Altering flight paths to reduce the effects of non-CO2 emissions can be problematic. Rescheduling longer flight times would be difficult as there remain significant barriers to providing the required accuracy in predictions of wind, temperature and weather. A 2016 paper, Potential to reduce the climate impact of aviation by climate restricted airspaces, reported potential emissions reductions of 12%, but Cait Hewitt, deputy director of the Aviation Environment Federation, noted that coordinating management of restricted airspaces could be difficult to achieve.
Flying at lower altitudes to reduce contrails increases CO2 emissions as more fuel is burnt to counter the increased resistance of denser air at lower altitudes.
Long haul electric aviation powered by batteries at low enough costs and with high enough power to weight ratios is at the very least 10 to 30 years away. Norway’s state owned air transport operator, Avinor, plans to have all short haul flights, of up to 1.5 hours, entirely electric by 2040.
Adding biofuels to regular emissions-generating jet fuel does not eliminate emissions or contrails, and — despite being tagged ‘sustainable’ — biofuel production can increase overall emissions.
The ICAO’s biofuel initiative in their CORSIA ‘sustainable aviation’ package only targets a 10% greenhouse gas reduction for biofuels compared to regular jet fuel. Expanding demand for biofuel will devastate indigenous cultures and biodiversity, and exacerbate warming as rainforests are destroyed to make way for palm oil plantations.
Aviation emissions reductions claimed for biofuels can be misleading when ‘full life cycle’ reductions are quoted, as these include the CO2 drawn down by the growing feedstock.
So-called second generation biofuels (also known as advanced biofuels) use non-food based biomass feedstock. In NASA tests in 2013 and 2014, using a 50:50 mix of aviation fuel and camelina plant oil, fewer soot emissions and reduced contrail formation were recorded. In January 2018, a Qantas 787 Dreamliner flew from Los Angeles to Melbourne fueled by a 10% biofuel 90% regular jet fuel mix. The biofuel was sourced from a type of non-edible industrial mustard known as carinata seed. It’s manufacturer claims emission reductions of 65 to 85% per litre are possible, or, with maximum regular jet fuel substitution at 40%, a reduction of just 26 to 34%. These non-food crop feedstocks compete for arable land with food agriculture.
The production of enough biofuel to provide for Australia’s aviation needs, calculates Graeme Pearman, Adjunct Senior Research Fellow at Monash University’s School of Earth, Atmosphere and Environment, and Professorial Fellow at the University of Melbourne’s Australian-German Climate and Energy College, “would likely require an area in the order of that needed to grow Australia’s total wheat crop — around 11 million hectares.”
British Airways has entered a partnership to design a series of waste recycling plants that will convert household waste into renewable jet fuel to power its fleet. The jet fuel produced at the plant is hoped to deliver more than a 60% reduction in greenhouse gas emissions, compared with regular jet fuel. When feedstock is household or food waste, competition with agriculture for land is avoided but the supply of waste dirty oil, grease and fats is finite.
Despite the ambition of some, such as the Norwegian aviation industry, which aims to replace 30% of all aviation fuel used across its airports with biofuel by 2030, second generation biofuel production is too expensive at present and its supply at scale to replace regular jet fuel — 278 billion litres in 2016 — if possible at all, is years away.
Even to meet the CORSIA objective of ‘carbon neutrality’ by 2020, the transition to biofuels would, as the ICAO admits, “require the realization of the highest assumed increases in agricultural productivity, highest availability of land for feedstock cultivation, highest residue removal rates, highest conversion efficiency improvements, largest reductions in the GHG emissions of utilities, as well as a strong market or policy emphasis on bioenergy in general, and alternative aviation fuel in particular.” It concludes: “This implies that a large share of the globally available bioenergy resource would be devoted to producing aviation fuel, as opposed to other uses.”
Using more fuel-efficient aircraft could, according to some reports, cut fuel use by 15-20%. Airlines have continued to improve fuel efficiency. By 2016, fuel efficiency for total system-wide services had improved 10.2% compared to 2009, according to the IATA. The new CO2 emissions standard adopted by the ICAO in February 2017 is the world’s first global design certification standard governing CO2 emissions for any industry sector. The standard will apply from 2020 to subsonic jet aircraft over 5,700kg and propeller-driven aircraft over 8,618kg, and aircraft type designs, already in production, from 2023. Those in-production aircraft that do not meet the standard by 2028 will no longer be able to be manufactured unless their designs are sufficiently modified. As reported by Green Air Online, the standard “is said to be most stringent for … single-aisle 737/A320 families and larger, which account for more than 90% of international aviation emissions”.
But according to analysis by the International Council on Clean Transportation, “The standards will on average require a 4% reduction in the cruise fuel consumption of new aircraft starting in 2028 compared to 2015 deliveries, with the actual reductions ranging from zero to 11%, depending on the maximum take-off mass of the aircraft”.
With a typical working life of 20 years, it will be many years however before the worldwide aircraft fleet (24,000 in 2016) is completely refurbished to deliver in full these marginal reductions.
The International Energy Agency (IEA) reports that recent annual average fuel efficiency improvements of 3.7% have exceeded industry aviation targets. Yet, according to the IEA, “the pace of improvement required for the recently proposed CO2 standard by the ICAO for new aircraft falls short of [dangerous] 2°C emissions thresholds”.
Supersonic aircraft currently in production are likely to emit 70 percent more carbon dioxide than comparable new subsonic airplanes will be allowed to emit, and are also likely to exceed international subsonic limits for nitrogen oxides by 40 percent, according to a 2018 analysis by the International Council on Clean Transportation.
An academic research unit at Paris-Dauphine University focused on the economics of climate change, modelling nine different air traffic growth and aviation energy efficiency scenarios in a 2012 report, Will technological progress be sufficient to effectively lead the air transport to a sustainable development in the mid-term (2025)?. “According to our results”, they concluded, “CO2 emissions from aviation are unlikely to diminish unless there is a radical shift in technology and/or travel demand is restricted. Despite aircraft manufacturers and airlines initiatives, the control of CO2 emissions from aviation should require more binding measures from policy makers.”
The European Parliament’s Directorate General for Internal Policies concluded their 2015 report, Emissions reduction targets for international aviation and shipping, saying “There is general consensus in the literature that technical and operational measures will not be able to offset emission growth in the coming decades.”
Dr Scott Cohen, of the University of Surrey, one of the authors of a 2016 study, Are technology myths stalling aviation climate policy, says “The way in which new technologies are presented constitutes a ‘myth’, a form of propaganda which denies the truth that progress in climate policy for aviation has stalled. The use of these technology myths by industry and government relieves anxiety that nothing is being done, by pointing to future ‘miracle’ solutions, which in reality are unfeasible.”