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Feb. 12 (UPI) -- To reduce the impacts of air travel on Earth's climate, only slight flight plan adjustments are necessary. According to a new study, published Wednesday in the journal Environmental Science and Technology, policy makers could drastically cut contrail emissions by making slight alterations to the altitudes at which some airplanes fly.
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The new analysis showed shifting the altitudes of just 1.7 percent of flights, either 2,000 feet higher or lower than normal, would more than halve the warming impact of contrails.
"Contrails are line shaped clouds that form behind aircraft," Marc Stettler, co-author of the new study and an environmental engineer at Imperial College London, told UPI in an email.
When airplanes emit black carbon particles produced by incomplete fuel combustion, moisture quickly condenses on the particles, forming tiny ice particles.
Contrails formed under certain atmospheric conditions can quickly grow and persist.
"If the atmospheric conditions are such that there is high humidity, an individual contrail can live for up to 18 hours, and over that time it will spread out," Stettler said. "As it spreads, it will scatter incoming solar radiation and also reflect outgoing long-wave radiation, heat that would otherwise go out to space. These two effects are cooling and warming, respectively."
Because there is no solar radiation to be reflected at night, the clouds have a net warming effect on the atmosphere.
Previous studies have shown that contrails are responsible for just as much warming as the CO2 emitted by airplanes.
To better understand the dynamics of airplane contrail emissions and their effects on Earth's climate, Stettler and his colleagues used a combination of climate models.
"We combined detailed data on flight trajectories in Japanese airspace with a model of aircraft black carbon particle emissions, weather data, and a contrail model," Stettler said. "These different components allow us to calculate the contrail impact of individual flights. From there, we were able to rank the flights and focus on the one with the greatest contrail impact."
Their analysis showed that the warming effect of contrails is of roughly the same order of magnitude as airplane CO2 emissions, but that just 2 percent of flights are responsible for 80 percent of contrail emissions.
Altering the altitude of a flight can make the flight less efficient, boosting CO2 emissions, but the models showed just a slight changes to a tiny percentage of flights will reduce contrail emissions by nearly 60 percent. Simulations proved the cooling effects of such drastic reductions in contrail emissions safely offset the warming effects of efficiency losses.
Researchers are now working to analyze flight data from other parts of the world. Stettler and his collages are also working to get their findings in front of the eyes of aviation policy makers.
"We want to look at how our strategy could be implemented in practice," Stettler said. "In the aviation sector, safety is the priority and any implementation would have to fit within existing constraints. We're continuing to work to understand the practicalities of how such a strategy may fit into flight planning and air traffic management."
