Temporal and Spatial Distribution of Global Mitigation Cost: INDCs and Equity

Each country’s Intended Nationally Determined Contribution (INDC) pledges an emission target for 2025 or 2030. Here, we evaluated the INDC intergenerational and interregional equity by comparing scenarios with INDC emission target in 2030 and with an immediate emission reduction associated with a global uniform carbon price using AIM/CGE (Asian-Pacific Integrated Model/Computable General Equilibrium). Both scenarios eventually achieve 2 °C target. The results showed that, as compared with an immediate emission reduction scenario, the intergenerational equity status is not favorable for INDC scenario and the future generation suffers more from delayed mitigation. Moreover, this conclusion was robust to the wide range of inequality aversion parameter that determines discount rate. On the other hand, the INDC scenario has better interregional equity in the early part of the century than does the immediate emission reduction scenario in which we assume a global carbon price during the period up to 2030. However, interregional equity worsens later in the century. The additional emission reduction to the INDC in 2030 would improve both inter- and interregional equity as compared to the current INDC. We also suggest that countries should commit to more emission reductions in the follow-up INDC communications and that continuous consideration for low-income countries is needed for global climate change cooperation after 2030