This obsession with what comes out of a tailpipe of an aircraft engine really does miss the whole green issue regarding airlines I believe. Forget burning jet fuel it's the waste of food and resources providing an in-flight service which is the real green issue. When I think of all the food I've thrown away unused, plastic glasses, 1/4 wine bottles (many of them glass), gallons of wine spirits and minerals flown all over the world and not used. The co2 produced by production facilities must all make a contribution.
The big issue is not global warming it should really be about consumption of resources and being honest does anybody believe that airlines enjoy burning fuel. Scientists, airlines and governments should be working on research to increase further the efficiency of engines and aircraft rather than more research to prove their spurious argument, that's not going to help the planet.