Why is Reducing Aviation Emissions so Challenging?
Written by Jérémie Guedez
A Growing Carbon Footprint: Aviation’s Role in Global Emissions
As air travel is set to become a norm for millions, why is it so hard for planes to go green? Aviation only accounts for 2.5% of global carbon emissions, which some may consider a modest share. However, with increasing demand due to the growth of income in developing countries and the faster decarbonization in other sectors such as railroad, road transport, or shipping, aviation’s share of global emissions will grow. It should also be noted that airplane emissions occur at high altitudes, where their warming effect is stronger than most other emissions; that is why even a small share of 2.5% contributes to 4% of global warming.
The Paris Agreement is the current framework under which climate objectives are set. Its main goals are carbon neutrality by the year 2050 and a rise in global temperature well below 2°C above pre-industrial levels. The agreement flags the necessity of urgent improvement in all sectors, especially in aviation, which is highly energy-intensive.
To explain carbon emissions in aviation, three parameters are used: demand, expressed by the number of passenger kilometers; energy efficiency, referring to the amount of energy needed for one kilometer; and carbon intensity of energy, meaning the amount of carbon emitted per unit of energy. In order to reduce carbon emissions, efforts must be made to change one of these factors.
Through design and technological improvements, and also as airplanes can accommodate more passengers, by being larger and leaving fewer unoccupied seats, the energy efficiency of the aviation industry has doubled between the years 1990 and 2019. However, the number of people flying has been multiplied by four over this period, resulting in a doubling of aviation-related carbon emissions.
The carbon intensity of energy, which depends on the energy used to power the plane, remained the same throughout that period since the fuel used in planes, kerosene, is the same. Therefore, it did not have an impact on the evolution of emissions. What we get from that is an ever-growing trend in carbon emissions since the beginning of commercial flights. The only drop in eighty years was in 2020 during the COVID pandemic and lockdowns when demand suddenly shrank. Air travel demand has essentially reached its pre-pandemic level again by now. That highlights that a demand reduction is a solution to reduce emissions, but that it is also unpopular and undesirable for public policy as it is somehow linked to economic development and growth.
An Incomplete Solution: Sustainable Aviation Fuel
Jet fuel is essential in aviation because it packs more energy per kilogram than batteries or other sources of energy, making it crucial for long-distance flights and practical reasons. One of the solutions put forward for this matter is Sustainable Aviation Fuel (SAF), which is a liquid fuel made from waste organic products and certain plants. A switch to SAF can play a big role in getting to net-zero CO₂ emissions by 2050 because it emits far less CO₂ than regular jet fuel during production. This solution, however, comes with some drawbacks that entangle its implementation.
Currently, the production and use of Sustainable Aviation Fuel are in their infancy and come with high costs; it is about 2.5 times more expensive than conventional fuel and only accounts for 1% of the fuel consumed by airlines. To achieve net zero emissions, the SAF production needs to scale up massively.
European aviation will need €441 billion over the 2018-2050 period to develop SAF in order to meet the net zero objective.
Additionally, the biomass sources used in SAF production are insufficient because SAF competes with other sectors, such as road transport, which uses biodiesel, or food production. Thus keeping prices up and supply short, especially with the large volume of SAF necessary to achieve net zero emissions. Finally, these biomass sources are sometimes controversial (palm, soy, etc.) because their production can have an impact on land and biodiversity, nuancing the ’green’ potential of Sustainable Aviation Fuel.
The Limits of Regulation: Why Public Policy Struggles to Cut Aviation Emissions
The fight toward net zero cannot rely only on private airline actions; public policies such as carbon taxes or carbon markets and incentives are also inevitable. However, these policies have to take into account the distinct characteristics of the sector, which can limit their feasibility and efficiency.
According to a 2024 report from the International Air Transport Association (IATA) about airlines expected profitability, for each passenger, the industry earns a net profit of $6.14. Just enough to buy a cup of coffee in certain regions, as stated by the report. Even if airlines generate a very high income annually, they have accordingly high costs, resulting in what is considered a thin margin. Therefore, absorbing additional costs without impacting consumers is difficult, and these policies aim to place the tax burden on airlines rather than consumers. Some may also argue that increased costs reduce the profit allocated to innovation and slow down the development of green solutions like SAF.
Another important point is the lack of global policies. One of the main tools of the European Union to address climate change is the EU Emissions Trading System (EU ETS), which is a carbon market that requires polluters from certain sectors, including aviation, to pay for their emissions. But long-haul flights that land outside the European Union aren’t affected by the tax.
In 2023, the total income of the EU ETS was €2.9 billion, but it could have been €13 billion if extra-European flights that departed from the EU were included.
One of the first global policies is the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA), adopted by ICAO in 2016. CORSIA will require the global airline industry to offset its emissions through the funding of reductions in carbon emissions elsewhere. It can be criticized as it does not really address the emission problem in the sector, but only compensates with cuts in other sectors. Yet, it still remains a step forward.
The Non-CO₂ Impacts of Flying
We mentioned earlier how aviation accounts for 2.5% of carbon emissions but 4% of total global warming. That is due to the fact that the burning of jet fuel at high altitudes has other effects than just releasing carbon dioxide; we call those non-CO₂ effects. The two main non-CO₂ emissions are nitrogen oxides that generate ozone and methane in the upper atmosphere and contrail cirrus that trap heat.
Non-CO₂ effects are estimated to be accountable for two-thirds of aviation’s global warming to date.
The problem is that they aren’t included in international agreements because of the complexity and uncertainty of their effects. But if they aren’t addressed in future policies like carbon, we may not be able to meet the Paris Agreement objectives.
Conclusion
As the world seeks sustainable solutions, aviation’s journey toward net zero remains among the most challenging. Achieving meaningful reductions will require technological innovation, international cooperation, and policy adaptations that recognize aviation's unique position as both a critical service and a major emitter. But in the case that these measures were not enough, then ultimately, a demand reduction, whether desired or suffered, will be inevitable. In the end, it’s important to note that although the challenge is high, public awareness and industry commitment are accordingly high and offer hope for the future.
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