Simulated 2050 aviation radiative forcing from contrails and aerosols

Chih-Chieh Chen,Andrew Gettelman

doi:10.5194/acp-16-7317-2016

Chih-Chieh Chen, Andrew Gettelman

Open Access

https://doi.org/10.5194/acp-16-7317-2016

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Abstract

Abstract. The radiative forcing from aviation-induced cloudiness is investigated by using the Community Atmosphere Model Version 5 (CAM5) in the present (2006) and the future (through 2050). Global flight distance is projected to increase by a factor of 4 between 2006 and 2050. However, simulated contrail cirrus radiative forcing in 2050 can reach 87 mW m−2, an increase by a factor of 7 from 2006, and thus does not scale linearly with fuel emission mass. This is due to non-uniform regional increase in air traffic and different sensitivities for contrail radiative forcing in different regions. CAM5 simulations indicate that negative radiative forcing induced by the indirect effect of aviation sulfate aerosols on liquid clouds in 2050 can be as large as −160 mW m−2, an increase by a factor of 4 from 2006. As a result, the net 2050 radiative forcing of contrail cirrus and aviation aerosols may have a cooling effect on the planet. Aviation sulfate aerosols emitted at cruise altitude can be transported down to the lower troposphere, increasing the aerosol concentration, thus increasing the cloud drop number concentration and persistence of low-level clouds. Aviation black carbon aerosols produce a negligible net forcing globally in 2006 and 2050 in this model study. Uncertainties in the methodology and the modeling are significant and discussed in detail. Nevertheless, the projected percentage increase in contrail radiative forcing is important for future aviation impacts. In addition, the role of aviation aerosols in the cloud nucleation processes can greatly influence on the simulated radiative forcing from aircraft-induced cloudiness and even change its sign. Future research to confirm these results is necessary.

Highlights

Aviation fossil fuel consumption is projected to increase significantly during the 21st century due to population and economic growth
The second set of simulations include aviation water vapor emission only and the difference from the control run can be interpreted as the effect of contrails and contrail cirrus (“contrail cirrus” or “H2 O”)
Emissions, and the difference from the control run is due to the combination of contrail cirrus and aviation aerosols

Summary

Introduction

Aviation fossil fuel consumption is projected to increase significantly during the 21st century due to population and economic growth. Since future population and economic growth are most likely non-uniform, some regions may experience higher aviation impact than others. Spreading and shearing of contrails may increase cloudiness, called contrail cirrus (Schumann and Wendling, 1990; Minnis et al, 1998). Linear contrails and contrail cirrus produce a warming effect on the planet since the radiative forcing of these optically thin high clouds is dominated by longwave heating (Dietmüller et al., 2008; Rap et al, 2010; Kärcher et al, 2010; De Leon et al., 2012). Based on some recent studies using general circulation model simulations, Burkhardt and Kärcher (2011) estimated present-day contrail cirrus radiative forcing of 31 mW m−2 , Chen and Gettelman (2013) estimated 13 ± 10 mW m−2 and Schumann and Graf (2013) estimated 50 (40–80) mW m−2. Schumann et al (2015) estimated 60 (40–80) mW m−2

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