The white streaks that trail behind airplanes are called aircraft contrails. They are not suitable for the environment and could be as bad for climate change as carbon dioxide emissions. However, there may be a simple solution to lessening their negative impact. A new study by Imperial College London found that altering the altitude of less than 2% of flights could reduce contrail-linked climate change by 59%.
Applying this practice in addition to using cleaner aircraft engines could reduce contrail-caused fluctuations to the climate by up to 90%. The study has been published in the journal Environmental Science & Technology, and all the flight data used for it was obtained from the Electronic Navigation Research Institute, Japan.
Lead author Dr. Marc Stettler, of Imperial’s Department of Civil and Environmental Engineering, said:
According to our study, changing the altitude of a small number of flights could significantly reduce the climate effects of aviation contrails. This new method could very quickly reduce the overall climate impact of the aviation industry.
What exactly are contrails, and how are they made? They are condensation trails created when hot exhaust gases from the airplane meet the cold, low-pressure air in the sky. The exhaust fumes include black carbon particles – the surfaces for moisture to condense and form ice particles. The fluffy white streaks we see are condensation-covered pollution particles that have frozen.
Usually, contrails will disappear after a few minutes. However, if they spread and mix with cirrus clouds or other contrails, they form ‘contrail cirrus’ which idle in the atmosphere for up to eighteen hours. The contrail-formed clouds have as much of a warming impact on the climate as aviation’s cumulative carbon emissions. They cause an effect called ‘radiative forcing’ – which is when the balance between the sun’s radiation coming to earth and the earth’s heat emitted from the surface going out to space is disturbed.
On the plus side, while CO2 emissions remain in the atmosphere for hundreds of years, the burden of contrails is short-lived and could, therefore, quickly be reduced.
Dr. Stettler said:
A really small proportion of flights are responsible for the vast majority of contrail climate impact, meaning we can focus our attention on them. We’re conscious that any additional CO2 released into the atmosphere will have a climate impact stretching centuries into the future, so we’ve also calculated that if we only target flights that wouldn’t emit extra CO2, we can still achieve a 20% reduction in contrail forcing.
The study’s first author, Roger Teoh, also of Imperial’s Department of Civil and Environmental Engineering, added:
Our simulation shows that targeting the few flights that cause the most harmful contrails, as well as making only small altitude changes, could significantly reduce the effect of contrails on global warming.
The researchers also point out that black carbon particles are produced by incomplete fuel combustion, so the aircraft engines themselves play a significant part in how harmful contrails can be. With more efficient engine combustion technology, the contrails effects could be reduced by about 70%.
