finding 5.5 : key-message-5-5

Various strategies are available to mitigate livestock enteric and manure CH4 emissions. Promising and readily applicable technologies can reduce enteric CH4 emissions from ruminants by 20% to 30%. Other mitigation technologies can reduce manure CH4 emissions by 30% to 50%, on average, and in some cases as much as 80%. Methane mitigation strategies have to be evaluated on a production-system scale to account for emission tradeoffs and co-benefits such as improved feed efficiency or productivity in livestock (high confidence, likely).

This finding is from chapter 5 of Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report.

Description of evidence base: Non-CO2 GHG mitigation strategies for livestock have been summarized in several comprehensive reviews (Montes et al., 2013; Hristov et al., 2013b; Herrero et al., 2016).

New information and remaining uncertainties: Uncertainty exists in any measurement or projection of GHG emissions. Uncertainties of GHG mitigation options are related to 1) uncertainties in projecting emissions, 2) uncertainties in projecting mitigation potential, and 3) uncertainties in the extent of the adoption of mitigation options. The uncertainty of farm-scale projections is related to the uncertainty in projecting emissions from individual sources (Chianese et al., 2009). The IPCC (2006) suggested a ±20% uncertainty in projecting both enteric and manure management CH4 emissions. Through the use of process-based models representing common management strategies for the United States, the uncertainty for projecting enteric emissions may be reduced to ±10%, but uncertainty for manure management likely remains around ±20% (Chianese et al., 2009). Considering these uncertainties along with those of other agricultural emission sources, total GHG emissions can be determined with an uncertainty of ±10% to ±15%. As process-level models improve, verified with accurate measurements, this uncertainty can be reduced.

Assessment of confidence based on evidence: There is high confidence that mitigation technologies can reduce livestock enteric and manure emissions. These technologies include practices related to reducing emissions from enteric fermentation (i.e., cattle) and manure management (i.e., cattle and swine) as discussed by Hristov et al. (2013b) and Herrero et al. (2016). Other potential CH4 mitigation strategies include manure solids separation, aeration, acidification, biofiltration, composting, and anaerobic digestion (Montes et al., 2013).

This finding was derived from figure P.2: P.2. Likelihood and Confidence Evaluation

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