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Shang et al. Carbon Footprints 2025, 4, 24 https://dx.doi.org/10.20517/cf.2025.28 Page 3 of 18

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311.2-1,288.99 Gg, with methane-to-energy conversion potentials ranging from 2.08 × 10 to 9.86 × 10 MJ
in 2015 [15,16] . Liu et al. applied the FOD/bottom-up method to compare landfill methane emissions in the
[17]
United States and China, finding that U.S. emissions were 2.5 times higher . Zhang et al. applied a two-tier
satellite approach to measure emissions from 90 MSW landfills in China, India, and the U.S., showing that
China’s operational practices (e.g., HDPE covers and gas collection systems) reduced emissions more
[18]
effectively than those in India and the U.S. . Other studies [19-21] using diverse measurement techniques have
underscored the significance of landfill methane emissions. Li et al. developed a plant-level, technology-
specific methane inventory for China’s wastewater treatment plants (WWTPs) using a bottom-up approach,
estimating emissions of 150.6 Gg in 2020 . Song et al. systematically quantified methane emissions across
[22]
sewage treatment facilities and pipelines, identifying sludge treatment, particularly anaerobic digestion, as
[23]
the primary source . Liu et al. established a wastewater methane inventory for 31 Chinese provinces (2000-
2020), finding emissions rose from 1.4 to 2.7 Tg . Yin et al. quantified methane emissions from six
[24]
WWTPs in China and showed that sewer systems accounted for nearly 90% of CH emissions in Beijing
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WWTPs, underscoring the critical role of sewer-derived methane in mitigating underestimation . Overall,
[25]
methane emissions from MSW vary widely across cities globally, influenced by waste composition (linked
to industrial structures) and waste management practices (notably the presence of advanced gas collection
systems).

In agriculture, most methane research focuses on paddy cultivation, while methane from agricultural waste,
primarily crop residues, remains less studied. China's large volume of straw production represents a
potentially significant source of methane through thermochemical conversion, yet emission dynamics in
fuel production systems are insufficiently characterized. Xu et al. used the extended Logarithmic Mean
Divisia Index (LMDI) method and Tapio’s decoupling index to analyze methane reduction in China’s
agricultural sector (2010-2019) . Shen et al. assessed long-term methane emissions from rice cultivation in
[26]
China (2000-2060) using an integrated approach, identifying key drivers such as straw return rate (RSA),
fertilization, and climate factors . Other studies examine methane emissions from a broader perspective,
[27]
considering urban energy consumption, food production, and consumption. Brown reviewed greenhouse
gas accounting protocols for landfill diversion of food and yard waste, analyzing the Climate Action Reserve
(CAR) and U.S. EPA WARM models with a focus on methane avoidance through decay rate constants and
[28]
gas collection efficiency . Wang et al. developed a dynamic model combined with the LMDI method to
assess CH emissions from China's fossil-fuel and food systems . Livestock methane emissions primarily
[29]
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derive from manure management systems and vary depending on handling methods. Wang et al.
established a high-resolution dataset of livestock methane emissions in China (1990-2020), revealing that
low-cost interventions could cut emissions by 36% ± 8% (4.4-6.9 Mt) by 2030 . Zhang et al. reported a
[30]
fourfold increase in livestock methane emissions (31.8 to 131.7 Tg CH /year) since 1950, driven mainly by
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cattle, with 2019 levels ~20% higher than FAOSTAT estimates and hotspots in South Asia, South America,
and North Africa . Chen et al. examined manure management systems in livestock and poultry farming,
[31]
finding higher methane emissions in solid compared with liquid systems, due to differences in organic
matter, water content, and microbial activity . Overall, existing studies have focused more on agricultural
[32]
and industrial methane sources, while emissions from waste management remain underexplored. Moreover,
most methane accounting frameworks operate at provincial or municipal scales, with limited
spatiotemporal integration.

In summary, current methane research spans multiple sub-sectors - including municipal waste, domestic
sewage, livestock and poultry farming, and agricultural residues - but most studies examine single-source
generation pathways. Previous research typically evaluated waste alongside energy and agriculture under
IPCC classifications, without establishing a comprehensive framework that integrates waste generation from