A sociometabolic reading of the Anthropocene: Modes of subsistence, population size and human impact on Earth

We search for a valid and quantifiable description of how and when humans acquired the ability to dominate major features of the Earth System. While common approaches seek to quantify the human impact upon the carbon cycle by identifying the area of land cleared by humans, our point of departure is different human modes of subsistence, and we base our analysis on their social metabolism, in particular their energy metabolism. As a starting point, we use Ehrlich's classical IPAT formula, and give it a specific interpretation: human impact on Earth = population size x affluence (interpreted as energy available per person) x technology - for each mode of subsistence. The overall impact (or rather human pressure) then equals the composite sum of these. We qualitatively describe the functional characteristics of hunter gatherers, agrarian and industrial modes of subsistence such as population dynamics, energy regime and the technologies by which they interact with their environment. In a 'toy' model, we translate these considerations into global numbers for the past millennia: we estimate the respective population sizes and affluence (energy), and finally also technology concerning its impact on the carbon cycle. We see a major historical dividing line around AD 1500: until then, human population growth and metabolic rates carry about equal weight in increasing human pressure on the environment approximately fivefold from the year AD 1 onwards. From then on, the overall pressure of humanity upon the Earth increases by one order of magnitude; energy intensity contributes to this rise by roughly tripling the impact of population growth. Technology, because it is based upon a shift from biomass to fossil fuels (and other 'modern' energy carriers), does not moderate this impact, but enhances it by a factor of 1.5.