Delayed flights in 2007 wasted your time and $1.6 billion of fuel

Wow. I seriously don't even know what to say that figure. That's BILLION with a B!?

Yeah they really need to improve airport efficiencies.  If a plane isn't going to take off for 20 minutes, then don't start it up!

Airplanes aren't a big issue yet because there are relatively few flights (as compared to auto travel), so they only account for something like 2% of human greenhouse gas emissions.  The number is increasing though.

Well, as a pilot, I can tell you that its not that simple. The national air system is already over capacity... if you leave a plane at a gate for 20 minutes, then another plane that has just landed has to sit (engines idling) waiting for the gate. So you don't really save anything.

And if you have the plane leave the gate, then you (usually) need to keep its engines on, so it can move around and get out of the way of other planes. It's just like sitting in traffic in your (non-hybrid) car... you can't turn your engine off, because every few seconds you have to move forward a few feet.

There are really only two good options:

1. Build more runways, so planes can get off the ground faster. Pave over some wetlands to do it. Not very green, but will probably be necessary.
2. Get people to travel less, so there are fewer planes competing for the space. The good news is that the high cost of fuel is doing just that... United Airlines announced today that they are grounding 70 aircraft.

Air traffic control modernization will help too... right now some planes get bunched up in 'highways in the sky', when there is plenty of empty space next to them. The reason they can't move over is that they don't have the technology to avoid collisions on thier own, and thus air traffic control has to help them out. And in order to do that, ATC needs to keep them all in the same 'lane'.

Probably more than you wanted to know, but I find it interesting. :)

Yeah those are good points.  Unfortunately I've heard that air travel is supposed to triple by 2020 (or something like that) because of increases in developing nations like China.  They're building tons of airports over there (again from memory, as I recall China is currently building 92 new airports), which would help with the traffic issue, but also add to the total emissions.