Conceptually grounded, integrated, city-scale and comparative studies remain rare and are based mostly on meta-reviews of the literature or broad surveys. Conversely, debates about the limitations of incremental or transitional change and exhortations towards more ambitious processes of system or transformative changes are rarely grounded in adequate empirical analysis. Accordingly, this paper examines city-scale plans and actions in order to throw light on these issues in a carefully contextualised Global South-North comparison between Cape Town, South Africa, and Greater Manchester, UK. Cape Town has a considerable pedigree of citywide climate policy and action but achieving cross-departmental integration remains a key challenge, along with operationalisation and monitoring. Greater Manchester has abundant climate ambitions to become a leading European green city, but recent innovative policy processes revealed a lack of capacity and in-house expertise. The comparative analysis therefore focuses on capacity constraints hampering fulfilment of progressive city aspirations that engage with global agendas, and on how they use innovative planning and implementation processes and different forms of knowledge to address integrative or cross-cutting issues, as well as on their relative success to date in doing so in the face of different extents of inequality and power asymmetry.