In message , at 13:31:30 on
Tue, 11 Oct 2011, Bruce remarked:
Aircraft emissions are overall slightly greenhouse negative

Thanks. I'm still not sure what you mean by "slightly negative". A
negative contribution to greenhouse gases might be generally positive,
which is why I am confused.

That's why I didn't use the words "greenhouse *gases*", because they are
only part of the picture. The overall "greenhouse" or "global warming
effect" (taking into account all the factors I mentioned) can be
calculated to be negative.

The main message is that the positive CO2 isn't the only story, although
contrails are fairly well accepted. But even then the contrail effect is
an aggregate because they cool in the day and warm at night!
--
Roland Perry