Chapter 4. Disruptions in non-urban passenger transport

Today’s policies will not decouple demand for non-urban transport from emissions

Total non-urban travel reached an estimated 26 000 billion p-km in 2015. Of these, 17 000 passenger-kilometres represent regional travel. By comparison, air travel represented 7 000 billion p-km. By 2050, the total number of passenger-kilometres travelled in a non-urban setting is estimated to reach 85 000 billion p-km, of which almost 60 000 billion would be regional travel. In terms of CO₂ emissions, regional travel is responsible for 51% of all non-urban CO₂ in 2015, a figure that grows to 67% by 2050.

As a result of existing policies and goals targeting improvements in fuel efficiency in all modes and increased electrification of surface modes, non-urban transport CO₂ emissions are expected to grow significantly less than passenger-kilometres. In the current ambition scenario, non-urban travel grows by 225%, while CO₂ emissions increase by 74%.

Regional travel is a major part of non-urban travel and the main driver of emissions in this scenario (Figure 4.1 and Figure 4.3). In the base year 2015, regional travel corresponds to two thirds of all non-urban travel demand, a figure that is expected to grow to 70% by 2050.

Figure 4.1. Projected non-urban transport demand by sector and scenario to 2050

Billion passenger-kilometres

 StatLink https://doi.org/10.1787/888933972696

Domestic travel and emissions in non-OECD countries are set to increase drastically under assumptions of the current ambitions scenario. By 2050, domestic non-urban transport grows by 332% in non-OECD countries, driven by the growth of population and GDP. By comparison, the projected increase in OECD countries is only 35%.

The difference is even more pronounced in terms of CO₂ emissions. The policies planned in OECD countries with regard to the vehicle fleet can reduce emissions by 40% compared to 2015 levels. Non-OECD countries are not able to address the growing demand despite technological developments in the current ambition scenario. As a result, total non-urban emissions increase by 181% to 2050. The strongest growth in both non-urban transport demand and CO₂ emissions is expected in Asia (excluding India, the People’s Republic of China and OECD Pacific) and Africa (Figure 4.3). In Asia especially, non-urban travel and related emissions grow at the same rate. India and China would remain the biggest absolute contributor in both passenger-kilometres and emissions, but the rest of Asia is catching up fast in both parameters.

Aviation will see high growth in both domestic and international markets. Air travel demand is boosted by more Open Skies agreements (ITF, n.d.[7]) and relatively cheap air fares due to improved fuel efficiency of aircraft and stable long-term fuel price projections (IEA, 2018[5]).

International aviation reaches the highest compound annual growth rate of all non-urban travel modes, with 3.8% through 2050. Thus, international flights would provide a total of 16 500 billion p-km in the current ambition scenario that is 3.6 times the 2015 volume. Domestic aviation also grows fast, but less than international aviation since short-haul flights face direct competition from surface modes. Nevertheless, domestic aviation more than doubles volume to 2.2 times the 2015 level, reaching 5 520 billion p-km.

The air network grows with an average annual rate of 2.8% between 2015 and 2050. The highest growth is expected in developing countries, especially in Asia (excluding China and India). Despite aircraft fuel efficiency improvements in new generation aircraft, total aviation CO₂ emissions in 2050 are estimated to be 49% higher than 2015, reaching 1 061 million tonnes. As surface modes are also experiencing massive growth in this scenario, the share of aviation emissions to the total non-urban emissions decreases from 30% in 2015 to 25% in 2050.

In terms of passenger numbers, Africa, Asia and Latin America will see the strongest increases to 2050, with demand driven by growing incomes. Almost 180 million passengers are expected to travel between these regions and North America in 2050, compared with 63 million in 2015. China and India generate the most new demand for international aviation in the current ambitions scenario; a finding in line with projections by the International Air Transport Association (IATA, 2016[8]) By 2050, almost one billion trips by air will originate from these two countries, compared to 130 million in 2015. Almost two thirds of this new demand is directed towards other Asian countries, however (Table 4.1). Aviation markets in developed economies, notably in particular Europe and North America, are already liberalised and saturated. In conjunction with competition from high speed rail, this limits the growth of aviation in these regions.

Passenger numbers for airports follow a similar pattern. Asian (especially Indian) and African airports will see the biggest share of passenger growth. In China, some airports may eventually become the world’s largest, with large cities like Beijing or Shanghai passing more than 500 million passengers annually. Latin American airports are also expected to grow significantly, mainly in large cities and tourism destinations such as the Caribbean islands and Peruvian cities.

Figure 4.2. Projected traffic growth at airports, 2015-50

Current ambition scenario, million passengers

Passenger growth at European airports, on the other hand, could slow down compared to recent years. Some airports in northern European cities may even see a small decrease in passenger volumes. Reasons for the slow growth are demographic factors and the decreasing relevance of the hub-and-spoke model for intra-European air traffic. Airports in the United States could also face decreases traffic, mainly in the largest cities. A main factor here is the planned development of a high speed rail network in the US, which could absorb a significant share of domestic air traffic. A second factor is the greater prevalence of low-cost airlines which tend to avoid large airports and add direct connections between smaller airports.

A reduction of CO₂ emissions from non-urban passenger transport is possible

The high ambition scenario assumes a set of policies and technological developments that likely reduce transport CO₂ emissions to a greater extent than in the current ambition scenario. These policies make non-urban travel more costly (of USD 500 per tonne of CO₂ on average) than in the current ambition scenario. This affects predominantly fossil fuel-dependent aviation, fostering a faster development and uptake of alternative energy sources for aviation, such as synthetic fuels and electric planes, ultimately enabling carbon-neutral aviation at competitive cost. Surface modes see no additional investments; the high speed rail network remains the same as in the current ambitions scenario, with only planned lines being built. The uptake of electric vehicles is accelerated and vehicle occupancy increases Generally, the assumptions regarding technology in the high ambition scenario follow the International Energy Agency’s 30@30 scenario (IEA, 2018[5]).

Figure 4.3. Projected demand growth for non-urban passenger transport by world region and scenario, 2050

Billion passenger-kilometres.

 StatLink https://doi.org/10.1787/888933972715

Demand for non-urban travel in the high ambition scenario is affected significantly by higher travel costs that result from the increased cost of emissions. Global non-urban travel globally will total 65 700 billion passenger-kilometres in 2050, a 22% reduction compared to the current ambition scenario. Higher fuel-related costs affect longer trips more strongly, as for these fuel is a bigger share of the total cost. Therefore the reduction is more pronounced for aviation, and especially international aviation which sees a 30% fall in p-km in 2050 compared to the current ambition scenario. All transport modes see a drop in total distance travelled, however.

As the cost of non-urban transport rises, demand for inter-urban travel is expected to decrease faster than demand for regional travel. Regional travel in the high ambition scenario in 2050 is estimated at 46 thousand billion passenger-kilometres, a 22% reduction compared to the current ambition scenario. Amongst regional travel, the biggest reduction occurs for car travel (25%). This is because regional travel consists mostly of travel that is essential for the livelihood of citizens residing outside of cities. Inter-urban travel, however, has a large tourism component which is not essential travel.

The more ambitious decarbonisation policies and the technology development assumptions of the high ambition scenario show a pathway for the decarbonisation of non-urban passenger transport. Despite a growth of non-urban travel by 150% under the high ambition scenario compared to 2015, CO₂ emissions in 2050 are only 58% of those of the base year 2015. This reduction is the result of developments in both OECD and non-OECD countries. In OECD countries, the vehicle fleet is almost entirely electrified by 2050 and transport demand decreases by 18%. As a result, CO₂ emissions form non-urban passenger transport reach only 14% of the 2015 level. In non-OECD countries, CO₂ emissions fall by 10% over the same period - despite an increase in non-urban travel demand of 257%. These figures do not include international travel, where CO₂ emissions fall by 25%, while travel in terms of passenger-kilometres increases 150%.

Figure 4.4. Projected CO₂ emissions from non-urban passenger transport by sector and scenario, 2030-50

Million tonnes of CO₂

 StatLink https://doi.org/10.1787/888933972734

A possible solution for ending the dependency of aviation on fossil fuels is electric aviation, at least for short-haul flights. In the high ambition scenario, electric aircraft serve most short-haul routes up to 1 600 kilometres, so that these become true zero emission commercial air links, assuming that the electricity is generated from renewables. If synthetic aviation fuels also become available and cost competitive towards 2050, as the high ambition scenario assumes, the combined impact of these two developments would be impressive: Domestic aviation would produce only 20% of its 2015 CO₂ emissions by 2050, despite a projected demand increase of 78% over the same period, Similarly, international aviation would succeed in reducing its CO₂ emissions by 20% compared to 2015, despite a compounded annual growth rate of 2.7% that will take the sector 11 500 billion p-km travelled, up from 4 500 in 2015.

What promotes the development of ultra-high-speed rail systems?

The uptake of ultra-high speed rail will mainly depend on its effective construction costs, the resulting fare levels, and the corresponding demand. As Maglevs and Hyperloops offer transport services which are in many aspects comparable to traditional rail – reliable trips between city centres with smooth boarding processes – final demand will depend mainly on fares. Ultra-high speed rail will be competitive if fares match users’ willingness to pay for increased speed and if there is sufficient demand to cover upfront costs. The capital costs of UHS, and thus the fares required to cover them, are the key factors for their uptake.

With no large scale UHS service available today, the capital costs of these systems are largely uncertain. Multiple sources report variations in cost estimates differing by orders of magnitude (Table 4.3). The financial feasibility of the Hyperloop system in particular has received criticism see McLean and Nicolas (2016[13]) for a detailed costs analysis. While the original estimation for the Los Angeles–San Francisco project was USD 10 million per kilometre in 2013, subsequent commercial proposals put the figure at USD 40 million. Independent experts have also suggested the capital costs of the Hyperloop system (including vehicle costs) could exceed USD 75 million per km (for a review see Walker (2018[14])).

Furthermore, these estimates exclude cost of land acquisition as well as the various engineering and legal expenses required for large infrastructure projects. Also present may be the optimism bias seen in the costing of many large transport projects – an ex-post study of high speed rail projects in France, for instance, showed that actual construction costs were on average 20% higher than predicted (Meunier and Quinet, 2010[15]). Finally, ultra-high speed systems require relatively straight routes to avoid excessive lateral forces. The costs might thus slip to unstainable levels in regions with hilly topography, protected landscapes and high land values.

Maglevs are already in operation and the technology’s further development primarily depends on the financial model. As upfront costs are high, the long-term return on investment is uncertain and the level of risks is considerable, future Maglev infrastructure will likely not be funded from private funding sources in the near term. Government support will thus be essential, as it has been for high speed rail. As economies of scale should lower costs and demand for higher speed connections will probably increase, other financial models may well become viable in the long run.

Bringing Hyperloop systems into operation still requires technological advances. Significant technical issues need to be solved so that Hyperloop companies can meet their aim of having a fully operational system ready as soon as 2023. One of the steepest technological challenges is to maintain a vacuum in a tube several hundred kilometres long. The maximum speed Hyperloops have reached is slightly under 400 km/h, with a small-scale prototype on a test site. Traditional high speed trains have achieved test speeds of 570 km/h.

Questions have also been raised regarding the feasibility of Hyperloop’s value proposition. The original Hyperloop proposal suggested that it could carry up to 3600 passengers per hour, with one 28-seater pod departing every 30 seconds. Several experts have argued that 80 seconds would be a more realistic departure frequency, given the minimum headway required for the vehicle to stop safely. This would dramatically reduce the capacity of the system, however. Other concerns raised focus on passengers’ safety and comfort.

What impacts would ultra-high-speed rail systems have on passenger transport?

If implemented, UHS rail is likely to reshape transport patterns. Most adapted to provide trips in the 400 to 800 km range, UHS could potentially attract travellers now relying on short-haul aviation. The impact would thus be especially significant in regions with high levels of domestic aviation activity, such as the United States and China. They might also supersede traditional high speed rail services. Given that higher income levels are associated with higher values of travel time savings, new UHS rail projects could be favoured over new high speed rail projects, especially in countries such as the United States and the United Kingdom where extensive conventional high speed rail networks do not already exist.

Hyperloops and Maglevs could thus help to reduce congestion of airways and at airports. UHS rail would also contribute significantly to lower transport-related CO₂ emissions. Short-haul flights are particularly carbon-intensive, while electricity-powered UHS rail has a small carbon footprint, provided the source of electricity is sufficiently clean. That said, in terms of energy consumption the balance might not necessarily be positive for UHS. Maglevs require more energy per passenger-kilometre than traditional rail services, since air friction increases rapidly with speed, but do not offer significant energy savings compare to air transport. The Hyperloop system, on the other hand, consumes little energy as friction is limited in near vacuum. Its expected energy requirement could be 80% less than the one of an average US train. In principle this could be powered via solar panels mounted directly on the Hyperloop tubes (Taylor et al., 2016[12]).

UHS systems could also improve regional accessibility and stimulate regional economic development. This has arguably been a major impact of high speed rail, which can improve local business activity by changing the region’s economic profile. High speed rail projects alter the relationship between accessibility and urban productivity. An important body of literature within the field of New Economic Geography has shown that the spatial concentration of economic activities entails productive advantages, the so called economies of agglomeration.

For example, projections see the planned high speed rail connection between London and northern England generating productivity increases worth between EUR 700 million and EUR 1.3 billion annually. Although it is difficult to assess to which extent, UHS will likely have similar effects with a much higher magnitude. They will fundamentally transform the economies they serve, inducing significant households and firms relocations. This is not to say that there are more benefits obtained from UHS rail than aviation. The potential UHS connections however would bring additional benefits as they would be added on top of air connections.

There is thus a case for further developing the traditional high speed rail network development. There are still around 200 links between city pairs for which a high speed rail link could be economically viable, according to an analysis by ITF that examined demand, costs and distance, among other factors. This untapped potential represents 50 000 km of tracks. Of these 75% would be in North America, reflecting the fact that high speed rail has been historically underdeveloped in this region.

This potential for development is already being acknowledged to some extent, with high speed rail receiving increased attention in the United States over the past decade. A High Speed Rail Strategic Plan produced by the US Federal Railroad Association identifies strategic corridors with 10 000 km of potential high speed track. California’s high speed rail project is currently under construction and will run to a length of 1 200 km, assuming it is fully implemented.

The potential for high speed rail will become larger over time as transport demand grows and willingness to pay increases. Beyond the 50 000 kilometres of potential rail lines, an additional 25 000 km of tracks could be considered by 2050. At this time horizon, high speed rail is likely to also develop in middle income countries, especially in India, Latin America and, to a lesser extent, in North Africa. There are already signs of a growing interest for high speed rail in middle income countries. In Central Asia, Uzbekistan is successfully operating a 600 km network of high speed tracks allowing speeds of 250 km/h. India's first high-speed rail corridor between Mumbai and Ahmedabad started construction in 2017 and is slated to open by 2022. In North Africa, the Tangiers-Casablanca line opened in 2018, as the first phase of a planned 1 500 km high speed rail network in Morocco.

Figure 4.5. Projected development of rail lines worldwide to 2050

Note: HSR refers to high-speed rail

Developing high speed rail and UHS rail services are not the only possible path forward. Conventional and optimised rail services could serve as an alternative in many cases. Such services would not compete with aviation or high-speed rail in terms of travel time, but could be very competitive in terms of fare levels and thus able to attract a different user segment.

Simulation results

Investing into high speed rail can significantly increase rail traffic in terms of passenger-kilometres. Projections see an additional 170 billion rail passenger-kilometres to 2050 if all economically feasible high speed rail projects are implemented in the interim. This would represent a 14% increase in intercity rail traffic on 2015.

More than half of this increase would be in China and India. But the Americas would also see a notable increase in rail ridership, with an additional 35 billion passenger-kilometres in North America and 23 billion in Latin America. For city pairs located 400km to 800km apart, the market share of rail is expected to reach more than 50% by 2050. This is because the competiveness of high speed rail relatively to car and plane will increase with the expected increase in fuel prices and the progressive introduction of carbon pricing. Note that the total traffic expected on these new high speed rail systems is higher as a significant share of their patronage will come from traditional rail services. The total ridership of the new high speed rail services will amount to nearly 400 billion p-km in 2050 according to ITF estimates.

Yet globally this will have a minor impact on the total rail traffic. Currently rail traffic between large cities only represents 8% of total non-urban rail. Thus high speed rail has limited potential to increase significantly rail ridership. The projected additional 170 billion p-km only amounts for 1% of total rail ridership. Furthermore the impact of high speed rail projects on non-urban transport emissions is limited. The high speed rail projects would decrease CO₂ emissions by 5 million tonnes, which less than 1% of the domestic emissions of non-urban transport.

The prospects for UHS are more limited. Even if all the technological hurdles are passed and assuming there is no substantial subsidies, our estimates show a potential for 10 000 kilometres of UHS tracks, most of it located in Western Europe, North America and China. Although this implies that the UHS technologies as such could be viable, they will have a negligible impact on global transport pattern. UHS would generate an additional 40 billion p-km, with more than half of resulting for a modal shift from air transport.

What promotes the expansion of long-haul-low cost carriers?

Three main factors are behind the emergence of long-haul low-cost aviation. Firstly, the liberalisation of aviation markets makes it easier for new players to enter previously protected or closed markets in many world regions. Low-cost carriers in particular benefit from these regulatory changes, and many may soon offer cheaper flights also on long-haul routes where demand exists.

Secondly, the technological evolution of aircraft brings increased fuel efficiency and also allows new fuel mixes. Low-cost airlines rely on latest-generation planes to keep their costs low, therefor engineering advances in are more likely to translate into cost advantages and higher profit margins than for other airlines. Reductions in the fuel-related costs for longer flights or increased flight range of single-aisle aircraft put low-cost airlines in a good position to compete with full-service carriers on some long haul routes with high demand.

Thirdly, increased demand for air travel also leads to a growth of long-haul low-cost airlines. As more people want to go to specific destinations, their market becomes big enough to support new low-cost entrants. This is notably the case for the emerging aviation markets and of those in Asia in particular. Whether low-cost airlines generate new demand or absorb demand from full-service carriers has been much debated. The prevailing opinion holds that low-cost aviation does not add new demand, even if they need to absorb demand from full-service carriers in order to be viable (Gillen and Morrison, 2003[23]; Gillen and Lall, 2004[24]; de Wit and Zuidberg, 2012[25]). Therefore as demand is growing and is expected to continue growing, more routes will become viable for low-cost airlines.

Because of the characteristics of long-haul routes, the profit margin of low-cost airlines on these is smaller compared to short-haul routes. This makes operators very sensitive to oscillations in costs, and several initially successful low-cost airlines were forced out of business as fuel prices rose or the economy reduced the available budget of customers. The factors described above will likely make long-haul low-cost carriers more resilient.

Additional potential for long-haul low-cost airlines lies in absorbing market share from charter flights, similarly to what happened in the short-haul market (Rodríguez and O’Connell, 2018[26]). The characteristics of the typical charter passenger and the provided service are quite different from those of low-cost airlines, however, so that it is unlikely that low-cost carriers will completely replace long-haul charter flights. Nonetheless, this is another aviation market that long-haul low-cost carriers are likely to disrupt.

What are the impacts of long-haul low-cost aviation on air travel?

Low-cost airlines have had a huge impact on short-haul passenger aviation. Many network carriers initially ignored them, expecting them to fail. The aggressive stance of low-cost operators in combination with air liberalisation completely reshaped the aviation market. They development forced mergers between network carriers, pushed them to lower their prices and follow suit with other attributes of the low-cost model, such as service de-bundling.

Today, the entrance of low-cost carriers is disrupting the business model of network carriers on the long-haul routes. The low fares offered by budget operators will almost definitely absorb some cost-conscious customers from full-service carriers. Since the long-haul market is one of the most profitable sections for full-service carriers (Morrell, 2008[22]), full-service carriers are likely to compete aggressively; their larger profit margin might even allow them to sustain losses for a certain time. Overall, the arrival of low-cost airlines on the long-haul market will lower the cost of flying on these routes, thus increasing demand for these destinations, and ultimately traffic. Because all these additional trips will cover comparatively great distances, they will have a disproportionate impact on aviation’s overall passenger-kilometres travelled and CO₂ emissions.

Currently, low-cost airlines offer medium- and long-haul flights mainly between Europe and North America and within East and Southeast Asia. Their market share in these regions was about 10% in 2018. Few low-cost flights exist for long- and ultra-long-haul routes, which points towards a maximum length for profitable low-cost services. Growth is more probable firstly on the shorter routes of the long-haul market, especially those that that can be covered with long-range single-aisle aircraft, and secondly in regions with a lot of untapped travel potential.

The first category includes route pairs such as North America and Europe, Europe and Asia, South and Central America to North America. The second category consists of South, Southeast and East Asia. These routes are also likely to first appear between cities that are already characterised by high demand. Routes that are today served by charter airlines are also likely to be see other operators offering low-cost flights for instance from Europe or North America to Central America or the Caribbean. This could be either new low-cost airlines entering that market or a full-service carrier flying a low-cost service.

The number of seats on medium- and long-haul flights provided by low-cost carriers will increase as aviation volumes continue to increase over the coming decades. Their market share will likely plateau at around 20% of the total aviation market, however, given the threshold conditions for profitable low-cost operations, the market characteristics and passenger preferences and priorities.

Continued liberalisation of aviation markets will increase the competition between network carriers and low-cost airlines on medium and long-haul routes. The result could be a further market consolidation that would reduce the number of big players, which could then compete more aggressively with low-cost carriers, either directly or with their own low-cost subsidiaries. Direct competition between the low-cost carriers will also become more intense as their market share grows.

Simulation results

A completely liberalised global aviation market in which low-cost carriers have entered most medium- and long-haul markets would be 9.5% bigger in terms of the number of air links in 2050 than in 2015 in the current ambition scenario. In terms or total passenger-kilometres, it would be 3.6% bigger. All of this growth would occur in international aviation, where the total passenger-kilometres increase by 5%. This section examines a scenario in which international air travel would reach 1 000 billion passenger-kilometres more in 2050 compared to the current ambition scenario.

Logically, the share of low-cost aviation in this scenario is higher. In the current ambition scenario, the share of low-cost airlines stays stable around 12-13% of the total aviation passenger-kilometres throughout the period 2015 to 2050. In a scenario in which low-cost carriers disrupt the aviation market, their share of total aviation p-km reaches 16% by 2050. This increase might not seem significant, but it represents a 20% market growth. The biggest market share increases for low-cost airlines in a disruption scenario are expected on routes between certain regions, particularly Middle East and transition countries. Nonetheless, the biggest absolute growth occurs in areas where low-cost carriers are already widespread, such as Europe and between Asia and China/India.

What encourages the uptake of alternative energy sources in aviation?

The prospects for electric aircraft and synthetic aviation fuel depend heavily on the development of the respective technologies. The pace of development of battery technology in particular will play an important role in determining the prospects for electric aviation, as the weight and energetic capacity of electric batteries constitute a prominent barrier to their use in planes. Until constraints regarding power output, weight, and range can be eased, the role of electric planes will be limited.

Another major factor behind the extent and speed of electrification and synthetic fuel use in the sector will be cost, and their uptake will be strongly influenced by the evolution of oil and electricity prices. Commercial aviation costs are very sensitive to oil prices, and demand for aviation is also relatively sensitive to changes in price (Doganis, 2005[19]). Given current technology and energy prices, all-electric planes are more expensive than conventional aircraft (Schäfer et al., 2016[29]). Strong incentives favouring electric aviation will be needed to close the gap between the total costs of electric vs. conventional planes. The availability of cheap and renewable electricity will be a prerequisite for the scaling up of both technologies and will play an important role in determining the trajectory of their growth.

Increased prices of carbon in the future will translate into higher fares for conventionally-powered air travel, which could diminish demand. The price of flights powered by electricity and synthetic fuels would be relatively unaffected by a carbon tax. Thus, these technologies can play a role for decarbonising aviation as well as for ensuring mobility needs will continue to be met by aviation.

What are the impacts of alternative fuels on the aviation sector?

The electrification of short-haul flights and the use of synthetic fuels can significantly reduce the carbon intensity of air travel. As a matter of fact, Norway aims to become the first country where all short-haul flights are carried out with electric aircraft by 2040. Although both electrification and synthetic fuels emit no net tank-to-wheel emissions, the well-to-tank emissions generated by their production should also be considered when evaluating their mitigation potential. Fully decoupling aviation from fossil fuel consumption requires the use of renewably-generated electricity. If the decoupling can be achieved, this would facilitate significant growth in the demand for air travel, which could in turn result in a modal shift away from other inter-urban transport modes such as rail and road transport. A growing segment of the population avoids air travel for environmental reasons and emission-free aviation would allow them to consider using planes for their mobility needs.

A large share of the emissions from aviation is released in the upper atmosphere. There, the climate impacts of non-CO₂ pollutants can be significantly greater than the impact of their CO₂ emissions alone (Wickrama, Henderson and Vedantham, 1999[31]). Scientists debate the magnitude of this radiative forcing (Williams, Noland and Toumi, 2002[32]; Köhler et al., 2008[33]; Borken-Kleefeld, Berntsen and Fuglestvedt, 2010[34]). Electric planes and planes powered by synthetic fuels would significantly reduce radiative forcing effects because electric aviation does not produce any tank-to-wheel emissions and the combustion of synthetic fuel produces fewer non-CO₂ pollutants than conventional jet fuel.

Electric planes have the potential to disrupt the aviation market for short-haul flights up to 1 000 km. This segment accounts for 15% of aviation’s revenue passenger-kilometres and about half of all take-offs and landings (Schäfer et al., 2018[35]). Given the weight, space and range limitations associated with currently foreseeable battery technologies, electrification is unlikely to extend beyond medium-sized planes and short-haul flights. Electric aircraft are also particularly likely to be used on routes for which other inter-urban surface modes require the construction of expensive infrastructure, for instance between islands or to connect remote locations. The uptake of electric aircraft is also more likely to occur first in countries where environmental concerns are more pronounced or where regulations for aviation emissions and noise pollution are more stringent.

The uptake of synthetic fuel in aviation will be heavily influenced by the evolution in the cost of conventional fuel (which may vary between countries or regions) and the costs involved in the production of synthetic fuel itself. In regions where electricity is relatively cheap and conventional oil relatively expensive, the cost basis of synthetic fuel will become more attractive than that of conventional jet fuel, and this will accelerate its uptake. Fuel taxes or carbon pricing could also contribute to increasing the cost advantage of synthetic fuel over conventional fuel.

Simulation results

The impact of alternative fuels on total aviation emissions does not depend solely on the development of the respective technologies and their cost. Switching to a new energy source will be mainly a cost decision, with few exceptions. Therefore the cost of conventional fuel and related policies will also affect the how fast and to what extent alternative energy sources will penetrate aviation.

In the setting of the current ambition scenario, conventional fuel will remain cheaper than alternative energy sources for most flights until 2045. Only in 2050 will electric aviation begin to be competitive and dominate some routes, covering 2% of all flights. In a disruptive alternative fuels scenario, the technological development of alternative energy sources happens more quickly and the related cost drop faster. With all else remaining equal, electric aviation replaces 42% of all flights in this disruption scenario. This share comprises most short-haul flights, since the assumed maximum range of electric planes is 1 600 km. The result would be drastically reduced emissions from short-haul aviation, particularly from domestic flights by 2050. Domestic aviation in the current ambition scenario would emit 293 million tonnes of CO₂ by that year, while it would be only 130 million tonnes of CO₂ in the alternative fuels scenario. International aviation will be less affected, as it includes mostly longer-distance flights. Nevertheless, emissions from international aviation will fall from 768 million tonnes of CO₂ in 2050 in the current ambition scenario to 700 million tonnes of CO₂ in the alternative fuels scenario.

The high ambition scenario provides a different policy and technology background than the current ambition scenario. Under high ambition policies, airplane efficiency increases compared to current ambitions and alternative fuel technology matures faster, albeit not as fast as in the disruptive scenario. More importantly, the carbon emission-related costs reach USD 500 by 2050. The combination of these elements fosters the development of carbon-free or zero net-carbon aviation. Thus, almost 37% of all flights would be in electric aircraft by 2050, while 2% would be powered by synthetic fuel. This would reduce CO₂ emissions, especially in domestic aviation, where they fall to 55 million tonnes of CO₂.by 2050, from 290 million tonnes in 2015. International aviation CO₂ emissions drop by 20% to 2050, reaching 343 million tonnes of CO₂, despite providing 2.7 more passenger-kilometres. Combined with the technological assumptions made in the high ambition scenario, the use of alternative aviation fuels on a large scale has even more ground-breaking results. In such circumstances, only 24% of all flights would use conventional fuel by 2050. All flights under 1 600 km would be carried out with electric planes and almost 50% of medium- and long-haul flights are powered by synthetic fuel. Aviation’s CO₂ emissions in 2050 would consequently stand at 40% of the base year 2015, at 288 million tonnes of CO₂.