Patent data have long been used to measure innovation, and patent indicators have become a valuable tool for tracking technological change, analyzing knowledge diffusion and assessing the effects of policy interventions. While patents have limitations – not all innovations are patented and patents vary in technical and economic significance – they remain among the most reliable and widely used proxies for inventive activity. Their use to monitor green technology innovation is now common practice among major intellectual property offices and international organizations, including China National Intellectual Property Administration (CNIPA), the EPO, the Japan Patent Office (JPO), WIPO and the OECD.
Identifying green technologies within patent data, however, presents distinctive challenges. Green technologies span a wide range of domains – energy, transport, manufacturing, agriculture, construction and waste management – and are defined by environmental function rather than technical domain. Since patent classification systems such as the IPC and the Cooperative Patent Classification (CPC) are organized around technical principles rather than environmental purpose, green technologies are dispersed across hundreds of classification categories, with no single class labelled “green technology.” Identifying them requires recognizing which specific technical categories contain environmentally relevant innovations.
A further challenge concerns boundaries: what qualifies as “green”? While some technologies – such as solar photovoltaic (PV) or wind turbines – are universally recognized as green, many cases involve genuine ambiguity. Nuclear power, for instance, is considered green by some and excluded by others. The term itself encompasses a broad range of related concepts – clean technology, low-carbon technology, climate mitigation technology, environmentally sound technology – each emphasizing different environmental objectives. Ultimately, what counts as green depends on users’ policy priorities, environmental criteria and analytical objectives, underscoring the need for a clearly defined and transparent classification framework.
Several major intellectual property offices and international organizations have developed specialized classification systems to identify and measure green technologies within patent data. Five principal systems exist: CNIPA's IPC Green and Low-carbon Technology Inventory, the EPO's Y02/Y04S CPC tagging scheme for Climate Change Mitigation Technologies, the JPO's Green Transformation Technologies Inventory (GXTI), the OECD's ENV-TECH classification, and WIPO's IPC Green Inventory. While all aim to categorize green technologies, they differ significantly in methodology. Some rely exclusively on IPC codes, others supplement these with CPC tags, JPO-specific File Index (FI) codes and F-terms, or keyword searches. These differences have important implications for accessibility and international comparability: IPC-only systems can be applied by any user with standard patent data access, whereas systems requiring CPC databases, JPO-specific tools, or complex keyword searches present higher barriers, particularly for developing countries and statistical offices with limited resources.
Despite these methodological differences, a meaningful degree of convergence exists across systems. A core group of technologies – including solar PV, wind energy, electric vehicles, battery storage, hydrogen fuel cells, energy-efficient lighting, and waste and wastewater management – is consistently recognized across all or most classification systems, enabling robust international comparisons. A second group of moderate-consensus technologies, including biofuels, nuclear energy, carbon capture and storage, and sustainable agriculture, shows variable inclusion reflecting differences in policy priorities, sustainability criteria, and technical assessments. These divergences underscore the need for a harmonized reference classification that can serve as a common, transparent and internationally comparable baseline – the central objective of the WIPO-GTIS presented here.