GC54C-01
A Millennium of Anthropogenic Land Cover Change and its Effects on Climate
Anthropogenic climate change is generally thought to have begun with the industrial revolution, when humans started to considerably alter the composition of the atmosphere by emissions from fossil fuels. Human impact on the environment, however, started much earlier: Thousands of years ago, land was already transformed for use in agriculture and livestock farming. It is recognized that anthropogenic land cover change at today's scale has a significant impact on local to global climate. Yet, the effects of pre-industrial land use are not well understood. A main obstacle is the lack of quantitative data on historic land use activity prior to AD~1700 and a detailed analysis of its effects on the surface energy balance and the carbon cycle. This contribution presents advancements in both aspects. First, we present a simple method that consistently estimates the extent of crop and pasture areas for AD~800 to 1700 on a geographically explicit scale based on population data. Published land use data are used from AD~1700 until present. Uncertainties associated with data and method, including the effects of agrotechnical development, are assessed, and data sets of highest and lowest possible land use dynamics are provided. This land use reconstruction can be used to assess the human impact on the environment in pre-industrial times at high spatial and temporal resolution. It will be made freely available to the scientific community. The millennial land use reconstruction is then used in a complex climate model to quantify changes in radiative forcing. Results show that the energy balance was significantly influenced by human activity already in AD~800. Regional monthly means of radiative forcing reach up to 2.5~W/m2. Our results are in line with previous studies covering the recent centuries. The impact of pre-industrial land use change on the carbon balance is estimated using two independent approaches: a process-based soil and vegetation model, and a book-keeping model. Both methods show similar results with substantial carbon emissions in pre-industrial times. High regional dynamics are observed as a result of political and social changes.
GC54C-02
Climate Variability and the Settlement of Oceania
The initial discovery and settlement of the islands of Oceania is an important issue in Pacific anthropology. Settlement of this region generally proceeded against the direction of the dominant trade winds leading to questions concerning the degree of maritime skill possessed by early Pacific mariners. We use a computer simulation to test two basic exploration strategies: drift voyages and downwind sailing, focusing on the region of the initial eastward expansion into Oceania by the Lapita people. Simulations are driven by high resolution surface wind and current data from atmosphere and ocean models forced by real observations and which capture the high degree of seasonal and interannual variability in the region. We find that climatic variability associated with the Australian monsoon circulation and El Nino plays a key role in facilitating eastward crossings. Both drift and sailing voyages can account for the discovery of all the islands in the Lapita region based on initial starting points in the Bismarck and Solomon archipelagos. Many of our findings differ from an important, earlier modeling study performed by Levison et al. (1973).
GC54C-03 INVITED
A Simulation Framework for Exploring Socioecological Dynamics and Sustainability of Settlement Systems Under Stress in Ancient Mesopotamia and Beyond
The presentation will describe an object-oriented, agent-based simulation framework being used to help answer longstanding questions regarding the development trajectories and sustainability of ancient Mesopotamian settlement systems. This multidisciplinary, multi-model framework supports explicit, fine-scale representations of the dynamics of key natural processes such as crop growth, hydrology, and weather, operating concurrently with social processes such as kinship-driven behaviors, farming and herding practices, social stratification, and economic and political activities carried out by social agents that represent individual persons, households, and larger-scale organizations. The framework has allowed us to explore the inherently coupled dynamics of modeled settlements and landscapes that are undergoing diverse social and environmental stresses, both acute and chronic, across multi-generational time spans. The simulation framework was originally used to address single-settlement scenarios, but has recently been extended to begin to address settlement system sustainability issues at sub-regional to regional scale, by introducing a number of new dynamic mechanisms, such as the activities of nomadic communities, that manifest themselves at these larger spatial scales. The framework is flexible and scalable and has broad applicability. It has, for example, recently been adapted to address agroeconomic sustainability of settlement systems in modern rural Thailand, testing the resilience and vulnerability of settled landscapes in the face of such perturbations as large-scale political interventions, global economic shifts, and climate change.