Aircraft emit water vapor, which in the lower stratosphere can build up and warm the earth's surface

Water forms condensation trails or "contrails" that can act as artificial clouds impacting the daily temperature range. Cirrus clouds form following the formation of persistent contrails.

IPCC estimate that in 1992 contrails covered 0.1% of the earth’s surface, by 2050 this is expected to rise to 0.5% - at a rate that is faster than the growth in aviation fuel consumption.

IPCC estimate that in 1992 about 30% of the earth covered by cirrus clouds. Aircraft induced cirrus cloud cover was estimated to be in the region of 0.2%, this is estimated to rise by up to 0.8% by 2050.