Despite myriad efforts ranging from legal instruments, policies, transition to renewable energies and the creation of numerous high technologies, statistic shows that carbon emissions from multiple sectors were still increasing in 2024−aviation sector has increased up to 5.5% from the previous year [1]. The average contribution of the aviation industry now reaches 2.5% of global emissions, representing a 0.3% increase from the period of 2000–2019 [2]. Nevertheless, emissions resulted from commercial and private aviation differ. The latter produces emissions multiple times higher but the exact percentage is varied depending on types of aircraft, distances [3] and during special events−economic, cultural or political. For instances during 2023 at World Economic Forum (WEF), Conference of Parties (COP) in Dubai and Super Bowl, several private aircraft appeared at those events [4].

International Civil Aviation Organization (ICAO) is responsible for guaranteeing international aviation standards encompassing safety, security as well as impacts of civil aviation to the environment. In regards with climate change mitigation, the Kyoto Protocol authorizes ICAO to handle and regulate emissions from international civil aviation. This specific delegation is set out in the Protocol Article 2(2) as other climate treaties such as United Nations Framework Convention on Climate Change (UNFCCC) and Paris Agreement merely cover regulation on emissions from domestic aviation. Two of the ICAO’s measures−sustainable aviation fuels (SAF) and carbon offsetting and reduction scheme for international aviation (CORSIA)−are discussed below.

ICAO defines SAF as “renewable or waste-derived aviation fuels that meets sustainability criteria” [5] encompassing but not limited to, biofuels and synthetic fuels. The former derives from any renewable carbon-based material or feedstock [6], meanwhile the latter derives from chemical processes involving water and carbon dioxide [7]. Study shows that SAF can statistically eliminate carbon emissions up to 80% as well as emissions from other pollutants [8]. ICAO develops a global framework (ICAO Global Framework for SAF, Lower Carbon Aviation Fuels (LCAF) and other Aviation Cleaner Energies) to achieve the 5% reduction of CO₂ emissions by 2030.

ICAO Global Framework comprises four blocks: policy and planning, regulatory frameworks, implementation support and financing [9]. The first block encourages ICAO and its member States to develop SAF, LCAF and other cleaner energies in a socially, economically and environmentally sustainable manner taking into account the engagement of relevant stakeholders such as but not limited to aircraft operators, airports, aircraft and engine manufactures as well as fuel producers. The second block lies on more technical methodologies developing SAF in accordance with sustainability certification scheme, also taking into account obligations under CORSIA. The last two blocks concern on how the goals are implemented through cooperation from States, organizations and stakeholders as well as the importance of investment for the cleaner energies transition.

CORSIA was established in 2016 and is the first global market-based scheme requiring member States of ICAO to offset carbon emissions through carbon credits or investing in environmental projects reducing the emissions from international aviation [10]. Since the introduction in 2016, series of actions were taken by ICAO and its bodies in implementing CORSIA (table 1 below). Carbon offsetting applies to flights between States that voluntarily involve in CORSIA and it will be mandatory for all international flights commencing in 2027 with few modifications for least developed, land-locked and small island developing States [11]. Since the pilot phase in 2021, States’ participation is increasing each year−88 States in 2021, 107, 115 and 126 States in the following year respectively.

Table 1

Sources: Chapter 8 of ICAO Environmental Report (2022).

Both SAF and CORSIA encounter some challenges in its implementation. In regards with SAF, since the introduction of CORSIA in 2016 and its pilot phase in 2021, global demand for SAF has been increasing but its global production is still considered low as producers prioritizing other types of renewable fuels [12]. It is not a high priority partly due to the high cost of SAF, which is double that of traditional fuels [13]. Additionally, from a sustainability perspective, SAF in form of biofuels would increase dependency on raw materials (large number of crops) which lead to instability of global price and food security [14].

As for CORSIA, the challenges lie heavily on its voluntary nature and limited scope [15] [16]. Although 126 States participate in 2024, big States in aviation markets such as Brazil, India, Russia and China do not participate. For those participants, firstly, they are not obliged to publish offsetting requirement of their airlines operators leading to check and balance whether member States do implement CORSIA [17]. Secondly, as CORSIA requires the involvement of various stakeholders, State must develop domestic regulation for the better implementation and enforcement of CORSIA [18].

Regarding CORSIA’s scope, it merely covers CO2 emissions whereas other non-CO2 such as nitrogen oxides, water vapour and aerosols also contribute to two-third of aviation total emissions [19]. However, the exclusion of non-CO2 emissions under CORSIA derives from scientific debate whether the climate impact is clear; difficulty to calculate non-C02 of a particular flight; and the timescales−non-CO2 emissions may be gone in few hours while CO2 remains in the atmosphere [20]. Despite the complicatedness, precautionary principle should be taken. As an example, the European Union adopted Directive 2023/958 in 2023 amending Directive 2003/87/EC concerning EU Emission Trading System (ETS) that includes the non-CO2 in their MRV frameworks [21].

Achieving net-zero emissions in 2050 through SAF and CORSIA necessitate comprehensive policies encompassing technological development and financial assistance, sustainability of the non-fossil materials, cooperation and concrete action between relevant stakeholders as well as the more binding regulatory frameworks from ICAO. Then, hopefully, we will reach our final destinations with healthier and environment-friendly flights.