Social dilemmas, policy instruments, and climate adaptation measures: the case of green roofs

Green roofs contribute to both climate change adaptation and mitigation. Promoting green roofs is thus a key element in urban strategies to address climate change. How to actually promote green roofs, however, has so far proven elusive: attempts to link specific policy instruments to a more or less successful diffusion of green roofs have been few and far between. The present paper relies on institutional economics to advance the present understanding of the link between policy instruments and green roofs. It argues that different green roofs are confronted with different social dilemmas, and thus require different policy instruments. Specifically, small green roofs face a free-rider problem, which is best addressed through regulations and incentives. Large green roofs face instead a collective action problem, which is best addressed through communications and network-building. This perspective is tested empirically through a comparative analysis of 18 global cities on the forefront in the promotion of green roofs. The policy instruments observed in these cities match with the theoretical expectations laid down in the paper. Implications emerge for both policy and research.