Finding environmentally friendly ways to travel is becoming easier by the day.
From electric cars and trains to biofuel-powered buses, travelling no longer has to mean burning fossil fuels and pumping carbon dioxide into the atmosphere.
However, there is one mode of transport where increasing our carbon footprint is usually inevitable: air travel.
Flying burns 1.5 billion barrels of jet fuel every year. It is responsible for 12% of all transport CO2 emissions and 2% of global carbon emissions.
These figures are expected to rise as demand for air transport doubles by 2035 and other transport modes and sectors such as electricity generation move away from fossil fuels.
Norway’s airports are leading efforts by the global aviation industry to curb its growing carbon emissions.
The Scandinavian nation is one of 72 countries to have signed up to the UN’s International Civil Aviation Organization’s voluntary programme of carbon-neutral air travel growth, which will begin in 2020.
Norway’s state-run airport operator, Avinor, is focusing its efforts on promoting the mixing of biofuels with jet fuel.
At its two busiest airports – Oslo and Bergen – a special blend of jet fuel mixed with biofuels is made available to all aircraft.
Bergen began offering biofuels at its new terminal this summer, after BP Biojet made its first delivery in August.
This was after Oslo became the first airport in the world to offer biofuels to all airlines in 2016.
While certain airlines around the world have run specific flight routes on biofuels, Oslo was the first airport to offer them via the airport’s main fuelling system.
But using biofuels is not without its risk for airlines. They can cost twice as much as conventional jet fuel, and there are concerns about just how environmentally friendly many of them are.
Crop-based biofuels like palm oil are controversial as they can have negative environmental effects ranging from decreasing food production and increasing water use to deforestation of tropical rainforests.
In June, Norway became the first country in the world to ban procurement of palm oil-based biofuels by state-run bodies, such as Avinor.
With palm oil off the table, airlines and airport operators wishing to incorporate biofuels into their mix need to look at alternatives.
Alcohol-based biofuels are a more sustainable alternative, but the heat value per unit mass of alcohol fuel is small and is not suitable for jet fuel.
Others such as algae-based biofuels are difficult to mass-produce, and a report by the UK’s Royal Academy of Engineering earlier this year suggests they may be responsible for higher levels of greenhouse gas emissions than fossil fuels.
However, the report finds that making biofuels from farm and forestry waste, and from used cooking oil, always cuts emissions compared with the performance of fossil fuels.
It is from these more environmentally friendly sources that Oslo Airport takes its biofuels.
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Airport operator Avinor began with a biofuel made from the oil of camelina sativa plants (a flowering member of the mustard family, also known as false flax) which were imported from Spain. Refined by Finnish company Neste, the fuel is a 50:50 blend with traditional jet fuel.
Oslo airport followed this up by importing a biofuel from California made from waste cooking oil. It attracted some criticism over the environmental impact of transporting the biofuel thousands of kilometres before it was used.
In spite of this, Avinor senior strategy and development adviser Olav Mosvold Larsen told the UN that the carbon footprint from the biofuels was still lower than fossil fuels.
With the aviation industry targeting carbon-neutral air travel growth by 2020, it seems unlikely that jet fuel made from waste cooking oil will be a flash in the pan. Instead, expect to see more initiatives such as those currently underway in Norway.
Japan, for example, is aiming for all Japan Airlines and Nippon Airways flights to use bio jet fuel during the Tokyo 2020 Olympics.