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 NOx (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, NOx (in an indirect way) and contrails contribute most to radiative forcing;
  • The impact of NOx 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.

Category: past activities