population reached 6.5 billion on Saturday, February 25,2006.Leonard, David. "World Population to reach 6.5 Billion on Saturday". February 24,2006. MSNBC In line with population projections, this figure continues to grow at rates that are unprecedented prior to the 20th century. By some estimates, there are now one billion people in the world between the ages of fifteen and twenty-four.

Rate of population increase

Population (est.) 10,000 BC – 2000 AD.

World population 1950â€"2000

The 20th century saw the biggest increase in the world's population in human history. The following table shows estimates of when each billion milestone was met:
* 1 billion was reached in 1802.
* 2 billion was reached 125 years later in 1927.
* 3 billion was reached 34 years later in 1961.
* 4 billion was reached 13 years later in 1974.
* 5 billion was reached 13 years later in 1987.
* 6 billion was reached 12 years later in 1999.

These numbers show that the world's population has tripled in 72 years, and doubled in 38 years up to the year 1999.

Increase rate 1950â€"2000

Some estimates say that the human population around AD 950 was 250 million and in 2027 will be 8 billion, and the world population doubled (or will double) in the following years (doubling times in parentheses):
* AD 950 (650) 1600 (202) 1802 (125) 1927 (47) 1974 (50) 2027.Yet other estimates (beginning with 375 million around year 1420) say:
* 1420 (300) 1720 (155) 1875 (86) 1961 (38) 1999.Note how, during the 2nd millennium, each doubling has taken roughly half as long as the previous doubling.

The UN estimated in 2000 that the world's population was then growing at the rate of 1.14% (or about 75 million people) per year [1]. This growth rate has been generally decreasing from its peak at 2.19% in 1963.

Forecast of world population

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 these projections downward.

Current projections by the UN's Population Division, based on the 2004 revision of the World Population Prospects database World population prospects: the 2004 revision population database, are as follows.

Year	Population (billions)
2010	6.8
2020	7.6
2030	8.2
2040	8.7
2050	8.9

Other projections of population growth predict that the world's populationwill 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 other scenarios, disasters triggered by the growing population's demand for scarce resources (e.g., peak oil) will eventually lead to a sudden population crash, or even aMalthusian catastrophe (also see overpopulation).

Doomsayers

In 1798, Thomas Malthus predicted that population growth would eventually outrun food supply, resulting in catastrophe. In 1968 Paul R. Ehrlich reignited this argument with his book The Population Bomb, which helped give the issue significant attention throughout the 1960s and 1970s. The dire predictions of Ehrlich and other neo-Malthusians were vigorously challenged by a number of economists, notably Julian Simon.

On the opposite end of the spectrum there are a number of doomsayers who argue that today's low fertility rates will have severe negative consequences: The Death of the West: How Dying Populations and Immigrant Invasions Imperil Our Country and Civilization (ISBN 0312302592), by Patrick Buchanan, The Empty Cradle: How Falling Birthrates Threaten World Prosperity (ISBN 0465050506), by Longman, and Fewer: How the New Demography of Depopulation Will Shape Our Future (ISBN 156663606X), by Wattenberg.

Child poverty has been linked to people having children before they have the means to care for them.

More recently, some scholars have put forward the Doomsday argument applying Bayesian probability to world population to argue that the end of humanity will come sooner than we usually think (owing to toxic waste rather than to food shortages).

Population distribution

Population by region, 2005

Population density map of the world in 1994; Observe the very high concentration along the Ganges, Yangtze and Yellow river basins, Western Europe, the Indonesian island of Java, and the United States' BosWash megalopolis.

Asia accounts for over 60% of the world population with almost 3.8 billion people. China and India alone comprise 20% and 16% respectively. Africa follows with 840 million people, 12% of the world population. Europe's 710 million people make up 11% of the world's population. North America is home to 514 million (8%), South America to 371 million (5.3%) and Oceania to roughly 60 million (.9%).