By Chris Lyle, Chief Executive Officer Air Transport Economics. Contributing author ICRT global founder Harold Goodwin.
Air transport is already widely unsustainable in terms of its negative impact on climate change and, without radical transformation, it will become increasingly so for at least 25 years to come. Without an alternative fuel to kerosene with zero or very low greenhouse gas (GHG) emissions, the climate imperative will necessitate retrenching and restructuring of networks to reduce aviation pollution.
Aviation and tourism are currently joined at the hip, and air transport is the single, increasingly dominant element in tourism emissions, which contribute some 8-10% of global GHG emissions, the anthropogenic (human activity) driver of climate change.
According to research on tourism including aviation published in Nature Communications: “global tourism emissions grew by 3.5% per year between 2009 and 2019, double the growth rate of the worldwide economy, reaching 5.2 Gt CO₂-e, or 8.8% of total global greenhouse gas emissions in 2019. The primary drivers of emissions growth are slow technology efficiency gains (0.3% per year), combined with sustained high growth in tourism demand (3.8% per year in constant 2009 prices).”
Both tourism and aviation went into steep decline during the Covid-19 pandemic, but both have rebounded, reaching levels above those of 2019 and continuing to grow.
The consequences of climate change are increasingly apparent: drought, wildfires, storm-driven flooding and sea-level rise have become the new normal. There is already evidence of resulting aridity, insecure water supplies, migration, conflict, food shortages, and “mass human heat mortality”.
While there is increasing evidence that we are approaching peak carbon as anthropogenic GHG emissions in general fall, aviation emissions continue to grow, and we are going to have to live with the consequences of our production of greenhouse gases for many years:
“Even when human emissions peak, “natural” sources of greenhouse gases, aided and abetted by anthropogenic warming, will grow: Forest fires, thawing permafrost, and warming tropical swamps could delay a true peak in carbon emissions for years, if not longer. Making matters worse, the natural processes that absorb excess CO₂ in vegetation and the oceans seem to be faltering. Last year [2024], while human emissions only crept up, atmospheric levels of CO₂ grew a record amount.”
What will it take to achieve mainstream recognition and responsive action regarding the inconvenient truths of the necessities and actualities of curtailing aviation’s GHG emissions? Currently we have a blinkered and subsidised industry focused on growth, deluded expectations of technology and alternative fuels, not to mention climate change denial and indifference. We are characterising the prospects for the adoption of alternative aviation fuels with zero or very low greenhouse gas emissions as unlikely before 2050, with insufficient investment being made in the development of new technology. How can we confront and overcome this? The present article addresses the critical issues in the context of economic and social justice.
The climate imperative
The key driver of transformation in aviation in the next decades, particularly internationally, will almost certainly be climate change. Many destinations will be affected by rising temperatures and increasingly disruptive weather, with tourists seeking more amenable holiday spots.
As the Tourism Panel on Climate Change spelt out in its 2023 Stocktake Report, tourism is recognized as one of the sectors most vulnerable to climate hazards. Current forms of tourism will simply not be viable in some destinations (for example, ski tourism at low elevations, beach tourism in erodible coastlines, coral bleaching, desert destinations) – and some destinations will be affected by extreme heat, fire, water security, hurricane frequency and intensity, etc. But the Panel noted that no country, destination, or sub-sector had achieved meaningful reductions in tourism greenhouse gas emissions.
Air transport currently generates “only” some 2.5% of global CO₂ emissions but this is of the same order as the total emissions of Japan, the world’s fifth largest State emitter. And the sector generates at least 3.5% of the climate’s “effective radiative forcing”, with efficiency improvements still well exceeded by growth in traffic. Without markedly more effective climate policies, damaging emissions from air transport are projected to at least double current levels by 2050, the global “net-zero” target. Given developments in other sectors and without further intense remedial action, aviation’s share of global emissions is projected to rise to about 20% of the global total by 2050, with some sources indicating even higher proportions.
The scientific consensus is that if aviation is to make its requisite contribution to the Paris Agreement targets, its CO₂ emissions would have to be reduced by 2030 to half or less of 2019 levels and by 2050 to net zero (and net-zero should not include out-of-sector measures such as carbon offsetting, capture and storage).
But air transport’s contribution to climate change is currently on course to increase to the point where drastic measures will be required to cap the sector’s emissions, including some significant curtailment of operations, notably those of long-haul.
Aviation emissions mitigation
Technical and operational improvements will contribute somewhat to aviation emissions mitigation. Drawing board concepts such as open rotor engines and blended wing body and truss braced wing aircraft may ultimately contribute significant reductions, as may improved air traffic management, but the key for all aircraft to reduce emissions will be changes in the power source away from fossil fuels.
“Sustainable” Aviation Fuels (SAF) are the critical in-sector measure on which hopes are presently focused, aimed at contributing 65% of the road to “net-zero 2050”. SAF are biobased or synthetic fuels producing much less life-cycle GHG than fossil fuels. They are “drop-in”, meaning they can be blended with conventional Jet A fuel and used in existing aircraft and airport delivery infrastructure without modification. However:
A significant proportion of the aeroplanes that will be flying in 2050 are already in the air or in the delivery chain. Many of the rest will also be crucially dependent on SAF, but supply will be woefully inadequate.
As for alternative propulsion other than SAF, there are a number of projects on the table or under development, notably including liquid and gaseous hydrogen powered aircraft. Hydrogen propulsion systems would generate virtually emissions-free flight, producing no CO₂, no NOx, and no particulates, with water as their only emission.
However, major obstacles are that liquid hydrogen for aircraft must be stored at a cryogenic temperature of -253°C – involving heavy storage tanks, while gaseous hydrogen involves massive storage volume requiring major redesign of aircraft.
One feasible avenue is hydrogen fuel cell propulsion, whereby a reaction between hydrogen and oxygen from the air produces water and releases electrical energy. An electric motor then uses this energy to drive a propellor via a gearbox. Ongoing research and development involving major aircraft manufacturer Airbus, some aircraft engine manufacturers and a number of specialised startup companies, suggest that small aircraft may well be available for introduction on shorter hauls within a decade, with significant quantities in service by the late 2040s. But heavy cryogenic tanks and fuel cell stacks along with thermal management and insulation issues mean that hydrogen fuel cell propulsion is not viable for longer routes. And its application will be limited to airports where the necessary delivery infrastructure is in place.
Proponents of hydrogen and electric power claim that they will be “zero carbon” – however, this usually relates only to the flights themselves and excludes the manufacturing and distribution process of the power source, a factor which needs to be incorporated. For the three technologies of fuel cell aircraft, gas turbine hydrogen jets and particularly e-fuels, hydrogen is a common denominator and there is already strong competition for green hydrogen amongst several economic sectors.
On a much smaller traffic scale, battery powered electric aircraft are under development but they are very limited in range because of the weight of the batteries. Hybrid electric aircraft increase range – to a limited extent – by using a combination of conventional fossil fuel engines and electric motors for propulsion. Typically, electric motors assist during takeoff and landing, while conventional engines provide sustained power during cruise flight; some designs allow in-flight recharging of batteries through the combustion engine.
In summary, alternative fuel options may well be established before 2050 for shorter hauls (including improved surface transport as well as hydrogen electric aircraft). But this is by no means the same for long-haul. That is critical – see the charts below ).
Even with all current mitigation measures taken together, it is increasingly evident that the only way civil aviation will achieve net-zero by 2050 will necessitate some form of demand management.
Social justice
This issue has been in the news recently with the publication of the 2026 Global Justice Report from the World Inequality Lab, by Thomas Piketty et al. The Report attempts to set out a new vision for global progress in the 21st century: grounding human development and equality in planetary habitability. Its main conclusion is simple: it is possible to reconcile planetary habitability and high well-being for all, but only if the transformation rests on three pillars simultaneously: fast decarbonization of energy systems; a major shift toward sufficiency – understood as a sharp reduction in consumption; and a drastic reduction in inequality of income, wealth and power, both between countries and within them.
Air travel is not specifically addressed but the implications are clear. According to a report by ScienceDirect, less than 10% of the world’s population will fly in a given year, only some 2-4% will fly internationally; less than 20% have ever flown at all. But 1% of the world’s population will contribute 50% of the emissions of all the 10% that do fly.
While common in North America and Europe, air travel is a rare luxury for billions worldwide. Global tourism emissions are heavily concentrated in a few high-income outbound markets. The unequal distribution of tourism emissions and potential mitigation strategies have important climate justice implications. Many of the poorest nations – Least Developed Countries (LDCs), Landlocked Developing Countries (LLDCs) and Small Island Developing States (SIDS) – are highly dependent on aviation for their tourism sectors, the employment they create and the foreign currency they generate. While these nations make up only 5.4% of all tourism transport emissions, they deserve special treatment in the name of social justice. As the proportion of emissions caused by aviation increases, the strength of the global justice argument will increase, compounded by crop failures, flooding and wildfires.
Changing parameters of tourism and trade demand
International air transport traffic patterns will look somewhat different by mid-century. Origin and destination tourism and trade markets will move with evolving economies and shifting tastes.
Developed markets will remain the largest travel source, but emerging markets will continue to gain importance. Some tourists are changing destinations, not only to seek cooler climes and avoid adverse weather and climate-related events but to seek new experiences and avoid overcrowding, with a number of smaller destination countries experiencing the fastest growth. The Tourism Panel on Climate Change has observed that a paradigm shift will be required in the transition to climate-resilient tourism development.
Geopolitical factors
The geopolitics of tourism is a complex and multifaceted field, involving the interactions between tourism, politics, and geography.
The present trend of military expansion is not likely to be temporary and there are some implications for the tourism sector:
Broad instability that undermines global tourism flows and some regions and nations are prominent; for example, the Middle East is a perennial flashpoint. But civil and military strife are likely to lead more people to switch destinations rather than an overall reduction in travel.
Key parameters of restructuring
So, what are the key parameters for a global restructuring of air transport:
Demand management
Fiscal traffic mitigation measures such as fuel, frequent flyer and many departure taxes fall foul of national sovereignty, privacy and competitive issues, and notably of the economic regulatory framework unique to international air transport services. The vast majority of the 3 000 or so bilateral air services agreements between countries specifically exempt from taxation certain aspects of international aviation, notably fuel purchase. Even restricting ‘air miles’ programmes would raise all sorts of discrimination issues amongst both airlines and passengers. And any pricing mechanism has an imprecise effect on demand and consequential emissions.
As with GHG emissions from any other source, those from aircraft emissions obviously signify a direct cost as a consequence of their climate impact, and if such a cost could be definitively established then there would be a case for applying emissions charges consistent with policy of the International Civil Aviation Organization (ICAO). But we are a long, long way from establishment – and broad acceptance – of such a link.
The only multinational emission mitigation measures for air transport presently in place are market-based: a global carbon offsetting scheme known as CORSIA through ICAO and within Europe one based on the more effective approach of emissions trading. The latter is broader focused, targeting several sectors including power generation, heavy manufacturing industries, and maritime transport as well as aviation.
Carbon offsetting is by no means a definitive solution. It shifts the moral responsibility for carbon reduction to someone else; the quality of offset units is heterogeneous and far from reliable; and studies have shown that the majority of even those of the highest standards simply do not work. Eventually, everyone has to reduce emissions, which is why offsetting is not a workable strategy to reach planetary net-zero. Furthermore, the ICAO offsetting scheme is substantially limited in application, relating only to emissions above 85% of 2019 levels, containing loopholes through exemption criteria for SAF and “Lower Carbon Aviation Fuels”, and administratively weak with no direct enforcement provisions.
Emissions trading is more effective than carbon offsetting and has been shown in Europe to drive real emissions reductions, but ICAO summarily rejected its application to international aviation at an early stage of consideration for geopolitical reasons.
Carbon capture and storage is another out-of-sector measure under consideration but, in the words of the International Energy Agency: “Removing carbon from the atmosphere is costly and uncertain. We must do everything possible from putting it there in the first place”.
Capacity restrictions on emissions can be applied within the existing global air services regulatory framework and would provide a definitive result. Capping air transport emissions themselves – rather than the number of flights or through pricing mechanisms with their imprecise effects – would be direct and with a definitive impact. Imposing an effective regulatory structure to cap emissions in line with the Paris Agreement goals would set predetermined limits and, when other measures are insufficient, serve as a principal driver of mitigation.
Irrespective of the ‘ownership’ of flight emissions – generally attributed to passengers/shippers (consignors and consignees) and particularly addressed to air carriers – the best base for capping the emissions is the airport. At present, emissions from airports are defined to include only those directly from airport operations including landing and take-off cycles and, in some cases, also related local ground transportation and business activities (which can be several times larger than those from direct services). They do not include emissions from the flights once cruising, which the airport empowers.
Airports could become key enablers in aviation emissions reduction if they were held accountable for Scope 3 emissions beyond landing and takeoff cycles to encompass outbound flights in cruise en route to their first destination.
Reassessment of economic and social contribution and redefinition of essential services
The aviation sector provides essential services in humanitarian aid, disaster relief, medical transport, emergency response, and firefighting. Air ambulances and specialized aircraft provide rapid access to remote or disaster-stricken areas, saving lives and delivering critical supplies.
Much more widely, the sector enables economic development through tourism and freight trade. Much of this may also be categorised as “essential”, but to greatly differing degrees according to the circumstances. In the context of demand management there is thus a need to look beyond the air transport sector. There is also a related need to redefine “essential” in relation to aviation-related tourism (60% of GHG emissions from international tourism come from the air transport component) and the justification for shipment by air, some of which may also be classified as “essential”.
In many destinations, there is mounting anger regarding overtourism, and governments are concerned about low revenue retention and negative impacts on local communities and facilities, prompting a rethink of their tourism models. Aims include reassessing benefits against costs and restoring balance between “overtourism” and local quality of life, including reflecting the local environmental and ecosystem sustainability promoted by welcoming international tourists. More generally, tourist destination countries are encouraging longer stays and less frequent visits, non-peak travel, and alternative destinations (within the same country), as well as imposing restrictions on access to attractions and accommodation (notably Airbnb), hotel construction, and fast-food outlets. In a number of markets, a focus on higher-quality, higher-priced tourism and less attention to traffic volume may affect air transport.
While there are numerous reports assessing the economic contribution of air transport – globally, regionally and for individual countries – they largely emanate from industry bodies in the form of self-promotion. From the global perspective, it would be valuable to have a comparative assessment – standardised, transparent and independent, for as many countries as possible – of the economic and social contribution of aviation. This should notably include evaluation of the benefits and costs of aviation-dependent tourism for every receiving country; tools are already there in the form of UN Tourism’s Statistical Framework for Measuring the Sustainability of Tourism and Tourism Satellite Account .
In that context, consideration could be given to reassessing “essential air services” for destinations, linking the environmental pillar of sustainability with the economic and social pillars. The concept of such services has long been defined and given special regulatory treatment in a number of domestic jurisdictions and the travel and tourism community might think of working towards their development for widespread international application (for a descriptive methodology see the UN Tourism-initiated study by ICAO on An Essential Service and Tourism Development Route Scheme).
Connectivity
Air connectivity can be broadly defined as the ability and ease with which passengers and freight can reach destinations by air. Air connectivity plays a crucial role in enhancing economic development by facilitating tourism and inward foreign direct investment and supporting trade in goods and services.
There is a variety of approaches to defining and measuring air connectivity, ranging from simple metrics that are relatively easy to obtain from schedule or traffic data to more complex systems that rely on modelling techniques, multiple data sets, and expert judgment. But the most important dimension of air connectivity is the degree to which airports are connected to one another, both directly and – through flight transfer – indirectly.
Overcoming denial, downgraded priority and indifference
The prospects for substantive action globally to counter climate change are woeful today, with multilateralism on the wane and misinformation on the rise – in an increasingly partisan world. To illustrate. In 2007, the year after Al Gore’s An Inconvenient Truth came out, Gallup polling found that 55% of Democrats in the United States worried “a great deal” about climate change, versus 24% of Republicans. In 2026 it is 72% of Democrats and just 6% of Republicans. While the US is currently among a handful of negative outliers in emissions mitigation action, in the last few years a number of other countries have downgraded the imperative to address climate change. Some remain in denial; for others it is the new normal.
On the specific issue of aviation there is a fostered perception that pathways to net-zero are on course while in practice mitigation policy and measures are sadly inadequate. Not only are international flights free of fuel and value-added taxes, but they are also subsidized by duty-free purchases at airports. At the global level, they are only subject to out-of-sector mitigation measures (ICAO’s CORSIA), and even then, emissions below 85% of 2019 levels are exempt.
Where does the obligation lie? In essence, the purchaser of any good or service is ultimately responsible for the emissions. In aviation, it is the passenger or the shipping initiator. But mitigation measures are generally addressed to the supplier of the good or service and in the case of aviation this is essentially the air carrier (along with associated airport and air navigation operations). At the same time, both the origin and destination countries, as well as the air carrier, are economic beneficiaries. In the case of aviation-related products, outgoing tourism is an import while outgoing freight is an export.
There are various players in travel and tourism who may thus be held accountable:
Passengers and shippers. For the end users, there is a disjunct between those who recognise that air transport is a significant factor in climate change and the relatively few who take direct mitigation action by reducing their use of it.
Flygskam (flight shame) has become an issue, notably in Scandinavian countries, but has had a limited impact. One reason is the absence of a direct link between cause and effect for people to get a handle on the impact of their decisions to fly or not. Attitudes may change somewhat as carbon labelling and awareness spread. At the same time, limited voluntary take-up of carbon offsets, as well as surveys, suggest that passengers are less gullible about the value of carbon offsets than those who profit from them. Passengers may prefer some sort of mandated requirement rather than making their own assessment and taking action whilst others free ride. People are willing to make more sustainable travel choices, but they currently believe the responsibility lies chiefly with governments and the travel industry.
Shippers seem to be unaware or unduly concerned with their negative impact on climate change. Shipping is also a component that is essentially beyond the influence of end-use consumers; the decision to use air transport is at the dealer’s discretion and unknown to the end purchaser.
Airlines. Remain cognisant of the goal of net-zero 2050 but remain focused on growth and seem increasingly doubtful that the goal will be achieved. They do pay more than lip service to emissions mitigation and publicly espouse SAF as the primary mitigation tool. But fuel represents some 29% of their operating costs on global average and while a substantial premium on fossil fuel may be bearable with SAF at 0.8% of total fuel consumption, at the targeted 65% it may well be considered intolerable. Airlines have no real incentive in the absence of government regulation. But the air transport industry tends to see demand management as a Damocles Sword and studiously eschews any serious contemplation of the subject. The industry is a massive influence on aviation emissions policy (see for example InfluenceMap’s Corporate Capture and the UN International Civil Aviation Organization).
Airports. As mentioned above, emissions assessed for airport accountability are limited in scope. Crucially, they do not include complete origin to destination emissions from the flights that the airports enable. The volume of emissions from the first leg of all departing flights has been compiled since 2019 for the 1 300 largest global airports by Airport Tracker, a project attempting to visualise the climate impact of airports worldwide,.
Travel industry. More and more tourist destinations are recognising the need to mitigate climate change. Local entities – mostly SMEs, including hotels, tour operators, Destination Management Organizations and car rental companies – are actively working to reduce emissions under the umbrella of destination management. But these efforts are most frequently subsumed by the emissions contribution of flights to and from the destination, which are rarely if ever addressed by tourism bodies; and there is still a more general tendency for ‘build it and they will come’.
Fossil fuel industry. The development of SAF has been almost entirely by start-up companies. The primary fossil fuel providers (“big oil” – often actually subsidised!) remain focused on their lucrative profit-making activity and see little incentive for producing much more expensive SAF – for a market which is a very small part of their overall business. Ideally, there could be government mandates for specified contributions of SAF by big oil – alongside incentives and competitive safeguards for start-ups. But, in the words of Al Gore, “Fossil fuel companies are much better at capturing politicians than in capturing carbon”.
Governments. Clearly governments have to be the responsible actor. At present it is primarily governments who have assumed responsibility – and taken regulatory action – nationally, regionally (for example through the European Union) and globally (through the United Nations Framework Convention on Climate Change and ICAO). The basket of measures includes aircraft technology and operational improvements, SAF, and market-based measures. But, as stated above, action so far has been sadly inadequate.
While public perception of the reality of the anthropogenic contribution to climate change is generally high worldwide, and the particular role of aviation is well recognized in some regions, this has to be translated – as a matter of increasing urgency – into sufficient mitigatory action. Civil society (NGOs) need to pressure governments, strengthening and reflecting public opinion. It is increasingly supported by persuasive legal decisions and analysis. In July 2025 the International Court of Justice (ICJ) issued an Advisory Opinion on the Obligations of States in Respect of Climate Change asserting that States are legally bound to take ambitious actions to protect the climate. Key findings include that the 1.5°C temperature target above pre-industrial levels is legally binding under the Paris Agreement and that all States, in particular the largest emitters, must take ambitious mitigation measures in line with the best available science. While the ICJ’s opinion itself is not binding – neither on itself nor on domestic courts – it carries considerable legal weight and political legitimacy and will enhance ongoing and prospective legal action on aviation emissions. This means pursuing all current emissions-reduction measures while superimposing net-zero capacity constraints, conceivably through the airport mechanism promoted here.
In order to achieve transition to net-zero emissions, governments – individually or in concert – need to take action above and beyond existing mitigation measures – including any multilateral processes to which they are party.
A transformed air transport framework
A globally agreed approach is unlikely, to say the least. But for a committed country or like-minded group of countries, the framework might be as follows:
A dystopian outcome?
At what point will there be a fundamental shift, first to widespread recognition of the existential nature of the climate crisis and then to realisation of appropriate mitigation? The proliferation in recent times of humanity-induced and humanity-affected high-profile events such as severe heat domes, wildfires, hurricanes, tornados, storms and flooding has as yet to instill a widespread sense of urgency on mitigating GHG emissions in general, never mind on the contribution of civil aviation in particular.
Direct capping of flight emissions is not just an option – it is rapidly becoming an imperative if society is to have any chance of thwarting the existential threat of climate change. As shown above, there are rational, practical ways of doing this, but they have many implications. A profound rethink is required of the role of aviation and tourism in contributing to human welfare in light of the prevailing constraint: anthropogenic climate change. We have to move on from the euphemistic “aspirational” goals of bodies like ICAO and the International Air Transport Association, from expressions of hope to real-world practicality. We need firm commitments in step-wise progression, with intermediate targets, towards net-zero 2050.
If you have read this thinking that it takes an idealistic line to necessary action – well, perhaps consider it as an aspirational approach to an aspirational net-zero goal. But for sure, while climate change will not destroy the Earth, it will make it substantially uninhabitable for Homo Sapiens and many other species with which we share our planet.
About The Authors
Chris Lyle is a veteran of British Airways and three organs of the UN: the Economic Commission for Africa, the International Civil Aviation Organization (ICAO), and UN Tourism. In later years he has also run his own consultancy: Air Transport Economics. At ICAO his responsibilities encompassed the economic and environmental policy regulation activities of the Organization as well as leadership of strategic planning. In 1997, as the Director responsible, he facilitated acceptance of the role given to the Organization through the Kyoto Protocol of the UN Framework Convention on Climate Change and he has been actively involved in aviation emissions mitigation policy ever since. Chris has presented at many international meetings, including the Assemblies of ICAO and UNTourism, the Annual General Meetings of the International Air Transport Association and Airports Council International, as well as the Council for Trade in Services of the World Trade Organization. He has been a frequently invited speaker in international fora and is author of a number of articles on the economic and environmental regulation of air transport – the latter notably for GreenAir News and for the Tourism Panel on Climate Change – on which he is a designated Lead Expert.
Chris is a graduate of the University of Cambridge with postgraduate study at other British universities, and he has been a guest lecturer on aviation at McGill University in Montreal, where he is based. He is a Fellow of the Royal Aeronautical Society. Chris is a graduate of the University of Cambridge with postgraduate study at other British universities, and he has been a guest lecturer on aviation at McGill University in Montreal, where he is based. He is a Fellow of the Royal Aeronautical Society. Contact clyle@airtransporteconomics.ca
Harold Goodwin is Founder of ICRT global. Contact: harold@icrt.global
[1] One measure to prioritise retention of flights might be international tourism revenues at destination as a percentage of GDP. In the context of climate justice, this would seem to be one appropriate indicator of a country’s critical dependence on tourism rather than absolute revenue figures. Of the top ten tourism income States in the world, eight are developed countries with percentage of GDP contributions varying from 0.7 (Japan) to 5.2 (Spain); the contribution for the United States, by far the largest tourism income earner, is 1.2%. Of the 69 states where the proportional tourism contribution is above the world average, only 12 are developed countries.
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