Aircraft vapour trails 'could cause global warming'

Cloud-like white trails left by aircraft may be playing a significant role in global warming, a scientist said today.

The exhaust plumes contain carbon dioxide and chemicals which can lead to the production of ozone – which creates smog.

At the same time, the vapour trails, in the right conditions, can form feathery cirrus clouds which warm the surface of the Earth’s by trapping heat.

Patrick Minnis, of the USA’s National Aeronautics and Space Administration’s Langley Research Center in Virginia, studied how the average temperature of the US increased by one degree from 1975 to 1994.

While acknowledging that it was difficult to tell exactly how much of the warming was due to vapour trails, he said their contribution was “significant”.

Dr Minnis found that as air traffic in the US rose by more than 500% from 1970 to 1995, the number of cirrus clouds in the sky also increased.

Until now scientists have been unable to say whether they increased for natural reasons or because of aircraft.

According to the Minnis study the conditions needed to create natural cirrus clouds did not become more common from the 1970s to the 1990s.

He concluded, therefore, that aeroplane vapour trails – also known as contrails – which are clouds of ice crystals mixed with exhaust gases, must be responsible.

Andrew Carleton, a climate expert at Pennsylvania State University, who was not involved in the study, said: “It suggests we may be having a double whammy here.

He told the USA Today newspaper: “It’s not good news for the Earth when you’ve got greenhouse gas increases and you’ve got ... contrails (that) seem to warm the surface of the Earth.”