Abstract
Emission metrics aggregate climate impacts of greenhouse gases to common units such as CO2-equivalents (CO2-eq.). Examples include the global warming potential (GWP), the global temperature change potential (GTP) and the absolute sustained emission temperature (aSET). Despite the importance of biomass as a primary energy supplier in existing and future scenarios, emission metrics for CO2 from forest bioenergy are only available on a case-specific basis. Here, we produce global spatially explicit emission metrics for CO2 emissions from forest bioenergy and illustrate their applications to global emissions in 2015 and until 2100 under the RCP8.5 scenario. We obtain global average values of 0.49 ± 0.03 kgCO2-eq. kgCO2−1 (mean ± standard deviation) for GWP, 0.05 ± 0.05 kgCO2-eq. kgCO2−1 for GTP, and 2.14·10−14 ± 0.11·10−14 °C (kg yr−1)−1 for aSET. We explore metric dependencies on temperature, precipitation, biomass turnover times and extraction rates of forest residues. We find relatively high emission metrics with low precipitation, long rotation times and low residue extraction rates. Our results provide a basis for assessing CO2 emissions from forest bioenergy under different indicators and across various spatial and temporal scales.
Highlights
Bioenergy is currently the most important renewable energy option in the global primary energy mix[1], and its contribution is expected to further increase in the near future[2,3]
Metrics are typically classified according to three criteria[26]: i) emission type, i.e., for a single pulse or emission scenarios; ii) indicator, i.e., radiative forcing or temperature change; iii) time dimension, i.e., the indicator is used in its instantaneous or time-integrated form, with absolute or normalized values taken at a specific time horizon (TH)
Emission metrics are computed at 0.25° spatial resolution by coupling a global forest carbon model (G4M)[31,32] with the heterotrophic respiration model YASSO0733 and the climate impact protocol used by the IPCC for emission metrics and temperature responses[16,29]
Summary
Bioenergy is currently the most important renewable energy option in the global primary energy mix[1], and its contribution is expected to further increase in the near future[2,3]. ASET is an absolute metric that refers to the contribution to a global mean temperature peak (Δ Tpeak), with no time dimensions This metric is used for emission scenarios of shorter-lived climate forcers, with which bioenergy CO2 emissions can be grouped because they cause Δ Tpeak values dependent on emission rates rather than cumulative emissions[20]. Emission metrics are computed at 0.25° spatial resolution by coupling a global forest carbon model (G4M)[31,32] with the heterotrophic respiration model YASSO0733 and the climate impact protocol used by the IPCC for emission metrics and temperature responses[16,29] (see Methods). We demonstrate an application of these spatially explicit metrics through the characterization of the global CO2 emissions from bioenergy in 2015 and until 2100 under the Representative Concentration Pathway (RCP) 8.5 scenario[35], for which gridded wood fuel combustion flows are available[36]
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