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The main contributors of aviation-induced radiative forcing are: CO2, nitrogen oxides (NOx) and contrail/cirrus cloud formation. NOx creates ozone and destroys methane and is a net warmer. As are the contrails and resultant cloud formation which trap radiation escaping from the Earth. CO2 accumulates and has a very long life in the atmosphere (well over a 100 years), whereas the climate impacts of NOx, contrails and clouds have a very short lifespan – from minutes to some hours/days. The issue is that these short-lived warming forcers are so powerful that they heat the planet more every day than all the aviation CO2 that has accumulated in the atmosphere since the 1940s, Professor Dr Grewe's research shows.
‘The good news is that whether you fly a little bit further north or south you could avoid the contrails and ozone from nitrogen oxides depending on the meteorology of that region. So, with a little bit of a detour, flying a bit higher or lower or north or south of that region, you can change the climate impact of aviation via the non-CO2 effects dramatically, for example by more than 10% with a cost increase of less than 1 %,’ said Professor Dr Grewe.
The zones with certain weather patterns that facilitate the formation of contrails and the transformation of NOx emissions into ozone are called ‘climate sensitive areas’. The Section on Aircraft Noise and Climate Effects of Aviation (ANCE) at TU Delft in the Netherlands is collecting weather data and identifying these climate sensitive regions that can provide air traffic controllers, aircraft manufacturers and airlines with climate optimised routings (www.atm4e.eu).
Avoiding climate sensitive regions might be the most promising approach to reduce the climate impact of non-CO2 emissions. However, even without this concept, the climate impact of flying can be lessened with a more general approach. The latest research by Professor Dr Grewe and his colleagues from DLR shows that by optimising the speed and cruise altitude of long-range aircraft like the Airbus A330, the climate impact of aviation can be reduced by 30% with a cost increase of around 5%.
The EU included aviation in the emissions trading system (ETS) to tackle the ever-growing carbon emissions from aircraft but non-CO2 effects are unregulated. ‘An obvious thing to do would be to include the non-CO2 effects into the EU ETS. We could find ways to convert NOx emissions and contrail formation into equivalent CO2 emissions. We have shown in a scientific publication that if non-CO2 effects are accounted for in a market-based measure like the EU ETS, it would enable climate optimised routing of air traffic,’ said Grewe.
‘Currently, there are no incentives or regulations requiring airlines to implement climate optimised routings. Operations are driven by minimising direct operating costs and fuel burn. When aviation was included in the ETS in 2008 the directive in fact called on the European Commission to assess the non-CO2 impacts and propose action. Nothing transpired but this call was renewed in the revisions to the directive agreed last year requesting the Commission to assess and propose by 2020. The time to act is well overdue,’ said Bill Hemmings, T&E’s aviation director.
Read Prof. Grewe presentation and other scholars' here.