In message , at 12:36:09 on
Tue, 11 Oct 2011, Bruce remarked:

Aircraft emissions are overall slightly greenhouse negative

That sounds interesting, but could you explain what that means in
simple, non-technical English?

It means that if you add up the greenhouse contributions of the
emissions it's slightly negative. Although you can probably find people
who disagree. Greenhouse politics is a bit like that. "Often in error,
but never in doubt" [of their being correct] as someone said.

Some of the contributions a SO2 reflects heat as well as the
contrails. The engines burn some atmospheric Methane, but nitrous oxides
react with it as well, so there's another reduction in greenhouse
effect.

Looking at growth, air transport is increasing at 4% a year globally,
but set against that there's a 2% per annum increase in fuel efficiency.
--
Roland Perry