Abstract
Abstract. We examine historical and future land-use emissions using a simple mechanistic carbon-cycle model with regional and ecosystem specific parameterizations. We use the latest gridded data for historical and future land-use changes, which includes estimates for the impact of forest harvesting and secondary forest regrowth. Our central estimate of net terrestrial land-use change emissions, exclusive of climate–carbon feedbacks, is 250 GtC over the last 300 yr. This estimate is most sensitive to assumptions for preindustrial forest and soil carbon densities. We also find that land-use change emissions estimates are sensitive to the treatment of crop and pasture lands. These sensitivities also translate into differences in future terrestrial uptake in the RCP (representative concentration pathway) 4.5 land-use scenario. The estimate of future uptake obtained here is smaller than the native values from the GCAM (Global Change Assessment Model) integrated assessment model result due to lower net reforestation in the RCP4.5 gridded land-use data product.
Highlights
Over the past 500 yr of human-induced changes to the terrestrial environment, substantial changes in atmospheric CO2 concentration have been driven in part by land-use change (LUC), and substantial changes will continue to occur in the century
The first is net LUC emissions, which are defined as the net change in terrestrial carbon stocks not accounting for climate-carbon feedbacks, e.g., carbon releases minus uptake due to regrowth
We focus in this work on net LUC emissions in order to isolate the impact of human-caused changes in terrestrial carbon fluxes, as discussed further by Houghton (2013)
Summary
Over the past 500 yr of human-induced changes to the terrestrial environment, substantial changes in atmospheric CO2 concentration have been driven in part by land-use change (LUC), and substantial changes will continue to occur in the century. This model allows analysis of the quantitative implications of land-use and carbon-cycle assumptions in more complex earth systems models (ESMs) We will approach this issue by posing the following question: given a set of spatially detailed LUC scenarios (Hurtt et al, 2011), how do different assumptions for ecosystem properties and the representation of anthropogenic land uses impact estimates of the resulting net release in terrestrial CO2 over time? The analysis here focuses on the net change in terrestrial carbon stocks, e.g., land-use change emissions, without considering the influence of changing climate and carbon dioxide concentrations We refer to these influences here generically as climate–carbon feedbacks (Davidson et al, 2006; Friedlingstein et al, 2006; Thornton et al, 2006). The terrestrial carbon model will be described below, followed by the input data sets and the parameter values used, concluding with a discussion of results
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