Two decades of methane budgets at the sub-national scale in China

Accurate accounting of regional methane (CH₄) emissions and removals is essential for tracking national climate mitigation progress and assessing potential carbon-climate feedbacks. China is the world's largest CH₄ emitter, yet comprehensive sub-national estimates remain limited, constraining the development of effective mitigation strategies. This study analyzes CH₄ emissions across China from 2000 to 2019 using atmospheric inversion ensembles (top-down approach, TD) and process-based model estimates (bottom-up approach, BU). The datasets for both approaches were contributed by international research teams coordinated through the Global Carbon Project. The spatial distribution of various CH₄ fluxes exhibits high spatial heterogeneity. Approximately 60% of national CH₄ emissions come from three of the nine sub-national regions (North China, Southeast China, and Southwest China), which together account for <30% of China's land area. These emissions are dominated by the energy and agricultural sectors. Natural sources contribute 9%-16% of the total CH₄ budget, but they have the largest relative uncertainties, reaching approximately 150%-170% of their estimated magnitudes. This high uncertainty partly reflects the limited number of studies on natural CH₄ sources. The increase in anthropogenic emissions is the primary driver of the changes between the two decades, with increases of 10.4 [2.7-16.9] Tg CH₄ a^-1 (BU) and 6.1 [-2.6-10.7] Tg CH₄ a^-1 (TD). The largest increases occur in North China, Southwest China, Southeast China, and Northeast China. This study highlights the need for improved regional monitoring of CH₄ emissions and sinks in China to support integrated and spatially targeted mitigation strategies.