With conservative fuel savings of

With conservative fuel savings of 35% observed in the laboratory, one BDS will save about 4kg of CO2-e from entering the mao inhibitors list per day and will pay off its embodied CO2-e within a week of use (assuming 1:1 replacement of the TSF). At a cost of $20 per stove and a $0.97 per day fuel savings measured in field surveys, the BDS will pay back its capital cost in three weeks of use. Hence, the BDS provides a significant economic attraction to customers while providing great potential for CO2 mitigation. The dominance of use-phase emissions illuminates two important insights: (1) carefully documenting and monitoring use-phase emissions must be the centerpiece for understanding a cookstove\'s life cycle CO2-e impact, and (2) improving a cookstove\'s CO2-e performance relies almost exclusively on improving its use-phase emissions, even if this comes at the expense of dramatically increased non-use-phase embodied CO2-e. First, without a rigorous program to monitor use-phase emissions, an accurate claim of life cycle emissions is not possible. For example, in the case of the BDS, laboratory and field-measured fuel savings were 35% and 55%, respectively. This 20% discrepancy in fuel savings equates to a 4.2 tonne difference in predicted five-year use-phase emissions for the BDS. Similarly, uncertainties in cookstove combustion performance including CO2-equivalent emission factors and the mix of NRB and RB have significant consequences on estimated life cycle emissions. For example, the sensitivity of the BDS\'s life cycle emissions to the fraction of NRB being consumed is roughly 120kg per additional percent NRB; careful calculation of non-use-phase emissions becomes irrelevant if the NRB fraction is misjudged by just 0.2%. Therefore, given limited resources for monitoring and evaluation, an effective assessment of a cookstove\'s impact must be focused on the use-phase. Finally, it is critically important to understand a cookstove\'s emissions of products of incomplete combustion in order to accurately quantify a cookstove\'s use phase impact; even when burning renewable biomass, CO2-e attributable to PICs dominate the BDS\'s life cycle impact. In this particular case study, Fig. 8 demonstrates that the contribution of PICs to total CO2-e per mass of fuel burned was roughly equivalent for the TSF and BDS – hence, the contribution of PICs to life cycle emissions for the TSF and BDS scaled with their relative fuel efficiencies. In other words, the BDS reduced CO2-e attributable to PICs, but only because of its reduced fuel use. This study used laboratory-based measurement of PIC emission factors, but measurement of a statistically meaningful quantity of in-field emissions, as exemplified in Roden et al. (2009), would be critical to quantifying a cookstove\'s true PIC impact. A weakness of this study was our reliance on laboratory-based measurements of fuel consumption as a proxy for fuel savings in the field. Considering the significant dangers of field work in Darfur, we were precluded from collecting field data on fuel use. However, we fully recognize the many confounding factors influencing real-world fuel consumption such as rebound (e.g. “stove stacking”), seasonal changes, and cookstove abandonment found in other studies (Pillarisetti et al., 2014). Because we have demonstrated the importance of use-phase emissions, we recommend future researchers apply the Kitchen Performance Test, a fuel consumption standard maintained by the Global Alliance for Clean Cookstoves, in any life cycle assessment study that seeks to quantify the real-world global warming potential of a large-scale cookstove program (rather than comparing life cycle phases, as we have done here). Nevertheless, we believe that this study is a useful tool anchor for policy makers interested focusing on what matters when it comes to cookstoves and climate change, and we believe that this study will serve as a template for other cookstove researchers interested in quantifying the life cycle impacts of cookstoves.