Harmonization of Global Land-Use Scenarios for the Period 1500-2100 for the 5th IPCC Assessment

Over the next century and beyond, human interactions with the Earth system will continue to exert increasing pressures on ecosystems and the climate. In order to increase our understanding and of these future changes, new modeling approaches that incorporate the highly complex and coupled nature of the physical and social phenomena driving the Earth system will be required. Along these lines, in preparation for the fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), the international community is developing new advanced Earth System Models (ESM) to address the combined effects of human activities (e.g. land use and fossil fuel emissions) on the carbon-climate system. In addition, four Representative Concentration Pathways (RCP) scenarios of the future (2005-2100) are being provided by four Integrated Assessment Model (IAM) teams to be used as input to the ESMs for future carbon-climate projections. However, the diversity of approaches and requirements among IAMs and ESMs for tracking land-use change, along with the dependence of model projections on land-use history, presents a challenge for effectively passing data between these communities and for smoothly transitioning from the historical estimates to future projections. Here, we build upon our previous global gridded estimates of land-use transitions (e.g. agricultural land conversions, wood harvesting, shifting cultivation) and present a new harmonized set of land-use scenarios that smoothly connects historical reconstructions of land-use with future projections, in the format required by ESMs. Our land-use harmonization strategy estimates fractional land-use patterns and underlying land-use transitions (including resulting secondary lands) annually for the time period 1500-2100 at 0.5° x 0.5° resolution, based upon future crop, pasture, and wood harvest data from the IAMs implementations of the RCPs for the period 2005-2100. Our computational method integrates multiple data sources while minimizing differences at the transition between the historical reconstruction ending conditions and IAM initial conditions, and working to preserve the future changes depicted by the IAMs at the gridcell level. These new harmonized data products provide the first consistent set of land-use change and emission scenarios for studies of sustainability and human impacts on the past and future global carbon-climate system.