FEB 11, 2020 1:41 PM PST

The mark of a contrail on the atmosphere

Do you know what an airplane contrail is? Have you ever looked up into the sky with that azure blue backdrop and seen the elegant white tail slowly evaporating behind an airplane? Those white tails are called condensation trails, contrails for short, and form when hot exhaust gases from aircraft meet the cold, low-pressure air of the atmosphere. But although they may look pretty, they pose a serious threat to the environment.

The negative climate impact of contrails stems from an effect called radiative forcing, which refers to the disruption of radiation coming to earth from the sun and heat emitted from the surface of the earth going out to space. The result is an imbalance that forces a change in the climate. Watch the video below to learn more about radiative forcing.

Previous research has shown that the fumes of contrails, composed of black carbon particles, form contrail cirrus clouds, ultimately warming the planet the same amount as aviation's cumulative CO2 emissions. Now new research from scientists at Imperial College London suggests a way of reducing the harm that contrails pose: change planes’ altitudes. The research was published recently published in Environmental Science & Technology.

Lead author of the study, 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."

Dr. Stettler and his colleagues collected data from Japan’s airspace in order to run an analysis on how airplane altitude affects the number of contrails and how long they linger. These variables are directly linked to the impact they have on the climate. They simulated flights that flew either 2000 feet higher or lower than their actual flight paths and found that doing so to just 1.7% of flights could cut the contrail climate forcing by 59%!

But why only 1.7% of flights? From their analysis, the researchers determined that 2% of flights were responsible for 80% of radiation forcing within the airspace. This gave them hope because it provides a clear target. 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."

New research suggests a way to reduce the negative climate impact from contrails. Photo: Pixabay

While the simulated changes in flight path did cause a rise in fuel consumption, it was less than a 0.1% increase, and the reduced contrail formation more than offset the CO2 released by the extra fuel. "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," says first author Roger Teoh, of Imperial's Department of Civil and Environmental Engineering.

The researchers plan to continue their investigations in order to hone their knowledge on the climate impacts of contrails and possible mitigation strategies.  

Sources: Environmental Science & Technology, Science Daily

About the Author
Bachelor's (BA/BS/Other)
Kathryn is a curious world-traveller interested in the intersection between nature, culture, history, and people. She has worked for environmental education non-profits and is a Spanish/English interpreter.
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