Addressing Uncertainty and Rerouting Strategies in Aviation Climate Impact Assessments

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Aviation causes climate effects through both long-lived CO₂ emissions and short-lived but highly uncertain contrail cirrus. The radiative forcing (RF) of contrail cirrus is spatially and temporally very heterogeneous. This study evaluates the costs and benefits of rerouting by incorporating estimates of the social cost of CO₂ and contrail cirrus, applied to nearly half a million flights over the North Atlantic (Johansson et al., 2024). We estimate contrail cirrus formation and RF uncertainty for individual flights using CoCIP and the 10-member ERA5 ensemble from the European Centre for Medium-Range Weather Forecasts (ECMWF) (Teoh, 2022), alongside additional assumptions on forcing and efficacy uncertainty.We explore the potential climate benefits of rerouting flights to avoid contrail formation, weighing additional fuel burnt against reduced contrail RF. Our results highlight that while rerouting can contribute to climate mitigation, its attractiveness depends on the probability that each rerouting case delivers a net climate benefit. For instance, with a 50% probability threshold (i.e., the median) that a net climate benefit is obtained, 33–35% of flights are beneficial to reroute with a 1% fuel penalty, depending on the social cost assumptions. This proportion decreases to 28–33% for a 5% fuel penalty. Raising the probability to 80% that a net climate benefit is achieved lowers the fraction of flights beneficial to reroute to 27–29% for a 1% fuel penalty and 22–27% for a 5% fuel penalty, where the ranges depend on the social cost assumptions.In this presentation, we provide further insights from the analysis and present an analysis of the value of improved contrail forcing predictability for more effective climate impact mitigation strategies.ReferencesJohansson, D. J. A., Azar, C., Pettersson, S., Sterner, T., Stettler, M., & Teoh, R. (2024, May 14). The social costs of aviation: Comparing contrail cirrus and CO2. Research Square Preprints. https://doi.org/10.21203/rs.3.rs-4329434/v1Teoh, R., Schumann, U., Gryspeerdt, E., Shapiro, M., Molloy, J., Koudis, G., Voigt, C., & Stettler, M. E. J. (2022). Aviation contrail climate effects in the North Atlantic from 2016 to 2021. Atmospheric Chemistry and Physics, 22(22), 10919–10935. https://doi.org/10.5194/acp-22-10919-2022

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