Carbon offsetting in city climate action: role, determinants and characteristics

To contribute to Paris Agreement objectives, non-state actors globally are setting voluntary emission reduction goals. Cities represent an important group with emission reduction plans, but vary in how they intend to meet targets. Some cities incorporate carbon offsetting to manage residual emissions. A lack of research exists on the role of offsetting in city plans, and better understanding this approach can inform city climate policy. This study uses a mixed-method design to explore the frequency, characteristics and role of offsetting in city climate action. We quantify how many cities globally include offsetting in their plan, create a random forest model to explore what characteristics of cities and their targets are associated with offsetting, and conduct a text analysis of city documents to explore how cities that intend to use offsets conceptualize the use. We find 363 cities globally with a population over 500,000 have a numeric GHG reduction target; 86 of these include offsetting in their plan. Larger cities, those with a higher per capita GDP, and those with more ambitious climate targets are more likely to offset. Further, of 44 cities included in our text analysis that intend to use offsetting, 29 discuss prioritizing emissions reductions but recognize that offsets will be needed for residual emissions. Less than half the cities discuss environmental integrity of offsets, and many lack detail on how to ensure integrity. Specifying concrete plans regarding offsetting and communicating these decisions is important for effectiveness and integrity of city climate action plans, knowledge sharing between cities, and planning for future offsetting. Most cities with a climate action target have yet to decide or publicly communicate whether they will use offsets to reach their target.Among cities that do intend to use offsetting, many lack details on estimating residual emissions, defining an upper limit on offsets, specifying from where and how to acquire offsets, and how to ensure environmental integrity.If used appropriately, offsets may allow cities to achieve more ambitious targets than otherwise possible.Additional guidance from city climate networks can help cities plan for high-integrity use of offsetting. Most cities with a climate action target have yet to decide or publicly communicate whether they will use offsets to reach their target. Among cities that do intend to use offsetting, many lack details on estimating residual emissions, defining an upper limit on offsets, specifying from where and how to acquire offsets, and how to ensure environmental integrity. If used appropriately, offsets may allow cities to achieve more ambitious targets than otherwise possible. Additional guidance from city climate networks can help cities plan for high-integrity use of offsetting.

为助力《巴黎协定》（Paris Agreement）目标实现，全球范围内的非国家行为体正纷纷设定自愿减排目标。城市作为制定减排计划的重要群体，其达成减排目标的路径却存在显著差异。部分城市通过碳抵消（carbon offsetting）手段管理剩余排放。当前针对城市规划中碳抵消机制的作用的研究仍较为匮乏，深化对该路径的理解可为城市气候政策制定提供有益参考。

本研究采用混合研究方法，探究城市气候行动中碳抵消的应用频次、特征与作用。我们首先量化全球范围内将碳抵消纳入减排计划的城市数量；随后构建随机森林模型，探究城市及其减排目标的哪些特征与碳抵消的使用存在关联；同时对城市官方文件开展文本分析，以探讨计划使用碳抵消的城市如何界定其应用方式。

研究结果显示，全球共有363座人口超过50万的城市设定了量化的温室气体（Greenhouse Gas, GHG）减排目标，其中86座城市将碳抵消纳入其减排计划。规模更大、人均GDP更高、气候目标更具雄心的城市，更倾向于采用碳抵消机制。进一步分析表明，在我们开展文本分析的44座计划使用碳抵消的城市中，有29座提及优先开展减排工作，但同时认可需通过碳抵消处理剩余排放。仅有不到半数的城市讨论了碳抵消的环境完整性问题，且多数城市未明确保障环境完整性的具体方案。明确碳抵消相关的具体计划并公开相关决策，对于提升城市气候行动计划的有效性与完整性、推动城市间知识共享以及未来碳抵消规划均具有重要意义。

大部分设定了气候行动目标的城市尚未决定或未公开说明是否将通过碳抵消来达成其目标。在计划使用碳抵消的城市中，多数缺乏关于剩余排放估算、设定碳抵消上限、明确碳抵消来源与获取方式以及保障环境完整性的具体细节。若使用得当，碳抵消可帮助城市实现比原本更具雄心的减排目标。城市气候网络提供的额外指导，可助力城市规划如何高完整性地应用碳抵消机制。

大部分设定了气候行动目标的城市尚未决定或未公开说明是否将通过碳抵消来达成其目标。在计划使用碳抵消的城市中，多数缺乏关于剩余排放估算、设定碳抵消上限、明确碳抵消来源与获取方式以及保障环境完整性的具体细节。若使用得当，碳抵消可帮助城市实现比原本更具雄心的减排目标。城市气候网络提供的额外指导，可助力城市规划如何高完整性地应用碳抵消机制。