Protocol for a Tier 2 approach to generate context-specific enteric methane emission factors for small ruminants’ production systems using the IPCC method

This protocol is a guide for the collection of data and calculation of context-specific enteric methane (CH4) emission factors (EFs = CH4 kg/head per year) for small ruminants (sheep/goat) production systems in low- and middle-income countries (LMICs) based on the Intergovernmental Panel on Climate Change (IPCC) Tier 2 method (IPCC 2006; IPCC 2019). Tier 2 enteric CH4 estimations are essential for accurately reporting national greenhouse gas (GHG) inventories for livestock and developing locally suitable mitigation strategies in line with the Paris Climate Change Agreement (Wilkes et al. 2017). The use of Tier 2 approaches is more accurate than the Tier 1 methodology currently used by most LMICs. It incorporates local animal activity data and diet characteristics, in contrast to Tier 1 approaches which use activity data averaged at a continental level. The approach described in this protocol uses year-long farm level data accounting for seasonal variations in feed availability, feed quality, and related variations in animal performance. Unless otherwise stated, the energy requirement calculations are based on net energy equations described in the revised IPCC method of 2019 (IPCC 2019); the initial method is described in IPCC 2006. Some of the examples in literature where the IPCC Tier 2 method has been used to estimate enteric methane emissions from small ruminants include Ndao et al. 2019, Wilkes et al. 2020a and Goopy et al. 2021. The protocol is primarily intended for use in smallholder mixed crop-livestock systems but can be adapted for other production systems (e.g., pastoral). Where such variations are necessary, the changes required have been described in the manual.