Methane Emission Status in the Crop Cultivation Section of Major Countries National Greenhouse Gas Inventory Reports Following Guideline Changes

This study analyzes the impact of guideline revisions by the Intergovernmental Panel on Climate Change (IPCC) on methane (CH4) emission estimates in the crop cultivation sector, particularly from paddy rice fields, as reported in the National Greenhouse Gas Inventory Reports of major countries. Over successive revisions (1996, 2006, 2019), the IPCC guidelines have introduced increasingly detailed calculation methodologies, incorporating factors such as cultivation period, water management practices, and organic amendment applications. These refinements have led to a gradual decrease in default annual emission factors. Using National Inventory Report (NIR) and Common Reporting Format (CRF) data from 14 countries, including the United States and Japan, the study compares changes in CH4 emissions based on water regime, organic input types, and cultivated area. The findings reveal significant differences in emissions between countries, primarily driven by variations in irrigation practices and organic amendment strategies. This study highlights the importance of adopting updated IPCC guidelines to improve the accuracy of emission estimates and supports the formulation of more effective national GHG mitigation strategies.