Existing socio-technical systems tend to be intransigent to change. Decarbonisation, on the other hand, is an imperative, leading to an obvious conflict between the need for, and highly effective resistance to, change. Moreover, the abandonment of fossil fuel-based technologies in favour of more sustainable alternatives will require substantial reallocation of government’s operational expenditure, particularly in countries like South Africa with high per capita greenhouse gas emissions and low per capita income. In this article, it is argued that reallocation will require more than niche experimentation and destabilisation of the present socio-technical regime. Based on a study of South Africa’s budget processes, it is concluded that change will only occur when four separate pre-conditions converge, namely a rapidly growing environmental problem capable of leading to civil unrest, a supportive and recently developed policy framework, decreasing techno-economic costs for its solution, and strong political support from an effective ministry or minister. Turning points for transition, although infrequent, can be reached through strategic attention to these pre-conditions. A modified Kingdon multiple streams approach, which introduces the additional dimension of techno-economic feasibility, is proposed as a useful framework for anticipating when and how to act in order to mobilise sufficient public resources for decarbonisation.