Mapping and clustering the adoption of carbon pricing policies: what polities price carbon and why?

Carbon pricing, including carbon taxes and emissions trading, has been adopted by different kinds of polities worldwide. Yet, beyond the increasing adoption over time, little is known about what polities – countries as well as sub- and supranational entities – adopt carbon pricing and why. This paper explores patterns of adoption (both implemented policies and those scheduled to be) through cluster analysis, with the purpose of investigating factors that could explain polities’ decisions to adopt carbon pricing. The study contributes empirically by studying carbon taxes and emissions trading together and by ordering the polities adopting carbon pricing into clusters. It also contributes theoretically, by exploring constellations of variables that drive the adoption of carbon pricing within individual clusters. We investigated 66 adopted policies of carbon pricing, which were divided into five clusters: early adopters, North-American subnational entities, Chinese pilot provinces, second-wave developed polities, and second-wave developing polities. The analysis indicates that the reasons for adopting carbon pricing have shifted over time. While international factors (climate commitments or influences from polities within the same region) are increasingly salient, domestic factors (including crises and income levels) were more important for the early adopters. Key policy insightsCarbon pricing has become a global mainstream policy instrument.Economic and fiscal crises provide windows of opportunity for promoting carbon pricing.The international climate regime can support the adoption of carbon pricing through mitigation commitments and international financial and technical assistance.Learning between polities from the same region is a useful tool for promoting carbon pricing.Carbon intensive economies tend to prefer emissions trading over carbon taxes. Carbon pricing has become a global mainstream policy instrument. Economic and fiscal crises provide windows of opportunity for promoting carbon pricing. The international climate regime can support the adoption of carbon pricing through mitigation commitments and international financial and technical assistance. Learning between polities from the same region is a useful tool for promoting carbon pricing. Carbon intensive economies tend to prefer emissions trading over carbon taxes.

碳定价（carbon pricing），涵盖碳税（carbon taxes）与碳排放权交易（emissions trading），已被全球各类政治实体所采用。尽管碳定价的采用率随时间不断攀升，但目前学界对全球范围内哪些政治实体——包括国家、次国家及超国家实体——采用了碳定价，以及其采用的动因，仍知之甚少。本研究通过聚类分析（cluster analysis）探究碳定价的采用模式（包括已实施政策与计划实施政策），旨在剖析可解释政治实体采用碳定价决策的影响因素。本研究在实证层面的贡献在于，将碳税与碳排放权交易结合研究，并将采用碳定价的政治实体划分为不同聚类；同时在理论层面，本研究探索了驱动各聚类内部政治实体采用碳定价的变量组合。本研究共调研了66项碳定价政策，并将其划分为五大聚类：早期采用者、北美次国家实体、中国试点省份、第二波发达经济体政治实体，以及第二波发展中经济体政治实体。分析结果显示，政治实体采用碳定价的动因随时间发生了变化：早期采用者的决策更多受国内因素（如危机与收入水平）驱动，而如今国际因素（如气候承诺或同区域政治实体的影响）的重要性日益凸显。

核心政策启示：
碳定价已成为全球主流政策工具。
经济与财政危机为推广碳定价提供了机遇窗口。
国际气候机制可通过减缓承诺及国际金融与技术援助，助力碳定价的推广采用。
同区域政治实体间的经验互鉴，是推广碳定价的有效途径。
碳密集型经济体往往更倾向于采用碳排放权交易而非碳税。

碳定价已成为全球主流政策工具。
经济与财政危机为推广碳定价提供了机遇窗口。
国际气候机制可通过减缓承诺及国际金融与技术援助，助力碳定价的推广采用。
同区域政治实体间的经验互鉴，是推广碳定价的有效途径。
碳密集型经济体往往更倾向于采用碳排放权交易而非碳税。