We study incentives to increase innovation in climate change adaptation technologies (CCATs). Many CCATs, such as sea walls, exhibit public good characteristics, since they are non-rival and non-excludable. Innovation in public goods suffers from twin market failures: imperfect appropriability which is common to all innovation, and more specifically, free-riding, which dampens private incentives to undertake public goods projects (Mandel 2015). Till date, there is no systematic evidence on the extent to this “twin externality” has impacted the development of CCATs. Using global patent data, we examine who develops different types of CCATs. Our hypothesis is that for CCATs with strong public good characteristics, technological development is mainly undertaken by public entities such as universities or publicly funded research labs; while for CCATs that resemble private goods (e.g. irrigation systems), there is more private sector participation. Thereafter, using patent citation data, we map the technological knowledge base of CCATs. We assess what scientific disciplines underpin CCATs and whether these fields are relatively “under-funded”. Our analysis elucidates the extent to which markets for CCATs are incomplete due to the twin externalities, and whether more government support is required.