Fairly sharing 1.5: national fair shares of a 1.5 °C-compliant global mitigation effort

The problem of fairly distributing the global mitigation effort is particularly important for the 1.5 °C temperature limitation objective, due to its rapidly depleting global carbon budget. Here, we present methodology and results of the first study examining national mitigation pledges presented at the 2015 Paris climate summit, relative to equity benchmarks and 1.5 °C-compliant global mitigation. Uniquely, pertinent ethical choices were made via deliberative processes of civil society organizations, resulting in an agreed range of effort-sharing parameters. Based on this, we quantified each country’s range of fair shares of 1.5 °C-compliant mitigation, using the Climate Equity Reference Project’s allocation framework. Contrasting this with national 2025/2030 mitigation pledges reveals a large global mitigation gap, within which wealthier countries’ mitigation pledges fall far short, while poorer countries’ pledges, collectively, meet their fair share. We also present results for individual countries (e.g. China exceeding; India meeting; EU, USA, Japan, and Brazil falling short). We outline ethical considerations and choices arising when deliberating fair effort sharing and discuss the importance of separating this choice making from the scholarly work of quantitative “equity modelling” itself. Second, we elaborate our approach for quantifying countries’ fair shares of a global mitigation effort, the Climate Equity Reference Framework. Third, we present and discuss the results of this analysis with emphasis on the role of mitigation support. In concluding, we identify twofold obligations for all countries in a justice-centred implementation of 1.5 °C-compliant mitigation: (1) unsupported domestic reductions and (2) engagement in deep international mitigation cooperation, through provision of international financial and other support, or through undertaking additional supported mitigation activities. Consequently, an equitable pathway to 1.5 °C can only be imagined with such large-scale international cooperation and support; otherwise, 1.5 °C-compliant mitigation will remain out of reach, impose undue suffering on the world’s poorest, or both.