From Forest to Farmland and Meadow to Metropolis; or, When Did the Anthropocene Begin?

Did humans affect global climate before the Industrial Era? While this question is hotly debated, the co-evolution of humans and the natural environment since the last Ice Age had an undisputed role in influencing the development and present state of terrestrial ecosystems, many of which are highly valued today as economic, cultural, and ecological resources. Yet we still have a very incomplete picture of human-environment interactions over the last 21,000 years, both spatially and temporally. In order to address this problem, I have prepared a new synthesis of demographic, technological, and economic development over preindustrial time, and a database of historical urbanization covering the last 8000 years. These data are combined with a dynamic global vegetation model to quantify the magnitude and timing of global anthropogenic land cover change in the late Pleistocene and preindustrial Holocene. This integrated model is driven with paleoclimate from GCM scenarios and simulates global land cover and human land use change, fire, soil erosion, and emissions of CO2 and methane (CH4). My results highlight the importance of the long histories of both climate change and human demographic, economic, and technological history on the development of continental-scale landscapes. We emphasize the need for improved datasets that use historical and archaeological data synthesis and build on recent theory of preindustrial economic and technological change. A large source of uncertainty in our results comes from assumptions we make about the rates and timing of technologically driven intensification of land use, and the importance of international trade for the subsistence of preindustrial societies.