Governments have known for more than half a century that emitting greenhouse gases increases temperatures and puts lives at risk. Yet global mitigation is minimal, for all the feted net zero commitments: emissions from fossil fuels have risen in every decade since records began. Some countries have made progress, including the United Kingdom where emissions have halved since 1990. But progress has so far relied on low-hanging fruit---the closure of coal mines; offshoring of industry; the recent growth of wind power. Future decarbonisation will be more challenging. Interdisciplinary collaboration, between scientists, engineers and economists among others, is necessary to overcome our carbon addiction.

This thesis asks how best to achieve urgent mitigation. It focuses on public policy as a lever for decarbonisation; governments' cross-sectoral influence authority to enforce give them unique power to accelerate change. Research is undertaken in three parts.

The first part considers the political economy of slow mitigation. It considers how political institutions and public beliefs affect the urgency of decarbonisation. Climate action faces opposition from incumbents and vested interests. This has led to a culture of myopic climate policy, defined as a high long- to short-term mitigation ratio. Every year mitigation is delayed makes it harder to achieve in future, transferring the burden from today's citizens to the future's. Moreover, public views over the issue salience of climate policy are lower than scientists', implying biased voter beliefs that impede adoption of the urgent policies needed to create near-term mitigation. This thesis postulates that policy myopia and biased beliefs can be ameliorated by setting a binding target on cumulative emissions, known as a carbon stock budget. For politicians, a carbon stock budget is an effective commitment mechanism. For the public, carbon stock framing alludes to threshold risks and appeals to the concept of household budgeting, both of which increase support for urgent policy. An economic model is presented that compares outcomes under a carbon stock budget and incremental climate policy. Results show that a budget increases nominal output by 40% in 2100. Implementing a carbon stock budget would help overcome barriers to meaningful decarbonisation.

Mitigation can be achieved with new technologies, new behaviours or a combination of both. The second part of this thesis asks what history can teach us about technological and social transitions. Researchers have previously analysed past energy transitions, but no studies have yet reviewed social transitions for clues about future decarbonisation. Here, five large-scale energy and seven social transitions are assessed in detail. Historical reviews are combined with metrics on transition progress. Results show that all transitions go through common stages and face similar challenges and opportunities. These are summarised in two transition frameworks, which enable measurement of the duration and scale of each transition. Technological transitions tend to be slower than their social counterparts, and delays between conception and growth are four decades longer for new technologies. Uptake also tends to be slower: technologies averaged an annual growth rate of 1.6%, versus 4% for social transitions. History suggests that social change could play an important role in achieving net zero by 2050.

The final part of this thesis asks what current climate strategies imply for the UK's timeline to net zero. It considers decarbonisation through the lens of disruption. A novel metric is proposed, which quantifies technological and behavioural disruption by measuring the implied change in a market or activity. A review of twelve proposed decarbonisation strategies yields 98 mitigation options and 538 distinct proposals. Applying the novel metric to these proposals reveals a bias towards technological mitigation. Two thirds of mitigation options rely solely on new technologies, one fifth rely on behavioural change, the remainder on a mix of both. Given the evidence that technological change can be slower than social change, these results suggest that the prevailing technological bias may impede near-term mitigation in the UK.

This research contributes to a growing discussion of alternative approaches to net zero. It supports a new climate narrative: one in which policymakers can overcome political barriers to ambitious, near-term action, by reframing climate targets and matching technological deployment with effective behaviour change. The fundamental contributions of this thesis are threefold. It postulates a political argument for a carbon stock budget by linking theories of myopic policy and biased voting. It develops a new method to compare the pace of social and technological transitions, and illustrates the relative promise of social change. Finally, it proposes a novel metric to capture disruption in decarbonisation strategies and shows that proposals for the UK are technologically biased.

Governments across the globe have pledged to reach net zero emissions by 2050. To live up to these promises, they must create change in the present by matching investment in prospective technologies with policies that utilise existing technologies and behavioural change. Accelerating the delivery of climate targets will require a balanced transition that places urgency at the heart of climate policymaking.