Alan Watt's take on media BS


By: Oliver Tree, 28th June 2010
If you are jetting off for an exotic holiday this summer, spare a thought for those you leave behind.

Because it seems that sun-seekers are responsible for leaving the rest of us languishing under grey skies – thanks to the emissions from aircraft engines.

These vapour trails create clouds which, experts claim, can block out sunlight for millions. This is the reason that our skies appeared unusually blue when the Icelandic volcano Eyjafjallajokull was erupting, and all flights over Britain were banned.


Vapour trails create clouds which, experts claim, can block out sunlight for millions

The phenomenon occurs when aircraft fly above 25,000ft, where the air temperature is around minus 30C. This causes water vapour emitted by the engines to crystallise and form the familiar white streaks across the sky, known as contrails.

These can be short-lived. But if there is already a significant amount of moisture in the atmosphere they can linger for hours, as the excess water vapour from the engines tips the surrounding air past its saturation point.

This acts as a catalyst to speed up the natural process of cloud formation. Cirrus clouds – the wisp-like formations seen at high altitude – begin to form around the contrails.

Scientists say these grow into thin layers of cloud and can cover up to an astonishing 20,000 square miles of sky – or about a fifth of the UK.

The level of moisture in the air at high altitudes is unrelated to weather conditions at ground level, which is why it is possible to see contrails on a clear day.

Reading University’s Professor Keith Shine, an expert in clouds, said that those formed by aircraft fumes could linger ‘for hours’, depriving those areas under busy flight paths, such as London and the Home Counties, of summer sunshine.


The Jet clouds that can cover 20,000 square miles

‘People from abroad are amazed by the number of vapour trails in the skies over London,’ he said. ‘When the air is wet enough, the cloud formed by contrails can last for hours.’

Experts have warned that, as a result, the amount of sunlight hitting the ground could be reduced by as much as ten per cent. Professor Shine added:
‘Over the busiest areas in London and the South of England, this high-level cloud could cover the sky, turning bright sunshine into hazy conditions for the entire area. I expect the effects will get worse as the volume of air traffic increases.’

In a 2009 Met Office study into the effects of contrails, scientists from a number of UK institutions used a weather satellite to track a large military aircraft as it circled over the North Sea. The team expected high-level winds to disperse its contrails without trace.

But instead they helped to form clouds, which the researchers were astonished to find eventually covered a massive 20,000 square miles.


Source: http://www.dailymail.co.uk/