Another day another story about cutting airline emissions. Willie Walsh is going to today announce some proposals that will cut airline emissions by half the 2005 level by 2050.

The proposals are:

• to halve net carbon dioxide emissions by 2050, compared with 2005 levels

• to make all industry growth carbon-neutral by 2020

• to improve fuel efficiency by 1.5% each year over the next decade

• to submit plans for joining a global carbon trading scheme to the UN by November 2010. 

What i like about these proposals is it is challenging engineers and manufacturers for greener technology as it is only through this kind of innovation that larger scale changes will happen. Trying to force a demand drop for air travel is difficult, especially when high speed trains are not going to substitute many peoples' journeys.

Aviation should have been included in Kyoto but it is one polluter among many. Its about time that we do something rather than talking about it every time 

IMO it's impossible, mainly because air travel is expected to double in the next few decades, and by 2050, it might have even tripled. As long as we are using hydrocarbonated fuel, even if the plane is completely CF and uses unducted fans, the most efficient configuration possible, if these expansion goals are going to be met, the environmental goals will not be. There are only two options.

 - Don't expand

- Use hydrogen

In aviation the real only alternative fuel is hydrogen. It is the only thing with a high enough energy content to run something like a jet engine, but has no carbon footprint.

At the risk of seeming somewhat "picky", in the nicest possible way, to separate hydogen in operationally significant quantities, one needs a lot of electricity. If you produce that by burning hydocarbons, you must produce emissions. They just won't be shed from the aeroplane but will still enter the atmosphere. Down here in New Zealand where we are rain-rich and have a substantial hydro-generating infrastructure; we could fuel aircraft engines to a degree which I have not calculated. But that would just increase our need for alternative generation using coal, oil or gas. Regardless of new engine and propeller technology, the only way to reduce emissions is to reduce energy use...burn less fuel...cut air travel by force of law. How do you do that? Have Emission Police in the ATC units preventing the issue of Take-off clearances. Sure rail is great. But how do you build rail bridges across oceans? We are worried down here too as we have a large tourist industry reliant on people wanting to escape from the pollution of the Northern Hemisphere.

It is either prioritise air transport according to some need-based formulae, or to say: "To hell with it...let's just fly and see what happens!"

Hydrogen certainly is no option. On th ground especially in stationery applications it may be an alternative to current fuel, perhaps even in cars. But aircraft are probably the most stupid application fot it.

I think the most promising solution are algae based 3rd generation bio fuels. The United States Department of Energy estimates that if algae fuel replaced all the petroleum fuel in the United States, it would require just 15,000 square miles without interfering with food production.

It would not require

• changing engine technology or
• building a separate infrastructure or
  
• replacing the entire fleet
  

If increasingly added to the current jet fuel it would reduce carbon emissions immediately. There remains a lot of work to be done before those algae fuels will be available. But they are the only viable alternative I can see today.