Session: Benchmarking & cross-cutting Group 1 (Isotope modelling, COMPARE)
Author: Benjamin Stocker / email@example.com / CREAF, Barcelona, Spain
Co-author: Sandy Harrison, School of Archaeology, Geography and Environmental Science (SAGES), University of Reading, UK;
Marie-José Gaillard, School of Natural Sciences, Linnaeus University, Kalmar, Sweden;
Timing, extent, and impacts of preindustrial land use and land use change (LUC) are uncertain, yet crucial for understanding the role of humans in the Earth’s environmental history and in particular their impact on greenhouse gas concentrations during the Holocene. While the total terrestrial C balance is relatively well constrained from ice core CO2 and ẟ13C data, contributions from different components of the terrestrial biosphere are less well known and direct empirical data is often missing. Thus, insights into global land carbon cycle changes during the Holocene heavily rely on model simulations. CO2 emissions from LUC are commonly estimated using global dynamic vegetation models, forced by spatio-temporal scenarios of the extent of past anthropogenic land use. However, available scenarios diverge heavily by suggesting widely different extents of LUC prior to industrialisation, and land C budget constraints and archaeological evidence indicate incompatibilities in all of the available LUC scenarios. The PAGES Landcover6K initiative addresses this challenge and brings together palaeoecologists, historians, archeologists, and modellers to improve LUC scenarios. Here, we propose a roadmap for the inclusion of these improved LUC scenarios in a new set of multi-model land C cycle simulations covering the Holocene and their evaluation within given global C cycle constraints. A first special focus will be placed on the period around and after the Mid-Holocene (7-3 ka BP), to separate anthropogenic from natural impacts in a period where agriculture emerged, climatic shifts lead to large changes in biome distributions, and atmospheric CO2 gradually increased. A second focus will be placed on the extent of LUC prior to 1850 and to address the important but uncertain temporal allocation of well-constrained total present-day LUC emissions. Global C budget constraints can be used to evaluate LUC scenarios and respective cumulative CO2 emissions by 1850. This is directly relevant for the global C budget of the historical period and CMIP6 simulations with prescribed historical LUC.