Come fly with me, we’ll fly, we’ll fly away
If you can use some exotic booze
There’s a bar in far Bombay
Come on fly with me, we’ll fly, we’ll fly away
Flying has served as an inspiration for many great songs-writers, either by symbolizing freedom (“vogelvrij”) or, like in the above example of Frank Sinatra, as something romantic and spontaneous. Who did not dream as a child of sitting on Aladdin’s magic flying carpet? One could argue that current commercial airline flights might not be as romantic and adventurous as a flying carpet, nonetheless, it did not constrain us from flying increasingly more in the last decade. Just like the love-story in Aladdin had the villain Jafar, our love for flying has a grim side too. As we flew more, greenhouse-gas emissions increased as well: the aviation sector increased its emissions by 76.1% between 1990 and 2012. In 2012, the aviation sector was responsible for around 2% of the global CO2 emissions and is predicted to grow between 200%-360% by 2050, as developing countries are expected to fly more in the future (figure 1). The best way to reduce our personal carbon footprint is to take less flights. Yet, would it also be possible to make flying itself more environmentally-friendly with the use of biofuels?
Multiple airline companies have been asking this very same question. In 2007 the first bio-jet fuel powered non-commercial flight flew on waste vegetable oil. The years after this event, various companies experimented with a wide range of biofuels (coconut, algae, agricultural residues). Currently, a regular commercial flight between Amsterdam and Los Angeles is powered by used cooking oil. This almost sounds too good to be true: Is it merely a stunt by the aviation industry to appear greener or are they actually planning to use bio-jet fuels in the near future?
It appears that airlines are taking bio-jet fuels seriously. Members of the International Air Transport Association (IATA), which is around 85% of all commercial flight operators, have agreed to aim for a carbon-neutral growth by 2020 and a 50% reduction of green-house gas emissions relative to 2005 by 2050 (figure 2). To reach this goal, the first step is to improve efficiency. This can be done by improving the industry’s technology, operations and infrastructure, for example with aircraft modifications or optimized navigational systems. However, to reach the 50% emission reduction by 2050, greater efficiency is not enough and renewable technologies need to implemented. Although electric- or solar-powered planes are being developed, replacing whole aircrafts is often not an option for airlines, as planes are expensive and thus airlines want to use their current planes as long as possible. This leaves one option: biofuels. As the engines of the planes do not need to be replaced or modified, the use of biofuels is easily integrated.
So, if we are already able to safely fly regular commercial flights on bio-jet fuels, why are we not implementing it on a larger scale? To answer this question, we have to take a closer look at the bio-jet fuel itself (as described in a technology brief by the International Renewable Energy Agency (IRENA)). These commercially available bio-jet fuels often are oleochemical-derived, so called HEFA-jet. To produce HEFA-jet, oil and fat feedstocks like cooking oil or tallow are used, which must go through various deoxygenation processes that require significant inputs of hydrogen (figure 3). Unfortunately, HEFA-jet without subsidies is still more expensive than fossil fuel. Next to this, as the same process also produces renewable diesel, HEFA-jet competes with HEFA-diesel, which has a larger market with higher sales prizes. Consequently, most companies that produce HEFA-fuels mainly focus on HEFA-diesel. Another concern for the currently available HEFA-jet is regarding its sustainability. Upscaling the production would require a significant amount of land to provide the feedstock necessary. More sustainable options, for example waste cooking oil, are often only available in smaller quantities, making it impossible for larger production.
Therefore, the solution for making flying more renewable does not lie with the currently used HEFA-biofuels. Luckily there are other technologies for producing bio-jet fuels that might be able meet the future demand, however, it might take five to ten years before they are commercially available. Other options make use of different chemical processes (thermochemical instead of biochemical/oleochemical) as well as different feedstocks (agricultural matter, lignocellulosic biomass, algae, municipal or industrial waste). A more detailed description of these alternatives can be found within the IRENA-report.
Thus, there is still a lot of uncertainty regarding bio-jet fuels. Oddly enough, the IRENA-report mentions that the IATA predicts bio-jet fuels can reduce emissions in comparison to fossil jet fuel between 50-95%. Upon closer inspection these numbers were based upon data provided by E4tech that did not include direct and indirect land use change. Depending on the carbon-storage of the land being cleared for the production of bio-fuels, it could take decades or centuries before the biofuel contributes relatively less emissions than fossil fuels, ultimately compromising the actual sustainability of using bio-jet fuels.
In conclusion, due to economical constraints and uncertainty surrounding the sustainability of bio-fuels, most commercial flights will not be using bio-jet fuel soon. Nonetheless, the fact that there is uncertainty does not mean it is impossible. With hopefully the right research and policies, a safe, economically viable and, most importantly, sustainable bio-jet fuel can be developed for commercial use. For now it might not be the most environmentally-conscious choice to spontaneously take a flight to Bombay for some exotic booze like Frank Sinatra. But a beer whilst camping in Texel would just be as romantic, right?
Aviation biofuel. (2019, May 01). Retrieved from https://en.wikipedia.org/wiki/Aviation_biofuel#cite_note-one-10
CarbonBrief. (2016, August 10). Retrieved from https://www.carbonbrief.org/explainer-aviations-battle-to-limit-rising-emissions
E4tech (2009). Review of the potential for biofuels in aviation. Retrieved from: https://www.theccc.org.uk/archive/aws2/Aviation%20Report%2009/E4tech%20%282009%29,%20Review%20of%20the%20potential%20for%20biofuels%20in%20aviation.pdf
Fargione, J., Hill, J., Tilman, D., Polasky, S., & Hawthorne, P. (2008). Land Clearing and the Biofuel Carbon Debt. Science,319(5867), 1235-1238. doi:10.1126/science.1152747
Goodall, C. (2017, January 19). How to reduce your carbon footprint #GlobalWarning. Retrieved from https://www.theguardian.com/environment/2017/jan/19/how-to-reduce-carbon-footprint
KLM. (2016, September 08). Retrieved from https://news.klm.com/klm-to-operate-biofuel-flights-out-of-los-angeles/
IATA (2015). IATA Sustainable Aviation Fuel Roadmap, International Aviation Fuel Roadmap, Montreal-Geneva. Retrieved from: https://www.iata.org/whatwedo/environment/Documents/safr-1-2015.pdf
IRENA (2017), Biofuels for aviation: Technology brief, International Renewable Energy Agency, Abu Dhabi. Retrieved from: https://www.irena.org/documentdownloads/publications/irena_biofuels_for_aviation_2017.pdf