Reconstructing emission pathways for developing countries

Addressing climate change requires accurate emission baseline and robust model-based projections to simulate future emission mitigation pathways. However, emission baseline data in existing Integrated Assessment Models (IAMs) are inaccurate and inconsistent. In particular, they cannot capture recent emission surges in those small and medium-sized developing countries, causing large discrepancies of projections of global carbon space, which are crucial for setting climate policy. We compiled time-series emission inventories for 60 developing countries, ensuring consistency and full validation using all available regional, national and international energy and socioeconomic data. We refine emission baseline for six leading IAMs, and find that their original baselines differ from the new estimates in a range of -45.7% to 76.4% between 2010 and 2020, primarily due to inappropriate growth rates settings. Adopting refined historical emission trends, we re-calculate future emission pathways for developing countries and the globe. Our new estimates show that countries in Asia would require a median of 81 Gt of carbon space (2.2 times of global total emission in 2023) in the SSP245 scenario from 2020 to 2050 cumulatively, a difference of -30.3% to 35.5% compared to the estimates provided by IAM models. Even under the fast decarbonization scenario of SSP119, developing countries like Vietnam, Benin and Ethiopia reliant on fossil fuels, would need a median carbon space of 120.6 Mt, 4.9 Mt, and 11.5 Mt, respectively, by 2040. In the short term, constrained capacities impede these countries from shifting emissions trajectories, as inertia scenarios incorporating historical trends frequently align with SSP585 scenarios, revealing the dilemma between development priorities and the pursuit of low-carbon goals. These findings emphasize additional carbon space needed by swiftly growing developing countries, which is shadowed by projections from current IAM models and should be fully considered in global carbon budget allocations and future mitigation effort needed.