what factors affect the environment for airlines?

This is the beginning of a brainstorm and a bit of research into what factors affect the environmental impact in the airline industry... From a 50,000 foot view (ha ha right) there are a few key types of waste in the airline industry. The use of jet fuel that is burned in the atmosphere, food and waste from the flights, the typical office energy use and waste, and than the airports themselves which are more in the hands of the local cities. So what factors are under the airlines control (Aside from getting you to your destination luggage in hand..)?

Type of plane- Planes such as the new Boeing 777 should be better performers
Type of engines
Use of wingtips- reduces drag and increases fuel economy
Recycing waste and efficient use of food and plastic containers
Number of connects versus non-stops- Connecting flights use more fuel with increased takeoffs and landings.
Investment/support/research into future fuels that are friendlier to the environment
Support for carbon offsetting
Standard office practices- Such as recycling, use of renewable energy, efficient buildings, etc.

This is what I have with my first brain storm... a little research should bring more variables that are out there. Do you have any ideas!?