Aviation is actually very green it just depends on how you view it. The problem is that all the greenies focus on is fuel burn.
If the green movement was serious about all this they would have to consider the environmental impact that building railways and roads (and the all raw materials that go into it) has on the environment additional to the fuel burnt. IF you start taking these issues into consideration aviation is very efficient.
This is why aviation is used often in remote areas as the cost/logistics of building other forms of infrastructure is prohibitive. All you need for a plane is a runway the rest can be pristine rainforest.
I feel that the Aviation is a bit of a soft target when it comes to these sorts of issues. I would imagine that if a green movement starting pointing out the amount if environmental damage roads and motor vehicles really do I think you would find that the car companies would come down on them very very heavily, much like the electric car. Instead greenies can shoot down aviation as being ungreen, yet noone in aviation really stands up for it.
The green movement is usually the biggest hyporocrites, as they want to live in new houses with all the mod cons, new cars etc yet still crap on about being green. If people want to get serious about saving the planet you will have to go back to a lifestyle that your forefathers lived. Zero travel, real organic food grown by you, meat is for celebrations only, mud brick housing, water tanks, solar power etc etc
That kind of lifestyle is achievable, but is actually hard work, so it will never happen. A good start to being green would be to abolish fast food, and instead of turning all that food into burgers, they should selling it to the third world as REAL food and help easing starvation.