Browsing by Author "Lefebvre, David"

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    An anticipatory life cycle assessment of the use of biochar from sugarcane residues as a greenhouse gas removal technology
    (Elsevier, 2021-06-02) Lefebvre, David; Williams, Adrian; Kirk, Guy J. D.; Meersmans, Jeroen; Sohi, Saran; Goglio, Pietro; Smith, Pete
    Greenhouse gas removal technologies are needed to reach the targets of the UNFCCC Paris Agreement. Among existing technologies, the use of biochar is considered promising, particularly biochar derived from the large quantities of sugarcane residues available in South America and elsewhere. However, the net greenhouse gas removal potential of sugarcane biochar has not been assessed hitherto. We use a scenario-based anticipatory life cycle assessment to investigate the emissions associated with a change from the combustion of sugarcane residues in a combined heat and power plant to the pyrolysis of these residues for biochar production and field application in São Paulo State, Brazil. We define scenarios based on different mean marginal electricity production and biochar production share. The results indicate that emissions from covering the electricity deficit generated by partial combustion of biomass during biochar production is the main emitting process. Overall, the processes associated with biochar production lower the net greenhouse gas benefits of the biochar by around 25%. Our analysis suggests that allocating 100% of the available sugarcane residues to biochar production could sequester 6.3 ± 0.5 t CO2eq ha−1 yr−1 of sugarcane in São Paulo State. Scaled up to the entire State, the practice could lead to the removal of 23% of the total amount of GHGs emitted by the State in 2016.
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    Assessing the carbon capture potential of a reforestation project
    (Nature Publishing Group, 2021-10-07) Lefebvre, David; Williams, Adrian G.; Kirk, Guy J. D.; Burgess, Paul J.; Meersmans, Jeroen; Silman, Miles R.; Román-Dañobeytia, Francisco; Farfan, Jhon; Smith, Pete
    The number of reforestation projects worldwide is increasing. In many cases funding is obtained through the claimed carbon capture of the trees, presented as immediate and durable, whereas reforested plots need time and maintenance to realise their carbon capture potential. Further, claims usually overlook the environmental costs of natural or anthropogenic disturbances during the forest’s lifetime, and greenhouse gas (GHG) emissions associated with the reforestation are not allowed for. This study uses life cycle assessment to quantify the carbon footprint of setting up a reforestation plot in the Peruvian Amazon. In parallel, we combine a soil carbon model with an above- and below-ground plant carbon model to predict the increase in carbon stocks after planting. We compare our results with the carbon capture claims made by a reforestation platform. Our results show major errors in carbon accounting in reforestation projects if they (1) ignore the time needed for trees to reach their carbon capture potential; (2) ignore the GHG emissions involved in setting up a plot; (3) report the carbon capture potential per tree planted, thereby ignoring limitations at the forest ecosystem level; or (4) under-estimate tree losses due to inevitable human and climatic disturbances. Further, we show that applications of biochar during reforestation can partially compensate for project emissions.
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    Assessing the potential of soil carbonation and enhanced weathering through Life Cycle Assessment: a case study for Sao Paulo State, Brazil
    (Elsevier, 2019-06-11) Lefebvre, David; Goglio, Pietro; Williams, Adrian; Manning, David A. C.; de Azevedo, Antonio Carlos; Bergmann, Magda; Meersmans, Jeroen; Smith, Pete
    Enhanced silicate rock weathering for long-term carbon dioxide sequestration has considerable potential, but depends on the availability of suitable rocks coupled with proximity to suitable locations for field application. In this paper, we investigate the established mining industry that extracts basaltic rocks for construction from the Paraná Basin, Sao Paulo State, Brazil. Through a Life Cycle Assessment, we determine the balance of carbon dioxide emissions involved in the use of this material, the relative contribution of soil carbonation and enhanced weathering, and the potential carbon dioxide removal of Sao Paulo agricultural land through enhanced weathering of basalt rock. Our results show that enhanced weathering and carbonation respectively emit around 75 and 135 kg carbon dioxide equivalent per tonne of carbon dioxide equivalent removed (considering a quarry to field distance of 65 km). We underline transportation as the principal process negatively affecting the practice and uncover a limiting road travel distance from the quarry to the field of 540 ± 65 km for carbonation and 990 ± 116 km for enhanced weathering, above which the emissions offset the potential capture. Regarding Sao Paulo State, the application of crushed basalt at 1 t/ha to all of the State's 12 million hectares of agricultural land could capture around 1.3 to 2.4 Mt carbon dioxide equivalent through carbonation and enhanced weathering, respectively. This study suggests a lower sequestration estimate than previous studies and emphasizes the need to consider all process stages through a Life Cycle Assessment methodology, to provide more reliable estimates of the sequestration potential of greenhouse gas removal technologies.
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    Life cycle assessment of land-based greenhouse gas removal technologies.
    (2021-06) Lefebvre, David; Williams, Adrian; Kirk, Guy
    Greenhouse gas removal technologies (GGRT) are needed to meet the UNFCCC aim to limit the global average temperature increase to 2°C above pre-industrial levels. GGRTs vary in carbon sequestration potential, readiness level, scalability, cost, required surrounding environment and related environmental and social effects. Quantifying these components in every context is critical to ensure maximum greenhouse gas removal efficiency while minimising negative effects. In this thesis I use life cycle assessment (LCA) to assess the carbon sequestration potential of three GGRTs: enhanced weathering, biochar and reforestation. I use case studies in São Paulo, Brazil for biochar and enhanced weathering, and in the Peruvian Amazon for reforestation. In addition, I use LCA to identify the most important processes in each system and to determine context-specific limits that switch the systems from net GHG sequestration to net GHG emission. Overall, this work promotes the use of LCA to consider GGRTs in their entirety and predict their context-specific carbon capture potential, along with their limitations and potential caveats to guide both the science and policy communities. This thesis was made possible thanks to funding through the SOILS-R-GGREAT (NE/P019498/1) project of the greenhouse gas removal (GGR) program. The GGR program is financed by the UK Natural Environment Research Council (NERC), Engineering and Physical Science Research Council (EPSRC), Economic and Social Science Research Council (ESRC) and the UK department for Business, Energy and Industrial Strategy (BEIS).
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    Modelling the potential for soil carbon sequestration using biochar from sugarcane residues in Brazil
    (Nature Publishing Group / Nature Research / Springer Nature, 2020-11-10) Lefebvre, David; Williams, Adrian; Meersmans, Jeroen; Kirk, Guy J. D.; Sohi, Saran; Goglio, Pietro; Smith, Pete
    Sugarcane (Saccharum officinarum L.) cultivation leaves behind around 20 t ha−1 of biomass residue after harvest and processing. We investigated the potential for sequestering carbon (C) in soil with these residues by partially converting them into biochar (recalcitrant carbon-rich material). First, we modified the RothC model to allow changes in soil C arising from additions of sugarcane-derived biochar. Second, we evaluated the modified model against published field data, and found satisfactory agreement between observed and predicted soil C accumulation. Third, we used the model to explore the potential for soil C sequestration with sugarcane biochar in São Paulo State, Brazil. The results show a potential increase in soil C stocks by 2.35 ± 0.4 t C ha−1 year−1 in sugarcane fields across the State at application rates of 4.2 t biochar ha−1 year−1. Scaling to the total sugarcane area of the State, this would be 50 Mt of CO2 equivalent year−1, which is 31% of the CO2 equivalent emissions attributed to the State in 2016. Future research should (a) further validate the model with field experiments; (b) make a full life cycle assessment of the potential for greenhouse gas mitigation, including additional effects of biochar applications on greenhouse gas balances.