Fig. 2: Relationships between human population (millions) and key economic indicators.

Relationships between human population (millions) and key economic indicators: a rate of population growth (%/y), b energy consumption per capita (E in GJ/y/capita), c per capita productivity (P as GDP in 1990 international dollars, $/y/capita), and d P/E ratio, each across Holocene and Anthropocene epochs. Purple circle = 1850 CE; blue square = 1950 CE. A marked change in GDP per capita after 1850 CE reflects the global spread of industrialization and technology. The rate of change in population sharply increases around 1950 CE. The P/E ratio fell for most of the Holocene, until 1850 CE, when human society became more productive per unit energy use. Data references are listed in Supplementary Online Material.