The widespread availability and affordability of air travel has delivered unprecedented opportunity to travel and a world that is more closely interlinked than ever before. But air transport is also a substantial contributor to greenhouse-gas emissions, leading to a flurry of discussion about what could be done to reduce its 'carbon footprint'.

The airlines and the aerospace industry are increasingly conscious that this concern could put a damper on the growth of their businesses. The Boeing 787, the first exemplar of which is expected to be rolled out of the factory next week and flown next month, is said to be 20% more fuel efficient than the airliners it will replace. Richard Branson's Virgin Airlines said earlier in the year that it plans to begin testing unspecified biofuels in airliners. And EasyJet, a low-cost European airline, has said that it hopes to halve its emissions per passenger kilometre by 2015.

It is by no means clear how much of this is public-relations talk, aimed at deflecting growing public disquiet about the carbon emissions associated with flying. But in the long term, there can be no doubt that the industry will pursue technologies to cut emissions.

One such technology — the use of light carbon-fibre composites in place of aluminium alloys for airframe construction — is incorporated, for the first time in civil aviation history, in the Boeing 787. Further improvements in the strength-to-weight ratio of aircraft structures will come from composites that rely on carbon nanotubes, instead of polymer-based fibres. The cost of the bulk manufacture of nanotubes is steadily decreasing, although important technical barriers still need to be overcome. Problems associated with optimizing the properties of these composites are discussed in a News and Views Q&A in this issue (see page 1066).

But although the use of new high-performance materials can contribute substantially to the sort of efficiency improvements attained by the 787, truly impressive reductions in airliner emissions would require the industry to take the thoroughly radical (and currently inconceivable) step of replacing the gas turbine engine as the airliners' means of propulsion.

A paper published earlier this month (P. J. Masson et al. Supercond. Sci. Technol. 20, 748–756; 2007) puts forward a hypothesis that high-temperature superconducting technologies could provide a route to all-electric aircraft that burn hydrogen fuels and have electrical systems powered by fuel cells. Although highly speculative as to its practicability, it would greatly reduce carbon emissions assuming also that the hydrogen could be produced by nuclear or renewable technologies.

If 'clean' air travel is indeed achievable, it remains a long way off, and will only be developed through a concerted effort between scientists, engineers, governments and businesses. At the Paris Air Show last week, European research commissioner Janez Potočnik announced a 'clean sky' research initiative, under which the European Commission will invest €800 million (US$1 billion) from 2008, while hoping to attract a similar amount from private industry. But it will take more than that. Equally commendably, Louis Gallois, the chief executive of Airbus, called for an unprecedented meeting of airliner and aeroengine makers (including Airbus and arch-rival Boeing) later this year to discuss global collaboration on the technical challenges ahead. These obstacles are considerable, but such an approach gives hope of surmounting them.