Recommendations for calculation of the global warming potential of aviation including the radiative forcing index

Abstract

Purpose: There are specific effects of emissions in high altitude, which lead to a higher contribution of aviation to the problem of climate change than just the emission of CO 2 from burning fuels. The exact relevance is subject to scientific debate, but there is a consensus that aircrafts have an impact that is higher than just their contribution due to the direct CO 2 emissions. The gap between this scientific knowledge on the one side and the missing of applicable GWP (global warming potential) factors for relevant emissions on the other side are an important shortcoming for life cycle assessment (LCA) or carbon footprint (CF) studies which aim to cover all relevant environmental impacts of the transport services investigated. Methods: In this paper, the state of the art concerning the accounting for the specific effects of aircraft emissions in LCA and CF studies is discussed. Therefore, the relevant literature was evaluated, and practitioners were asked for the approaches used by them. Results and discussion: Five major approaches are identified ranging from an RFI (radiative forcing index) factor of 1 (no factor at all) to a factor 2.7 for the total aircraft CO 2 emissions. If only emissions in the higher atmosphere are considered, RFI factors between 1 and 8.5 are used or proposed in practice. Conclusions: For the time being, an RFI of 2 on total aircraft CO 2 (or 5.2 for the CO 2 emissions in the higher atmosphere if using present models in ecoinvent) is recommended to be used in LCA and CF studies because it is based on the latest scientific publications; this basic literature cannot be misinterpreted. Furthermore, it is also recommended by some political institutions. These factors can be multiplied by the direct CO 2 emissions of the aircraft to estimate the total global warming potential.