Net zero ambition and fairness: a comprehensive analysis for fair global mitigation

Limiting global warming under the Paris Agreement—with its goal of keeping temperatures well below 2 °C while pursuing 1.5 °C—requires rapid, sustained emissions cuts. Within this constraint, fairness concerns arise because implementation must reflect fairness and Common but Differentiated Responsibilities and Respective Capabilities (CBDR‑RC). This study develops an effort‑sharing framework that varies weights on equality, capability, and responsibility across 10 regions, combining them with diverse decarbonization rates and assumptions about end‑century net‑negative emissions to generate a wide set of regional pathways. The results show substantial variation in climate‑fair net‑zero CO 2 years: developed regions face earlier and steeper reductions due to greater historical responsibility and capability, while developing regions receive more near‑term emissions space to support development. Two themes emerge: deep, front‑loaded mitigation in high‑income regions is essential, and reliance on future removals can weaken early action and shift burdens to lower‑income regions.