Bretthauer – Winter 2024

Bunker Down: How Bunker Fuel Use Gets Counted (and Discounted) in International Emission Reporting

Josh Bretthauer

The Paris Climate Agreement was a landmark international agreement, signed onto by 196 countries agreeing to develop “Nationally Determined Contribution” (NDC) plans to keep global warming below 2ºC.[1] Nations’ “economy-wide absolute emission reduction targets,” where countries track, report, and act to lower their anthropogenic emissions of greenhouse gasses (GHGs), are a key metric of these NDCs.[2] However, how did world leaders account for their international flights home from France?

            The short answer: they didn’t. In accordance with guidelines most recently affirmed by the International Panel on Climate Change in 2006, countries omit so-called “bunker fuel” emissions from their national totals.[3] Although “bunker fuel” is a technical term for an umbrella of fuel oil types used by maritime vessels,[4] the term has been adopted by the United Nations Framework Convention on Climate Change (UNFCCC) to refer to all fuels used in international shipping and transportation. In effect, this excludes all emissions from both international air travel and international maritime trade from national emission reporting. Although there has been no comprehensive study of the impact of international aviation and shipping specifically, the aviation and maritime shipping industries overall account for nearly 5% of global CO2 emissions.[5] While countries do separately report their bunker fuel usage,[6] because these emissions are not subject to the reduction targets outlined in wake of the Paris Agreement, they can be obscured from the same social pressure to improve.

            Instead, bunker fuels are regulated by the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO), for international air travel and maritime shipping respectively. These organizations were created during the first UN Climate Change Conference in Berlin in 1995 (COP 1).[7] Their most recent directive came from the 1997 Kyoto Protocol, which guided them to “pursue limitation or reduction of emissions of greenhouse gases not controlled by the Montreal Protocol from aviation and marine bunker fuels.”[8] However, bunker fuel regulations typically lack the salience of major international climate treaties. High public salience provides social pressure that helps magnify the impact of the otherwise weak enforcement arm of international civil law.[9] Without public attention, actors and regulatory agencies are less incentivized to push for expensive emissions reductions.

            Despite lower salience, pressure from consumers for more sustainable travel options and business practices has spurred these agencies to move towards improved sustainability standards for global industry. In December 2023, the ICAO concluded its Third Conference on Aviation and Alternative Fuels (CAAF/3), where 900 attendees, representing 97 states and 23 organizations,[10] discussed sustainable aviation fuels (SAF) (conspicuously hosted in Dubai, UAE, a leading oil-producing state[11]). Following up on the ICAO’s ambitious goal to reach net-zero carbon emissions by 2050 set out during their 2022 assembly, CAAF/3 outlined a plan to reduce CO2 emissions in international aviation by 5% by 2030.[12] At first glance, this number seems minimal. Is this proposal cause for excitement?

            First, the ICAO seems correct to focus their attention on bolstering the use of SAFs. In their initial proposal for carbon-neutrality, the ICAO projected that fuel improvements will account for 55% of carbon emission reductions in international air travel by 2050.[13] However, even if an airline company today aimed to drastically expand SAF use, total sustainable fuel supply account for only roughly .2% of total jet fuel consumption in 2023.[14] In part due to the limited supply of SAFs available, SAFs also currently are significantly more expensive for airlines to use.[15] These are costs that will ultimately be passed onto consumers, leading SAF pioneers acting independently to be less competitive with airlines sticking with traditional fuel sources. A collective, industry-wide action towards SAF adoption may be required to spark the necessary investment in SAF production. Although the ICAO’s 5% CO2 emission reduction target may seem modest, the cooperative objective may help catalyze demand for an international SAF market that has struggled to compete economically.

            The framework also proposes a number of other tangible mechanisms towards meeting the agency’s carbon-neutrality goals. First, it establishes the “ICAO Finvest Hub,” which aims to channel investment from various financial institutions into SAF research and development.[16] Second, it begins implementation of the Carbon Offsetting and Reduction Scheme for International Aviation and provides a certification process for states to ensure sustainable biofuel sourcing.[17] Third, it establishes the “Buddy Partnerships” plan, where 17 supporting states offer compliance expertise and training resources to 119 requesting ones.[18]

            While many aspects of the framework seem like legitimate steps in the right direction, its weakness reflects a common refrain: all state actions are entirely voluntary. In outlining the framework’s plan for policymaking in accordance with ICAO targets, the agency clarifies that “each State’s special circumstances and respective capabilities will inform the ability of each State to contribute to the Vision within its own national timeframe, without  attributing  specific  obligations or commitments in the form of emissions reduction goals to individual States”.[19] The framework substantially links the interests of a broad array of international aviation stakeholders, but provides no binding enforcement mechanism for the standards set.

            With enforcement mechanisms for decreasing emissions from bunker fuels proving to be elusive, are there other means of accounting for their use that would cover them in more mainstream reporting and accountability schemes, such as the Paris Climate Agreement? In fact, the UN Subsidiary Body for Scientific and Technological advice posed eight accounting options back in 1996 in wake of COP 1.[20] These options ranged from allocating emissions to countries where bunker fuels were sold, to countries where planes departed or arrived, to allocating to states all emissions generated in their air space.[21] Some commentators have noted that while penalizing the country of departure seems straightforward, this metric may over penalize tourism hubs like Iceland and Portugal.[22] Another of the accounting options, crediting emissions by passengers’ country of residence, may properly allocate emissions to wealthier countries whose citizens tend to engage in the most international travel.[23]

            Until such alternative accounting mechanisms are considered in the next major climate agreement, we are left with the agency’s ultimate selection: “Option 1: No allocation.”[24] This designation keeps the administrative role of the ICAO and IMO hugely important, though widely unknown. True, the two agencies may lack significant enforcement mechanisms for adherence to their targets. However, it may be a source of optimism that they are nonetheless proceeding with significant steps towards sustainable international air travel, despite their regulations receiving relatively less scrutiny than major international climate accords. The ICAO’s Fourth Conference is scheduled to occur “no later than 2028,” with on-the-ground monitoring sites expected to be ramped up in all regions before then.[25] Though bunker fuels’ use allocation may want for national accountability, and perhaps even their improvement for urgency, sustainable international air travel is in the hands of a UN underdog doing its best.

[1] Paris Agreement to the United Nations Framework Convention on Climate Change, Dec. 12, 2015, T.I.A.S. No. 16-1104.

[2] Id. at 4, 17.

[3] UNFCCC Secretariat, Rep. of the Conference of the Parties on its nineteenth session, held in Warsaw from 11 to 23 November 2013, at 12, U.N. Doc. FCCC/CP/2013/10/Add.3 (2014).

[4] Riley E.J. Schnurr & Tony R. Walker, Marine Transportation and Energy Use, in Reference Module in Earth Systems and Environmental Sciences (2024).

[5] Hannah Ritchie, Climate Change and Flying: What Share of Global Co2 Emissions Come From Aviation?, Our World in Data (Oct. 22, 2020),; International Maritime Organization, Fourth IMO GHG Study 2020 Full Report 1 (2021).

[6]  UNFCCC Secretariat, supra note 3, at 12.

[7] UNFCCC Secretariat, Emissions from Fuels Used for International Aviation and Maritime Transport, (last visited Feb. 22, 2024).

[8] Kyoto Protocol to the United Nations Framework Convention on Climate Change, Dec. 10, 1997, 2303 U.N.T.S. 162.

[9] Catherine Tinker, Note, Environmental Planet Management by the United Nations: An Idea Whose Time Has Not Yet Come?, 22 N.Y.U. J. Int’l L. & Pol’y 793, 796 (1990) (“The lack of enforcement power by the U[nited] N[ations] is well known and is often used by skeptics to criticize not only the UN, but public international law in general. Although the UN cannot order or control member states, it does wield significant power by using diplomatic pressure and public opinion to induce compliance from states seeking legitimacy in the international arena.”).

[10] International Civil Aviation Organization (ICAO), Statement by the International Civil Aviation Organization (ICAO) at UNFCCC SBSTA59, at 1, 3 (2023), (the IMO hosted a concurrent conference on emission reduction that is not the focus of this post).

[11] What Countries are the Top Producers and Consumers of Oil?, U.S. Energy Information Administration, (last visited Feb. 22, 2024).

[12] ICAO, supra note 10, at 1.

[13] ICAO, Report on the Feasibility of a Long-Term Aspirational Goal (Ltag) for International Civil Aviation Co2 Emission Reductions, at 5 (2022),

[14] Marisa Garcia, Aviation Sets SAF Framework To Make Air Travel More Sustainable, Forbes (Nov. 27, 2023, 10:54 AM),

[15] Id.

[16]  ICAO, supra note 10, at 5.

[17] Id. at 8; ICAO, Guidance to Sustainability Certification Schemes (SCS) for application of CORSIA Sustainability Criteria (2022),

[18]  ICAO, supra note 10, at11.

[19] Id. at 4 (emphasis added).

[20] Subsidiary Body for Scientific and Technological Advice (SBSTA), Communications From Parties Included in Annex I to the Convention: Guidelines, Schedule and Process for Consideration (July 16, 1996).

[21] Id. at 11.

[22] Fernanda Ferreira, How do national governments calculate their share of greenhouse gas emissions from international air travel?, MIT Climate Portal (Nov. 28, 2022),

[23] Id.

[24]  SBSTA, supra note 20, at 11.

[25] ICAO, supra note 10, at 4.

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