Yeah, I tend to skip the last 20% of post when the first 80% doesn't seem to address the main point of what it's responding to. Like a lot of bleary-eyed peopl

Yeah, I tend to skip the last 20% of post when the first 80% doesn't seem to address the main point of what it's responding to. Like a lot of bleary-eyed people here. Which is why I try to make a habit of getting to the most important part of what I'm responding to first, and deal with secondary or tertiary parts after that. But that's just me. That said I didn't mean to be condescending, and apologize for it ending up that way. As to what you were originally saying: I'm not sure your argument will "fly", as it were -- for the simple reason what most strongly predicts the carbon impact of a means of transport is not transit time but, generally, the amount of energy expended to get from A to B (not the transit time). And even though the flight may be shorter, something tells me the energy expenditure has to be much higher for supersonic than for subsonic flight -- in part precisely it needs to get to a much higher speed (i.e. get there with "decreased flight time") and attain a higher altitude before coming down again.