Flying Greener
Ways to reduce aviation's effect on the climate without changing the planes
Although planes are getting more efficient, until they run on renewable and green sources like hydrogen or sustainable fuels, they will continue to contribute to climate change. However there are multiple factors that effect planes influence on the environment other than the use of fossil fuels.
Direct Environmental Impacts - Combustion
Unless the engine is electric powered, it will undergo the combustion process to extract energy from the fossil fuels. Combustion is the process where fuel mixes with oxygen at a high temperature to burn releasing by products, but it depends on the conditions that these products get released. In an ideal combustion cycle, there is perfectly proportioned amounts of fuel and oxygen at the perfect temperature. In this case carbon dioxide, water vapour, nitrogen and oxygen get produced.
Indirect Environmental Impacts - By products & Contrails
However, due to the changes in atmospheric conditions like temperature and pressure non-ideal combustion occurs. Here additional by-products get produced like carbon monoxide, nitrogen oxide, soot, sulfur oxide and unused fuel. This is where, with the products of ideal combustion the formation of contrails and the additional gases have adverse effects on the environment and contributes to about 2/3 of the total effect of aircraft. Products like the carbon monoxide and nitrogen oxide can breakdown and mix to create methane and ozone molecules which are indirect greenhouse gas. Methane is 80 times more damaging than CO2 in terms of heat trapping and the ozone creation, which behind methane and CO2, comes third in the amount of heat trapped.
The Carbon monoxide and unburnt fuel can also have an aerosol effect. However, this may not seem as bad as you think. Aerosols, banned in many countries, can damage the ozone layer and effect the environment negatively. But the aerosol effect is a cooling effect where these particulates reflect parts of the sun’s energy1. Another result in the additional by products are contrails. Contrails are the clouds that you see form behind the planes and is formed due to the sudden change in temperature. These contrails have both a cooling and warming effect but only during the day. At night contrails will only have a warming effect, since there is no sunlight to reflect. But, where we start the solutions is with these contrails.
Mitigating Indirect Effects
The first way to mitigate the Non-CO2 effects is by climate sensitive routing. Here, flights get diverted to avoid highly sensitive ozone formation zones and can have a climate effect reduction of 20% with only an increase of around 1-2% of fuel consumption. Another way is to avoid flying at night. This way contrails will have a balanced effect rather than only negative and is because contrails only stay for a few hours.
Another way to reduce it is by flying two or more aircraft 1-2km apart so that they surf in the planes wake reducing the fuel consumption by 5-8%. Additionally you’ll benefit with the negative effects overlapping, reducing the overall combined effect (if they were flying apart).
The next way we can reduce these effects is by increasing the reliance on turboprops for short to medium flights. By using turboprops instead of turbofans/jets which reduces the fuel consumption up to 70%. They also fly outside the contrail and ozone formation zone, but does increase the time since their cruising speed is 70% that of a turbofan.
Special mention to Kieran Tait who is a PhD at the University of Bristol who accumulated a lot of this research.
Just 5 Questions on Aerosols - NASA
https://climate.nasa.gov/news/215/just-5-questions-aerosols/#:~:text=Aerosols%20can%20control%20how%20much,energy%20back%20out%20into%20space.