Half of the greenhouse gas emissions from China's food system occur during food production

Global greenhouse gas emissions have risen with industrialization, and while carbon dioxide is often the main policy focus, non-CO2 gases such as methane and nitrous oxide have higher global warming potentials over 100 years. Reducing non-CO2 gases can yield substantial climate benefits and lower mitigation costs. Setting sector-specific emission reduction targets is a practical foundation for comprehensive mitigation strategies, and food systems—responsible for about one-third of global anthropogenic GHGs—are a priority, especially in developing countries. GHGs are released across all food-system life cycle stages (production, transport, processing, packaging, consumption, and waste), including from energy use and upstream inputs like fertilizers. In developing countries, emissions at the farm-gate production stage often dominate. While many studies quantify agricultural CO2 and non-CO2 emissions, systematic, full food-system accounting and attention to interregional transfers via trade remain limited for China. This study develops a multi-regional input–output-based hybrid life cycle assessment (MRIO-based hybrid LCA) framework to quantify China’s food-system GHG emissions from farm to fork at national and provincial scales, including supply chains and interregional trade, to identify emission components, sources, and mitigation opportunities.

Prior research highlights that non-CO2 mitigation is crucial for efficient climate strategies and that food systems account for roughly one-third of global anthropogenic GHG emissions. Numerous studies quantified agricultural emissions (CO2, CH4, N2O) and advocated for systematic food-system accounting frameworks to capture emissions across life cycle stages and supply chains. Emerging literature links food-system and agricultural emissions to interregional and international trade, revealing significant embodied emissions transfers across regions. For China, however, detailed food-system-wide estimates that integrate supply chains and regional trade are scarce. Existing global assessments (e.g., FAOSTAT and Crippa et al.) provide national totals for China but differ due to system boundaries and emission factors. Studies targeting China often focus on subsets of stages (e.g., production and processing) rather than an integrated framework that includes all stages and trade. This work addresses these gaps by combining MRIO with hybrid LCA at provincial resolution.

Scope and system boundary: The study assesses China’s food-system GHG emissions across full life cycle stages—production (crop cultivation and animal breeding), processing (primary and deep processing), transport (road, rail, sea), packaging, retail (including refrigeration), consumption (household energy for food-related activities), and waste (solid waste disposal and wastewater). Four gases are included: CO2, CH4, N2O, and F-gases. The analysis covers 30 provinces in mainland China (excluding Tibet, Hong Kong, Macao, and Taiwan) for year 2019. MRIO-based hybrid LCA model: A multi-regional input–output (MRIO) framework describes intersectoral and interregional linkages of intermediate trade and final consumption. The environmentally extended IO model introduces sector- and region-specific GHG intensities. Sectoral food-system shares (SFSs, 0–1) allocate sectoral emissions to the food system (SFS=1 for fully food-related sectors like agriculture; 0<SFS<1 for partially related sectors such as transport). Food-system emissions are computed by multiplying sectoral emissions by SFSs and aggregating by stage, gas, sector, and province. Non-CO2 gases are converted to CO2e using GWP100: 28 for CH4 and 273 for N2O. Life cycle inventory components: - Production (non-energy): CH4 from enteric fermentation, manure management, and rice cultivation; N2O from manure management and synthetic fertilizer application. Livestock CH4 and N2O emissions follow IPCC Guidelines (2006, 2019 refinements) with provincial livestock populations and emission factors. Rice CH4 considers planted area, emission factors, and growing period by rice type. N2O from synthetic fertilizers uses provincial fertilizer consumption (nitrogen and compound), a nitrogen share in compound fertilizer (0.3), and a correction factor (R=1.571) with crop-specific emission factors. - Energy activities: Emissions include (1) direct fossil fuel combustion in agriculture, industry, transport, households, and waste management; (2) electricity and heat consumption (converted to primary energy); (3) upstream fuel-chain emissions (mining, processing, transport, leakage); and (4) indirect emissions. Emissions are calculated from energy consumption by fuel type using net caloric values, emission factors, and oxygenation efficiencies. Sectoral emissions are mapped to food-system stages (consistent with MRIO’s 42-sector scheme). - Fuel production (upstream): CH4 from coal mining (underground and surface) uses improved province-level emission factors derived from data on 787 coal mines to reduce uncertainty. Fugitive CH4 from oil and natural gas systems (venting, production, processing, storage, transport, distribution) uses literature-based emission factors; the average oil-system emission factor is 2.9 kg CH4/m3 and the natural gas fugitive emission rate is 1.5%. - F-gases: Retail-stage refrigeration-related F-gases (HFC-134a, HFC-32, HFC-143, HFC-125) are included. Due to data limitations, national retail-stage F-gas emissions from EDGAR-Food v6.0 (projected to 2019) are allocated to provinces based on provincial electricity use in the retail stage. - Waste management: CH4 from solid waste landfilling uses provincial solid waste quantities with methane correction factors (MCF), degradable organic carbon (DOC=0.151), DOC fraction degradable (DOCF=0.5), and CH4 share (FD=0.5). CH4 from industrial wastewater is based on COD loads for directly discharged and treated wastewater with IPCC factors and MCFs. Domestic sewage CH4 uses BOD loads for discharged and treated fractions with IPCC factors and MCFs; CH4 and N2O from domestic wastewater are further informed by a recent province-level dataset that accounts for treatment processes and discharge pathways. Data sources: Provincial agricultural statistics (2019) from China Agriculture Yearbook (livestock inventories, fertilizer use, crop areas/yields, rice types); MRIO tables (42 sectors, 30 provinces) from CEADs (2017 table used to represent trade and input coefficients due to 2019 unavailability); provincial energy inventories (2019) from CEADs (20 energy types); solid waste from China Urban Construction Statistical Yearbook; industrial wastewater and COD from China Environmental Statistical Yearbook. Uncertainty analysis: Major uncertainties arise from emission factors and activity data. Assigned uncertainties include: 40% for non-energy production activities, 30% for energy activities, 46% for F-gases, 30% for solid waste, and for wastewater: 60% (CH4), 150% (N2O), 4% (CO2). Uncertainties are combined per IPCC methods using appropriate formulas for related and unrelated sources.

- National total: China’s food system emitted 2.4 Gt CO2e in 2019 (95% CI: 1.6–3.2). - By gas (Mt CO2e; shares): CO2 1,159 (47.6%); CH4 831 (34.1%); N2O 343 (14.1%); F-gases 102 (4.2%). - By life cycle stage (Mt CO2e; notable shares): Production 1,223 (50.2% of total); Processing 148; Transport 126 (lowest, 5.4%); Packaging 427 (largest CO2 source within the system); Retail 160; Consumption 199; Waste 153. - Production stage composition (2019): 25.0% CO2, 52.5% CH4, 22.5% N2O. Within production, non-energy activities contributed 82.2% of production emissions; energy activities 17.8%. - Provincial totals (Mt CO2e, 2019): Highest—Inner Mongolia 128 (CI 83–173), Qinghai 127 (CI 87–167), Hunan 118 (CI 74–163), Guangdong 117 (CI 83–151), Shandong 111 (CI 79–143). Lowest—Tianjin 28 (CI 19–37); also low: Beijing 39 (CI 26–52), Hainan 40 (CI 27–53), Shanghai 41 (CI 29–53). - Provincial composition varies: Some provinces dominated by CO2 (e.g., Beijing, Shanxi, Ningxia), others by CH4 (e.g., Jiangxi, Sichuan, Yunnan). N2O shares range from very small (e.g., <3% in Beijing) to large (e.g., 33.3% in Hainan). Provinces with higher production and waste shares tend to have higher CH4 shares; provinces with higher packaging shares tend to be more CO2-dominant. - Non-CO2 importance: Provinces with high total GHGs typically have high non-CO2 emissions, indicating non-CO2 gases are key drivers of food-system emissions. Guangdong had >20 Mt CO2e from waste; Beijing, Tianjin, Ningxia had non-CO2 shares <0.3 (Beijing 0.27). - Interregional trade: 0.7 Gt CO2e (95% CI: 0.5–0.9), or 30.5% of food-system emissions, were embodied in interregional trade in 2019; 79.2% via final consumption and 20.8% via intermediate inputs. Largest final-consumption transfer: Gansu → Henan (13.7 Mt CO2e). Xinjiang exported 48.5 Mt CO2e (highest exporter for final consumption); Guangdong imported 56.8 Mt CO2e (highest importer for final consumption). Total trade balance: Guangdong imported 73.9 Mt CO2e (largest); Henan 63.5 Mt CO2e; Guangdong’s largest net import 59.2 Mt CO2e. Largest net exporter reported as Xinjiang (2.8 Mt CO2e), followed by Qinghai (63.0 Mt CO2e). - Spatial trade patterns: Net exporters of embodied GHGs cluster in the northwest and southwest; net importers concentrate in wealthier eastern and central regions. Exporting regions’ embodied emissions are more non-CO2-heavy and production-stage dominated; importing regions have higher waste and consumption-stage shares.

The study set out to quantify China’s food-system GHG emissions comprehensively across life cycle stages and provinces while capturing interregional trade. Results show total emissions consistent in magnitude with prior global assessments but differing due to system boundaries and emission factors. The bottom-up, province-specific framework yields estimates closer to Chinese realities and includes upstream energy supply-chain emissions, helping explain discrepancies with FAOSTAT and other global studies. The dominance of production-stage emissions and the significant role of non-CO2 gases address the research question by pinpointing where and which gases to target. Regional disparities and trade-driven separation of production and consumption reveal that wealthier coastal and central provinces import food (and embodied GHGs) from western and northeastern regions. This highlights the need for policies that incorporate interregional synergies and shared responsibilities, moving beyond production-only accounting to include embodied emissions in trade. The findings underscore that mitigation strategies must emphasize non-CO2 gases (notably CH4 from livestock and rice, and N2O from manure and fertilizers) alongside CO2 from energy and packaging, and that interventions should be tailored to provincial profiles and stage-specific drivers.

This work provides a national and provincial, life-cycle-resolved assessment of China’s food-system GHG emissions using a MRIO-based hybrid LCA that integrates supply chains and interregional trade. Key contributions include quantifying that roughly half of emissions occur at the production stage, that non-CO2 gases account for slightly more than half of total CO2e, and that embodied emissions are extensively transferred from western and northern producing regions to wealthier central and coastal consuming regions. Policy implications are clear: mitigation must target non-CO2 gases in addition to CO2, prioritize production and waste stages, and consider embodied emissions in interregional trade when allocating responsibilities and designing cooperative strategies. Demand-side measures (e.g., labeling, certification, diet shifts, waste reduction) can complement supply-side improvements and propagate upstream decarbonization. Future research should develop commodity-specific analyses with more granular models and data, account for regional dietary differences and evolving trade networks, and refine province-level inventories to further reduce uncertainties.

- F-gases were not estimated via bottom-up provincial data; national retail-stage F-gas totals from EDGAR-Food were projected to 2019 and allocated to provinces based on retail electricity use. - MRIO tables are not annual; the 2017 MRIO table was used to represent 2019 trade structures and input coefficients, potentially missing economic structure changes. - MRIO accounts are monetary; physical quantity differences are not explicitly captured. - Geographic coverage excludes Tibet, Hong Kong, Macao, and Taiwan due to data limitations. - Emission factor and activity data uncertainties remain, particularly for agricultural non-energy emissions, wastewater, and parts of the energy system, though uncertainty analysis was conducted.