One more thing to worry about!

[AJE]

BBC News - How aircraft contrails form cloud

Looks like contrails DO turn into clouds... we now have proof

[AJE]

Well I thought that it was interesting...

[nicnac]

its all vapour to me

[brianb]

Looks like contrails DO turn into clouds... we now have proof

We have had for years ... the increasing sheets of thin cirrostratus largely derived from jet transport contrails which occur around dense air routes are well known.

Here's another point. As well as interfering with astronomy, these thin high cloud sheets are far better at reflecting heat radiation back at the ground than they are at blocking incoming solar radiation. They therefore contribute significantly to increasing temperatures in the lower atmosphere ... contrails increase the warming effect of aviation by a factor or 5 to 20 over the fuel use alone. There was a clear illustration of this in the shutdown of civil aviation in the US following 9/11 when the daytime temperatures in the US hardly changed at all but night time temperatures fell on average about 1C under clearer skies - effect localised to the North American continent and timewise exactly corresponding to the shutdown.

If jet transports would cruise at an altitude where persistent contrails do not form, the impact of aviation on the environemt would be hugely reduced. Unfortunately no-one wants to regulate the aviation industry, and the industry won't do this voluntarily as it would cost about 4% extra in fuel consumption.

Personally I think 4% extra fuel consumption for a 80-95% reduction in enviromental impact is a good bargain, especially since we astronomers would get clearer skies. But then I'm not an aviation industry shareholder, not voluntarily anyway.

[Tim]

well, we could have told them that

I have an animation somewhere of all the commercial flights in the world over a 24 hr period. I'll see if I can find it. It will demonstrate the scale of the problem.

[Tim]

Heres the animation on youtube, including time/hour overlay.

[AJE]

Thanks for posting the link TJ, the animation really brings it home just how many planes are in the air!