Reducing global warming by airline contrail avoidance: A case study of annual benefits for the contiguous United States

Abstract

High thin clouds are generated by airliners when hot exhaust gases and water vapor from the jet engines mix with cold, humid air to form high thin clouds. These anthropogenic (human made) condensation trails, or “contrails,” create a green-house effect by absorbing or directing back to Earth approximately 33% of emitted outgoing longwave radiation. Although this effect is estimated to be <2% of the Earth's total anthropogenic radiative forcing, the effect on global warming is immediate, unlike CO2 emissions which have a two decade delay in affecting global warming. Policy makers and industry have asked what is the potential for mitigating contrails through operational changes in air traffic control and flight planning.Previous research calculated contrail inventories for the whole U.S. National Airspace System (NAS) over one year: on an average day only 15% of the flights (34% maximum) generated contrails, most of the contrails were generated in the south-eastern United States and the Pacific coast, and 63% of the total Contrail Along Track Distance was generated from June to September. This information suggests a possibility of mitigating the green-house effect of contrails by seasonally targeting a small set of flights.This paper describes the benefits of adjusting the Cruise Flight Level of a limited number of flights in the U.S. NAS that are flight planned to fly through Ice Super Saturated (ISS) regions that are conducive to the formation of persistent contrails. The analysis found that elevating the Cruise Flight Level of contrail generating flights by 2000′ or 4000′, reduced the number of average daily flights with contrails by an average of −14.8%, the Net Radiative Forcing by an average of −92%, with an average net small decrease in fuel-burn of <1% (due to lower Drag at higher altitudes). The implications of these results and the limitations of the method are discussed.