Following two decades of debate, the aviation industry yesterday announced the first sector-specific pledge on cutting emissions. 191 countries have signed up to the agreement, formalised at the International Civil Aviation Organisation (ICAO)’s 39th Assembly and, though it falls short of any binding commitments, it does specify the dates by which the different phases of the Carbon Offset and Reduction Scheme for International Aviation (CORSIA) should be implemented, starting in 2021.
Industry representatives have welcomed the deal  but environmentalists were said to be scornful of the emphasis on “offsetting” instead of reducing carbon emissions; the BBC’s environment analyst twice mentioned “activities like tree planting” in a short summary.
However, not only is the sector the first to unite globally to propose measures but there is also evidence  to corroborate its claim that it is responsible for little more than 2% or the world’s carbon dioxide emissions. Nor has the sector been sluggish in striving for greener flight. For over a decade, national carriers have been working with their governments to develop alternatives to 100% carbon-based fuels, a fact that is not referred to in the BBC’s report but is mentioned in the ICAO press release.
At present, the best solutions are a hybrid mix of traditional jet fuel with up to 50% biofuel ‘drop in’. Virgin Atlantic pioneered biofuel aviation in 2008 with a 20% drop-in derived from nuts and coconut oil. It was followed, in December of the same year, by a test flight in New Zealand, using a 50/50 jet fuel/jatropha mix. In March 2015, a Boeing aircraft flew from Shanghai to Beijing using a drop-in fuel created from waste cooking oil collected from restaurants across China.
Jatropha is an appealing feedstock as, unlike sugar beet, it could never be used as food. Its oil also has a low freezing point, making it particularly appropriate for high altitudes. But the real stars of the feedstock show are algae since they use carbon dioxide to grow. In 2010, at an air show in Berlin, EADS, the group that includes Airbus, gave a demonstration flight of a light aircraft whose engine relied 100% on algae-based biofuel. Rolls Royce, the engine maker, believes that algae-fuelled flight could be a commercial reality by 2033. Algae are high in energetic oil content and produce 30 times more biomass than rapeseed. Like jatropha, they do not compete with food products for land or water during cultivation so show considerable promise.
Meanwhile, Nasdaq-listed Gevo has been authorised by the Federal Aviation Authority to produce a fuel based on isobutanol, a product that is much more potent than ethanol and can be transported in the same pipes and containers as the petrol derivatives with which it is mixed. Alaska Airlines has used a 30% isobutanol drop-in on recent test flights.
There is no shortage of initiatives but the trick is in bringing the price down. Aviation biofuel is currently 250% more expensive than its traditional counterpart and, without subsidies, airlines will not be able to pass this green premium on to passengers. Investors will need to keep pumping money into research and development until commercial-scale production is a reality.
 International Civil Aviation Organisation. Historic agreement reached to mitigate international aviation emissions. 6 October 2016. www.icao.int
 Business Green. ICAO deal: a new chapter in international aviation. 7 October 2016. www.businessgreen.com
 BBC. Aviation industry agrees deal to cut CO2 emissions. 7 October 2016. www.bbc.co.uk
 International Civil Aviation Organisation. ICAO Environment Report 2010: Aviation and Climate Change. 2010. www.icao.int