Methane (CH₄) has a 28-fold greater global warming potential than CO₂ over 100 years. Atmospheric CH₄ concentration has tripled since 1750. Anthropogenic CH₄ emissions from China have been growing rapidly in the past decades and contribute more than 10 % of global anthropogenic CH₄ emissions with large uncertainties in existing global inventories, generally limited to country-scale statistics. To date, a long-term CH₄ emission inventory including the major sources sectors and based on province-level emission factors is still lacking. In this study, we produced a detailed annual bottom-up inventory of anthropogenic CH₄ emissions from the eight major source sectors in China for the period 1980–2010. In the past 3 decades, the total CH₄ emissions increased from 24.4 [18.6–30.5] Tg CH₄ yr⁻¹ in 1980 (mean [minimum–maximum of 95 % confidence interval]) to 44.9 [36.6–56.4] Tg CH₄ yr⁻¹ in 2010. Most of this increase took place in the 2000s decade with averaged yearly emissions of 38.5 [30.6–48.3] Tg CH₄ yr⁻¹. This fast increase of the total CH₄ emissions after 2000 is mainly driven by CH₄ emissions from coal exploitation. The largest contribution to total CH₄ emissions also shifted from rice cultivation in 1980 to coal exploitation in 2010. The total emissions inferred in this work compare well with the EPA inventory but appear to be 36 and 18 % lower than the EDGAR4.2 inventory and the estimates using the same method but IPCC default emission factors, respectively. The uncertainty of our inventory is investigated using emission factors collected from state-of-the-art published literatures. We also distributed province-scale emissions into 0.1° × 0.1° maps using socioeconomic activity data. This new inventory could help understanding CH₄ budgets at regional scale and guiding CH₄ mitigation policies in China.

Most forests worldwide are located in upland landscapes. Previous studies have mainly focused on ground methane (CH₄) flux in upland forests, and living tree stem‐based CH₄ processes and fluxes are thus relatively poorly understood. This study investigated the relationship between CH₄ concentration and water content in the heartwood of living trees in midtemperate, warm temperate, and subtropical upland forests and also measured seasonal changes of in situ stem CH₄ flux and the CH₄ concentration and water content in the heartwood of Populus davidiana Dode in a warm temperate upland forest. We found that approximately 4–13% of tree stems or approximately 8–31% of tree species had a substantial CH₄ concentration of ≥10,000 μL L⁻¹ in their heartwood across the three types of upland forests. The heartwood CH₄ concentration was related to water content by a power function. A threshold of water content occurred beyond which CH₄ was produced at high levels in the heartwood. The CH₄ emissions from the breast height stems of P. davidiana ranged from 202.1 to 331.6 μg m⁻² h⁻¹ on a stem surface area basis during July–October 2016 and were significantly linearly correlated with the CH₄ concentration or water content in the heartwood throughout the experimental period, but the linear correlation was not significant at daily and monthly scales. Temperature was not a limiting factor for CH₄ production during July–October 2016, and thus, most of the CH₄ production may be explained by water content in the heartwood of living trees in upland forests.