Comparison of enteric methane emissions in China for different IPCC estimation methods and production schemes

Accurate estimation of methane (CH4) emission (ME) from enteric fermentation in China is essential to establishing and maintaining a reliable global ME inventory and developing strategies to mitigate such emissions. Based on modern animal production statistics, i.e., feed quality and quantity data for different feeding systems, enteric methane emissions (EME) in China during the period of 1990 to 1998 were estimated using Intergovernmental Panel on Climate Change (IPCC) estimation methods for various production scenarios. The estimation was conducted based on: (1) Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories (Revised 1996 IPCC Guidelines) Tier 1, designated M1; (2) Revised 1996 IPCC Guidelines Tier 2, designated M2; (3) IPCC Good Practices Guidance and Uncertainty Management in National Greenhouse Gas Inventories (IPCC Good Practices Guidance) without incorporation of treated straw effect on ME, designated M3; and (4) IPCC Good Practices Guidance with incorporation of treated straw effect on ME, designated M4. The results revealed variability in ME among the four estimation methods and production conditions. Specifically, the estimated ME values in China for the peak emission year (1996) were 8,614; 11,039; 10,533; and 11,469 Gg, respectively, with M1, M2, M3, and M4, i.e., up to 33% difference from one method to another. These ME values for 1996 were 31%, 28%, 27%, and 20% higher than their respective values for 1990, the base year for evaluating future emission changes. Yellow cattle contribute more than 50% of EME in China. The methane emission factor was found to be 26% to 30% lower for yellow cattle fed treated residues than for those fed non-treated residues due to improved digestibility. This reduced ME factor translated into an estimated ME reduction of 935.7 Gg in 1996 and 1,253.5 Gg in 1998 for yellow cattle. To further improve the validity of EME estimation, it is suggested that certain quality control measures be taken, such as adjusting emission factors to reflect the changing livestock production systems and management practices, measuring ME factors in the field, and collecting and integrating current animal production statistics.