Evaluating IPCC methodologies for estimating methane emission from lagoon-based swine manure management systems

Authors: Sohoulande Djebou, Dagbegnon; Vanotti, Matias; Szogi, Ariel

Submitted to: Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2025
Publication Date: 3/24/2025
Citation: Sohoulande Djebou, D.C., Vanotti, M.B., Szogi, A.A. 2025. Evaluating IPCC methodologies for estimating methane emission from lagoon-based swine manure management systems. Environmental Quality. 34(4). Article e70079. https://doi.org/10.1002/tqem.70079.
DOI: https://doi.org/10.1002/tqem.70079

Interpretive Summary: To support national estimates of methane (CH4) emissions from manure management systems, the Intergovernmental Panel on Climate Change (IPCC) proposed Tier 1 and Tier 2 methodologies. The choice of each methodology depends on data availability. The application of the Tier 1 methodology uses default emission factors and requires less data compared to the Tier 2 methodology, which is considered a more advanced approach. Nevertheless, no study has addressed the implications of the choice of methodology on estimating CH4 emission from swine manure management systems. As a result, there is no quantitative information on the difference to expect when using the Tier 1 or Tier 2 methodology for estimating CH4 emissions from significant sources such as open-air swine waste treatment lagoons. This study applied the Tier 1 and Tier 2 methodologies to estimate CH4 emissions from North Carolina feeder-to-finish swine waste treatment lagoons. Results show that Tier 2’s estimates of CH4 emissions are slightly higher, sustaining a difference of 6.7% between the two IPCC methodologies. Quantitatively, the differences between the two estimates totaled 7320 Mg CH4/year at the state level and were unequally distributed among counties and farms. These results highlight the trade-off related to the emission estimation approaches and should be considered for planning strategies that promote CH4 emission control.

Technical Abstract: To support national estimates of methane (CH4) emissions from manure management systems, the Intergovernmental Panel on Climate Change (IPCC) proposed guidelines that include three tiers, of which Tier 1 and Tier 2 methodologies are the most used. The choice of each methodology is often driven by data availability. The application of IPCC Tier 1 approach uses default emission factors and requires less data compared to IPCC Tier 2, which is considered a more advanced methodology. Nevertheless, no study has addressed the implications of the methodology choice on the estimation of CH4 emission from swine manure management systems. Subsequently, there is barely any quantitative information on the discrepancies to expect when using the IPCC Tier 1 or Tier 2 approach for estimating CH4 emissions from significant sources such as open-air swine waste treatment lagoons. Hence, this study, used the IPCC Tier 1 and Tier 2 methodologies to estimate CH4 emissions from feeder-to-finish swine waste treatment lagoons across the North Carolina region. Precisely, updated IPCC guidelines were applied to farm, county, and state levels data of feeder-to-finish swine farms to quantify CH4 emissions from open-air anaerobic swine waste treatment lagoons. Results show that IPCC Tier 2’s estimates of CH4 emissions are slightly higher, sustaining a discrepancy of 6.7% between the two IPCC tiers’ methodologies. Quantitatively, the differences between the two IPCC tiers’ estimates totaled 7320 Mg CH4/year at the state level and were unequally distributed among counties and farms. These results highlight the trade-off related to the emission estimation approaches and could be useful to plan strategies that promote CH4 emission control.