A bumpy ride toward decarbonizing aviation

Aviation, which represents around 2-3% of global greenhouse gas emissions, is a significant contributor to anthropogenic warming, with estimates suggesting its total impact is closer to 3.5%. Decarbonizing this sector is crucial, but it's not an easy task due to the value and unique properties of jet fuel. Several potential solutions include sustainable aviation fuels (SAFs), hydrogen, electrification, and synthetic fuels. However, each comes with its challenges. Dan Rutherford, director of aviation and maritime programs at the International Council on Clean Transportation, shares his insights on the viability of these pathways. Aviation's economic importance, with it transporting half a percent of global trade volume but 35% of its economic value, adds complexity to the decarbonization efforts.

While aviation contributes significantly to global warming, accounting for around 12% of transportation emissions (not including other pollutants), the industry is currently facing financial challenges due to the COVID-19 pandemic. Despite this, there is a renewed focus on decarbonization, with airlines making net zero commitments and exploring sustainable fuel options. However, the cost of these changes and how it will be funded remains an open question, as affordability and accessibility of flights are key considerations. The aviation sector's future lies in striking a balance between reducing emissions and maintaining affordability for consumers.

Sustainable aviation fuels are a promising solution for decarbonizing the aviation industry while maintaining the convenience of air travel. These fuels, which include waste, fats, oils, and greases, as well as advanced biofuels, are meant to be drop-in alternatives to fossil jet fuel and can reduce climate impacts, including CO2, NOx, and contrails. However, they currently make up less than 0.1% of global jet fuel use and are significantly more expensive than conventional jet fuel, with costs ranging from 6 to 8 dollars per gallon. Despite these challenges, sustainable aviation fuels offer the potential for significant emissions reductions, with waste fuels expected to reduce emissions by 40-50% on a life cycle basis. The most readily available and cheapest sustainable aviation fuels come from waste, fats, oils, and greases, but their supply is limited. Advanced biofuels, which include cellulosic fuels and municipal solid wastes, have the potential for much larger supplies, but the technology for producing them is still emerging. Overall, sustainable aviation fuels present an important step towards decarbonizing aviation and reducing the industry's climate impact.

The transition to sustainable aviation fuels involves exploring various options, each with its unique potential for reducing greenhouse gas emissions. The first bucket includes biofuels derived from agricultural feedstocks, offering up to 80% reduction in emissions. The second bucket includes waste-based biofuels, which can provide even larger reductions, up to 100%. The third bucket consists of synthetic fuels, such as eFuels, which have the potential for near-zero emissions and virtually unlimited supply, but are currently expensive. Lastly, the cheapest but most problematic option is crop-based biofuels, which can emit more carbon than traditional jet fuel and contribute to deforestation. The aviation industry is actively pursuing all these options, with commitments and plants being built to increase their production. However, it's essential to ensure that the production of sustainable fuels doesn't compete with food production or prolong the life of coal power plants.

The production costs and the timing of payments for sustainable aviation fuels (SAFs) differ significantly between traditional fuels like crop-based biofuels and advanced biofuels or power-to-liquids. The former primarily have operational costs, while the latter have high upfront capital costs. To bridge this gap and make SAFs economically viable, potential solutions include regulatory mandates, proper jet fuel taxation, and complex incentives like contracts for difference. The aviation industry's low margins and the cheap price of jet fuel pose significant challenges. Hydrogen aviation and electric aviation are other promising decarbonization pathways, with Airbus exploring hydrogen-powered designs for potential implementation by 2035. These shifts represent a fundamental technology transformation for the aviation sector.

Airbus and Boeing, two major players in the aviation industry, have different approaches to reducing carbon emissions in commercial aviation. While Boeing is focusing on Sustainable Aviation Fuels (SAFs), Airbus is exploring hydrogen as a potential solution for long-haul flights. Hydrogen is energy dense on a mass basis but not on a volume basis, making it suitable for storing large amounts of fuel in planes, despite its lower energy density per unit volume. Airbus is planning to make a decision on building hydrogen-powered planes by 2025, and the challenge lies in maturing and deploying the technology and infrastructure. Europe, where Airbus is headquartered, is more advanced in climate policy and hydrogen infrastructure, potentially influencing the company's hydrogen ambitions. However, it's essential to consider the source of hydrogen production, as clean hydrogen is the only sustainable option for reducing carbon emissions in aviation.

Airbus is exploring the use of hydrogen as an alternative to sustainable aviation fuels (SAFs) for short and medium haul flights, as hydrogen has the potential to offer larger reductions in CO2 emissions and other climate impacts compared to SAFs. However, there are challenges associated with hydrogen, including its high production cost, the need to build new infrastructure for storage and fueling, and the energy density issue which requires large storage tanks. From a design perspective, there are also complexities related to the placement and weight distribution of hydrogen fuel tanks on aircraft. While these challenges are significant, Airbus is optimistic that they can be addressed. The use of SAFs, hydrogen, and electrification (battery-powered planes) are currently the three main categories of alternative fuels being considered for the aviation industry, with each having its advantages and challenges. The transition to these alternatives is expected to be complex and will require significant investment and innovation.

The mass penalty of batteries in aviation is a significant challenge for electrification, especially for long-range flights. While there is optimism about battery technology improvements, the unique requirements of aircraft, such as cooling, packaging, and safety certifications, make it uncertain whether these improvements will be enough to overcome the constraints. The mass penalty is a result of the battery staying with the plane throughout the entire flight, unlike jet fuel, which is burned off during the flight. For now, electric aircraft are best suited for short-range, commuter flights, and may not be able to compete with single-aisle jets or larger aircraft. However, distributed propulsion technology, which uses multiple small props instead of large engines or props, could offer additional efficiencies and may help electrification in aviation progress. Ultimately, the decarbonization of aviation in the 2030s and 2040s will likely involve a combination of technologies and approaches, with electrification being just one part of the solution.

The aviation industry is making strides towards decarbonization, but significant challenges remain. Sustainable Aviation Fuels (SAFs) are expected to become more prominent after 2025, with hydrogen potentially taking over by 2050. Consumer-facing initiatives, such as Google Flights and Kayak providing emissions data, can help consumers make more carbon-conscious choices. However, these efforts have limitations, and standardization and improvement are necessary. The aviation industry, including airlines and manufacturers, has committed to net-zero emissions by 2050, but past goals have had little impact on emissions reduction. The road to decarbonization is complex, with various fuel pathways, technologies, and non-CO2 climate impacts to consider. Continuous refinement and expansion of these efforts are crucial for meaningful progress.

The aviation industry is making more concrete commitments towards using sustainable aviation fuels (SAFs), with some airlines aiming for a 10% SAF supply by 2030. However, the industry's ability to meet these targets depends on the availability and cost of sustainable fuels. The public disclosures provide overall volume targets, timeframes, and the companies involved, but determining the feedstock and estimating life cycle emissions requires some judgment. Additionally, there's excitement about next-generation aviation, such as eVTOLs and supersonic aviation. While eVTOLs might not decarbonize the existing fleet significantly, they represent a new market. Supersonic aviation faces economic and environmental challenges, and its potential impact on decarbonization depends on the fuel used. Boom Supersonic, for instance, claims to use SAFs, but the extent of its environmental impact remains to be seen.

While supersonic aircraft manufacturers claim their planes can use sustainable aviation fuels, the reality is that the fuel used is largely out of their control. The aircraft themselves are estimated to be 5 to 7 times more carbon intensive than comparable subsonic designs, and the cost premium for sustainable aviation fuels makes a profitable market for supersonics hard to see. Currently, less than 0.5% of aviation fuel is decarbonized, and it's unrealistic to expect that to reach 100% within the next few decades. The aviation industry is aiming for 60-70% mitigation through alternative fuels by 2050, but the economics and political will needed for such a transition are significant. Dan Rutherford, the director of Aviation and Maritime Programs at the International Council on Clean Transportation, emphasized that while it's not impossible to transition to sustainable fuels, it will require significant investment and political commitment.