Reservoir CO2 and CH4 emissions and their climate impact over the period 1900–2060

Reservoirs are essential for human populations, but their global carbon footprint is substantial (0.73–2.41 PgCO 2 -equivalent yr −1 ). Yet the temporal evolution of reservoir carbon emissions and their contribution to anthropogenic radiative forcing remains unresolved. Here we quantify the long-term historical and future evolution (1900–2060) of cumulative global reservoir area, carbon dioxide and methane emissions and the resulting radiative forcing. We show that global reservoir carbon emissions peaked in 1987 (4.4 TmolC yr −1 ) and have been declining since, due largely to decreasing carbon dioxide emissions as reservoirs age. However, reservoir-induced radiative forcing continues to rise due to ongoing increases in reservoir methane emissions, which accounted for 5.2% of global anthropogenic methane emissions in 2020. We estimate that, in the future, methane ebullition and degassing flux will make up >75% of the reservoir-induced radiative forcing, making these flux pathways key targets for improved understanding and mitigation. Reservoir-induced radiative forcing is increasing globally due to rising methane emissions outweighing declining carbon dioxide emissions, according to modelling based on reservoir surface area observations.