Greenhouse gas emission timing in life cycle assessment and the global warming potential of perennial energy crops

Abstract

Presently, climate metrics in life-cycle assessment (LCA) aggregate the emission of greenhouse gases in one impact-triggering instant, rather than accommodating its distribution along a timeline. There have been efforts to make the global warming potential (GWP) metric dynamic to study temporary carbon storage in wood products. In this article, we test the use of dynamic LCA on bioenergy production from Jatropha oil in Mali, which offers temporary carbon sequestration in biomass and soil. We built a life-cycle inventory for land conversion to jatropha after cropland and fallow land. The assessment was made for one and for 10 consecutive rotations, and yielded dynamic emission profiles over the years. We found that dynamic LCA is sensitive to variations in emission over time, and that it resulted in lower GWP compared to the conventional static approach following IPCC rules, except for early times of analysis. But the largest variation occurs within dynamic LCA between readings at different times of analysis. The choice of time of analysis in the dynamic LCA methodology has no theoretical grounds and is therefore subjective. In the particular case of this short-lived product, we did not find an added value for the provoked increase in complexity of LCA.