Net Land-use Change Research Articles

Land use policies and their effects on Brazilian farming production

For decades Brazil has faced a dilemma based on a perceived dichotomy between natural preservation and economic progress. Since 1988, more than 446,000 km2 of native land has been cleared by clearcutting in Brazilian Legal Amazon alone, an area comparable to Sweden. In addition to the biodiversity loss associated with this activity, it is a significant global warming source since more than 72% of gross CO2e emissions of Brazil come from land use, land-use change, forestry, and agriculture. As such, the national commitment to reduce greenhouse gas emissions by 37% by 2025 and 43% by 2030, with respect to 2005 levels, is likely to be at risk. Here, a simulation model has been created to provide decision-makers with knowledge about the future of Brazilian farming production in deforestation, neutral net land-use change, and reforestation scenarios. It has been found that farming demand and capital supply impact farming production significantly more than land availability. If reforestation policies to 2005 natural coverage levels were to be implemented, there would be no significant differences in Brazilian major farming crop production to a reference scenario of continuous deforestation. However, this would be at the expense of secondary crops usually earmarked for the domestic market. For Brazil to preserve its natural coverage, it must also inevitably improve crop productivity, especially in the Northeast region, while also being cognizant of the impact on domestic food prices. Lastly, Brazil needs to have incentives to foster intensive livestock farming. These results provide evidence that can support policies towards the profitable and sustainable scenarios described in the simulations.

Bookkeeping estimates of the net land-use change flux – a sensitivity study with the CMIP6 land-use dataset

Abstract. The carbon flux due to land-use and land-cover change (net LULCC flux) historically contributed to a large fraction of anthropogenic carbon emissions while at the same time being associated with large uncertainties. This study aims to compare the contribution of several sensitivities underlying the net LULCC flux by assessing their relative importance in a bookkeeping model (Bookkeeping of Land Use Emissions, BLUE) based on a LULCC dataset including uncertainty estimates (the Land-Use Harmonization 2 (LUH2) dataset). The sensitivity experiments build upon the approach of Hurtt et al. (2011) and compare the impacts of LULCC uncertainty (a high, baseline and low land-use estimate), the starting time of the bookkeeping model simulation (850, 1700 and 1850), net area transitions versus gross area transitions (shifting cultivation) and neglecting wood harvest on estimates of the net LULCC flux. Additional factorial experiments isolate the impact of uncertainty from initial conditions and transitions on the net LULCC flux. Finally, historical simulations are extended with future land-use scenarios to assess the impact of past LULCC uncertainty in future projections. Over the period 1850–2014, baseline and low LULCC scenarios produce a comparable cumulative net LULCC flux, while the high LULCC estimate initially produces a larger net LULCC flux which decreases towards the end of the period and even becomes smaller than in the baseline estimate. LULCC uncertainty leads to slightly higher sensitivity in the cumulative net LULCC flux (up to 22 %; references are the baseline simulations) compared to the starting year of a model simulation (up to 15 %). The contribution from neglecting wood harvest activities (up to 28 % cumulative net LULCC flux) is larger than that from LULCC uncertainty, and the implementation of land-cover transitions (gross or net transitions) exhibits the smallest sensitivity (up to 13 %). At the end of the historical LULCC dataset in 2014, the LULCC uncertainty retains some impact on the net LULCC flux (±0.15 PgC yr−1 at an estimate of 1.7 PgC yr−1). Of the past uncertainties in LULCC, a small impact persists in 2099, mainly due to uncertainty of harvest remaining in 2014. However, compared to the uncertainty range of the LULCC flux estimated today, the estimates in 2099 appear to be indistinguishable. These results, albeit from a single model, are important for CMIP6 as they compare the relative importance of starting year, uncertainty of LULCC, applying gross transitions and wood harvest on the net LULCC flux. For the cumulative net LULCC flux over the industrial period, the uncertainty of LULCC is as relevant as applying wood harvest and gross transitions. However, LULCC uncertainty matters less (by about a factor of 3) than the other two factors for the net LULCC flux in 2014, and historical LULCC uncertainty is negligible for estimates of future scenarios.

Towards a more complete quantification of the global carbon cycle

Abstract. The main components of global carbon budget calculations are the emissions from burning fossil fuels, cement production, and net land-use change, partly balanced by ocean CO2 uptake and CO2 increase in the atmosphere. The difference between these terms is referred to as the residual sink, assumed to correspond to increasing carbon storage in the terrestrial biosphere through physiological plant responses to changing conditions (ΔBphys). It is often used to constrain carbon exchange in global earth-system models. More broadly, it guides expectations of autonomous changes in global carbon stocks in response to climatic changes, including increasing CO2, that may add to, or subtract from, anthropogenic CO2 emissions. However, a budget with only these terms omits some important additional fluxes that are needed to correctly infer ΔBphys. They are cement carbonation and fluxes into increasing pools of plastic, bitumen, harvested-wood products, and landfill deposition after disposal of these products, and carbon fluxes to the oceans via wind erosion and non-CO2 fluxes of the intermediate breakdown products of methane and other volatile organic compounds. While the global budget includes river transport of dissolved inorganic carbon, it omits river transport of dissolved and particulate organic carbon, and the deposition of carbon in inland water bodies. Each one of these terms is relatively small, but together they can constitute important additional fluxes that would significantly reduce the size of the inferred ΔBphys. We estimate here that inclusion of these fluxes would reduce ΔBphys from the currently reported 3.6 GtC yr−1 down to about 2.1 GtC yr−1 (excluding losses from land-use change). The implicit reduction in the size of ΔBphys has important implications for the inferred magnitude of current-day biospheric net carbon uptake and the consequent potential of future biospheric feedbacks to amplify or negate net anthropogenic CO2 emissions.

Impact of feedstock, land use change, and soil organic carbon on energy and greenhouse gas performance of biomass cogeneration technologies

Abstract Bioenergy (i.e., bioheat and bioelectricity) could simultaneously address energy insecurity and climate change. However, bioenergy’s impact on climate change remains incomplete when land use changes (LUC), soil organic carbon (SOC) changes, and the auxiliary energy consumption are not accounted for in the life cycle. Using data collected from Belgian farmers, combined heat and power (CHP) operators, and a life cycle approach, we compared 40 bioenergy pathways to a fossil-fuel CHP system. Bioenergy required between 0.024 and 0.204 MJ (0.86 MJth + 0.14 MJel)−1, and the estimated energy ratio (energy output-to-input ratio) ranged from 5 to 42. SOC loss increased the greenhouse gas (GHG) emissions of residue based bioenergy. On average, the iLUC represented ∼67% of the total GHG emissions of bioenergy from perennial energy crops. However, the net LUC (i.e., dLUC + iLUC) effects substantially reduced the GHG emissions incurred during all phases of bioenergy production from perennial crops, turning most pathways based on energy crops to GHG sinks. Relative to fossil-fuel based CHP all bioenergy pathways reduced GHG emissions by 8–114%. Fluidized bed technologies maximize the energy and the GHG benefits of all pathways. The size and the power-to-heat ratio for a given CHP influenced the energy and GHG performance of these bioenergy pathways. Even with the inclusion of LUC, perennial crops had better GHG performance than agricultural and forest residues. Perennial crops have a high potential in the multidimensional approach to increase energy security and to mitigate climate change. The full impacts of bioenergy from these perennial energy crops must, however, be assessed before they can be deployed on a large scale.

Carbon density and anthropogenic land-use influences on net land-use change emissions

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.

Evaluation of spatially explicit emission scenario of land-use change and biomass burning using a process-based biogeochemical model

Using a socioeconomic scenario of representative concentration scenarios, terrestrial emissions from biomass burning and anthropogenic land-use change for the twenty-first century are evaluated in a spatially explicit manner using a biogeochemical model. The model is validated with the historical net land-use change CO2 emission and biomass-burning trace gas emission: net land-use change CO2 emission for 1990s to be from 1.03 to 1.53 Pg C year−1 and black carbon emission from biomass burning during 1997–2000 to be 3.1 Tg BC year−1. For future emissions, uncertainty due to CO2 concentration and land-use change scenario is examined using sensitivity experiments and reveals significant effect of CO2 on the biomass-burning emissions in terms of direct effect of vegetation mass and the indirect feedback through the fire ignition probability. It also reveals the importance of CO2 fertilization on net land-use change CO2 emission through the regrowing absorption in abandoned agricultural land.

Development of spatially explicit emission scenario from land-use change and biomass burning for the input data of climate projection

In the preparatory phase of IPCC AR5 development, Representative Concentration Pathways (RCPs) have been constructed by Integrated Assessment Models (IAMs) groups as new forcing scenarios used for climate modeling and earth system modeling groups. In the process of RCP 6.0 scenario development, which has been conducted by the Asia-Pacific Integrated Model (AIM), we constructed a scenario of spatially explicit long-term aerosol emissions from biomass burning and net land-use change CO2 emissions in order to complement energy use and industrial emissions scenarios projected by socio-economic component of AIM.To estimate the emissions from biomass burning, we incorporate a vegetation fire component into the terrestrial biogeochemical process model VISIT (Vegetation Integrative SImulation Tool). For the net land-use change CO2 emission, we use gridded land-use change transition matrix data developed in the process of downscaling the RCP6.0 land use scenario for the evaluation of emission from deforestation (primary land and secondary land into cropland, pasture, and urban), and also the evaluation of regrowth absorption from abandonment of cropland and pasture. In this process, uncertainty of land emissions due to the effect of CO2 concentration and land-use scenario is examined, and reveals significant effect of CO2 fertilization effect on vegetation to the land emissions.