A Contrail Inventory of U.S. Airspace (2015)

Abstract

High thin clouds are generated by aircraft when hot exhaust gases from the jet engines mix with cold, humid air. These anthropogenic (human made) clouds, known as condensation trails or contrails, provide a net global warming effect. Although they block approximately 23% of the incoming shortwave radiation, they also reflect back to Earth approximately 33% of outgoing longwave radiation. Although the contrails generate only 2% of total anthropogenic radiative forcing they affect global warming immediately (unlike CO2 that affects global warning in 20-40 years). In this way contrails could be used to reduce global warming now to buy-time for CO2 mitigation initiatives to take effect. For this reason it is necessary to inventory contrails in the National Airspace System (NAS).This paper provides an inventory of contrails for the U.S. NAS for 2015. The analysis is based on publicly available weather data, flight surveillance track data, models of contrail formation and persistence, and models of net radiative forcing. During this period an average flight schedule of 24,095 flights in 365 historic weather days generated a daily average of 83.7K nautical miles of contrails. The contrails resulted in an estimated daily net radiative forcing of +7.08 mW/m2. The diurnal effect was minimal, but the seasonal effect was significant: 63% of the total Contrail Along Track Distance was generated from June to September. Furthermore, less than 25% of the flights generated contrails on a given day and the most of the contrails are generated in the south-eastern United States. The implications of these results for contrail mitigation are discussed.