Why is aviation’s true climate impact being kept under the radar?

Twelve years ago, the IPCC Fourth Assessment estimated aviation’s total climate impact at two to four times that of its past CO2 emissions alone. This is because aircraft at altitude generate significant additional climate warming – from NOx, the formation of line contrails and cirrus clouds, water vapour, soot, aerosols, black carbon and other factors. When discussing aviation’s inclusion in the EU emissions trading system a year later, the European Parliament called for airlines to surrender additional allowances to cover the non-CO2 impacts. Pressured by airlines and aircraft manufacturers, this proposal was dropped.

The finalised directive called for all impacts of aviation to be addressed “to the extent possible” and included a recital proposing legislation for 2008 to deal with NOx emissions separately. A NOx study by CE Delft, commissioned by the European Commission’s transport directorate, DG Move, and drawing on eminent experts, recommended a cruise NOx charge possibly dependant on flight length. Nothing came of it. 

A decade later, civil society and the European Parliament insisted. The 2017 reform to the EU ETS includes language that requires that “before 1 January 2020, the Commission shall present an updated analysis of the non-CO2 effects of aviation, accompanied, where appropriate, by a proposal on how best to address those effects”. The 2017 regulation also calls on the Commission to speed up work on the 2008 NOx proposal, promote research into contrail formation and evolution into cirrus clouds, into the direct effects of sulphate aerosols and soot, and on effective mitigation including operational and technical measures.

In November 2018, DG Move (although the ETS is a DG Clima responsibility) informed a hearing of the European Parliament’s environment committee that work still hadn’t started nor had the 2008 NOx proposal been advanced. This was clearly disappointing, as firstly a NOx measure is needed (there is a tradeoff; reducing CO2 generally increases engine NOx). Secondly, it again reflected a consistent line that industry, ICAO, member states and the Commission have taken for years: that scientific uncertainties warrant further research but no action. And still, very little money has been made available under the EU’s Horizon 2020 programme – €2.5m, or 0.003%, this year, of its €80 billion overall budget. 

Countries measure their climate performance by how much CO2 they emit each year. Aviation is more complex because, as the IPCC pointed out, non-CO2 warming effects well exceed – possibly by two to four times – the total (not annual) warming impact of all aviation CO2 accumulated since the industry began. Accumulated CO2 warming is fairly accurately calculated using the radiative forcing (RF) metric. But non-CO2 effects are shortlived. How firstly to quantify, then equate all that into a temperature response via a metric to the known radiative forcing of accumulated CO2, when these two effects act on very different timescales, remains a central question. You can’t just multiply annual EU aviation CO2 (about 175Mt). It’s the warming impact of accumulated CO2 which counts for the comparison. The IPCC was very clear 12 years ago; this issue is potentially very significant, so get moving. Europe and the world didn’t.

Recent scientific proposals now offer metrics that can potentially resolve the equivalence question between the short and long-term effects: Dahlmann et al and Scheelhaase. These proposals remain under discussion. Another paper by Scheelhaase from the German Aerospace Centre (DLR) suggests that long-haul flights such as Paris-Los Angeles might have a total climate impact some 4.5 times that of their CO2 alone. Short-haul flights, as in Europe, would have a lower impact and their non-CO2 emissions could be regulated, for the first time anywhere, under the EU ETS.

Last summer, the Commission finally signed a contract with the European Aviation Safety Agency (EASA), which reports to DG Move. The work was outsourced to a framework contractor without public tender (none is required for a framework contract). One lead scientist chosen was on record six months earlier advising the UK government that “mitigation of non-CO2 impacts tends to raise complex questions regarding both scientific uncertainty and trade-off (with CO2) consequences, whereas reducing CO2 emissions has clear and long-term benefits, and does not suffer from the same levels of scientific uncertainty”. The Royal Aeronautical Society’s (RAS) Greener by Design group RAS take the opposite view. They are almost ready to conduct virtual and physical trials to divert aircraft on transatlantic flights away from cold air flight levels over the Atlantic where contrails form most often. They estimate only one in 20 flights would need to fly higher or lower for 20% of the flight duration, resulting in about 0.5% more fuel being burned/CO2 emitted – while significantly reducing contrail warming. 

A group of scientists and experts is meeting with the EASA project team behind closed doors in Brussels this week to review and support its work. Who they are (and indeed who/which organisations comprise the actual EASA project team itself) or what is the exact remit of either group is not known. The Commission has prevented all participants including EASA itself from speaking. However, it is known that an offer by the Royal Aeronautical Society to contribute their scientists and engineers’ expertise was not taken up. It is also unclear whether the EASA scientists’ conclusions will even be published when the Commission finally issues its report to parliament.

All of this contributes to our distinct sense of déjà vu and raises questions about the robustness of the process. The good news is that the new European Commission is committed to a green deal, and has made aviation one of its priorities. Sweeping the non-CO2 problem under the carpet wouldn’t make for a great start and would sour relations with the European Parliament, which has been demanding action on this for years. Europe is the second fastest growing aviation market in the world, after China, driven not by demographics but untaxed low fares and expanding capacity. It’s essential that the report to parliament be transparent as to what the scientists say, reflect the facts, and set out a serious follow-up plan and proper funding to execute it.

Add new comment

Filtered HTML

  • Allowed HTML tags: <a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd>
  • Lines and paragraphs break automatically.
  • ShortCodes usage

    1. [mailchimp_signup title="Interested in this kind of news?" placeholder="Enter your email address" form_url="https://transp..." button_label="Sign Up"]Receive them directly in your inbox[/mailchimp_signup] Outputs Mailchimp sign up widget. All values have defaults, shown in snippet.

  • Web page addresses and e-mail addresses turn into links automatically.

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

About the author

Bill Hemmings's picture

Senior Adviser, Aviation and Shipping