The book by Joel E. Cohen, “How Many People Can the Earth Support?” in Appendix 3 (p.402-18) lists many authors’ answers to that unanswerable question. Perhaps a better question would be, looking back from the distant future after humanity has passed on into oblivion, “What was the maximum population of humans the Earth ever achieved?” Ultimately, that will be a very specific number which in fact may be known at some time in the not to distant future by people now living, whereas the book’s title has a huge number of imponderable variables built into its  question which can never be answered even after the fact. It was a poor question from a scientific point of view. Below is a list of various authors attempts to put a number to that question. Numbers are in billions. The current world population is approximately 6.8 billion.

Minimum Maximum Author Year Comment
Billion ~ Billion ~ 13.4 Leeuwenhoek 1679 First known estimate
6.3 12.5 King 1695
4.~ 6.6 Sussmilch 1741
13.9 Sussmilch 1765
6.0 Ravenstein 1891
8.1 Fircks 1898
10.9 Pfaundler 1902
2.3 22.4 Ballod 1912
132.~ Knibbs 1917
5.2 Edward M. East 1924
2.~ Pearl & Reed 1924
6.- 12.~ Wickens 1925
7.7 15.9 Penck 1925
6.2 Fischer 1925
5.7 Warren D. Smith 1935
2.6 Pearl & Gould 1936
13.3 Hollstein 1940
5.6 13.3 Boerman 1940
.9 2.8 Pearson & Harper 1945
7.0 8.6 Mukerjee 1946
5.~ Salter 1946
6.5 10.~ Fawcett 1947
1.8 7.2 Spengler 1949
6.- 10~ C. Galton Darwin 1952
50.- Brown 1954
3.7 7.7 Brown, Bonner,W 1957
28.~ Clark 1958
30.~ Baade 1960
16.~ 800.- Kleiber 1961
10×10 raised 18 Fremlin 1964 Heat dissipation limit
10.~ Cepede 1964
30.~ Schmitt 1965
41.~ Zierhoffer 1966
47.~ 157.~ Clark 1967 Americans/Japanese
79.- 1,022.- De Wit 1967 Total usage
1.- Hulett 1970 American style
40.- 60.- Austin & Brewer 1971
0.5 1.2 Ehrlich 1971 Permanent & stable
35 40.~ Muckenhausen 1973
100.~ Lieth & Blaxter 1973
38.- 48.~ Revelle 1974
6.7 Buringh 1975
5.~ 7.~ Whittaker & Likens 1975
40.~ Revelle 1976
17 Eyre & Blaxter 1978
1,000.~ Marchetti 1978
14 Kovda 1980
4.5 Mann 1981
2.0 3.9 Westing 1981
12.~ Gates 1982
7.5 Gilland 1979
4.0 32.8 Higgins 1983
6.1 Ferrell, Sander, Vo 1984
300 Hardin 1986
22 Calvin  & Hudson 1986
9.8 19.3 Hudson 1989
2.8 5.5 Chen 1990
5.3 Raven 1991
7.7 Meadows 1992
23.8 Tuckwell & Koziol 1992
much less 5.5 Ehrlich 1993
12.- 14.~ Heilig 1993
10+ Waggoner 1994
3.~ Pimentel 1994
10.~ 11.~ Smil 1994
11.~ 44.~ Dutch Gov. 1994
11.6 Daily & Ehrlich 1992
~12.~ WikiAnswers 2008
2.0 Pimentel 1999 At American style
2.7 OPT 2008 Optimum Pop.

As you can see for yourself there is little agreement among these projections and that is why the question is flawed. If each of these researchers was asked “What is the maximum number the population the Earth would reach before retreating,” there would probably be a number much nearer Leeuwenhoek’s first prediction of 13.4 billion made back in 1697. He may have been looking through the first microscope but surely he had a reasonably clear distant vision also.

  1. See also:
  2. Population, Sustainability by Daily & Paul Ehrlich
  3. How Many People Should the Earth Support? by Ross McCluney
  4. Wikipedia article on – Overpopulation
  5. World Prout Assembly gives a generalized smoothed version.
  6. https://i1.wp.com/www.worldproutassembly.org/population-1.jpgThe chart above seems to indicate that the population will smoothly top out in 2040 and then smoothly drop back to a more sustainable number. This scenario would be possible if every person on the planet was reasonable but my modest experience has led to believe the exact opposite it closer to the truth.
  7. Doomsday chart

    Doomsday population crash with food shortfall as a precursor

    Probaway’s Doomdsay chart above doesn’t predict an exact day for Doomsday or an exact population when that day comes but it does imply that the Earth’s population will be very near its maximum when that day does arrive.

  8. World population (UN).svg

Pick a number, any number at all from 0 to 1,000,000,000,000,000,000 for the maximum number that the Earth will support and there will be a scholarly supporter for that number. This is especially true if you fund a univiersity chair for that scholar.

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