Whilst the industry has spent a significant amount of time over the last 15 or so years investigating our decarbonisation pathway — with important progress being made towards the net zero carbon goal — one of aviation’s other climate impacts has not historically received as much attention: contrails. However, the last few years has really seen progress in this area as well, as I was reminded at a gathering of academics, researchers and industry experts held at the Royal Aeronautical Society in London this week, coordinated by the International Air Transport Association (IATA).
Contrails — the white lines that sometimes appear in the skies behind aircraft flying at cruise altitude — are, in basic terms, just clouds. They don’t always form. There needs to be specific atmospheric conditions in which contrails form and then persist — some contrails form and disappear in a few seconds or minutes. During the day, the contrails that persist and spread into whispy ‘cirrus’ clouds can have a cooling effect as they block the sun’s rays from hitting the surface. At night, however, they can have a warming effect on the planet as they prevent warmth from the earth escaping into space. The science gets very complicated very quickly, but the general scientific consensus is that they are, on balance, warming and could even contribute around the same effect as aviation’s CO2 emissions over the long term. More details can be found in a paper we published last year.
This week’s discussion has been a good reminder of the significant work going into researching not only the details of contrail formation and the atmospheric chemistry involved, but also options for how to avoid those areas of the airspace where persistent warming contrails are likely to form.
So, what in my mind has changed in the last few years?
First off, the industry has really taken on board the scientific advice about the overall warming nature of contrails and the need for action to avoid them, if practical. There is really impressive industry / research cooperation to understand the complexities and try and answer the operational questions of how we could use options such as flight deviations to avoid contrail areas. Colleagues from airlines, air traffic management organisations and aerospace technology experts are all involved.
There have been a number of organisations suggesting that contrails are ‘a simple fix' which can be operationalised quickly — the RAeS symposium showed that as soon as you scratch below the surface, there are still many complexities to be solved. If I were to make an educated guess, I would say we may be around 5–7 years from having some workable solutions in place. But, before we regulate, we must continue research in a number of key areas:
- getting better at meteorological forecasting of the areas where contrails can form;
- developing reliable and lightweight sensors that could be installed on commercial aircraft could be an important benefit to understanding where contrail formation might take place;
- understanding how contrail avoidance measures would impact on the air traffic system;
- the scientific community identifying what the trade-off metric is between contrail avoidance and CO2 (in many cases, if we were to fly around or below a contrail prone area, we would burn a bit more fuel and therefore increase CO2 emissions — this might be beneficial to the overall climate impact, but it needs to be considered carefully).
The event this week reminded me of some other important messages to the scientific community:
- continuously sharing information between research groups working on this topic is vital if we are to avoid duplication and make rapid progress;
- science needs to be able to speak to industry in a language that makes sense;
- although a lot of the deep atmospheric science is ‘interesting’, we need to also determine if reaching further and further into the details is going to lead to better operational decisions, and if not, focus on those areas that will help with contrail avoidance measures.
It also is important to not exclude one climate solution space in favour of another — I have heard a few academics say we should concentrate on contrails instead of SAF, for example. This is not a useful approach. We need to look at all impacts and ensure we are making progress everywhere: technology, operational improvements, new fuels and yes, contrail avoidance as well. I’m very pleased to see just how much work is taking place across all these areas to gain better understanding.