@drugsworker, via Twitter asked:
Are big planes really damaging the ozone layer? If they are, when will we have better engines?
Chris - We've got to bear in mind that big planes are going to pump out a lot of CO2 and CO2 will increase global temperatures and at high temperatures, I think, the equilibrium has shifted in favour of making less ozone and degrading more ozone. So you would have less ozone.
Dave - And I think, if the plane is flying through the stratosphere, as concord was, then just pumping water in there can form little ice crystals which are very bad for ozone, but lower down, I don't think that's a big effect.
Chris - So the height is important thing.
Dave - I think that's certainly a very, very important thing.
Chris - But presumably quite small in comparison with CFCs, chlorofluorocarbons, the things we used to put in fridges, which are known to be terrible for ozone.
Dave - Yes and I think essentially there arenít many planes up in the stratosphere flying around, especially now, since concord has given up the ghost.
Doc - that really isn't much of an answer, more casual casual speculation.
I heard someone say that the airlines each year transport more people than the population of China. If that is true surely that too must have an impact?