Research leading to this thesis aims to assess the policy relevant mitigation potential of Indian forests as well as aims to assess the impact of climate change on carbon stocks, vegetation boundary shifts, Net Primary Productivity (NPP) and the mitigation potential of Indian forests. To project the impact of climate change we chose a dynamic global vegetation model ‘Integrated Biosphere Simulator’ (IBIS V.2.6b4). We selected A2 and B2 scenarios for projecting the impacts. Mitigation potential was assessed using the ‘Generalized Comprehensive Mitigation Assessment Process’ (GCOMAP) model. We assess the mitigation potential of Indian forests in the light of India’s long-term policy objective of bringing 33% of its total geographical area under forest cover. We analyzed the mitigation potential of this policy objective under two scenarios: the first comprising of rapid afforestation scenario with the target to achieving the goal by 2020 and the second a moderate afforestation scenario in which this goal is achieved by 2030. We estimate that afforestation could offset about 9% of India’s average national emissions over the 2010-2030 period, while about 6.7% could be mitigated under the moderate afforestation scenario over the same period. We analyze the impact of climate change on the four key attributes of Indian forests, i.e. impact on vegetation distribution, impact on forest productivity (NPP), impact on soil carbon (SOC) and impact on biomass carbon. IBIS simulations suggest that approximately 39% and 34% of forest grids are projected to experience change in vegetation type under A2 and B2 climate scenarios, respectively over the period 2070¬2100. Simulations further indicate that NPP is projected to increase by an average of 66% under the A2 scenario and 49% under the B2 scenario. The increase is higher in the northeastern part of India. However, in the central and western Indian forests NPP remains stable or increases only moderately, and in some places even decreases. Our assessment of the impact of climate change on Soil Organic Carbon (SOC) suggests a trend similar to NPP distribution, which is to be expected as increased NPP is the primary driver of higher litter input to the soil. However, the quantum of increase in this case is lower, around 37% and 30%, for the A2 and B2 scenario respectively (averaged over India). The biomass carbon is also projected to increase all over India on the lines similar to NPP gains. However, projected gains in biomass, NPP and SOC should be viewed with caution as IBIS tends to simulate a fairly strong CO2 fertilization effect that may not necessarily be realized under conditions of nutrient and water limitations and under conditions of increased pest and fire outbreaks. Further we analyzed the impact of climate change on the mitigation potential of Indian forests by linking impact assessment models to mitigation potential assessment model GCOMAP. Two impact assessment models BIOME4 and IBIS are used for simulating the impact of climate change. IBIS is a dynamic vegetation model while BIOME4 is an equilibrium model. Our assessment suggests that with the BIOME4 simulations the cumulative mitigation potential increases by up to 21% under the A2 scenario over the period 2008 to 2108, whereas, under the B2 scenario the mitigation potential increases only by 14% over the same period. However cumulative mitigation potential estimates obtained from the IBIS simulations suggest much smaller gains, where mitigation potential increases by only 6% and 5% over the period 2008 to 2108, under A2 and B2 scenarios respectively. To enable effective policy analysis and to build a synergy between the mitigation and adaptation efforts in the Indian forest sector, a vulnerability index for the forested grids is constructed. The vulnerability index is based on the premise that forests in India are already subjected to multiple stresses including over extraction, insect outbreaks, live¬stock grazing, forest fires and other anthropogenic pressures -with climate change being an additional stress. The forest vulnerability index suggests that nearly 39% of the forest grids in India are projected to be vulnerable to the impacts of climate change under the A2 scenario, while 34% of the forest grids are projected to be vulnerable under the B2 scenario. The vulnerability index suggests that forests in the central part of India, a significant part of the western Himalayan forests and northern and central parts of the Western Ghats are particularly vulnerable to the impacts of climate change. Forests in the northeastern part of India are seemingly resilient to the impacts of climate change. It also suggests that given the high deforestation rate in northeast, this region be prioritized for reducing deforestation and forest degradation (REDD) projects under the United Nations Framework Convention on Climate Change (UNFCCC) mechanisms.

Cette thèse est une évaluation du potentiel d'atténuation technique et économique global dans l'agriculture Chinoise et des conditions nécessaires à la formation d’un prix du carbone dans ce secteur. Le champ de recherche inclut les émissions venant de terres cultivées et en particulier celles liées à l'utilisation d'engrais azotés synthétiques. Il s'articule autour de la construction d'une courbe de coûts marginaux de réduction (MACC), qui offre un cadre rationnel pour combiner les données biophysiques et économiques afin de refléter les coûts d'atténuation. Cet outil permet d'agréger le potentiel d'atténuation découlant de l'application d'un sous-ensemble de mesures coût-efficacité en dessus d'un niveau de référence désignée. Une analyse des politiques climatiques chinoises révèle que l'agriculture est presque absente de la stratégie nationale d'atténuation. Nous avons donc l'intention d’examiner la faisabilité du point de vue technique, économique et politique, d’intégrer l'agriculture dans les politiques domestiques d’atténuation. En premier lieu, la tendance et les méthodes de calcul des émissions sont évaluées afin de déterminer une approche rigoureuse permettant de construire des scénarios de référence à partir de prévisions des activités ‘business-as-usual’ pour 2020. Deuxièmement, nous identifions neuf mesures d'atténuation des sols cultivés, nous évaluons leur taux d'abattement et leur applicabilité future au-delà du scénario de base pour obtenir un potentiel total d'atténuation techniquement faisable. Leur traduction en potentiel économique est alors faite en comparant les coûts de mise en œuvre des différentes options d'atténuation relatives aux pratiques agricoles conventionnelles. Les résultats des MACC montrent que l’agriculture offre un potentiel d'atténuation important, qui pourrait compenser environ un tiers des émissions de référence et dont un tiers pourrait être réalisé au coût négatif pour les agriculteurs. Nous examinons enfin l’utilisation des instruments économiques pour réduire les émissions au moindre coût dans le secteur agricole. Compte tenu des obstacles institutionnels, comportementaux et sociaux, nous suggérons fortement d’engager une réforme dans le système des subventions d'engrais afin d'envoyer un signal politique clair aux agriculteurs. L’utilisation de l’intensité du carbone comme référence normalisée est recommandé pour améliorer et élargir l'accès aux projets de compensation, et peut aussi préparer le terrain pour un possible programme expérimental d'échange de quotas d’émissions dans l'agriculture. En cohérence avec la priorité de protéger la sécurité alimentaire en Chine, des études de cas sur la production régionale de céréales sont introduites dans toutes ces étapes, y compris l'analyse de l'intensité des gaz à effet de serre de la production dans chaque province, le potentiel régional de réduction des émissions liées à l'utilisation d’engrais azotés ainsi que la disparité de coûts de mise en œuvre dans certaines régions. / This thesis is an evaluation of the overall technical and economic mitigation potential in China agriculture and the conditions of putting a carbon price in this sector. The research scope is cropland emissions and particularly those related to synthetic nitrogen fertilizer use. The thesis is articulated around the construction of a bottom-up marginal abatement cost curve (MACC) which offers a rational framework for combining biophysical and economic data to reflect mitigation costs. This tool allows the aggregation of the mitigation potential arising from the application of a subset of cost-effective measures above a notional baseline level. An analysis of Chinese climate policies reveals that agriculture is nearly absent in the current national mitigation strategy. We therefore intend to assess the technical, economic and political feasibility of integrating agriculture into domestic mitigation policies. In the first place, the emissions trends and calculation methods are assessed to determine a rigorous approach to build baseline scenarios from projected business-as-usual activities to 2020. Secondly, we identify nine cropland mitigation measures, evaluate their abatement rates and future applicability beyond the baseline scenario to conclude a total feasible technical mitigation potential. The translation to the economic potential is then made by comparing the implementation costs of different mitigation options relative to conventional farming practices. The MACC results show that agriculture provides significant mitigation potential to be able to offset about one-third of baseline emissions and realisation of one-third of the potential is cost-negative for farmers. We finally examine the conditions of using economic instruments to reduce emissions at the lowest cost for the agricultural sector. Given the institutional, behaviour and socials obstacles, we strongly suggest a reform in agriculture fertilizer subsidies to send a clear political signal from central planning. Scaling-up offset projects using carbon intensity as the standardized baseline is recommended and can prepare the grounds for a possible experimental emission trading programme in agriculture. In light with the top priority of safeguarding food security in China, cases studies on regional cereal production are carried out in all these steps, including the analysis of provincial greenhouse gas intensity of production, regional abatement potential related to synthetic nitrogen fertilizer use as well as implementation cost disparities in certain regions.

Stickstoffdüngung und Bodenbewirtschaftung sind die Hauptquellen für Treibhausgase aus Anbausystemen. Dennoch sind diese Maßnahmen in Ackerbaubetrieben unerlässlich. In Anbetracht der Notwendigkeit, rasch Maßnahmen gegen den Klimawandel zu ergreifen, ist es notwendig Minderungspotentiale und Kosten in diesen Betrieben zu ermitteln und vergleichen. Es wurden Fallstudien in den USA, in Brasilien und in Deutschland durchgeführt, wobei jeweils eine Kultur in jeder Region untersucht wurde. Wissenschaftliche Literatur und Fokusgruppen mit lokalen Experten wurden genutzt, um realistische Ergebnisse zu generieren, die den lokalen Kontext abbilden. Diese Arbeit zeigt, dass die Wirtschaftlichkeit der Minderungsstrategien von dem betrachteten Zeithorizont abhängt, der sich aus der Kohlenstoffdynamik im Boden ergibt. Kurzfristig bieten Strategien, die die Kohlenstoffbindung fördern, ein größeres Minderungspotenzial, was jedoch langfristig nicht zutrifft. Kurzfristig wurden in Brasilien und den USA die geringsten Minderungskosten durch die Optimierung der Stickstoffdüngung erreicht. Diese Kosten sind negativ, was bedeutet, dass die Anwendung dieser Strategien, nicht nur ihre Emissionen, sondern auch ihre Kosten senken würden. Weitere kosteneffiziente Strategien waren die Verringerung der Bodenbearbeitungsintensität und Zwischenfrüchte, die in allen Fällen mit vergleichbaren Minderungskosten durchführbar waren und die Kohlenstoffbindung fördern. Der Einsatz von Hemmstoffen schließlich, der in den USA und in Brasilien möglich war, hatte die höchsten Minderungskosten. Langfristig betrachtet stiegen die Minderungskosten von Strategien mit Kohlenstoffbindung an und waren ähnlich hoch oder höher als bei Strategien ohne Kohlenstoffbindung. Da in allen Fällen dieselbe Methodik angewandt wurde, sind die Ergebnisse vergleichbar. Darüber hinaus sind die Ergebnisse zwar spezifisch für den Kontext, in dem sie berechnet wurden, sie liefern jedoch Erkenntnisse für ähnliche Regionen. / Nitrogen fertilization and soil management are the main sources of greenhouse gases from cropping systems. Yet these operations are essential on arable farms. Considering the need to take quick action against climate change, it is necessary to understand which mitigation potentials and cost can be attained in these farms and how they compare. Case studies in the USA, Brazil and in Germany were conducted, assessing one crop in each region. Scientific literature and focus groups with local experts were used to generate realistic results which depict the local context. This thesis identified that the economics of the mitigation strategies depended on the time horizon considered, which results from the carbon dynamics in the soil. In the short term, strategies promoting carbon sequestration offer a larger mitigation potential, yet this is not valid in the long term. In the short term, the lowest mitigation costs were attained by optimizing the nitrogen rate, feasible in the USA and Brazil. These costs are indicated to be negative, implying that adopting the strategy would not only lower emissions, but also reduce their costs. The next most cost efficient strategies were the reduction of the tillage intensity and cover crops, which were feasible in all cases with comparable mitigation costs and promote carbon sequestration. Lastly, the adoption of inhibitors, feasible in the USA and in Brazil, had among the highest mitigation costs. Assuming the long term, the mitigation costs of strategies with carbon sequestration increased, becoming similar to or higher than strategies without carbon sequestration. By applying the same methodology in each case, the results are comparable. Moreover, while the findings are specific to the context in which they were calculated, they provide insights for similar regions.