>Viv,
>
>>Water vapour at high altitude is considered so - though estimates of it's actual effect vary.....
>>I think it's explained in the link. Basically the effect of CO2 emissions at high altitude are much more of a problem than at lower levels.
>
>Short-haul flights don't go to high altitude so I think we can neglect that component.

Not altogether I would have thought. Short haul flights probably climb to about FL180-200. I think the con trail problem may be reduced at this level but countered by the reduced time spent at cruise altitude.

This trivial bit of software might provide the answers:http://www.lissys.demon.co.uk/pug/c00.html (g)

Regards,
Viv