Aircraft engines produce emissions that are similar to other emissions resulting from
fossil fuel combustion. However, aircraft emissions are unusual in that a significant
proportion is emitted at altitude. These emissions give rise to important environmental
concerns regarding their global impact and their effect on local air quality at ground level.
Aircraft emit gases and particles which alter the atmospheric concentration of
greenhouse gases, trigger the formation of condensation trails and may increase cirrus
cloudiness, all of which contribute to climate change.
Aircraft are estimated to contribute about 3.5 per cent of the total radiative forcing
(a measure of change in climate) by all human activities and that this percentage, which
excludes the effects of possible changes in cirrus clouds, was projected to grow.
The effects of some types of aircraft emissions are well understood, and the effects
of others are not, and a number of key areas of scientific uncertainty that limit the ability to
project aviation impacts on climate and ozone.
