Big disparities in CH4 emission patterns from landfills between the United States and China and their behind driving forces

Waste is the bridge linking resource consumption and greenhouse gas generation, and waste landfills are the main anthropogenic source of methane (CH₄). The United States (US)–China Joint Glasgow Declaration and the Global Methane Pledge are committed to reducing tractable CH₄ emissions; however, differences between the involved countries as well as their generation forecast processes have hampered cooperation. In this study, we provide a deep insight into CH₄ emissions from municipal solid waste (MSW) landfills and identify the disparities in CH₄ emissions with local socio-economic conditions. The US and China, the world's two largest economies, generated approximately 3.73 and 1.48 million tonnes of CH₄ from 1248 to 1955 landfills in 2012 using the FOD/bottom-up method, with corresponding 26.93 and 11.94 kg per tonne waste and emission value from each landfill ranging between 10⁰ and 10⁵ and 10⁻⁵–10⁵ tonnes. The spatial distribution was also quantified and compared with national, state/province, and urban agglomeration perspectives based on historical MSW variations (1990–2015) to clarify the triangular relationship between the economic situation, waste properties, and landfill CH₄ emissions. High-density CH₄ emission regions spatially overlapped with highly developed urban agglomerations, positively correlated with the local gross domestic product (GDP) and population (p < 0.01), with more emissions generated per thousand US dollars in the US (0.25 tonnes) than in China (0.16 tonnes). The US tertiary industry and China's secondary industry contributed to high CH₄ emissions from the waste sector. The increase in tertiary industry might reduce the waste sector's CH₄ emissions. This study will help to understand this new triangular relationship and predict future patterns of CH₄ emissions.