IPCC Tier 1 methodology overestimates the carbon footprint of smallholder cattle production systems in Kenya

Abstract Most Sub-Saharan countries still rely on the basic Intergovernmental Panel on Climate Change's (IPCC) Tier 1 methodology for reporting greenhouse gas (GHG) emissions from their livestock sector. This approach is, however, associated with high uncertainty and cannot detect changes in GHG emissions resulting from mitigation interventions. The present study aimed to quantify the effect of replacing the IPCC Tier 1 methodology with Tier 2 approaches in assessing total farmgate GHG emissions and products' emission intensities (EIs) in smallholder cattle production in Western Kenya. Additionally, the study assessed the effect of using locally measured methane yield (MY) instead of regional defaults in Tier 2 estimations. A partial life cycle assessment (LCA) was conducted using aggregated activity data from two contrasting study sites, one with moderately performing and another with low-performing cattle production systems. The total farmgate GHG emissions were allocated to the co-products, namely milk and live weight gain, using the novel energy expenditure allocation method, in comparison to the traditionally used protein mass allocation. Compared Tier 1 methodology, the use of Tier 2 approaches resulted in 18-44% lower total farmgate GHG emissions and milk EIs across the two study sites. When the IPCC regional MY default was substituted with locally measured MY, the total GHG emissions and milk EI increased by 19-25%. These findings suggest that the continued use of IPCC Tier 1 methodology or Tier 2 MY defaults by East African countries are resulting in considerable uncertainty in their livestock GHG inventory reporting. There is therefore a need for these developing nations to adopt higher-tier methodologies as well as measure and utilize locally relevant MY for more accurate inventory reporting and to be able to assess suitable GHG mitigation strategies for local cattle production systems. Additionally, the study found that the energy expenditure allocation method apportioned a lower proportion of GHG emissions to milk production compared to live weight gain, reflecting the greater nutrient use efficiency by cattle in producing milk than gaining weight. As developing countries are faced with the double challenge of increasing animal-sourced food to feed the growing population and a need to reduce GHG emissions associated with food production, it is sensible for these countries to report changes in product EIs rather than absolute emissions. It is, therefore, imperative to continually refine LCA methodology for more relevance in multifunctional smallholder systems for unbiased measurement of products' EIs from such systems.