The pressing need for a strategy to ramp up ambition on mitigating emissions from aviation

The pressing need for a strategy to ramp up ambition on mitigating emissions from aviation | Chris Lyle

Mon 29 Apr 2019 – Greenhouse gases from aviation will continue to increase globally despite prevailing mitigation actions, whose effects are well outdistanced by traffic growth. ICAO is in the process of finalising CORSIA, the final link in the Organization’s ‘basket of measures’ defined a decade ago for dealing with CO2 emissions from international aviation. This is a significant accomplishment, but one aimed at levelling off through carbon offsetting rather than actually reducing emissions. Chris Lyle (right) argues there is a pressing need for a more ambitious aviation emissions mitigation strategy in the light of the Paris Agreement and the IPCC Special Report on Global Warming of 1.5°C, building on the ICAO basket but going above and beyond the current ICAO process.


In 2009 the air transport industry targeted reducing its net carbon emissions by 50% by 2050 compared to 2005 levels; however, the industry has yet to elaborate on the practicalities of achieving this target. In 2013 the ICAO Assembly agreed on an unsubstantiated ‘aspirational goal’ for a global fuel efficiency improvement of 2% per annum through to 2050. The ICAO Council has had a mandate from the Assembly since 2010 to “explore the feasibility” of a long-term global aspirational goal for mitigation of international aviation emissions, with specific reference added in 2016 “in light of the 2°C and 1.5°C temperature goals of the Paris Agreement”, but the Council continues to equivocate on this.


More definitive and robust targets and actions do need to be established, looking beyond the aviation silo and in the light of increasing and overarching global greenhouse gas emissions exigencies. A target date of 2050 (with intermediate goals and revisits for 2030 and 2040) would seem appropriate both in the context of more general emissions reduction ambitions aimed at that year and given the long lifespan of existing aircraft types.


In order to establish technology driven and demand management targets, a robust evaluation of number of factors needs to be made, including:


The scope of greenhouse gases to be covered – should others beyond CO2 now be included in mitigation action, if only on the basis of the precautionary principle?


The scope of services to be covered – should for example business aircraft operations, which are small in terms of contribution but very high in per passenger emissions, be included, particularly if present concepts of supersonic operations evolve towards practice?


The potential realistic contribution of technology and streamlined operations – is the ICAO 2% per annum fuel efficiency goal practical? Could strengthening ICAO’s CO2 standards be a driver? Blended wing-body, truss-based wing, distributed propulsion, hydrogen-fuel-cell-powered and solar-assisted aircraft exist at present only on the drawing board and heavy investment in research is required soon if they are to have a major and timely impact. Could open-rotor, electric and notably hybrid-electric aircraft play a significant role before 2050, if only for small scale and the short-haul? What might retrofitting with winglets or geared turbofan engines contribute? How much will optimising flight paths help?


The potential contribution of modal switch to surface transport – will rail travel in particular have an impact at the shorter haul? Should government action be taken to enhance its use relative to air transport?


Drop-in alternative fuels – will they make a significant reduction when assessed in terms of full life-cycle, land use, price and availability at scale? Could ‘power-to-liquid’ (electrofuels), with their clear environmental sustainability advantages over biofuels, become key?


Market-based measures – what are their potential and effectiveness beyond CORSIA? Should carbon offsetting, even if of verified high quality, continue to be considered efficacious as an emissions tool? Is the international aviation sector currently favourably biased through exemption from fuel, value added and some other taxes? Are carbon taxes/duties a way forward (see here)? Could they be applied directly on individual passengers (for example, frequent flyers) and shippers?


An initial evaluation of several of the above factors and exploration of what aviation’s fair share of global efforts to meet the 2°C and 1.5°C targets might be is available from the key insights and speaker presentations of an Aviation Decarbonization Forum held in Montreal last February for ICAO Council members and other State representatives.


In 1999, at ICAO’s request, the UN’s Intergovernmental Panel on Climate Change (IPCC) produced a Special Report on Aviation and the Global Atmosphere, which formed a scientific basis for ongoing work on emissions mitigation. The IPCC has very briefly referenced aviation in its later Assessment Reports but another more extensive analysis, addressing questions such as those above, is overdue. The increasingly critical contribution of aviation to GHG emissions suggests early initiation.


At the policy level, an iterative approach might be followed, taking some ‘top down’ desirable objectives such as the 2050 industry goal and for comparison a more challenging but possibly necessary ‘net zero’ aviation GHG emissions by 2050, and seeing the extent to which practical factors from ‘bottom up’ would be necessary to achieve each of these objectives.





When in 1997 the UNFCCC’s COP3 adopted the Kyoto Protocol – under which industrialised countries and those with economies in transition (Annex 1 countries) took on GHG emissions mitigation targets – international aviation and shipping, with their transborder and trans-international territory operations, proved too difficult to allocate to countries against the then existing data availability and pressures of the meeting’s time constraints. These sectors were thus assigned to ICAO and the IMO respectively and remain so to this date, despite the global emissions mitigation process being overhauled by the Paris Agreement in 2015 under which all participating countries provide and periodically strengthen Nationally Determined Contributions (NDCs), as well as by the effective lapsing of the Kyoto Protocol after the current commitment period through to 2020.


In 2016, ICAO finally completed its framework for mitigation, aimed at achieving carbon-neutral growth (CNG) from 2020. This will still mean that over 600 Mt of CO2 from international civil aviation (that below CNG) will be unchecked annually from 2020 onwards, and exemptions will increase this unrestricted amount. UNEP’s Emissions Gap Report 2017 stated “international aviation emissions are expected to grow from 0.5 Gt CO2e in 2017 to around 1.1 Gt CO2e in 2030”; moreover, “ICAO’s CORSIA is estimated to have a reducing impact of 0 to 0.3 Gt CO2e per year on global emissions in 2030”, and that this wide range “implies that the result will depend on the way the offsetting rules will be set”.


The ICAO remit proved to have substantial constraints, particularly as far as market-based measures are concerned. ICAO’s geographic and policy ambit reflects its membership of 193 States, well beyond the UNFCCC’s 40 Annex 1 countries. Moreover, there are significant barriers to applying an industrialised/other-country concept in relation to equality of treatment and certain other provisions in the Chicago Convention. The need to achieve a common approach worldwide has resulted in the complex ‘lowest common denominator’ CORSIA scheme which only indirectly reflects the UNFCCC’s principle of Common But Differentiated Responsibilities (CBDR) and which does not allow for greater ambition by individual States.


The ICAO Council has also faced difficulties when developing measures which are beyond the Organization’s usual remit, for example in establishing criteria for determining what constitutes acceptable alternatives to fossil fuels in the context of full life-cycle emissions, and what Emissions Unit Criteria should apply for carbon offsetting. The Council in March this year established a Technical Advisory Body (TAB) of experts to make recommendations on these issues, replicating some elements of the UNFCCC’s Clean Development Mechanism’s Executive Board, which supervises the CDM and the registration of projects and issuance of Certified Emission Reductions (see here).                                                                         


CO2 emissions from international aviation currently match the total emissions of the 129 lowest-emitting countries combined, ranking just behind Saudi Arabia and ahead of Canada. But ICAO’s basket of measures will contribute pro rata much less than any of the first NDCs to which 183 Parties have committed under the Paris Agreement as at the end of March 2019. Thus the sector is predicted to take a substantially increasing share of the global carbon emissions budget. Targeted emission reductions for aviation may understandably be lower than for other sectors due to the current non-availability on scale of alternative fuels, but if Paris Agreement targets are to be achieved, actual reductions from aviation may be necessary.


One elemental weakness in the treatment of international aviation emissions through ICAO is that there is no directly identifiable national commitment, only a global ‘sector-determined’ contribution. Not only is potential action diluted, international aviation is treated in a silo and not in the context of differing national circumstances and the relative contribution of aviation to the economy – notably for cases where tourism is critical. Moreover, while membership of the UNFCCC and ICAO is essentially the same, the UNFCCC’s mandate is to reduce greenhouse gas concentrations in the atmosphere while the general motivation of ICAO is to protect and promote international aviation. The Economist recently expressed concern that ICAO had been “captured by producer interests.”


Another issue to be considered is freedom of ambition. A directive in the relevant ICAO Assembly Resolution that “CORSIA, or any other scheme decided by the Assembly, is to be the MBM applying to CO2 emissions from international aviation”, is designed to counter additional ambition. Such exclusivity contrasts with the generic application provisions of the Paris Agreement, where Article 6 recognises that some parties will choose to pursue voluntary cooperation to allow for higher ambition.


A further issue arises from having different mechanisms for international aviation and for various sectors domestically – including domestic aviation, which is difficult to separate from international aviation, and the land-based transport and other emissions generated in and around airports.


Aviation emissions mitigation action and governance needs to be considered in the broader context of tourism, trade, economic development and overarching global emissions imperatives, with a more integrated process amongst ICAO and UNFCCC provisions. This is not to marginalise the extensive and impressive work carried out by ICAO, which has produced a comprehensive database and raised comprehension of the issues worldwide, but rather to build on that work under broader regulatory conceptualisation.



Ways and means


One action to which consideration might be given at an early date would be to include international aviation into the NDCs of States. This would give States direct accountability, putting aviation mitigation activities in the context of national circumstances including the carbon budget. While this action would preferably be taken at the global level through the UNFCCC, failing that it could be determined by individual States or in regional co-ordination. It would enable (and encourage) individual States or regional groups to take mitigation measures beyond those agreed within ICAO.


A variety of data are nowadays readily available to do this and different forms of attribution could be envisaged (see author’s extended article here). The attribution methodology could even, for example, include a creative form of CBDR. The emissions attributed to a country could be based on the originating market for passengers (round trip, which would tend to apportion towards more wealthy passengers and countries) and origin or destination market for freight. Consolidated data could be filed without breaching privacy, and public registries used for monitoring and verification. 


Appropriate fora for initiating a more balanced, beyond sectoral, strategy perspective on aviation emissions would be the UNFCCC’s Climate Neutral Now Initiative and Talanoa Dialogue Platform aimed at evolving GHG emissions goals for 2050 and in the context of the Sustainable Development Goals. Contributions from tourism and trade entities as well as aviation would preferably be incorporated. During COP24, a tourism event was included for the first time, at which the World Travel and Tourism Council and UN Climate Change addressed the links between tourism and climate change and presented a pathway for the sector to achieve carbon neutrality by 2050 – but notably did not take account of international air travel, and aviation was also not represented by either government or industry in the Talanoa Dialogue. Opportunities to set in motion a multilateral conversation on long-term aviation emissions mitigation strategy are coming up this year with the Bonn Climate Change Conference in June, the UN Climate Summit and the ICAO Assembly in September, and COP25 in December.


The Paris Agreement and the IPCC’s Special Report on Global Warming of 1.5⁰C have created a political and scientific consensus on the need for all sectors to step up their actions to tackle climate change and international aviation is by no means an exception.                                                                                    



Chris Lyle is Chief Executive of Canadian-based Air Transport Economics, a Fellow of the Royal Aeronautical Society and a veteran of British Airways, the UN Economic Commission for Africa, ICAO and the UN World Tourism Organization. He has been actively involved in aviation emissions mitigation policy since before the adoption of the 1997 Kyoto Protocol. He can be reached at


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