Mitigation of Non-CO2 Aviation’s Climate Impact by Changing Cruise Altitudes

Abstract

Aviation is seeking for ways to reduce its climate impact caused by CO2 emissions and non-CO2 effects. Operational measures which change overall flight altitude have the potential to reduce climate impact of individual effects, comprising CO2 but in particular non-CO2 effects. We study the impact of changes of flight altitude, specifically aircraft flying 2000 feet higher and lower, with a set of global models comprising chemistry-transport, chemistry-climate and general circulation models integrating distinct aviation emission inventories representing such alternative flight altitudes, estimating changes in climate impact of aviation by quantifying radiative forcing and induced temperature change. We find in our sensitivity study that flying lower leads to a reduction of radiative forcing of non-CO2 effects together with slightly increased CO2 emissions and impacts, when cruise speed is not modified. Flying higher increases radiative forcing of non-CO2 effects by about 10%, together with a slight decrease of CO2 emissions and impacts. Overall, flying lower decreases aviation-induced temperature change by about 20%, as a decrease of non-CO2 impacts by about 30% dominates over slightly increasing CO2 impacts assuming a sustained emissions scenario. Those estimates are connected with a large but unquantified uncertainty. To improve the understanding of mechanisms controlling the aviation climate impact, we study the geographical distributions of aviation-induced modifications in the atmosphere, together with changes in global radiative forcing and suggest further efforts in order to reduce long standing uncertainties.

Influence of weather situation on non-CO<sub>2</sub> aviation climate effects: the REACT4C climate change functions

“…5 shows that a negative net RF may only occur for contrails with lifetimes less than 10 h, independent of the weather situation. This is due to the fact that contrail RF may only be negative during daytime within a short timeframe (during and close to twilight; Meerkötter et al, 1999). The strong shortwave cooling during twilight is caused by the flat angle of incidence and a comparably longer path through the contrails and therefore a higher reflective impact (Meerkötter et al, 1999).…”

“…This is due to the fact that contrail RF may only be negative during daytime within a short timeframe (during and close to twilight; Meerkötter et al, 1999). The strong shortwave cooling during twilight is caused by the flat angle of incidence and a comparably longer path through the contrails and therefore a higher reflective impact (Meerkötter et al, 1999). The longer a contrail lives, the higher is the probability that a larger amount of its lifetime lies outside this timeframe.…”

A Roadmap Toward a Sustainable Aviation Ecosystem

“…This means that airports modifying flight altitudes can potentially reduce aircrafts' effects on our atmosphere. Current research shows that due to air drag, fuel consumption increases by about 1% if aircraft fly lower by 2000 feet (600 m) and decreases by 1% if aircraft fly higher by the same distance (Matthes et al 2021). However, although CO2 impacts from fuel consumption increase by 1% at lower altitudes, the radiative forcing of the non-CO2 impacts decrease by about 33%, causing an overall reduction of climate impacts by 21% by flying lower.…”

“…The need to identify, coordinate, and implement deep decarbonization of the aviation industry grows more apparent each day with greater scientific validation linking climate change with increased carbon dioxide (CO2) levels in the upper atmosphere and other aviation-induced factors (Grobler et al 2019). CO2 and non-CO2 aircraft emissions exacerbate climate change with impacts varying with the altitude at which they are emitted (Matthes et al 2021). Non-CO2 impacts from aircraft include nitrogen oxides, contrail cirrus, water vapor, aerosol sulfate, and soot emissions that-combined with CO2create a positive radiative forcing effect that causes warming (Grobler et al 2019).…”

Review: The Effects of Supersonic Aviation on Ozone and Climate

“…Their occurrence is driven by the combination of the engine/airframe performance characteristics, the chemical composition of the jet engine fuel and the ambient meteorological conditions, while their persistence and evolution into cirrus-like clouds will depend mainly on ambient conditions that should be sufficiently cold and humid. Contrail formation has mostly been studied for subsonic aviation [7,75,76] as most air traffic occurs at subsonic speeds and all commercial civil supersonic aircraft stopped since the retirement of Concorde in 2003. Only a few studies have quantified the global climate effect of contrails linked to supersonic aviation.…”