Whatever your take on climate change (personally I think it's inevitable, and if we spike the atmosphere with CO2 now, we'll get it over and done with quicker...)
As the efficiency of aircraft increases, so does the aviation industry's CO2 emissions. This seems counter-intuitive at first, but the reasoning is:
1. Aircraft become more efficient
2, Price of air travel comes down (as it's dominated by the fuel cost)
3. Demand then goes up - in excess of the efficiency saving.
The only way to break this cycle is to impose a carbon tax, perhaps on each ticket.