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.

中文翻译：

---

社会困境，政策工具和气候适应措施：绿色屋顶的情况

绿色屋顶有助于气候变化的适应和缓解。因此，推广绿色屋顶是应对气候变化的城市战略的关键要素。然而，迄今为止，如何真正促进绿色屋顶的普及还难以捉摸：将具体政策工具或多或少地成功推广绿色屋顶的尝试很少，而且相去甚远。本文依靠制度经济学来增进对政策工具与绿色屋顶之间联系的当前理解。它认为，不同的绿色屋顶面临着不同的社会困境，因此需要不同的政策手段。具体来说，小的绿色屋顶面临着搭便车的问题，最好通过法规和激励措施来解决。大型绿色屋顶面临集体行动问题，最好通过通信和网络建设来解决。通过对18个全球领先的绿色屋顶城市进行比较分析，对这种观点进行了实证检验。在这些城市中观察到的政策工具与本文中提出的理论预期相符。对政策和研究都产生了影响。