Comparison and analysis of mitigation ambitions of Parties' updated Nationally Determined Contributions

Understanding mitigation ambitions of the Nationally Determined Contributions (NDCs) should include both the equity of supporting the Paris Agreement goals and the costs of achieving the proposed mitigation targets. This study presents a new framework that combines equity and economic costs to compare and analyze mitigation ambitions of Parties' updated NDCs. Under representative 2 degrees C and 1.5 degrees C pathways, this framework uses multiple equity-principled allocations to derive the alignment of the updated NDCs with the Paris Agreement goals, and further applies a computable general equilibrium model to assess the economic costs of implementing the updated NDCs. The results show that global 2030 emissions may meet the selected global 2 degrees C pathway if all Parties achieve their most ambitious mitigation efforts, but there is still an emissions gap of 10-15 GtCO(2) to follow the selected 1.5 degrees C pathway. From the perspective of equity, the updated NDCs of the USA, the EU (including the UK in this study), and Japan lack ambition with respect to 'equal cumulative per capita emissions' under 2 degrees C and do not align with any equity principles under 1.5 degrees C. The updated NDCs of China, India, Brazil and South Africa reflect their claims to 'equity' and 'common but differentiated responsibilities'. From the perspective of economic costs, the GDP and welfare losses of China, Brazil and South Africa incurred by achieving the updated NDCs are not lower than those of the three developed Parties. China's GDP loss is estimated at 0.43%-0.55% in 2030, which is higher than that of the USA (0.30%-0.38%) and the EU (0.25%-0.28%). This study suggests that developed Parties take the lead in further ratcheting up the NDCs and strengthen financial and technological support to developing countries so that the world could close the gap to 1.5 degrees C.