Can sustainable fuels help address the environmental impacts of flying?

Can sustainable fuels help address the environmental impacts of flying?
By Mike McCurdy, P.E. and Angus Reid-Kay
May 13, 2020

Sustainable aviation fuels offer an opportunity to substantially reduce CO2 emissions from flying, but they are not a universal panacea.

Despite the significant number of aircraft and airlines currently grounded due to COVID-19, the subject of the industry’s carbon emissions is still making headlines. Some individuals and groups, including the former EU climate chief Miguel Arias Cañete, believe that financial support for airlines should be contingent upon the industry’s agreement to tighter restrictions on CO2 emissions.

In its Environmental Report 2019, the International Civil Aviation Organization (ICAO) sets out the aviation industry’s initiatives to address climate change and reduce its environmental impact. ICAO emphasizes the role of alternative aviation fuels, which are often referred to as Sustainable Aviation Fuels (SAF). The report outlines that they are “critical for aviation to meet its commitments to greenhouse gas (GHG) emissions reduction.” But do SAFs represent a pragmatic opportunity for the global aviation industry to reduce its emissions?

The nature of the problem

The aviation industry certainly faces unique challenges when it comes to CO2 emissions. Commercial aviation worldwide accounted for roughly 2.4% of anthropogenic CO2 emissions in 2018 (i.e., those emissions directly attributed to human activity). Compounding the issue, new research from the Institute of Atmospheric Physics Oberpfaffenhofen and others indicates that when the nighttime insulation effect of contrails is added to the CO2 emissions, the total effect of aviation’s contribution to global warming could be as much as 5%. Aviation is also recognized as the transport type that is potentially the most difficult to decarbonize, with new long-haul airframes, batteries, hydrogen, and other technologies not expected within the next decade by even the most optimistic advocates.

Fuel makes up the main operating cost for airlines—around a third of their costs—so fuel saving measures are typically a key focus to airlines. The industry has relied on the properties of fossil fuels since its inception. Although SAFs’ life-cycle carbon emissions are much lower than conventional fossil-based sources, SAF is currently more expensive and hence the tradeoff airlines face.

What are alternative fuels and SAFs in particular?

These substances are alternatives to the customary fossil-derived sources of jet fuel. Alternative fuels are processed from a number of different feedstocks including plant oils, used cooking oil, inedible fats, and municipal waste. ICAO recognizes alternative fuels to be those that have “the potential to generate lower-carbon emissions than conventional kerosene on a life-cycle basis.” It’s assumed that atmospheric CO2 captured by plants during their growth offsets part of the emissions from the production, use, and transport of SAF from its production facility to the airport.

SAF is also considered sustainable when compared with a fossil-fuel source because the latter is a finite commodity. The industry has been mindful of the need to identify globally acceptable standards for sustainability of SAFs. To comply, SAFs must be capable of being repeatedly resourced and can deliver “the three pillars” of economic, social, and environmental objectives without disrupting ecological balance, reducing natural assets, or accelerating climate change compared to business as usual.

While it is generally agreed that SAF feedstocks are less carbon intensive than fossil feedstocks over their life cycle, there is a certain amount of CO2 released during the production and refinement of the SAF feedstocks. GHG studies of SAF feedstocks include emissions from farming practices and fertilizers, transport of the feedstock to the SAF production facility, and—in certain circumstances—land use changes. Palm oil, for example, has generally been excluded from use as a SAF feedstock due to concerns about deforestation in Southeast Asia to make way for new palm oil plantations.

The use of waste streams for the production of SAF has been particularly beneficial for the environment. Reusing used cooking oil, municipal solid waste, and other waste materials both reduces GHG emissions and keeps those waste products out of our natural environment. In fact, the aviation industry prefers SAFs to the term biofuels because although SAF can be derived from grown-for-purpose plant material, it can also be derived from waste products that include fossil derived waste. Plastic, inorganic textiles, synthetic elastomers, and other fossil-derived products comprise a significant—and increasing—percentage of municipal solid waste worldwide.

Fuel qualification, safety first

While we strive to make air transport more sustainable, it’s important to recognize that all of the industry participants have maintained a focus on safety first above all else. SAF producers, airplane manufacturers, airlines, regulators, and engine original equipment manufacturers (OEM) have collaborated to develop exacting specifications for SAF used in air transport. New SAF products are subjected to the rigorous, three-phase ASTM International qualification process that includes detailed chemical analysis of the fuel properties versus Jet-A1, extensive testing in both test rigs and jet engines, and multistage reviews by OEMs, the FAA, and ASTM technical committees prior to its approval for use in commercial aircraft.

There are currently six approved annexes for producing ASTM-compliant sustainable aviation fuels. Each of these annexes is distinct, including definition of the feedstock, production method, and final fuel composition. Each fuel has its own set of economic and social benefits and drawbacks, such as the availability and cost of feedstock, carbon and other pollutant reductions, labor requirements, and cost of processing. While some may be more suitable than others in certain areas of the world, all six SAF pathways have the potential to help the aviation sector reduce its carbon footprint significantly, assuming all sustainability criteria are met.

With chemical characteristics and physical properties that are equivalent to that of conventional jet fuel, approved alternative fuels can be blended into Jet A-1 up to 50% and used within existing aircraft engines without any modifications. These SAFs that can be safely added to and mixed with conventional fuels are designated as “drop-in fuels,” which means that they can be incorporated into the existing airport fueling systems. Today, SAFs are typically blended with conventional fossil fuels for safety and technical reasons. However, as the availability of SAF improves and blending techniques mature, future operators may be able to dispense with the fossil blend-stock to enable greater reductions in the carbon footprint and other pollutants.

The critical work of SAFs in meeting the industry's GHG emissions

ICAO recognizes that SAFs have the potential for availability over a longer term and the potential to meet 100% of international aviation jet fuel demand by 2050. In this scenario, ICAO estimates that SAFs could reduce international aviation emissions by 63%. However, “extremely large capital investments” in the SAF production infrastructure would be required to produce this required amount of sustainable aviation fuel. The industry would also need “substantial policy and regulatory support” as production volumes would far exceed the historical precedent for other similar fuels such as ethanol and biodiesel used in road transport.

ICAO acknowledges that it is extremely hard to predict the contribution that SAFs might make in the future. If such a vast expansion in the use of alternative fuels were to come about, ICAO suggests a pronounced and beneficial effect on net CO2 emissions from international aviation as shown in the figure below.

Go to ICF
Climate Change Trends

Benefits of using SAFs to reduce emissions

There are obvious attractions to using SAFs as a way of addressing the significant amount of CO2 emissions and GHGs within the aviation industry. In the short-to-medium term, the four types of gas turbine engine used in aircraft are well-known, tried, and tested after 50 years of development and refinement. They have proven to be dependable, viable, and have an enviable power-to-weight ratio. Therefore, coupling this mature technology with emerging SAFs presents a pragmatic and realistic choice for reducing the sector’s CO2 emissions in our current scenario where global aviation is likely to be reliant on liquid fuels for many years to come. As SAFs are functionally equivalent to conventional jet fuel, they are easy to combine with current aircraft as well as the existing supply infrastructure and storage systems.

In addition to the environmental benefits outlined above, SAFs usually contain fewer impurities—most notably sulfur and aromatic carbons—such that existing engines produce significantly less sulfur dioxide and particulate emissions compared to operation with conventional jet fuel. Reductions in these contaminants allows land-based power plants using aeroderivative turbines to significantly increase their maintenance intervals. While additional testing is required, preliminary testing indicated that neat SAFs fuels have the potential to notably reduce engine operating temperatures, increasing power while reducing maintenance requirements.

Finally, SAFs constitute a more diverse (global) geographic fuel supply. This renewable technology presents economic and social opportunities, including rural jobs, associated economic growth, and the potential for poverty and inequality reduction within developing countries in particular.

Risks and challenges to overcome to increase penetration levels

With the first test flight using SAF occurring in 2008, SAF technology is still in its infancy compared to conventional fossil fuel use in aviation. Despite SAF’s potential, there are still some significant barriers to overcome.

  • Lack of commercial facilities: Even with six pathways to approval and certification, only the Hydroprocessed Esters and Fatty acids (HEFA) pathway has been used to produce SAF for commercial sale. While technical challenges can be substantial, commercial facilities face challenges with feedstock availability, price volatility of fossil jet, and other traditional business trials. Operating commercial analogues are critical to attract equity investment in the space as well as secure debt financing for the construction and operation of new facilities in the absence of loan guarantees or other government support for development.
  • Difficulties in monetizing the benefits of SAF: Feedstock costs and the processing costs of waste feedstocks such as municipal solid waste are generally higher than the cost of crude oil at current market prices. These increased costs result in a product that is generally considered to be between two and seven times more than that of jet fuel derived from conventional fossil fuels. Global blending standards and energy security policies have enabled the construction of several SAF production facilities to date, but construction has been slow given limited commercial opportunity. Recent GHG reduction policies—such as the California Low Carbon Fuel Standard that allow producers to monetize GHG reductions—have been critical in incentivizing the private sector to construct new SAF facilities that are coming on line in 2020 and beyond.
  • SAFS have cornered a very minor share of the market: Even with multiple partnerships springing up between the likes of Finnair and Neste, SkyNRG and KLM, United and World Fuels, etc., the growth of SAFs in commercial flights is still very much in the minority. New Scientist’s Adam Vaughan makes the point that roughly 220,000 flights have used SAF since 2008. While this might sound like a lot, it’s quite insignificant when compared with the 39 million total number of flights in 2019.

A call for policy support

Many fledgling industries have received government support to help them progress towards a commercial-scale innovation. Strong support is needed to shift emphasis from carbon-based fuels to sustainable, low-carbon options as soon as possible. An ICCT paper suggests that a precedent for anticipating some of the immediate challenges might be drawn from the journey taken in switching to advanced alternative road fuels. Potential barriers can be overcome through policies and incentives such as mandates, fiscal incentives, sovereign guarantees, decarbonization programs, and grants. Procurement contracts and associated measures can and have helped improve the feasibility of SAF projects and mitigate some of the risks associated with SAF production. It may also help to implement a tax regime and specific financing to help reduce operational costs and boost investment in SAF projects to accelerate projection and deployment.

Special consideration

The incremental gains in technical performance that SAFs can offer on their own are unlikely to increase uptake to the level necessary to address global climate change. Smart policy, regulatory, and economic support for SAF production and use has the potential to unleash immense benefits in combating climate change, creating rural jobs, securing our energy supply, and reducing the impact of waste on our natural environment.

The tragedy of COVID-19 has levied—and continues to levy—untold suffering on humanity and the aviation industry, the true extent of which is still unknown. Amidst the uncertainty there is one certainty: that we will survive. It is our hope that SAF is part of the solution as we emerge stronger and more resilient than ever before.

Meet the authors
  1. Mike McCurdy, P.E., Director, Fuels and Power
  2. Angus Reid-Kay, Senior Consultant

    Angus specializes in traffic forecasting, operational modelling, airport transaction advisory and aviation market reviews, as well as measuring carbon emissions and noise at airports. View bio

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