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Quantitative assessment of the sustainability of greenhouse gas mitigation strategies in the AFOLU sector at the global scale

Abstract : The large-scale implementation of emission reduction strategies in the agriculture, forestry and other land uses (AFOLU) sector raises questions about their sustainability. For example, second-generation bio-fuels threaten biodiversity and the reforestation of agricultural land increases food prices. In addition, these emission reduction strategies are highly dependent on socio-economic conditions describing the rest of the food system (agricultural trade liberalization, economic development, population growth, etc.). For example, an increase in food demand, due to population growth and economic development, can increase pressures on the food system, leading to ecosystem degradation and increased greenhouse gas emissions. In this thesis, we seek to clarify the impacts on biodiversity, food and greenhouse gas emission of large-scale mitigation strategies in the AFOLU sector under different socio-economic conditions. To do this, we used prospective modeling to simulate various global land uses in 2030, 2050 and 2100 under different scenarios. More specifically, to study the impact of different mitigation strategies on biodiversity indicators, we coupled the Nexus Land-Use (NLU) model with the Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (PREDICTS) biodiversity model. A nitrogen balance is also built to specify the link between intensification and environmental impact.In the first chapter, we assessed the impact of scenarios of increased legume production in Europe on greenhouse gas emissions in the AFOLU sector. We found that the main environmental benefit of legumes is to provide proteins as a substitute for animal products rather than enabling a lower consumption of synthetic fertilizer through the increased leguminous nitrogen fixation. Most of the emission reduction takes place in the animal production sector and outside Europe. This first chapter also highlights the importance of indirect mechanisms that lead to a reduction in N2O emissions associated with nitrogen fertilization in the plant sector. The sensitivity of these results to different reforestation scenario led me to then focus on the interactions between mitigation strategies.In the second chapter, we analyzed the trade-offs and synergies between biodiversity and food security for different combinations of mitigation scenarios. Large-scale bioenergy production had negative effects on different biodiversity indicators (species richness and biodiversity intactness index) as well as on different food security indicators (food prices and production costs). Although presenting a trade-off between biodiversity protection and food security, a combination of diet change and reforestation scenarios can improve biodiversity and food security in many cases compared to a situation without mitigation.In a third chapter, we identified global land-use scenarios that ensure to stay within planetary boundaries in terms of nitrogen cycle, biosphere integrity, non-CO2 emissions from the AFOLU sector and forest conservation. We showed that despite the uncertainty surrounding the determination of global boundaries, the most robust environmental scenarios that ensure to stay within these global boundaries are mainly composed of reforestation, dietary changes and increased efficiency in the use of inputs in crop production.
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Rémi Prudhomme. Quantitative assessment of the sustainability of greenhouse gas mitigation strategies in the AFOLU sector at the global scale. Global Changes. Université Paris Saclay (COmUE), 2019. English. ⟨NNT : 2019SACLA014⟩. ⟨tel-02368885⟩

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