Contrails in the sky

A number of contrails (condensation trails of artificial cloud left by jet planes) can be seen in the bright blue sky, They appear to be very beautiful, but  it appears that there is more to it.

Consider this article - There has been concern for many years over the extent to which thin contrails affect the Earth's climate. These contrails are triggered by the water vapour emitted from the exhaust of aircraft into cold air, or through changes in air pressure around the wings. Just like regular clouds, they are made up of water in a suspension of tiny droplets or ice crystals.

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Despite their frail appearance in the sky, contrails tend to be long-lived and spread out into thin, bright clouds that can be up to 150 kilometres in length.

These high-altitude clouds have both warming and cooling effects on the climate, as they reflect both sunlight back into space and heat back down to the surface. In recent years, however, a consensus has built that the warming effect is more significant than the cooling.

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Some researchers have suggested that planes fly at a lower altitude to avoid the cooler air, but this means burning significantly more fuel (as the air isn't so thin) and the resulting CO2 emissions may offset any reductions in the clouds. <wired.co.uk, 19 June 2014>