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How many people can the Earth sustain? It has varied tremendously from 3000 BCE’s 0.03 billion (30 million) to 2014 CE’s 7.1 billion. That’s roughly 237 times as many people now living as then, and that early date is after agriculture was several thousand years old. The population had grown to about 0.2 billion (200 million) by 1 CE and that’s 36 times as many people now as then. The population growth was roughly steady until about 1625 when it reached 0.5 billion (500 million), but then the land became able to support more and more people. For four thousand years growth was so slow, that what would have been almost imperceptible on any local level then became a population explosion that is easily experienced almost everywhere today. New houses are going up every day. Population went from 30 million in 3000 BCE to 300 million in 1000 CE; that’s a growth of ten times in four thousand years. But, going back from the 7.1 billion of the present to one tenth or 710 million, that is only to 1750, just before the American Revolution. Ten times growth in 260 years versus 4,000 years, and that means we are now living with a sustained growth rate 15 times faster than before.

We are presently experiencing a population explosion, and have grown up for generations expecting that to be a normal situation. It isn’t normal; normal for almost all species almost all the time is no population growth whatsoever over a period of a many generations. Normal is living in balance with the environment. When there are too many of a given species, their food supply is eaten up by the other members of their own species, because those other individuals can eat exactly the same foods. The population expands to the sustainable food supply and then, in a complex web of living things, stays fairly close to an optimum number.

I have created a graph showing this ongoing population explosion. It is based on professional demographers, Hyde, McEvedy and the UN’s works. I have simply drawn a line through their existing data points, smoothed it and tagged it to specific and easily remembered dates. These points are within the error limits of those professional demographers’ estimates of historical populations, and between their estimates.

World Population History smoothed

World population history estimates from United Nations, Hyde, McEvedy, and Probaway

The chart above demonstrates that my smoothed estimates are almost always within the estimates of the professional demographers. I have also drawn high and low limit lines that all known estimates are clearly within. The Probaway numbers are only estimates, as it is impossible to know precisely any of the data, but this presentation although it has precise numbers doesn’t imply precision. 200 million people at year 1 CE only means the actual population was somewhere near halfway between the 400 million high estimate and the 100 million low estimate. It is all soft estimates of very real but impossible to know facts.

World population history smoothed by Probaway

World population estimates smoothed with high and low error estimates.

World population 3000 BCE to 2025 CE

World population history 3000 BCE-2025 CE smoothed to easy to remember dates.

5000 ~ 0.005 ~ 5 million humans at 5000 BCE
4000 ~ 0.01
3000 ~ 0.02
2000 ~ 0.05
1000 ~ 0.1 ~ 100 million humans in 1000 BCE
1 CE ~ 0.2
1000 ~ 0.3
1626 ~ 0.5
1825 ~ 1. ~ One billion humans in 1825 CE
1925 ~ 2.
1975 ~ 4.
2000 ~ 6.
2025 ~ 8. ~ Eight billion humans in 2025 in eleven years ?

Note the world population approximately doubled each 1000 years from 5000 BCE to 1000 CE, but it doubled in only 50 years from 1925 to 1975. That is 20 time faster than that previous 6000 year period. We are still living in times of explosive growth. The growth of humanity is based on our being ever more capable of converting natural resources occurring in nature to creating food for our consumption.

At first it was human labor creating food by digging gardens with hand tools, then came draft animals pulling ever better plows, that coupled with ever improving quality of genetically domesticated crops getting more edible food from a given crop plant. With coal-driven steam power more human energy could be given to other things like building steam tractors could till the soil deeper; then came gas-powered machines that were cheaper and capable of other farming tasks, then came bigger and more efficient machines for doing the many tasks needed for the creation and preservation and transportation of food.

The problem looming for humanity is that nearly all of the growth since the 1600 take-off of population is powered by the use of stored energy sources, like coal, oil, gas, uranium, but these are one time use energy sources, when they are consumed they are gone forever, and there is a limited supply that will become scarce in a hundred years. Only the sun can last forever, in human terms, so ultimately we will have to generate our energy and derive our food more directly from the sun’s energy. If that proves difficult to do then the population must drop back to what can be done.

[Update September 30, 2014 – World Population history tweaked.]