Non-CO2 climate impacts of aviation

On the 10th of December 2019 Airneth organised a seminar on the non-CO₂ climate impacts of aviation. Three renowned academics in the field of non-CO₂ impacts were invited to share their views on the topic.

Dr. Peter van Velthoven provided an introduction into the climate impacts of aviation. Prof. Dr. Volker Grewe presented the warming and cooling impacts of CO₂ and non-CO₂ species and discussed various options to reduce or mitigate the non-CO₂ impacts of aviation. Dr. Janina Scheelhaase from DLR showed how the non-CO₂ impacts of aviation could be translated into CO₂-equivalents. The presentations were followed by a discussion with the audience on how non-CO₂ impacts could be taken into account in (economic) impact assessments such as Social Cost-Benefit Analyses (SCBAs). The various presentations and a summary of the entire seminar can be downloaded below. The key takeaways are as follows:

• Aviation contributes to global warming and climate change in various ways;
• The combined contribution of non-CO₂ species, such as NO_x (nitrogen oxides), H₂O (water vapour), SO₂ (sulphur dioxide), soot, contrails and induced cloudiness is potentially large;
• The individual contributions differ and depend on many different flight parameters and situational factors as well as the lifetimes of the various non-CO₂ species;
• CO₂, NO_x (in an indirect way) and contrails contribute most to radiative forcing;
• The impact of NO_x is especially large when emitted at high (cruise) altitude; the impact of contrails mainly depends on location and time of day;
• When the actual flight parameters and situational factors for a specific flight are known (ex-post) the non-CO₂ impacts can be modelled in a detailed fashion, though uncertainties remain;
• For ex-ante impact assessments such as SCBAs the actual flight parameters and prevailing situational factors are unknown and simplifying assumptions are necessary and possible;
• A globally uniform multiplier on CO₂ is considered too simple by academics as it fails to take the driving factors (quantity of emissions in cruise mode and geographical location) of the non-CO₂ impacts into account;
• Modelling the non-CO₂ impacts based on a multiplier differentiated by destination (region) appears to provide a good estimation of the total climate impact under mean conditions;
• The relative impact of CO₂ and non-CO₂ species on radiative forcing or temperature can be measured with various metrics, such as GWP, GWP*, GTP and ATR;
• The non-CO₂ impacts of aviation can be reduced by (amongst other things): optimization of cruise speeds and altitudes, avoidance of climate sensitive regions, inclusion of non-CO₂ species in cap-and-trade or offsetting schemes and through the use of Sustainable Aviation Fuels;
• Due to their relatively short lifetimes, non-CO₂ species have a relatively large impact on the climate over a relatively short period of time. This means that aviation’s climate impact can be reduced in the short-term by reducing non-CO₂ species. However, if this goes at the expense of CO₂ reduction, more CO₂ needs to be reduced in later years.