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Society’s efforts to ‘manage’ the problem of human-induced climate change – for example through setting targets, tracking progress, imposing sanctions and incentives, and creating markets in emission rights and offsets – have given rise to numerous calculation, measurement, attribution, monitoring, reporting and verification challenges, which are being addressed by many different communities (including scientists, governments, businesses and accountants) in many different ways. Carbon accounting – this diverse and ever-expanding assemblage of calculative practices – is a rapidly evolving phenomenon, which has only recently become a subject of academic accountancy-related research. This thesis explores what carbon accounting means, who it involves, and how different communities define and lay claim to competence in the field. It also examines, through case studies on the emergence of the Climate Disclosure Standards Board and the controversies around generating tradable carbon offsets from forestry projects in the UK, the immense technical, cognitive, social and political work required to make carbon measurable, commensurable and thereby amenable to various forms of management. The thesis contributes to both conceptual and practical understanding of carbon accounting as an emerging field of study. Bringing together a wide range of empirical examples of different types of carbon accounting practices, it proposes a unique definition of carbon accounting which expands the horizons of the field. It provides a conceptual basis for making sense of carbon accounting by considering it not as a unitary phenomenon but rather as a set of overlapping frames, each associated with different communities of practice. It shows that competence in carbon accounting is contested, particularly where these frames overlap, and that boundary organisations are emerging that offer the opportunity to negotiate such tensions and lead to more productive policy-making. Finally, it makes the case that engagement with the detail of the ‘nuts and bolts’ of carbon accounting is essential, as these apparently technical details can have major implications for the effectiveness of society’s response to climate change, and it is only by opening them up to rigorous scrutiny that we can make progress, both conceptually and practically.

In responding to climate change, one of the most serious threats facing humankind today, recent climate movements have aimed to decarbonise different parts of society, in particular energy generation and industrial production. These movements have culminated in international climate agreements, such as the 2015 Paris Agreement, which set ambitious emission reduction targets at national levels, and industries respectively have followed suit in taking climate action. The steel sector is one such industry. The steel sector is the second highest industrial sector by emissions, only second to the cement sector. Efforts to decarbonise steelmaking have largely focused on improving energy-efficiency measures which do not suffice for meeting the global climate ambitions. As such, breakthrough innovative low-carbon technologies which have the potential to radically reduce emissions from steelmaking have become a necessity. However, while such technologies do exist, they remain in the research or demonstration phases, with limited potential for implementation at the scale and pace required to meet those climate targets. While some have been tested and are technically proven, implementing breakthrough low-carbon technologies such as Carbon Capture, Utilisation and Storage (CCUS) or hydrogen reduction remain hampered by their high capital costs, which, in the absence of regulatory mandates, would deter steelmakers who operate on small profit margins from pursuing them. This thesis aims to address this by exploring innovative business models which would accelerate the adoption of such technologies in steelmaking. To do so, this work undertakes a multi-method qualitative research involving semi-structured interviews and a survey questionnaire with leading steelmaking and low-carbon technology experts worldwide. The research sets out to first explore potential business models for CCUS technologies as a case study, given their technical maturity over alternative technologies (Paper 1). This study builds upon literature on existing CCUS business models in the oil and gas industry and draws on commonalities with industrial sectors such as steel. This leads to the identification of a new potential revenue stream to support low-carbon integration into steelmaking, that is the creation of a niche market for 'green steel' products, which would be sold at a premium over traditional steels. Green steel as a concept is then explored in Paper 2, including an appraisal of what defines greenness in the steelmaking context, what policy support mechanisms would see the product penetrate a highly-competitive market, and what sectors may be potential consumers of green steel. As the automotive sector is identified as a likely outlet for green steel demand, green steel adoption within the sector is subsequently explored as a case study in Paper 3. The main finding of this paper is that certain types of automakers, specifically heavy-duty and electric vehicle manufacturers, may be more prone to adopting green steel in their production lines than others. This overall work was initially undertaken with the intention of writing three separate papers, or 'chapters'. However, the research conducted in the first three papers led to the identification of gaps in the literature and areas worthy of further exploration. These are then explored in Paper 4, where a novel business modelling tool is proposed, and in Paper 5, which proposes a model to replicate the green steel example amongst steelmakers and potentially in other material production industries.

The variability of flows can cause challenges to the long term integrity of the carbon dioxide (CO2) transport and storage infrastructure. In particular, repeated cycling and periods of low flow in injection wells can lead to a range of deleterious effects that impair the integrity of injection wells and reduce their lifetimes. How flow variability will be managed cost-effectively across clusters of CO2 sources or CO2 sinks is still unclear. At the time of writing, CCS deployment has indeed focused on single source-to-sink projects operating continuously, and, in most cases, supplying CO2 continuously for the purpose of enhanced oil recovery. Using a combination of economic dispatch models of power stations, including wind, solar, nuclear and combined cycle gas turbines with CO2 capture, with hydraulic models of dense phase CO2 pipelines, a method to characterise the magnitude and frequency of the variability of flow changes in CO2 transport networks and at injection wells is presented for the first time. A case study of the electricity system of Great Britain shows that CO2 flow variability and repeated periods of low flow are prevalent at high levels of deployment of wind power and at carbon intensity of electricity generation of approximately 60g/kWh, and very likely beyond. The effects on flow variability of the deployment of large levels of solar capacity are, however, limited. It is possible to reduce the number of occurrences of periods of low flow at injection by increasing the diameter of dense phase CO2 pipelines, and by extension their line-packing capabilities. For an offshore pipeline of 100 km and 24 inch (36 inch) diameter, this number is reduced from 202 to 32 per year (7) in the reference electricity system scenario of this study. The use of solvent storage in combined cycle gas turbines with post-combustion CO2 capture can balance flow variability, within the boundaries of CCS power plants, reducing further the need for injection wells to operate flexibly. A rigorous state-of-the-art process model determines operating limits for an 804MW power plant in terms of output of electricity and CO2, and the extent and duration to which electricity and CO2 production can be decoupled. An additional solvent inventory of 6200m3 (7.8 m3/MWe) allows decoupling electricity and CO2 production for up to 3hrs, with a fixed pressure operating strategy for steam extraction from the combined cycle. Smoothing of flows with solvent storage, sized to deliver at least 10% of nominal pipeline flow, further reduces the number of occurrences of low flow periods to 2 per year (2) representing an overall 99% reduction for the reference electricity system scenario.

As part of the response to the threat of dangerous climate change a variety of methods have emerged for measuring greenhouse gas emissions to the atmosphere, assigning responsibility for those emissions, and informing decisions on mitigation actions. Many of these greenhouse gas accounting methods have developed in semi-isolated fields of practice, and this raises questions about how these different methods relate to each other, and whether they form ‘families’ of conceptually similar approaches. A useful distinction has developed within the field of life cycle assessment (LCA) between attributional and consequential methods, and this thesis explores the possibility of extending that distinction to categorise other forms of greenhouse gas accounting. Broadly, attributional methods are inventories of emissions/removals for a defined inventory boundary, while consequential methods aim to estimate system-wide changes in emissions that result from a decision or action. This thesis suggests that national greenhouse gas inventories, city inventories, corporate inventories, and attributional LCA are all attributional in nature, while project-level assessments, policy-level assessments, and consequential LCA are all consequential in nature. The potential benefits from creating this categorical framework include ensuring that individual methods are conceptually coherent, transposing lessons between methods of the same categorical type, and ensuring that the correct type of method is used for a given purpose. These various benefits are explored conceptually through the analysis of existing greenhouse gas accounting standards, and also empirically with the use of a bioenergy case study. The findings suggest that the attributional-consequential distinction is highly useful for conceptualising and developing greenhouse gas accounting methods, which is important, ultimately, for addressing dangerous climate change.