Global greenhouse gas (GHG) emissions, primarily carbon dioxide (CO2), have increased due to industrialization, causing climate change. Non-CO2 GHGs like methane (CH4) and nitrous oxide (N2O) are also significant contributors to global warming. Mitigating these emissions is crucial for effective climate change mitigation. Food systems are responsible for a substantial portion (one-third) of global anthropogenic GHG emissions, making them a priority area for emission reduction strategies, especially in developing countries. GHG emissions occur throughout the food system lifecycle, from production and harvest to processing, transportation, packaging, consumption, and waste disposal. Each stage involves energy consumption and resource use, contributing to overall emissions. While research on GHG emissions from agriculture is extensive, a comprehensive, systematic approach is needed to fully understand food-system emissions, particularly including the effects of regional trade networks. This study focuses on China, a major GHG emitter, to provide a detailed analysis of its food-system GHG emissions, considering the complexities of supply chains and interregional trade. Using a multi-regional input-output-based hybrid life cycle assessment (MIRO-based hybrid LCA) model, the study aims to quantify national and provincial food-system GHG emissions, identify key emission sources, and explore the impact of interregional trade on emission patterns. This comprehensive understanding is essential for stakeholders to develop effective mitigation strategies.

Existing research highlights the significant contribution of food systems to global GHG emissions, with estimates suggesting that they account for about one-third of the total. Much of the research focuses on agricultural emissions, covering various gases including CO2, CH4, and N2O. Recent studies advocate for a systematic approach to account for food-system GHG emissions to understand mitigation potential more effectively. The growing body of literature is increasingly acknowledging the role of interregional food trade in transferring GHG emissions across geographical regions. However, detailed knowledge of food-system GHG emissions, particularly considering supply chains and regional trade networks, remains limited in many regions, including China. This research gap underscores the need for a comprehensive and spatially explicit analysis, such as the one conducted in this study, to comprehensively understand China's food-system GHG emissions.

This study employed a multi-regional input-output-based hybrid life cycle assessment (MIRO-based hybrid LCA) model to estimate China's food-system greenhouse gas (GHG) emissions. This approach combines the strengths of life cycle assessment (LCA) in identifying environmental factors and influences of food-system supply chains with the capabilities of multi-regional input-output (MRIO) analysis in investigating sector linkages and interregional trade. The model assessed national and provincial food-system emissions, considering emissions from four main GHGs (CO2, CH4, N2O, and fluorinated gases (F-gases)) across seven life cycle stages (production, processing, transport, packaging, retail, consumption, and waste). The methodology involved developing a detailed GHG emission inventory, which included various sources, such as enteric fermentation, manure management, rice cultivation, fertilizer use, agricultural fuel combustion, and energy consumption across different stages of the food system. The data incorporated agricultural statistics from the China Agriculture Yearbook, providing provincial inventories of livestock, fertilizer use, crop acreage and yields. The MRIO table from the Carbon Emission Account and Datasets (CEADs) provided information on intermediate trade and final consumption across 42 sectors in 30 of China's provinces. The energy inventory from CEADs covered 20 types of energy, and the waste inventory used data from the China Urban Construction Statistical Yearbook and China Environmental Statistical Yearbook. The study also incorporated refined emission factors for certain aspects, such as methane emissions from coal mining. Uncertainties in emission factors and activity data were carefully considered using uncertainty analysis techniques recommended by the IPCC. The study calculated GHG emissions at both national and provincial levels, evaluating the contribution of various GHGs and life cycle stages. Interregional trade was analyzed to understand the spatial distribution of GHG emissions and their transfer across provinces.

The study's key findings provide a detailed picture of China's food-system GHG emissions: * **National Food System Emissions:** The total GHG emissions from China's food system in 2019 were estimated to be 2.4 (95% CI: 1.6–3.2) Gt CO2-equivalent. CO2 was the primary GHG, accounting for 47.6% of total emissions, followed by CH4 (34.1%), N2O (14.1%), and F-gases (4.2%). Notably, half (50.2%) of the total GHG emissions originated from the production stage. * **Provincial Variations:** Significant disparities in GHG emissions were observed across different provinces. Inner Mongolia and Qinghai were the largest emitters, while Tianjin had the lowest emissions. Provincial variations in the composition of GHG emissions were also significant, with some provinces showing a higher proportion of CO2 emissions and others having higher proportions of CH4 or N2O. The share of different gases within provincial food-system GHG emissions varied considerably from the national average. For instance, CO2 had a larger share in Beijing, Shanxi, and Ningxia, while CH4 was more dominant in Jiangxi, Sichuan, and Yunnan. The proportion of N2O and F-gases also showed substantial variation across provinces. * **Life Cycle Stage Contributions:** While the production stage contributed most to overall national emissions, the importance of various life cycle stages varied significantly across provinces. In some provinces, like Beijing, production contributed only a small percentage, while in others, such as Sichuan, it dominated. The packaging stage was the most significant contributor to CO2 emissions nationally, releasing 0.4 (95% CI: 0.2–0.6) Gt CO2-e. The transport stage contributed the least (5.4%). * **Non-CO2 GHG Contributions:** Non-CO2 GHGs were significant contributors to China's food-system emissions. Provinces with high total GHG emissions also tended to have higher non-CO2 emissions, suggesting that non-CO2 gases are important drivers of overall emissions. Production and waste stages were the primary sources of non-CO2 GHGs. * **Interregional Trade Impacts:** Interregional trade accounted for 30.5% (0.7 Gt CO2-e) of China's food-system emissions. Wealthier eastern and central regions were net importers of GHG emissions embodied in traded food products, while less wealthy western and northern provinces were net exporters. The study illustrated the largest interregional transfer flows (via final consumption) from Gansu to Henan (13.7 Mt CO2-e) and Xinjiang as the highest exporter (48.5 Mt CO2-e). Guangdong was the major importer (56.8 Mt CO2-e). Net trade flows showed that eastern and central provinces are net importers of food-related GHGs, while western and northern provinces are net exporters. The study identified geographical patterns in interregional trade, with net GHG export regions located mainly in the southwest and north and import regions concentrated in the wealthier east and center.

This study provides important insights into China's food-system GHG emissions, addressing the existing research gap by comprehensively incorporating the impact of interregional trade and employing a robust methodological framework. The findings highlight the significant contribution of the production stage, emphasizing the need for targeted mitigation efforts in this sector. The considerable variations observed across provinces underscore the necessity of region-specific policies that consider the unique characteristics of each province's food system. The significant contribution of non-CO2 GHGs highlights the importance of addressing these gases beyond solely focusing on CO2 reduction strategies. The study's analysis of interregional trade reveals the complex interplay between food production and consumption patterns, emphasizing the need for interregional cooperation in developing effective emission reduction strategies. The results are comparable with other national estimates within the range of uncertainty reported, indicating the reliability of the study's findings. However, differences exist, likely due to variations in methodology, system boundaries, and emission factors used. The study's findings have considerable implications for policy-making and support the need for a holistic approach to address the environmental impacts of China's food system.

This research offers a comprehensive analysis of China's food-system GHG emissions, revealing significant variations across provinces and highlighting the substantial role of interregional trade. The study underscores the dominance of the production stage and the importance of non-CO2 GHGs in the overall emission profile. The findings strongly advocate for region-specific mitigation policies that address both CO2 and non-CO2 emissions, promoting interregional cooperation to achieve ambitious climate change targets. Future research could explore more detailed modeling, incorporating specific food commodities and incorporating dynamic factors like changing dietary habits and trade patterns.

This study has several limitations. The lack of detailed data on F-gases at the provincial level necessitated the use of a proxy method, which introduces uncertainty. The use of the 2017 MRIO table instead of a 2019 table may influence the accuracy of the results, as economic structures may have changed between these years. The study excluded Tibet, Hong Kong, Macau, and Taiwan due to data limitations. The model's reliance on aggregate data may mask variations at the level of individual agricultural operations or food products. Furthermore, uncertainties associated with emission factors could affect the precision of the findings.