Farming and population density

From Harvesting the Biosphere:

Half a million years ago, there were between 15,000 - 125,000 people, total. Today there are about 8bn. What changed? How we farm.

Human population Density (People/km^2)
min max
Foraging 0.01 1
Pastoralism 1 2
Shifting Cultivation 20 30
Traditional Farming 100 400
Modern Farming 400 1400
Smil, 2013. Note: all densities for foragers and pastoralists are per unit of exploited land; all densities for traditional and modern agriculture are per unit of arable land.
  • During the late Paleolithic, the climate was too cold and C02 levels too low for agriculture to develop.

  • As the climate warmed in the Neolithic, first pastoralism, and then agriculture took off.

  • The shift from foraging to pastoralism meant a 100x increase in the number of people that could be supported for the same amount of land.

  • Pastoralism also unlocked previously inaccessible energy stored in grassland. By grazing animals, then eating them, people could survive in places too arid for cropping.

  • Shifting cultivation produced between 6-30x the energy expended doing the farming.

  • Traditional agriculture hit its limit after 1850. It could not produce enough food for expanding populations, rapid industrialization and urbanization.

  • Before the discovery of the Haber process, soil replentishment was the major bottleneck. Nitrogen and phosphorus depletion in the soil limited crop yield and how often you could grow.

    • Slash and burn agriculture and crop rotation provided limited workarounds.
  • Modern agriculture (1900s-1950) has ratcheted up the people-per-land ratio even more. The Green Revolution, synthetic NPK fertilizer, industrial automation and new crop varieties are the driving forces. There are now 7.4bn of us.

Related: fundamental needs.