Non-CO2 climate impacts of aviation mean it is 2 – 3 times more damaging than the industry claims




Aviation: 2 to 3 times more damaging to the climate than industry claims

Airlines lobby group, IATA, claims that aviation produces only 2% of global man-made CO2 emissions. While this is true, they are telling barely half the story.

According to Professor Dr Volker Grewe, researcher at DLR [The German Aerospace Centre] and chair for climate effects of aviation at Technical University Delft, air transport’s contribution to climate change is roughly 5%. This is because in addition to emitting CO2, aircraft flying at altitude impact the atmosphere in various ways which have a large, albeit transient, additional warming effect.

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 (

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.

Bill Hemmings, T&E’s aviation director, said:

“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.”


See earlier:

European Parliament make progress on dealing with aviation non-CO2 impacts

The meeting on 17th October between the European Council and EU Parliament has finally come to an agreement on how to deal with non CO2 emissions. This is at least 9 years overdue.  It opens a fundamentally new and important avenue of aviation climate mitigation work. The non-CO2 impacts on climate forcing are short-lived but they are potentially of great magnitude – potentially more than double CO2 according to the EC’s own assessment. A research consortium led by Professor David Lee will publish early next year a fresh report on non CO2 climate impacts. Then it will be necessary to follow through with further research including into ways to mitigate. The non-CO2 impacts issue is much more important in the northern hemisphere than the southern as there is where most land, and most flights, are. Europe is well placed to begin assessing what measures could potentially be implemented, such as operational re-routeing (altered flight levels) action on NOx, particulates and black carbon. The meeting reached a provisional agreement on a regulation to extend existing ETS provisions covering  aviation beyond 2016 and to prepare for the implementation of CORSIA from 2021.


See also

EU ETS: tightening regulations

Also in international news, the European Parliament has recently endorsed the views of its environment committee to agree that aviation’s inclusion in the EU emissions trading scheme should be subject to an annually declining emissions cap from 2021 with 50% of the allowances obtained through an auction rather than being distributed freely (with revenues earmarked for climate finance), and a request for the European Commission to come forward with proposals to address aviation’s non-CO2 effects by 2020. The parliament will now try to negotiate these changes with the Commission and European member states over the coming months.


The challenge of tackling the non-CO2 impacts of aviation – explained by Carbon Brief

In a long, but very informative article, Carbon Brief discusses the problems of the non-CO2 impacts of aircraft emissions. These are from water vapour, aerosols and nitrogen oxides emitted by aircraft at cruise altitudes. Though these impacts may be short lived, they have definite climate forcing effects, though these are complicated, while CO2 has easily understood impacts and lasts in the atmosphere for decades or centuries. The impact of contrails forming cirrus cloud is to slow the radiation of heat back into space, causing more warming. But this effect is greatest at night, when contrails persist, and also in areas where there is colder, damper air. So the impacts are not uniform across the globe. The article discusses possibilities of planes avoiding certain areas where contrails persist, either on a daily basis or with blocks of airspace out of use for particular periods. Or of planes flying less high. Both those options are likely to increase fuel use – and thus CO2 emissions – by planes, and so need to be carefully organised, to avoid having yet more overall climate impact. Even if the ICAO deal requires planes to pay a small amount to “offset” their CO2, they are not required to pay for non-CO2 impacts.  With the global aviation industry expected to increase its CO2 emissions by 200%-360% by 2050, the non-CO2 impacts are a very real problem, and one that should not be ignored.  Small changes to flight routes are unlikely to make more than a token difference.


See also

Government airbrushes aviation’s non-CO2 greenhouse gas emissions

AirportWatch briefing. June 2015