Synchronization of energy consumption by human societies throughout the Holocene

Abstract

We conduct a global comparison of the consumption of energy by human populations throughout the Holocene and statistically quantify coincident changes in the consumption of energy over space and time-an ecological phenomenon known as synchrony. When populations synchronize, adverse changes in ecosystems and social systems may cascade from society to society. Thus, to develop policies that favor the sustained use of resources, we must understand the processes that cause the synchrony of human populations. To date, it is not clear whether human societies display long-term synchrony or, if they do, the potential causes. Our analysis begins to fill this knowledge gap by quantifying the long-term synchrony of human societies, and we hypothesize that the synchrony of human populations results from (i) the creation of social ties that couple populations over smaller scales and (ii) much larger scale, globally convergent trajectories of cultural evolution toward more energy-consuming political economies with higher carrying capacities. Our results suggest that the process of globalization is a natural consequence of evolutionary trajectories that increase the carrying capacities of human societies.

Keywords: globalization; human ecology; radiocarbon; sustainability; synchrony.

Fig. 1.

A and B display the mean mutual information and percentage of significant pairwise mutual information values for calibrated radiocarbon ages. A mutual information value of zero indicates no shared information; higher values indicate a stronger relationship (more shared information between time series). Significance is calculated by constructing 1,000 null mutual information values for any two time series using a Markov process. If the actual mutual information value is higher than the 95th percentile of the 1,000 null mutual information values, we considered it significant. C and D display mean mutual information and percentage of significant mutual interactions for “raw radiocarbon ages.” Raw radiocarbon ages are ages that have not been transformed to a calendar date. The relationship between radiocarbon ages and calendar ages varies over time, in part, as the amount of solar energy hitting the earth changes the proportion of ¹⁴C in the atmosphere (see Data and Methods and SI Appendix, section 2 on the confounding effects of calibration). (E) The mean mutual information between solar and energy consumption records at different bin widths. Historic western Europe and Canada have an annual resolution. The number above each bar indicates the percent of significant pairwise mutual information values in that bin, and the number in parentheses is the percentage of simulated, randomly fluctuating radiocarbon records, once calibrated, that display significance with solar energy. Avg, average; n/a, not available.

Fig. 2.

(A) Boxplot of the pairwise mutual information values for 10-, 20-, and 30-y bins combined by continent (different vs. same). (B) Boxplot of the pairwise mutual information values among historical sequences. C and D display boxplots of Spearman’s correlations from the archaeological (C) and historical (D) records of energy consumption.