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As the impacts of climate change intensify, public actors around the world are increasing their adaptation efforts (Aguiar et al. 2018; Reckien et al. 2023; Schulze and Schoenefeld 2023). Initially, adaptation to climate change was primarily addressed in national and local settings, with modest attention from other levels of governance. Over time, however, state and nonstate actors at different levels have developed support schemes, networks, and (sub)national policies to strengthen adaptation governance by diffusing and scaling-up solutions and policies across jurisdictions. This includes higher levels such as the United Nations (Paris Agreement) and the European Union, which have increasingly emphasised adaptation to climate change, pushing for the diffusion of particular approaches and tools. While horizontal and vertical diffusion dynamics generally have the potential to reduce the risks emerging from climate change, distributional issues and political conflicts may arise if the diffusion of adaptation promotes elements that are poorly compatible with existing governance structures and practices. This raises the question of whether diffusing (local) solutions from the bottom-up and through networks can produce outcomes that are more effective, equitable, and accepted by local actors than top-down prescriptions (e.g. Baird et al. 2016; Bauer and Steurer 2014).

Against this background, diffusion processes and their underlying mechanisms are likely to play an important role in determining the pace, scale, and quality of adaptation. Despite a rapidly growing literature on adaptation, questions such as whether, how, and why adaptation governance and policies diffuse, for what purposes, and whether adaptation diffusion processes can reduce risks while promoting social justice, remain severely underexplored. Overall, the dynamic and global spread of adaptation governance and policies provides excellent opportunities for both theoretical and empirical explorations of the diffusion concept (Schoenefeld et al. 2022).

This Topical Collection addresses some of the gaps in our understanding of adaptation to climate change by exploring the diffusion of adaptation governance and policies. It brings together expert authors from diverse backgrounds who approach diffusion from different but complementary perspectives. It comprises six papers that use a range of qualitative and quantitative methods, applied in the context of single and comparative case studies. They explore the mechanisms underlying diffusion processes, such as coercion, competition, emulation, and learning, as well as the contextual drivers and barriers (Berry and Berry 2018). This includes both horizontal diffusion at the same (e.g., local) level of governance and vertical diffusion across levels, including interactions between national-local and global–local levels. In doing so, the collection offers a critical examination of the goals, effects, winners, and losers of diffusion processes. The empirical data originate from a variety of sources, including literature reviews, content analyses of policy documents and reports, expert interviews, and original large-n surveys. The different methods and perspectives complement each other in characterising large-scale patterns of diffusion and in working towards a deeper understanding of the underlying diffusion mechanisms, as well as their contextual drivers, barriers, and consequences.

Acknowledgements: The Topical Collection builds on two dedicated conference panels, that we organised at the European Consortium for Political Research (ECPR) General Conference (online) in 2020, and one for the International Political Studies Association (IPSA) in 2020—postponed to July 2021 due to the COVID-19 pandemic. We thank all the paper presenters, discussants, and participants at these events. We are grateful to Christopher Reyer for his very constructive comments and support in the realisation of this collection. The preparation of this Topical Collection was supported by the Fritz Thyssen Foundation, Grant/Award Number: 10.19.1.024PO.

Funding: Open Access funding enabled and organized by Projekt DEAL.