Pandora wrote: It is estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960.[66] Thereafter, the global population reached four billion in 1974, five billion in 1987, six billion in 1999 and, according to the United States Census Bureau, seven billion in March 2012.
[67] The United Nations, however, estimated that the world population reached seven billion in October 2011
In
demographics, the
world population is the total number of
humans currently living, and was estimated to have reached 7.7
billion people as of April 2019.
[2] It took over 200,000 years of
human history for the world's population to reach 1 billion,
[3] and only 200 years more to reach 7 billion.
[4] The world population has experienced continuous growth following the Great Famine of 1315–1317 and the end of the Black Death in 1350, when it was near 370 million.[5] The highest global population growth rates, with increases of over 1.8% per year, occurred between 1955 and 1975—peaking to 2.1% between 1965 and 1970.[6] The growth rate declined to 1.2% between 2010 and 2015 and is projected to decline further in the course of the 21st century.[6] However, the global population is still increasing[7] and is projected to reach about 10 billion in 2050 and more than 11 billion in 2100.[8]
According to current projections, the global population will reach eight billion by 2024, and is likely to reach around nine billion by 2042. Alternative scenarios for 2050 range from a low of 7.4 billion to a high of more than 10.6 billion.[71] Projected figures vary depending on underlying statistical assumptions and the variables used in projection calculations, especially the fertility variable.
Long-range predictions to 2150 range from a population decline to 3.2 billion in the "low scenario", to "high scenarios" of 24.8 billion.[71] One extreme scenario predicted a massive increase to 256 billion by 2150, assuming the global fertility rate remained at its 1995 level of 3.04 children per woman; however, by 2010 the global fertility rate had declined to 2.52
Interesting projections of 7.4B on the low side to 10.6B on the high side for 2050 and then a low of 3.2B(?) to a high of 24.8B in 2150 -- another 100 years later. An extreme guesser went with 250B on the high side. None of the assumptions are given to rationalize any of these numbers but there is definitely a wide spread.