Feedstock to Flight: The Importance of Lifecycle Analysis in SAF
What is Lifecycle Analysis (LCA)?
Sustainable Aviation Fuel (SAF) is the most readily available solution for reducing greenhouse gas (GHG) emissions within the aviation industry. Instead of extracting petroleum from the ground and introducing new carbon into the atmosphere, SAF is created from feedstocks made of existing carbon. This recycling process means that, although SAF has the same emissions out of the back of the engine as conventional Jet A, it offers a substantial sustainability improvement by reducing the net new amount of carbon added to the atmosphere. To see the benefit of SAF, it is essential to evaluate its emissions over the entire lifecycle of the fuel. This comprehensive approach is known as Lifecycle Analysis (LCA).
Lifecycle Analysis is a technique used to estimate the environmental impacts associated with a product, material, or service throughout its entire lifetime. By utilizing carbon that is already present in the atmosphere, SAF can achieve up to a 90% emissions reduction compared to Jet A. There are still residual net new carbon emissions produced when making SAF and this is why SAF is not a 100% reduction. When conducting a lifecycle analysis, everything from the moment of extraction or collection through transportation, refining, blending, and distribution is considered.
A lifecycle analysis is meant to capture the entire impact in terms of carbon emitted from the first point of origination to the last point of delivery. Comparing the life cycle analysis of SAF to fossil JetA is where we see the major net carbon benefit of SAF.
Typically, blended SAF achieves a 20-25% reduction in emissions, with variations depending on the feedstock and blend. Conducting a lifecycle analysis is what allows us to draw these comparisons, determining the final environmental footprint of a given batch.
It is important to note that while all SAF contributes positively to emission reductions, not all SAF is the same. The lifecycle emissions of SAF force the aviation industry to consider emissions attributes in a way it hasn't traditionally done. Although SAF is fungible with Jet A in terms of certification and performance, the emissions attributes of SAF are distinct, forcing new accounting, tracking and documentation.
How Lifecycle Analysis is Calculated
Calculated the LCA of a fuel is a complex process, with many variables such as origin and type of feedstock, electricity usage and source, distance and carbon intensity of supply chains, and production method having a considerable impact on the total greenhouse gas emissions.
This comprehensive view of fuel emissions is also known as "Well-to-Wake" (WTW) emissions or the carbon intensity (CI) of the fuel. This can also be referred to as "Well to Wheels/Wing" or the carbon cycle. Understanding WTW is easiest through a visual representation:
Well-to-Wake emissions (WTW) represent emissions of the activities across the value chain of jet fuel, including feedstock cultivation, feedstock ground transport, conversion, fuel transport, distribution, combustion. These are also known as the core LCA components. WTW emissions are further divided into Well-to-Tank (WTT) and Tank-to-Wake (TTW) emissions.
Well-to-Tank emissions (WTT): GHG emissions from origin to before combustion, including feedstock cultivation, feedstock ground transport, conversion, fuel transport, and distribution. These are the emissions generated by producing and moving the fuel to the airport it will be used at.
Tank-to-Wake wake emissions (TTW): GHG emissions solely from the combustion of the fuel (or the emissions coming out of the back of the engine).
Considering all the above, how can we understand the emissions reductions coming from a gallon of SAF? Jet fuel emissions are typically measured in grams of CO2 equivalent per megajoule of fuel produced and combusted in an aircraft engine (gCO2e/MJ). Depending on the variables considered and the methodology used, there can be slight variations in the final emissions factor of jet fuel. ICAO has identified the following WTW and TTW factors for traditional jet fuel under CORSIA:
Applicability: Why LCA Matters
Not all SAF is the same — Lifecycle analyses consider how a feedstock is cultivated, where and how it’s transported, and its ultimate conversion to fuel. Different feedstocks and production pathways have different LCA carbon intensities, meaning different SAF used in an aircraft will result in different carbon reductions. Effectively documenting the different LCAs is critical to accurately reporting emission reduction claims from the use of SAF.
Image Description: Graph shows the emissions resulting by the ASTM-certified production routes for Jet A1, ATJ, and HEFA.
Emissions Reporting
The lifecycle analysis of SAF introduces a reporting complication—jet fuel and SAF can be calculated and reported differently depending on the reporting scheme. These variations highlight the importance of aligning fuel and emissions tracking with your ESG or other corporate governance frameworks. Here are just a few examples:
It's important to note that "there is not yet an accepted practice for corporate customers to report the environmental attributes [from SAFc] in their climate disclosures or to demonstrate their contribution to meeting corporate goals under frameworks such as the Science Based Targets initiative (SBTi)." To invest in SAFc at scale, corporate aviation customers will require SAFc to facilitate bona fide claims towards their climate targets. "A formalized and agreed-upon approach will help stakeholders across the aviation value chain unlock significant investments from corporate aviation consumers for additional SAF and kick-start the SAF market on a pathway consistent with net-zero aviation."
LCA is a critical tool for understanding the environmental benefits of SAF. By evaluating emissions from feedstock cultivation through to fuel combustion, LCA accounts for the varying carbon intensities of different SAF production pathways, supporting more informed and impactful policymaking and emissions reporting. As the aviation industry embraces SAF, developing standardized methodologies and reporting practices will be essential for driving significant progress toward net-zero aviation.
Sources:
ASCENT 2023 SAF Meeting Presentation: 1240-04_25-LCA-Overview_Allroggen_04_10_23-v3.pdf (wsu.edu)
ICAO Life Cycle Emissions of Sustainable Aviation Fuels (icao.int)
ICAO document 07 - Methodology for Actual Life Cycle Emissions - March 2024.pdf
ICAO Annex 16 — Environmental Protection - Volume IV (icao.int)
SBTi Corporate Near-term criteria V5.2 (sciencebasedtargets.org)
GRI 305: Emissions 2016 - GRI Standards English Language (globalreporting.org)