Energetic origins of the Anthropocene: modeling human abundance, distribution and energy use in space and time

The origin of global human ecological dominance is central to the Anthropocene. We use macroecological rules, species distribution modeling, and bioenergetics to quantify how a world of just hunter-gatherers would compare to other populations of land mammals and today's human population of more than 7.6 billion. Metabolic scaling suggests that hunter-gatherers, who were powered by biological metabolism of ~100 watts or ~2000 kcals/day/person, lived at densities below mammalian expectation (< 0.1 person/km ² ). Species distribution models using environmental drivers of environmental productivity, biodiversity, and infectious disease burdens predicts a global carrying capacity of hunter-gatherers to be ~12 million people. In contrast, modern humans now mostly residing in cities, occur at densities up to four orders of magnitude greater than hunter-gatherers and use up to ~10,000 watts per capita from calories and extra-metabolic energy such as fossil fuels. Our preliminary analyses suggest that humans living as hunter-gatherers were appropriating energy similar to other land mammal species, per unit area, as well as globally. Total modern human metabolic (biological) energy use is still within the distribution of total energy use by other mammals. The combined effects of population and per capita energy use now exceeds global energy use by any other species and is approaching the limits of net global primary productivity.