Zusammenfassung
Ongoing climate change poses a formidable threat to human livelihoods and ecosystems and calls for a rapid reduction of anthropogenic greenhouse gas (GHG) emissions within the next decades. To contribute to global climate mitigation efforts, the European Union (EU) has legislated a target of reaching net-zero GHG emissions in 2050. This thesis investigates strategies, dynamics and challenges associated with deep energy system transformations towards the EU 2050 net-zero target. While there are a number of existing studies on EU net-zero pathways, important research gaps remain. In particular, there is the need to better understand how a transformation to an extensive or complete phase-out of fossil energy at net-zero can be achieved. This would not only avoid a potential over-reliance on carbon dioxide removal (CDR) technologies, but also further limit the geopolitically problematic dependence on (fossil) energy imports. After an introductory chapter 1, the thesis will address this in three steps: Chapter 2 studies overarching characteristics of the EU transformation in comparison to other regions of the Global North. Chapter 3 analyzes the roles of electrification and green hydrogen in the transformation. Chapter 4 investigates transformation dynamics, costs and feasibility of a full fossil phase-out by 2050. Methodologically, the thesis is grounded in the use of the Regional Model of Investment and Development (REMIND), an integrated assessment model (IAM) that links representations of the energy, economic and land-use systems. It is used to investigate cost-optimal transformation pathways with respect to regional or global climate targets. REMIND conducts an intertemporal optimization of macroeconomic welfare and includes all relevant GHG emissions sources. The model is particularly refined with respect to the energy system including a technology-rich energy supply system and increasingly detailed representations of the energy demand sectors, buildings, industry and transport. There are four particularly relevant model developments that enabled the analyses of this thesis: This includes the introduction of a higher regional resolution of the EU, the implementation of regional emissions targets, more detailed representations of the transport and industry sector as well as the option to produce synthetic fuels from hydrogen and captured carbon. Chapter 2 compares characteristics of transformation pathways to reach net-zero CO2 emissions by 2050 across the EU, the US, Japan and Australia. Viable pathways exist for each of the regions featuring common strategies such as renewable power expansion, electrification, energy efficiency gains, carbon-neutral fuels and CDR. However, sensitivity scenarios reveal distinct challenges across regions. Japan and to some extent also the EU could face challenges in large-scale renewable power expansion as well as the provision of renewable fuels and CDR. Australia and the US can tap into larger potentials in these areas. Yet, these regions are characterized by high per-capita energy use and rising population trends that keep overall future energy demand comparatively high. If CDR options are limited, Australia and the US, in particular, are confronted with rising marginal abatement costs to transform hard-to-abate sectors. The analysis of regional characteristics suggests that regions should seek cooperation along common themes and seize synergies, for instance, by exporting renewable fuels to regions with low renewable potentials. Chapter 3 investigates the competition and complementarity of electrification and green hydrogen in EU pathways to GHG neutrality by 2050. Both strategies are considered key to reduce emissions in the energy demand sectors. They are also referred to as direct and indirect electrification since green hydrogen is produced from renewable electricity. The analysis finds that there is a large scope for direct electrification as electricity shares in final energy increase up to 60% in 2050 (42% at minimum), while indirect electrification via green hydrogen or e-fuels plays a smaller role (9-26% of final energy). Some applications such as road freight transport and high-temperature industrial heat provision switch between the two options depending on technology assumptions. This indicates uncertainty about whether electrification or hydrogen-based fuels will be more economical. Furthermore, the penetration of green hydrogen and e-fuels as well as the availability of hydrogen imports have a large impact on the required scale-up of renewable electricity. The results support an adaptive policy strategy that prioritizes direct electrification, while promoting at the same time the scale-up of green hydrogen and e-fuels to be used in hard-to-electrify sectors. Chapter 4 investigates pathways to low or no fossil energy use by 2050 along with the GHG neutrality target. Understanding such full fossil phase-out pathways is of major importance as they have so far hardly been investigated by IAMs on regional or global scale. The analysis finds that even in a least-cost net-zero scenario with optimistic assumptions about carbon capture and storage (CCS) and CDR, 87% of fossil fuels are phased out by 2050 relative to 2020 at moderate marginal abatement cost of 300 EUR/tCO2. Residual fossils are mainly oil-based liquids and some natural gas used in chemicals, aviation and shipping. As electrification and efficiency potentials are largely exhausted at this point of the transformation, moving to a full fossil phase-out requires, in addition, an ambitious up-scaling of e-fuels. Abating these last 13% of fossils substantially increases marginal abatement cost to about 650 EUR/tCO2. A full fossil phase-out target by 2050 would be a strong political signal and could strengthen EU climate policy commitment. However, it needs to be weighed against additional transformation risks and challenges of rapidly ramping up expensive and still nascent e-fuel production. The final chapter 5 synthesizes the findings and discusses limitations and policy implications of the thesis. A deep transformation of the EU energy system to an extensive or complete fossil phase-out by 2050 is viable and could under certain circumstances be achieved already at moderate costs. However, there are three critical enablers: a rapid expansion of renewable power, widespread electrification of energy demand and the scale-up of carbon-neutral fuels. If one of these strategies is limited, transformation challenges increase substantially. Scenario comparisons across chapters and previous literature suggests that barriers to deep transformations (as measured by marginal abatement costs) may be lower than previously thought using more recent model versions of REMIND that better resolve mitigation options in the energy sector. However, the model still features simplifications in areas like energy demand modeling and sector coupling, which are relevant domains for future research. The findings of the thesis imply that EU policy making should focus on removing barriers to renewable power expansion, widespread electrification and the scale-up of carbon-neutral fuels. This would lay the ground for an extensive or even complete EU fossil phase-out by mid-century.
