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Decarbonization in civil aviation: transition strategies still don’t go far enough

The aviation sector faces significant challenges in transitioning to low-carbon alternatives due to its heavy reliance on fossil fuels, which are energy-dense and compatible with existing aircraft designs. Considering the full greenhouse gas impacts of aviation, including non-CO2 emissions and the warming effect of contrails, its contribution to global warming is estimated to be around 3.5 %–4 %, depending on the study. This figure represents a significant increase compared to its share of global CO2 emissions alone, which is approximately 2.5 % . Sustainable aviation fuel (SAF) is seen as a critical short-term solution, offering up to an 80 % reduction in lifecycle carbon emissions compared to traditional jet fuel [2]. However, SAF currently accounts for less than 1 % of global jet fuel demand, representing a significant gap between current usage and the proposed target of 13–15 % by 2040 to achieve net-zero emissions by 2050 . Reaching this intermediate goal would greatly reduce emissions, laying the groundwork for further advancements. As such, this would not only displace a significant portion of fossil-based jet fuel but also drive technological maturity, cost reductions, and infrastructure development for further SAF adoption. Combined with other measures like fuel-efficient aircraft and optimized operations, reaching this intermediate goal would pave the way for rapid scaling and deeper decarbonization in the 2040s, leading to net-zero emissions by 2050.

Literature has noted how challenging it is for this industry to transition to net zero. For instance, Tracey and Duygu argue that the aviation sector is stuck and trapped in a deadlock to take action and attend to regulatory concerns, customer demands, and the pressure from their shareholders to address decarbonization. Similarly, others debate that decarbonization solutions are not available, too complex to implement without specialized skills, or too expensive. While this affects all airlines, this situation is particularly dire for airlines whose revenue is heavily tied to their enterprise customers – corporate and cargo - with strict carbon-emission reduction targets. The ever-existing market growth and the long-term, perpetual need to travel for leisure or business or even to move cargo will be ever-present, which makes this decarbonization more difficult to achieve. In these circumstances, Ritchie claims, that by 2025, the airline industry is projected to emit 1,100 million metric tons of CO2, which is 200 million metric tons more compared to what this sector generated in 2019.

However, despite this gloomy scenario, sustainable aviation presents new market opportunities and alternatives to mitigate emissions. The decarbonization market for the entire aviation sector is substantial, with a projected value of United States Dollars (USD) 46 billion in 2025, growing to USD 104 billion in 2030. This valuation encompasses various carbon reduction solutions, including SAF, lower carbon fuel (LCF), and emissions reduction technologies aimed at addressing the cumulative CO2 emission of 200 million metric tons [8]. SAF, sourced from renewable resources, offers a significant reduction in emissions compared to conventional jet fuels, potentially reducing CO2 emissions by up to 80 %. LCF encompasses a broader range of fuels that emit less carbon dioxide than conventional jet fuels but may not meet the stringent sustainability criteria of SAF. These solutions contribute to the aviation sector's transition towards net-zero emissions, focusing on direct reductions within the sector rather than relying on external offsetting mechanisms.

Recent studies have explored various decarbonization technologies for aviation, including hydrogen-powered aircraft. However, it is crucial to acknowledge the significant challenges associated with using hydrogen as a direct fuel source due to its low energy density and safety concerns. Analysed the impacts of decarbonization technologies on the global energy system within the Paris temperature goals. They showed that integrating electric, synthetic fuel, and potentially hydrogen-powered aircraft (specifically through fuel cells) could contribute to emissions reductions aligned with Paris goals. It is important to note that the practicality of hydrogen-powered aircraft for long-haul flights remains uncertain due to energy density limitations and safety considerations. The low volumetric energy density of hydrogen necessitates a much larger storage volume to achieve the same energy output as conventional fuels. This poses a significant challenge for long-haul aviation, as a substantial portion of an aircraft's payload would need to be allocated to storing hydrogen fuel, reducing the space available for passengers or cargo.

Studies in the literature have highlighted that the use of hydrogen for long-haul aviation may only be feasible if hydrogen is used in fuel cells rather than in combustion engines due to the higher efficiency of fuel cells. Furthermore, hydrogen presents specific safety challenges due to its highly flammable nature and the presence of invisible flames when burning, which poses risks for both ground operations and in-flight scenarios. These risks require the development of sophisticated safety protocols, advanced materials for hydrogen storage, and detection systems to mitigate potential hazards. To address these risks, researchers propose a two-level risk assessment approach: an initial screening with rapid calculations followed by more precise computational fluid dynamics (CFD) modelling when necessary. This method helps identify potential hazards and optimize design solutions early in the development process.

Furthermore, Gupta A. et al. outlined a framework for an airline airport win-win partnership and examined the operational complexities of alternative fuel strategies. Their analysis emphasized the intricate nature of operationalising blended alternative fuel strategies, considering sophisticated operational safety and liability perspectives. This study highlights the challenges in transitioning to low-carbon aviation fuels, including hydrogen-based options. Despite these obstacles, the commercialization of alternative fuels is progressing, with efficiency improvements and operational changes contributing to emissions reduction efforts. Future adoption may depend on engine modifications, improved aerodynamics, and policy measures like subsidies or carbon taxes.

While studies such as provide insight into the global feasibility and safety challenges of alternative fuels and decarbonization technologies, this research differentiates itself by focusing on a regional analysis specific to the South East Asia and Oceania (SEAO) context. Building on this context, this research examines the practicalities of achieving sustainable aviation goals in the SEAO region, through expert interviews with airline industry executives, this research sheds light on the challenges and current efforts towards decarbonising this industry. Unlike broader global studies, this work provides a comparative understanding of how SEAO's strategic, economic, and policy environments shape its approach to sustainability and decarbonization. This regional emphasis highlights how varying regulatory, economic, and technological landscapes impact strategic decision-making, contrasting with findings from more developed aviation markets.

As the effects of climate change and the associated risks are increasingly being felt, several organizations have developed roadmaps that outline potential steps towards carbon neutrality in the aviation sector. These strategies include multiple levers, such as developing alternative fuels and introducing more efficient aircraft, and are supported by the International Civil Aviation Organization (ICAO), the Air Transport Action Group (ATAG) and the European Commission, among others. They are typically evaluated based on a single criterion: greenhouse gas emissions.

Roadmaps that take a broader view...The research team, which included bioeconomy, environmental and aeronautics experts, tested the transition strategies put forward by various organizations against all the planetary boundaries1. This was a first for this type of analysis, which sought to gain insights into issues such as the impacts of changes on the freshwater cycle or how much energy is needed to achieve a particular sustainability goal. To answer these questions, the scientists quantified the environmental impacts and associated resource needs for the roadmaps studied through 2050, while also testing various scenarios for changes in air traffic.

A scientific method based on “environmental budgets”...The scientists created an original method based on the concept of an environmental budget. It works in the same way as a carbon budget, which involves determining the maximum amount of CO2 emissions that must not be exceeded to keep global warming within a certain limit. For this study, the scientists used the planetary boundaries framework to create environmental budgets for all human activities. For example, the environmental budget for freshwater was based on the maximum annual consumption volume that must not be exceeded in order to stay within the associated planetary boundary.

To assign a share of these global budgets to the aviation sector, scientists tested two allocation principles: an economic one (based on civil aviation’s share of global GDP) and an ethical one (based on aviation’s share of the total environmental impact of the reference countries, which meet several environmental and human development criteria).

They then used life cycle assessments (LCAs) to calculate the environmental impacts generated by the production, distribution and combustion of the fuels used in the various international roadmaps. With this method, the researchers could assess, for example, the amount of freshwater required for each roadmap and compare these values with the budgets allocated to aviation. With regard to climate change, the study tracked the share of the historical climate budget consumed by aviation – i.e., the cumulative greenhouse gas emissions to date.

The study results show that aviation remains within the allocated budget for some planetary boundaries, but none of the decarbonization plans studied respects all the boundaries simultaneously. The budgets related to climate change and biosphere integrity were consistently exceeded, regardless of the scenario. The scientists also noted that implementing the most ambitious strategies would entail significant resource costs related to electricity, biomass, water, agricultural land use and carbon sequestration capacity.

Reconsidering supply and demand policies...For the global civil aviation industry, the path to sustainability is still fraught with challenges. To address them, the study’s authors advocate for maintaining the measures already suggested by the roadmaps studied: developing alternative fuels, improving aircraft efficiency, optimizing operations (manoeuvres, tests, etc.) and implementing offset strategies. Additionally, to move more decisively towards a path of environmental sustainability (characterized by simultaneous respect of all planetary boundaries), the researchers demonstrated the need to maintain and complement these technological advances with a more comprehensive rethinking of usage patterns, especially by implementing policies to manage air traffic demand.