The climate effect of aviation is not only caused by the greenhouse gas CO2, but about 2/3 is caused by what is known as ‘non-CO2 effects’. There is still considerable scientific uncertainty about the exact contribution. The two main non-CO2 components are nitrogen emissions at altitude and aircraft streaks (contrails).
Unlike CO2, which cumulatively increases its concentration in the atmosphere, non-CO2 effects break down much faster through chemical reactions and therefore exist for a much shorter period of time. In addition, the extent to which they contribute to global warming varies depending on the location of emissions and atmospheric conditions. As a result, the ratio of non-CO2 to CO2 (expressed as the CO2e factor, which is the amount of CO2 that would have the equivalent global warming effect) at individual flight level can vary considerably depending on flight distance, average latitude and aircraft size. For Schiphol, flights to Svalbard Airport (the northernmost airport in Norway) have the highest average CO2e factor (12.8). By comparison, flights to Barcelona have an average CO2e factor of 2.6. These variations are currently often not taken into account and a single average factor is applied in policy analyses.
This project was commissioned by the Ministry of Infrastructure and Water Management (Ministerie van Infrastructuur en Waterstaat) to develop the Aviation Non-CO2 estimator (ANCO). ANCO calculates the non-CO2 effects per route based on departure and arrival airport and a generalised aircraft type. The calculation methodology is based on the German Aerospace Institute DLR’s CO2eEstimator. ANCO also takes into account future aircraft efficiency improvements and the increasing use of renewable fuels, known as ‘Sustainable Aviation Fuels’ (SAF). As input, ANCO can read aviation forecasts prepared with the national Dutch aviation model AEOLUS. The outcomes are CO2 emissions and non-CO2 emissions expressed in CO2 equivalents. This makes it possible to identify the development of climate impact of aviation and the impact of policy on non-CO2 emissions much more precisely, for example as part of social cost-benefit analyses (SCBA).