Department of Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Environ Sci Technol. 2009 Nov 15;43(22):8509-15. doi: 10.1021/es901643a.
Many organizations look to carbon footprint protocols for guidance on measuring their greenhouse gas emissions, or carbon footprint. Existing protocols generally require estimation of direct emissions (Scope 1) and emissions from direct purchases of energy (Scope 2), but focus less on indirect emissions upstream and downstream of the supply chain (optional Scope 3). Because on average more than 75% of an industry sector's carbon footprint is attributed to Scope 3 sources, better knowledge of Scope 3 footprints can help organizations pursue emissions mitigation projects not just within their own plants but also across their supply chain. In this work, Scope 3 footprints of U.S. economic sectors are categorized using an Economic Input-Output Life Cycle Assessment (EIO-LCA) model to identify upstream emission sources that are likely to contribute significantly to different sectors' footprints. The portions of the upstream footprint captured by the sector's top-10 upstream suppliers are estimated at 3 different levels of specificity: general economy-wide, industry specific, and sector specific. The results show that enterprises can capture a large portion of their total upstream carbon footprint by collecting full emissions information from only a handful of direct suppliers, and Scope 3 footprint capture rates can be improved considerably by sector-specific categorization. Employee commuting and air transportation may be more important (7%-30%) for the services industries, but should not be a focus of detailed Scope 3 footprint estimates for the manufacturing industries (<1% of the total analyzed footprint). Protocol organizations should actively make more specific Scope 3 guidelines available for their constituents by developing sector-specific categorizations for as many sectors as they feasibly can and create broader industry-specific protocols for others.
许多组织寻求碳足迹协议来指导衡量其温室气体排放或碳足迹。现有的协议通常要求估算直接排放（范围 1）和直接购买能源的排放（范围 2），但较少关注供应链上游和下游的间接排放（可选范围 3）。由于平均超过 75%的行业部门的碳足迹归因于范围 3 来源，更好地了解范围 3 足迹可以帮助组织不仅在自己的工厂，而且在整个供应链中追求减排项目。在这项工作中，使用经济投入产出生命周期评估 (EIO-LCA) 模型对美国经济部门的范围 3 足迹进行分类，以确定可能对不同部门足迹有重大贡献的上游排放源。部门前 10 大上游供应商所捕获的上游足迹部分在三个不同的具体程度上进行了估计：一般经济范围、行业特定和部门特定。结果表明，企业可以通过仅从少数直接供应商收集完整的排放信息来捕获其大部分总上游碳足迹，并且通过特定部门的分类可以大大提高范围 3 足迹的捕获率。员工通勤和航空运输可能对服务业更为重要（7%-30%），但不应成为制造业详细范围 3 足迹估算的重点（占总分析足迹的<1%）。协议组织应通过尽可能为更多部门制定特定部门的分类，并为其他部门制定更广泛的行业特定协议，积极为其成员制定更具体的范围 3 指南。
