Impacts of multi-layer overlap on contrail radiative forcing

Abstract. Condensation trails (“contrails”) which form behind aircraft are estimated to cause on the order of 50 % total climate forcing aviation, matching impact all accumulated aviation-attributable CO2. The impacts these contrails highly uncertain, in part due effect overlap between and other cloud layers. Although literature estimates suggest that could change even sign contrail radiative (RF), cloud–contrail overlaps not well understood, contrail–contrail has never been quantified. In this study we develop apply a new model explicitly accounts for Assuming maximum possible provide an upper bound impacts, is found reduce shortwave-cooling attributable aviation by 66 while reducing longwave-warming only 37 %. Therefore, average 2015, increased net from contrails. We also quantify sensitivity cover with respect geographic location. Clouds significantly increase warming at high latitudes over sea, transforming cooling into ones North Atlantic corridor. Based same data, our results indicate disregarding given pair layers can result longwave shortwave being overestimated up 16 25 %, respectively, highest bias observed optical depths (> 0.4) solar zenith angles 75?). When applied global coverage data reduces both ? 2 relative calculations ignore overlap. greater radiation, resulting 3 reduction RF when correctly accounted for. This suggests effects likely be neglected current-day environmental aviation. However, may future as airline industry grows regions.