A study published in the journal Environmental Science & Technology argues that if planes fly about 2,000 feet (610 meters) lower than they are today, it would more than halve the contribution of airplane condensation to global warming. In addition, in this case, less than 2% of all flights are subject to route adjustments - those in which such traces are most often formed and linger in the atmosphere for a fairly long time.
Condensation - or contrails - occur when hot exhaust from aircraft engines enters a cold atmosphere at low pressure. Moisture condenses on the soot particles and forms the very white streaks that we often see in the sky.
Most contrails disappear in minutes, but some can persist for up to 18 hours, mixing with other trails and natural clouds. This "condensation cloud" traps long-wave infrared radiation in the atmosphere, contributing to its heating.
“According to our research, changing the altitude of a small number of flights can significantly reduce the climatic impact of air tracks,” says co-author Mark Stettler. "A very small proportion of flights are responsible for the vast majority of adverse climate impacts, which means we can only focus on them."
Graph that demonstrates that a very small number of flights provide the bulk of the contribution to global warming from their condensation trails / © Stettler, Teoh, Schumann, Mahjumar, Environmental Science & Technology, 2020
Scientists analyzed flight data in Japanese airspace for six weeks. They then built flight models in which the altitude of some flights was decreased or increased by two thousand feet. The simulation results showed that a decrease in flight altitude of only 1.7% of flights led to a decrease in the greenhouse effect of contrails by 59%. At the same time, the models constructed by the scientists take into account the increased fuel consumption when flying in a denser atmosphere.
The researchers add that the introduction of more sustainable aviation fuels could reduce the contribution of contrails to air temperature rise by 90%. However, to accurately assess this effect, scientists will need to run new simulations with more variables.