Modern airplanes burn kerosene to generate the forward propulsion needed to overcome drag and produce lift. Kerosene is a fossil fuel with excellent energy density, providing lots of energy per kilogram burnt. But when it is burnt, harmful chemicals are released: mainly carbon dioxide (CO₂), nitrogen oxides (NOₓ), water vapor, and particulate matter (tiny particles of soot, dirt, and liquids).
Aviation is widely known for its carbon footprint, with the industry contributing 2.5 percent to the global CO₂ burden. While some may argue that this pales in comparison with other sectors, carbon is only responsible for a third of aviation’s full climate impact. Non-CO₂ emissions (mainly NOₓ and ice trails made from aircraft water vapor) make up the remaining two-thirds.
Taking all aircraft emissions into account, flying is responsible for around five percent of human-induced climate change. Given that 89 percent of the population has never flown, passenger demand is doubling every 20 years, and other sectors are decarbonizing much faster, this number is predicted to skyrocket.
It’s not just carbon
Aircraft spend most of their time flying at cruise altitude (33,000 to 42,000 ft), where the air is thin to minimize drag.
At these altitudes, aircraft NOₓ reacts with chemicals in the atmosphere to produce ozone and destroy methane, two very potent greenhouse gases. This aviation-induced ozone is not to be confused with the natural ozone layer, which occurs much higher up and protects the Earth from harmful UV rays. Unfortunately, aircraft NOₓ emissions cause more warming due to ozone production than they do cooling due to methane reduction. This leads to a net warming effect that makes up 16 percent of aviation’s total climate impact.