1. Contrails or ‘condensation trails’ are line-shaped clouds which can be seen in certain altitudes in the skies behind airborne aircraft. These linear clouds are formed by water vapor in combination with soot and sulfur gases that come out of jet engine exhaust. See: U.S. Environmental Protection Agency: ‘Aircraft Contrails Factsheet’, September 2000 2. Lee, D.S. et al.: ‘The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018’, September 2020, URL: The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018 | Elsevier Enhanced Reader3. EASA report: ‘Updated analysis of the non-CO2 effects of aviation’, September 2020,4. Ed. NOx causes chemical disbalances in the atmosphere which have radiative effects.5. Ed. Contrail cirrus is persistent contrails which have been observed to lead to the formation of extensive cirrus clouds.6. Op. Cit. Lee, D.S. et al.: ‘The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018’7. German Aerospace Center (DLR): ‘Preventing contrails with the right flight altitude’, 3 November 20218. EUROCONTROL & Maastricht Upper Area Control (member of FABEC), Contrail prevention: ‘Mitigating the climate impact of non-CO2 emissions: EUROCONTROL MUAC Live Trial 2021’9. Keith Shine and David Lee: ‘Commentary – Navigational avoidance of contrails to mitigate aviation’s climate impact may seem a good idea – but not yet’, 21 July 202110. Op.Cit. Keith Shine and David Lee: ‘Commentary – Navigational avoidance of contrails to mitigate aviation’s climate impact may seem a good idea – but not yet’11. Ulrike Burkhardt, Lisa Bock and Andreas Bier: ‘Mitigating the contrail cirrus climate impact by reducing aircraft soot number emissions’, NPJ Climate and Atmospheric Science, 19 October 2018