Fig 1.
Global population size through time.
The inset shows a period of sub-exponential growth in recent history. Data from [25].
Fig 2.
Relationship between energy use (W) and population size for the world, the United States, Sweden, and England and Wales through time.
The relationships are highly variable, but overall, the slopes are greater than one (that is, the exponent in the power-law function relating energy use to population size overall), indicating support for a positive feedback between population size and energy use. Lines with slopes of one (ε = 1) are shown as reference. The black lines show overall fits and gray shaded regions show 95% confidence intervals on the regression lines.
Fig 3.
The scaling parameter for ε has been highly variable through time.
Each panel shows the running mean of ε (slope of the regression of logE on logN, see methods) with a 19-year window smoothed over 20 years. The light brown bar shows the confidence range of mean slope over the entire time period. A. For the world, ε showed a pronounced shift from a little over 2 to 1 from the 1960’s to the 1980’s, with the beginning of this decline coinciding with the peak world population growth rate in 1963 [9]. B. For England and Wales, ε was highly variable, plummeting during the Little Ice Age and during World War I and the Oil Crises of the 1970s. C. Sweden showed an increase in ε after the Industrial Revolution but also showed a decline in ε during both world wars. D. The United States showed a steadily increasing e until about the 1960s when it showed a severe drop coinciding with the Oil Crises of the 1970s.
Fig 4.
Variation in the scaling parameter e increased as major socio-political events approached and during the Little Ice Age for England and Wales.
The world data set is not long enough to include in this analysis.