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Climate change –one of the greatest threats to modern civilisation- has been largely driven by an exponential growth in world energy use in the last couple of centuries. However, societies and economies are dependent on energy use to maintain themselves and change. Thus, in this thesis I compare energy to a ‘golden thread’, which weaves through climate change, economic growth and human well-being. In this context, the challenge I set out to explore in this thesis was to find alternatives for decoupling societal and economic progress from environmentally harmful levels of energy use. In order to open the possibility space for decoupling the energy dependency of the economy from climate change, I used the holistic theoretical framework of surplus energy and developed a novel methodology for calculating Energy Return On Investment (EROI) at the national level. Similarly, in order to open the possibility space for decoupling the energy dependency of society (human well-being) from climate change, I developed an original theoretical framework, integrating the concepts of energy services and human needs, and tested it using an innovative methodology. I found that a national-level EROI can contribute to accelerate a transition away from fossil fuels, by providing evidence at a scale relevant for policymakers. Additionally, I found that the energy services and human needs framework, as well as the methodology to test it, provide a way to prioritise and explore alternatives of energy service delivery. I consider that both of these contributions point towards the possibility of having climate compatible energy dependent societies and economies, as long as there is a fundamental change in the framings, understanding, priorities and methodologies used to find and assess such possibility.

The global climate challenge is keeping below a 2⁰C global temperature rise (versus pre-industrial levels) to avoid runaway climate change. Urgent policy-based action is required to reduce global fossil fuel use and CO2 emissions, without breaking the economy. This policy conflict highlights the fact that energy-CO2 and energy-economy interactions are at opposite ends of the energy conversion chain: at one end fossil fuels are extracted, at the other it is exchanged (via monetary transaction) for energy services. The study of the whole energy conversion chain seems desirable, to provide a broad evidence base for policies aimed at meeting both energy and economic priorities. Such study requires an exergy analysis approach, examining exergy as ‘usable energy’ from extraction (primary exergy) to ‘useful work’ (when it is lost in exchange for energy services). However, such national-level exergy analysis is currently an underused approach. In response, I use a useful work accounting and exergy analysis approach to study energy use, rebound and economic growth for the UK, US and China. Several key findings and insights emerge. First, gains in national-level energy (exergy) efficiencies for the UK and US have slowed or stalled, due to efficiency dilution: the increasing use of lower efficiency processes. Second, the asymptotic national exergy efficiency limit is around 15%, suggesting current energy efficiency policies may not work effectively at the economy-wide scale. Third, my primary energy forecast in 2030 for China - the world’s largest energy consumer (and CO2 emitter) - was 20% higher than mainstream projections. Fourth, using an exergy-based approach, the UK and US exhibit partial energy rebound, but China’s energy rebound was higher (close to, or above backfire). If rebound is significant, this weakens the effect of current energy efficiency policies, and has implications for our understanding the role of energy efficiency in economic growth.

Biomass combustion with carbon capture and storage (Bio-CCS) has been identified as a key contributing technology to long-term carbon emissions reductions in many global and UK scenarios, but the development and implementation of this technology would require significant technical and non-technical barriers to be overcome. This thesis describes research undertaken to address these barriers, to contribute to the role that Bio-CCS could play in reducing carbon emissions for the UK electricity sector. Technical studies investigate the characteristics of coal and biomass combustion in atmospheres relevant to CCS at bench-scale and in a 20kW furnace. Analysis of bench-scale results, using a modified Coats-Redfern procedure, suggests oxygen-enrichment increases reactivity during the breakdown of cellulosic material and char oxidation. At 20kW scale, experiments that investigate biomass blending ratio and extent of oxidant staging conclude that, compared to air-firing of coal, cofiring in oxygen-enriched, oxidant-staged conditions results in enhanced combustion, reduced NO emissions and a flue gas richer in CO2. Cofiring of coal with 15% biomass is also carried out in partial-oxyfuel combustion atmospheres. The results suggest no major technical issues, showing biomass cofiring and oxygen-enrichment counter reductions in reactivity due to higher CO2 concentrations. However, further tests show that dedicated firing of biomass in such conditions would likely require modifications to the combustion set up. The development of an industry depends on more than its level of technological readiness. Modelled as a technical innovation system, development of Bio-CCS is gauged from the results of an expert survey on the wider UK CCS industry and analysis of relevant publications. Findings show that, as well as biomass sustainability criteria and a need to reward negative emission processes, the development of Bio-CCS is dependent on the wider CCS industry in the UK which, driven by uncertainties, has suffered due to a lack of market creation and entrepreneurship.

Humanity’s greatest challenge is to improve the living standards of billions of people across the world without surpassing the planetary boundaries, and especially within the carbon space compatible with a 2°C future. Mitigation actions are thus required to create synergies and address climate and development goals simultaneously. It has been recognised that technology-led mitigation measures can accomplish this task, as long as they are also complemented with demand-side measures. Several bodies of literature have emphasised, for example, the urgent need to reduce consumption levels, particularly in industrialised economies. However, in the context of an ever more globalised world, the climate benefits delivered by demand-side mitigation policies can be offset by the existence of potential negative consequences in developing nations via international trade. This thesis assesses the compatibility between climate change mitigation actions taken in industrialised nations and improving development prospects in the developing world from a demand-side approach. The study contributes to the existing knowledge base by providing answers to four separate but related research questions that were proposed to examine relevant aspects associated with this issue. The results reveal that CO2 emissions have increased monotonically with income without showing signs of having decoupled over time. The findings also show that while curbing final demand for imports in developed countries can contribute to reduce their consumption-based emissions and free carbon space, they can also curtail the development opportunities available to the global South. Moreover, specific policy instruments, like border carbon adjustments, can potentially distort trade flows and jeopardise development in developing nations. Finally, the analysis unveils that the available carbon space compatible with a 2°C target is insufficient to deliver significant improvements in living standards in less developed countries given the continuity of the status quo. The sharing of the development and carbon spaces should be done in an equitable manner. The longer it takes developed countries to significantly cut their emissions, the smaller is the carbon space available particularly to the poorest nations who need it the most. The conclusions from this work evidence the necessity to formulate alternative development pathways capable of facilitating a transition towards an equitable, low-carbon, high-developed, and sustainable global economy.