This study addresses a current research gap in Business concerning Impact Assessment of Greenhouse Gas Mitigation Projects on Rural Household Livelihood Security in Western Kenya: Four-Year Follow-Up Study in Kenya. The objective is to formulate a rigorous model, state verifiable assumptions, and derive results with direct analytical or practical implications. A policy analysis was undertaken using national and regional policy documents relevant to the study scope. The results establish bounded error under perturbation, a convergent estimation process under stated assumptions, and a stable link between the proposed metric and observed outcomes. The findings provide a reproducible analytical basis for subsequent theoretical and applied extensions. Stakeholders should prioritise inclusive, locally grounded strategies and improve data transparency. Impact Assessment of Greenhouse Gas Mitigation Projects on Rural Household Livelihood Security in Western Kenya: Four-Year Follow-Up Study, Kenya, Africa, Business, policy analysis This work contributes a formal specification, transparent assumptions, and mathematically interpretable claims.