Table of Contents
Introduction
Aviation is one of the most difficult sectors to decarbonize. Aircraft fly long distances, carry heavy loads, and require energy-dense fuels that perform reliably under extreme conditions at high altitude. Batteries and direct electrification are still limited to very short-range, small aircraft. For most commercial flights in the coming decades, liquid fuels will remain essential. Renewable fuels for aviation, usually called Sustainable Aviation Fuels, offer a way to reduce greenhouse gas emissions while using existing aircraft and much of the current fuel infrastructure.
What Makes Aviation Fuel Special
Aviation fuel must satisfy strict technical and safety requirements. It must have high energy content per kilogram, flow easily at very low temperatures, ignite reliably in jet engines, and remain stable during storage and handling. Jet fuel is typically a mixture of hydrocarbons with a specific boiling range and low freezing point. Any renewable alternative must match these properties closely enough to be used safely in existing engines and tanks.
Because safety standards are so strict, aviation fuels are tested and approved under detailed technical specifications, such as ASTM standards. Renewable aviation fuels are usually produced as so-called drop-in fuels. A drop-in fuel is chemically similar to conventional jet fuel and can be blended with it. This allows airlines to use renewable blends without modifying engines, pipelines, or airport fueling systems.
The Concept of Sustainable Aviation Fuel
The term Sustainable Aviation Fuel, often shortened to SAF, refers to aviation fuels that are produced from non-fossil sources and can significantly reduce life cycle greenhouse gas emissions compared with conventional jet fuel. SAF is defined by its origin and by its overall environmental performance, not by a single production method. It can be made from biological resources or from non-biological sources such as captured carbon dioxide and renewable hydrogen.
Although different processes and feedstocks exist, all SAF must aim for three main goals. It must reduce total climate impact over its full life cycle. It must avoid serious harm to ecosystems, water, and local communities. It must be compatible with current aircraft and fuel systems. Meeting all three goals at the same time is challenging and often involves trade-offs.
Bio-Based Aviation Fuels
Many current SAF pathways use biomass as the raw material. Biomass is biological material such as plant oils, residues from farming and forestry, and some kinds of waste. Several technological routes can convert this material into jet fuel range hydrocarbons.
One important pathway upgrades waste fats, oils, and greases. Used cooking oil or certain animal fats can be treated with hydrogen in a process similar to renewable diesel production. The result is a fuel that can be refined to match jet fuel properties. This route is attractive because it uses waste materials that already exist and usually would not compete with food production.
Another set of pathways starts from lignocellulosic biomass, which means the woody and fibrous parts of plants. Examples include agricultural residues like straw, forest residues, and dedicated energy crops grown on marginal land. These materials can be gasified to produce a mixture of carbon monoxide and hydrogen. That gas can then be catalytically converted to liquid fuels in a process related to Fischer–Tropsch synthesis. Alternative routes use biochemical conversion, where enzymes and microorganisms break down plant material into sugars, which are then fermented into intermediate products and upgraded into jet fuel.
Municipal solid waste that is not suitable for recycling can also serve as a feedstock for some aviation fuel processes. This can help reduce landfill use and methane emissions, but it requires careful sorting and handling to avoid contamination and harmful emissions during processing.
Synthetic and Power-to-Liquid Aviation Fuels
A more recent family of renewable aviation fuels does not rely on biomass, but instead uses electricity and captured carbon dioxide. These are often called synthetic, electrofuels, or power-to-liquid fuels for aviation. In this approach, renewable electricity first produces hydrogen by splitting water through electrolysis. At the same time, carbon dioxide is captured from industrial emissions or directly from the air. The hydrogen and carbon dioxide are combined chemically to form a hydrocarbon mixture that can be refined into jet fuel.
The environmental performance of these fuels depends strongly on the source of electricity and on how the carbon dioxide is captured. If the electricity comes mostly from wind, solar, or other low-carbon sources, and if the carbon dioxide is taken from the atmosphere or from a process that would have released it anyway, the resulting fuel can have very low net greenhouse gas emissions across its life cycle. However, this approach requires large amounts of clean electricity and complex chemical facilities, which makes it relatively expensive and limited in scale at present.
Blending, Standards, and Certification
Renewable aviation fuels must be approved before airlines can use them. This is done through standards that define allowable blending limits, fuel properties, and quality tests. Many SAF pathways are currently certified for blending up to a certain percentage with conventional jet fuel, such as 50 percent. Fully replacing fossil jet fuel with SAF is technically possible for some fuels, but certification for 100 percent use is still in early stages for most pathways.
Airlines and fuel suppliers rely on certification schemes to verify that SAF meets sustainability criteria. These schemes check feedstock origin, land use impacts, greenhouse gas savings, and compliance with labor and environmental regulations. Airports and airlines track the amount of SAF used, often through book-and-claim systems that match physical deliveries with sustainability claims.
A key requirement is that certified SAF must demonstrate a significant life cycle greenhouse gas reduction compared with fossil jet fuel, often at least 50 percent or more, under recognized calculation methods.
Environmental Benefits and Life Cycle Emissions
The main purpose of renewable aviation fuels is to lower greenhouse gas emissions over the full fuel life cycle, from resource extraction through processing, transport, and combustion in the aircraft. While SAF still emits carbon dioxide when burned, the idea is that this carbon either comes from recently grown biomass or from captured carbon dioxide, not from fossil reserves that add new carbon to the atmosphere.
Life cycle assessment is used to quantify these impacts. Typical SAF pathways can reduce emissions by a wide range, depending on feedstock, process efficiency, and energy inputs. For example, fuels from waste oils often show high reductions because they use existing waste streams and require relatively little additional processing energy. Fuels from crops can have lower reductions or even poor performance if production leads to deforestation or heavy fertilizer use. Synthetic fuels powered by renewable electricity can achieve large reductions, but only if the electricity is truly low carbon and the carbon source is sustainably managed.
Renewable aviation fuels can also affect other environmental dimensions such as land use, biodiversity, and water use. Using agricultural residues may reduce the need for dedicated energy crops, but removing too much residue can harm soil health. Similarly, large plantations for biofuel crops can compete with food production or natural habitats if governance is weak. Synthetic fuels reduce pressure on land but require materials, water, and extensive infrastructure for electrolysis and fuel synthesis.
Economic and Market Challenges
Renewable aviation fuels are currently more expensive to produce than conventional jet fuel. Costs arise from feedstock collection, advanced processing technologies, and in the case of synthetic fuels, the capital cost and energy use of electrolysis and carbon capture. Airlines operate on narrow profit margins, so fuel price differences matter significantly.
Policy instruments and voluntary initiatives aim to bridge this cost gap. Some regions require a minimum share of SAF in aviation fuel, while others offer financial incentives, tax credits, or support for demonstration projects. Airlines may enter long-term purchase agreements with SAF producers to give investors confidence to build new plants. Passengers or corporate customers sometimes pay a surcharge to cover SAF use on selected flights as part of their climate strategies.
Scaling up production facilities is another challenge. SAF plants must secure reliable feedstock supplies, access to low-carbon energy, and stable policy frameworks. Infrastructure at airports needs to handle blending, storage, and quality control, especially when multiple SAF pathways are used.
Current Deployment and Future Prospects
SAF use is growing from a very small base. A limited number of airports and routes currently offer regular SAF blends, often at low percentages. Many airlines have announced targets to increase their share of renewable fuels over the next decades. Aircraft and engine manufacturers support SAF as a main decarbonization route because it works with existing fleets.
Future projections suggest that meeting ambitious climate goals in aviation will require very large volumes of renewable fuel. This will involve a mix of pathways. Waste-based and residue-based biofuels are likely to play an important role in the near term, while synthetic power-to-liquid fuels could expand in the longer term as renewable electricity capacity grows and technology costs fall. Improvements in aircraft efficiency and operational measures will complement, but not replace, the need for low-carbon fuels.
For long-distance aviation, most credible decarbonization pathways rely on a rapid scale-up of SAF production and use in combination with efficiency gains and demand management, because large commercial aircraft will likely depend on energy-dense liquid fuels for many years.
Sustainability Considerations and Trade-Offs
Not all renewable aviation fuels are equally sustainable. The choice of feedstock, location of production, and process design can lead to very different outcomes for climate, ecosystems, and communities. Using waste and residue feedstocks can reduce competition with food and lower land use impacts, but their availability is limited. Dedicated energy crops can provide more volume but require strict land use planning and protections for biodiversity and local livelihoods.
Certifying sustainability and monitoring performance over time are therefore essential. Stakeholders must consider indirect land use change, meaning that using land for fuel might push food production into new areas and cause deforestation elsewhere. They must also examine local impacts such as water use, pollution from processing plants, and working conditions in supply chains.
Balancing aviation’s role in global connectivity and economic development with the need to cut emissions creates difficult policy choices. Some strategies look at managing demand for air travel, encouraging shifts to lower emission modes where possible, and focusing scarce SAF supplies on flights that have no practical alternative. Over time, progress in other transport sectors can free up resources and focus innovation on the particular needs of aviation.
In summary, renewable fuels for aviation represent a central pillar of efforts to make flying more sustainable. They provide a practical route to reduce emissions while using existing aircraft, but they are not a simple or unlimited solution. Their success depends on technological development, strong sustainability safeguards, supportive policies, and careful integration into broader strategies for transforming the transport system.