Technological advances
Over the last 30 years there has been a 50% improvement in aircraft fuel efficiency per passenger. Fuel efficiency is currently improving by about 1–2% a year. However, aviation is predicted to grow more quickly than this, so technological improvements by themselves won’t be enough to solve the problem. Renewable biofuels and fuel cells may be another way for technological improvements to reduce greenhouse gases.

Airspace management 
Around six million tonnes of CO2 have already been saved by shortening existing air routes and BAA is pushing for a unified system of air traffic management within the European Union (EU). This could help cut aviation CO2 emissions by 12%.

Infrastructure constraints
Airport infrastructure constraints already form part of UK aviation policy but are “an inefficient way of regulating demand” according to the Stern Review.

Taxes and charges
The main tax on flying is currently Air Passenger Duty (APD). However, the Government has just announced that from late 2009 duty will be paid per flight rather than per passenger. The Government has agreed to consult on this and will consider way to make the aviation duty better linked to the distance travelled, as well as ways to encourage more planes to fly full.

Emissions trading 
This would force airlines to cut their own emissions or pay for others to do so. It would deliver a clear cut in CO2 emissions in an economically efficient way. The advantages of emissions trading are:
• The environmental result is clear from the start
• Carbon dioxide reductions are made in the most efficient way possible
• Money raised goes directly towards reducing emissions
• The quantity of emissions is important, not their source
• It works internationally.