Well ... it's far from being a prototype, but with everyone racking their brains about how aviation can continue in a world where we are all tightening our carbon belts, there is a consensus that the days of air-travel powered by Jet A1 are numbered.

Hope for intercontinental eco-savvy globe trotters could come from a small firm in Oxfordshire, UK, who claim to have designed a hypersonic plane that can do the jaunt from the UK to Australia in under five hours.

With a top speed of 4000, it's fast, and there are claims that it could be prototyped within 25 years - by which time aviation fuel and environmental taxes will surely have made air travel blindingly expensive.

Hypersonic flight has been achieved before, but whether it could be sustained on a scale to make it commercially viable is yet to be seen.

However, at EcoGeek, we like the fact that it runs on "liquid hydrogen." Whilst the bulk of hydrogen is currently produced from those nasty fossil fuels at the moment, hydrogen does offer a solution as an energy carrier in a post-carbon world, and if Reaction Engines' design does "take off," combined with clean sources of hydrogen, it could go a long way toward making air travel sustainable.

Via BBC World