Mitigating Aviation Impacts on Climate

Abstract:

The International Civil Aviation Organization estimates that in recent years there have been more than 100,000 daily commercial flights across the world. Over the past few decades, demand for flights has been increasing attributed to population and economic growth and socio-cultural practices, which in turn leads to a growth in a range of environmental impacts. One of the ways that aviation alters climate is through formation of condensation trails or ‘contrails’. A contrail is a visible white track of cloud in the upper troposphere due to condensation of water vapour from aircraft’s engine exhaust, which reflects and absorbs solar and terrestrial radiation. Contrails formed by night-time flights (N-contrails) predominantly absorb longwave radiation emitted by the Earth, so in turn enhance warming. In contrast, daytime contrails (D-contrails) have a negligible warming or even cooling impact on climate due to a balance of negative and positive radiative forcing. The magnitude of contrail effect depends on time of day, geographical location, contrail coverage, lifetime, and contrail properties. Previous studies indicate that significant uncertainties remain regarding our understanding of contrails and current Global Climate Models do not explicitly simulate contrails. Hence, to effectively mitigate the climate impact caused by air travel, a deeper understanding of ways in which to influence contrail-induced warming is required.

Here it is hypothesised that a flight scheduling management (FSM) approach - shifting flights predominantly operating in a night-time sky to predominantly operating in a daytime - has the potential to reduce the amount of N-contrails coverage and influence those D-contrails that may exert a net cooling effect on the climate. Consequently, a FSM approach could make a significant and immediate difference in the warming impact of aviation-induced clouds. This paper will describe how the research aims to improve the quantification of the climate impacts of aviation-induced clouds and model the climate response to shifting the current operational norms. This will include discussing the off-line contrail model being developed to simulate the effects of FSM by taking into account short- and long-lived contrails and contrail induced cirrus clouds.