Gidden, M.J., Gasser, T., Grassi, G., Forsell, N., Janssens, I., Lamb, W., Minx, J., Nicholls, Z., Steinhauser, J., Riahi, K.

Aligning climate scenarios to emissions inventories shifts global benchmarks

in Nature, 22.11.2023

Peer Review , Applied Sustainability Sciences

Taking stock of global progress towards achieving the Paris Agreement requires consistently measuring aggregate national actions and pledges against modelled mitigation pathways¹. However, national greenhouse gas inventories (NGHGIs) and scientific assessments of anthropogenic emissions follow different accounting conventions for land-based carbon fluxes resulting in a large difference in the present emission estimates^2,3, a gap that will evolve over time. Using state-of-the-art methodologies⁴ and a land carbon-cycle emulator^{2 emissions from land use and land cover change and their uncertainty. Biogeosciences 17, 4075–4101 (2020).">5}, we align the Intergovernmental Panel on Climate Change (IPCC)-assessed mitigation pathways with the NGHGIs to make a comparison. We find that the key global mitigation benchmarks become harder to achieve when calculated using the NGHGI conventions, requiring both earlier net-zero CO₂ timing and lower cumulative emissions. Furthermore, weakening natural carbon removal processes such as carbon fertilization can mask anthropogenic land-based removal efforts, with the result that land-based carbon fluxes in NGHGIs may ultimately become sources of emissions by 2100. Our results are important for the Global Stocktake⁶, suggesting that nations will need to increase the collective ambition of their climate targets to remain consistent with the global temperature goals.