Analysis of cost-effective reduction pathways for major emitting countries to achieve the Paris Agreement climate goal

Achieving the global climate goal of the Paris Agreement depends on collective action by individual countries, as reflected in the Nationally Determined Contributions (NDCs). To inform the next NDCs to be submitted by 2025, which should include emission reduction targets for 2035/2040, this study aims to identify the reduction pathways required for major emitting economies to achieve the Paris Agreement climate targets at the lowest possible global mitigation costs. We selected least-cost mitigation scenarios from Integrated Assessment Models of the latest IPCC’s Sixth Assessment Report scenario database for five major emitting economies (EU-27, China, India, Japan and the United States) and the world. We downscaled modelled regional emission pathways to the regional level for the five economies, harmonised the emission data with national inventory data, and analysed the results and assessed their robustness with respect to the methodology used. Since the results do not indicate how to account for equity and feasibility considerations, policymakers should not regard them as directly indicative of national targets. Our study shows that to keep global warming to 1.5 °C with at least 50 % probability and limited overshoot, the least-cost greenhouse gas reductions by 2040 for the EU-27, Japan and the United States are around 70 %–100 % relative to 2015 levels (including LULUCF). If the selection of scenarios is limited to those consistent with existing national targets, this range increases substantially to around 85–115 %. For China and India, ranges for both selections of scenarios are similar and around 65 %–80 % and 30 %–80 %, respectively.