The evolving boundary of green technology

Green patents are a key indicator to track technological efforts aimed at fighting climate change. Using an original dataset that merges different Patstat releases, we identify three mechanisms that may bias green patent statistics, potentially leading to contradictory findings. First, patent reclassifications due to updates in (green) classification codes result in an 9.2\% increase in the number of green patents when using the most recent classification structure. Second, delays in the adoption of the Cooperative Patent Classification (CPC) system introduce regional biases, as approximately 10\% of green patents from late-adopting countries remain undetected in less recent versions of the database. Third, we provide evidence that quality thresholds used to identify high-value inventions significantly shape observed trends in green patenting. Analyzing these mechanisms, our paper reveals that in many studies a substantial number of green patents is systematically overlooked, with the strongest effects observed for recent years and patents originating from Asian patent offices. These findings lead to relevant policy implications. Our results indicate not only that the global rate of green innovation has accelerated, but also that its epicenter has shifted, with an increasing share of green patents originating from emerging technological leaders, particularly in Asia.