This article argues that an improved legal methodology is needed to ensure that states’ greenhouse gas emissions mitigation obligations are specified in line with best available science and the equity principle. In this vein, the article explores the extent to which the ‘meta-equity assessment’ of states’ emissions by the Climate Action Tracker (CAT) can contribute to this aim. The article finds that the CAT's PRIMAP Equity tool, embedded in the Potsdam Real-time Integrated Model for the probabilistic Assessment of emission Paths, offers the best available approach to distributing a global carbon budget among states in line with equity criteria recognized by the Intergovernmental Panel on Climate Change. The emissions data and global pathways used in the PRIMAP Equity tool can be updated. The major challenge ahead lies in understanding which of the emissions and temperature pathways can be applied in the legal context, and how.
