Markoz wrote on Nov 18^th, 2011 at 1:10am:

If you replace 1 old aircraft, that emit 100 units of pollution into the atmosphere, with 5 modern aircraft, that emit 30 units of pollution into the atmosphere, then you are still releasing more pollution into the atmosphere than you were back when you were using that single aircraft (5 x 30 = 150). So the point that CoolP makes is still valid. More pollution IS being emitted into the atmosphere today, than it was many years ago. The only difference is that it takes more aircraft to do it. I'm not using exact figures because I don't know what they really are.

It's true that there are more pollutants being released now, but if you look at the ratio of passengers to planes, just as Peter pointed out, we're doing well (not that there isn't room for improvement, though). However, my original point, at its simplest, was that in the development of SST's and other aircraft in the future, environmental concerns are something which needs to be taken into account.

And Peter, I don't know about you, but I think we need more ozone in the atmosphere (at least in the stratosphere).  ;D