1 Motivation

Traditionally, economic development was thought to be achieved at the expense of the environment and, as a result, the objective of economic growth frequently got ahead of the social and environmental objectives. Mobility and transport have represented perhaps the best cases in which this trade-off has been evident. Despite the irruption of new technologies, services and approaches in the mobility sector which are radically transforming the concept of transportation, the transport sector is steadily increasing its GHG emissions since 1990.

As carbon dioxide emissions are directly related to fossil fuels consumption, the role of specific transport modes in improving the sector’s share of GHG emissions is clear. The aviation industry plays a prominent part in this trend: studies revealed that 3.16 tons of CO2 are released out of the consumption of one ton of kerosene, a hydrocarbon liquid commonly used as a fuel.Footnote 1 As of 2015, Europe is the second-largest region in the world for commercial passenger flights.Footnote 2 In this sense, commercial airlines play a relevant role in the European transport sector GHG emissions. Moreover, studies as the one by Alonso et al. (2014) underline how air traffic in Europe is concentrated on short distances below 1000 km, including almost 60% of all flights and 46% of all passengers. These findings are indeed puzzling, since the Union offers a broad range of surface transport alternatives.

The GHG emissions resulting from the transport sector are not the only cause for concern. In the context of heavy rains, rising temperatures and storms arising from global warming with predicted impacts on the air transport sector, the sustainability of the current trend vis a vis air passengers transport is challenged. The railway’s higher resilience, on the other hand, might play a more suitable role in the context of climate change unfortunate effects. In the context of intra-European mobility, can railway transport offer a better, less carbon-intensive alternative than air transport for a sufficient number of cases? As the increase in awareness for environmental issues and carbon dioxide production can have impacts not only on end-user choices of mobility and transport, but also on the policymaking behind transport planning, this study aims at exploring novel possibilities other than aeroplanes to reconcile green policies and high levels of mobility.

The relevance of the question this study aims to address is high not only in relation to the EU goal vis a vis GHG emission, but also in the context of the COVID-19 pandemic aftermath. In particular, despite the Union has been characterised by a low production of GHG emission in the spring of 2020, this trend is expected to reverse course once recovery measures are working at full throttle. Transport will have an important role in the predicted rebound effect of GHG emissions; thus, the development of green new mobility and a high involvement of railway is essential (Tardivo et al., 2020).

2 Problem Formulation

The rail transport can improve the environmental situation in Europe if it were to be at the centre of sustainability-driven policies. By calculating the amount of carbon dioxide equivalent produced in the years 2017–2019 by passenger air transport between major cities within the European Union, this study aims at providing a sound evaluation of the amount of carbon dioxide equivalent which could have been saved if better mobility policies would have been in place enhancing the railway’s passenger share.

After providing the data for a solid background, this study calls for a more profound cost–benefit analysis not only of traditional air transport in itself but also of low-cost airlines. This analysis is highly relevant for the EU given both its post-COVID-19 pandemic recovery as well as its position in the international system, which as a whole is striving to reach the Sustainable Development Goals (hereinafter “SDGs”) by 2030.

This study looks at the results of the lack of policies over last two years with the objective to keep them as a light for the future, since it will be necessary to match the need for governments to avert a deep recession and the needs for safeguarding the environment. Since the transport sector plays a fundamental role in GHG production, it is time to acknowledge this fact and act accordingly.

3 The Position of This Contribution Within Academic Literature

This study is not the first contribution to compare CO2 emissions from air and rail transport. Prussi and Lonza (2018) calculated in detail the CO2 emission from rail and air transport on seven routes within the EU. We take advantage of their work and build upon their so-called high-rail scenario, including 175 routes and calculating the precise CO2 emissions from the air sector. Always related to the topic, Alonso et al (2014) investigated the distribution of air transport traffic and CO2 emissions within the EU. Despite their focus on the year 2010, their findings must be held into consideration as they calculated total CO2 emissions from the air sector in 216 million tons, with a large concentration of emissions in a few countries.

On the same line with the previous studies, this contribution aims at providing a solid base for policy measures capable of curb the sector emissions. In this context, Mendes and Santos (2008) provided a forecast on the impacts of incentive-based regulation, suggesting that results were likely to be minimal. The failure of the EU emission trading system (EU ETS) in curbing CO2 emissions from the aviation sector is evident in the 2020 Commission decision to amend the EU ETS regarding aviation. While academia focused greatly on the effects of aviation’s inclusion in the EU ETS (Anger, 2010; Mendes and Santos, 2008; Morrell, 2007), it is clear that the academic literature lacks cross-sectoral analysis vis a vis CO2 emissions, probably due to the complexity of detailing addressing these trends on a European scale.

Lastly, this contribution aims at developing an understanding of the implications for the CO2 production by air transport on an international level. Following the footprint of Chèze et al (2013) —which estimated the scenarios for the air transport to reduce emissions to comply with the IPCC scenarios before the Paris Agreement—this contribution stresses the significance of reducing CO2 emission from the transport sector in regard to the UN Sustainable Development Goals.

4 Objectives

As highlighted above, this study aims at picturing the amount of CO2 that could have been saved in the 2017‒2019 period provided that some of the passenger transport were to be shifted from air travel to railways.

Currently, an increasing number of Europeans are moving towards major urban centres which are interconnected via air, road and rail. The user’s choice in transport mode has clear effects on the transport sector CO2 emissions, thus we aim at understanding the magnitude of the effects of the transport sectors between these urban centres.

There is a number of these conurbations that are less than 800 km away from each other, a distance assumed to be still competitive for rail, and yet have dense air transport connections between them. The threshold of 800 km has been chosen on the blueprint of the Japanese bullet train Shinkansen, capable of having a greater market share than airlines on routes up to 965 km (Albalate and Bel 2012). Since the Shinkansen performance is deeply related to the type of infrastructure present in Japan, this study deemed feasible to take a more conservative approach in relation to the European infrastructure and limit its scope to routes up to 800 km long. The present study calculated the total amount of carbon dioxide equivalent produced between these major cities resulting only from air transportation. The objective is then to compare the level of emissions generated from air and railway transport and understand how much CO2 could be saved if a modal shift to railway was in place.

Addressing an exact value to CO2 emission from air transport is not particularly straightforward, as fuel consumption and therefore emission levels are not only related to physical characteristics of the aircraft, as engine types, winglets and number of seating, but also to how the aircraft is operated. Number of passengers carried, cargo loaded, flight distance, airspeed, landing procedure are factors that play a role in how environmentally impacting a flight can be. The flight distance deserves particular attention. At first glance, fuel consumption and carbon emissions are directly proportionate to the total flight distance. However, studies reveal that short-haul flights compared to medium-haul flights consume more fuel per 100 km. This result is based on the fact that the departure and take-off procedures require the use of a large amount of energy, and their implementation is a very energy-intensive step in a flight. Since those flights which are less than three hours long are considered short-haul flights, most domestic and intra-European flights are of this nature. At the same time, long-haul flights consume more fuel than the medium-haul flights per 100 km, as the fuel must be carried for most of the flight.Footnote 3

5 Research

This study aims at identifying the effects of sustainability-driven policies in the transport sector vis a vis its production of carbon dioxide equivalent. After having acknowledged that air transportation plays a crucial role in both Europe’s mobility and in the Union’s global share of CO2 emissions, this study undertakes three steps.

Firstly, it calculates the number of passengers travelling between the major European cities and estimates the total CO2 production from the sector.

Secondly, it takes advantage of the current literature on CO2 consumption from railway passenger transport and identifies the difference in CO2 emissions between the two transport modes.

Lastly this study estimates the possible scenarios in terms of CO2 production that would have followed the application of adequate sustainability-driven policies to the transport sector, analysing the potential carbon dioxide equivalent savings resulting from an ideal transfer of passenger transport from air carriers to the rail network within the European Union.

This study employs quantitative analysis, elaborating data from EU sources as Eurostat, the European Commission, EASA, EEA; from private sources as the Centre for Asia Pacific Aviation Pty. Ltd., Eurocontrol, Ryanair and Lufthansa; and scientific publications as Prussi and Lonza (2018), and Albalate and Bel (2012).

Data, which was produced by different stakeholders prior to this study, has been extracted by open-access websites and included into a new database. This database has been developed and manipulated through Microsoft Excel software.

We recognise that no data set is perfect, thus the present study has limitations in addressing factors such as the number of each type of aeroplanes from any EU country. However, data has been selected amongst public entities’ databases with the aim of providing the most possible transparent data. As such, this study, despite focusing on theoretical losses in CO2 savings which have not been achieved, does employ sound data and it expects to stimulate a new approach to the quantification of GHG emission and its effects on a cross-national EU-wide level.

6 Implementation of the Research

The study takes into consideration the routes between European cities with a population larger than 500.000 inhabitants as well as European urban areas with a metropolitan population of over 1 million inhabitants. These thresholds are arbitrary; however, the researchers consider that this selection is representative enough for the target of the study. Having this study as objective the evaluation of the possible effects of sustainability-driven policies on an EU-wide scale, it focuses on major routes and macro-trends.

The selected cities and urban areas together with their respective countries are the following: (Table 1)

Table 1 Cities with over 500.000 inhabitants and urban areas with a metropolitan population of over 1 million inhabitants within the EU
Full size table

As this study will analyse the potential carbon dioxide equivalent saving resulting from a transfer of the passenger transport from air carriers to the rail network, only some air and rail routes were taken into account, and only the current infrastructure has been evaluated. As such, Bucharest, Dublin, Helsinki and Palermo were not included in the study. In fact, although being suitable as far as population is concerned, given the long distances between them and the other major EU cities and/or the lack of infrastructure as bridges to connect them to continental Europe, this study would not have benefited from their inclusion.

The data regarding the number of passengers carried on each air route has been obtained from the European Commission´s statistical office Eurostat. Since the provided data display certain discrepancies regarding the passengers’ traffic between airports according to each national database, the study provided a mean between the given passengers’ data. In those cases in which the Eurostat database: (https://ec.europa.eu/eurostat/web/transport/data/database) does not present information on one of the two airports involved in a selected route, the only value available has been considered. More information on Eurostat and the transport statistics can be found at the following address: https://ec.europa.eu/eurostat/web/transport.

The data regarding each flight´s carbon dioxide equivalent emission has been found employing the Atmosfair online calculator. Atmosfair, a German non-profit organisation, designed a software tool able to calculate precisely the amount of carbon dioxide and non-carbon emission from each flight. In particular, since aircraft engines emit various pollutants that contribute to rising global temperatures, Atmosfair calculates both CO2 and other pollutants as well, such as methane, perfluorocarbons, nitrous oxide and others. These pollutants and their effects are summarised by Atmosfair and then converted into CO2. From the “atmosfair Flight Emissions Calculator” of 2016: “first, the Emissions Calculator calculates the fuel consumption per passenger and based on this result, determines the amount of CO2 that has a comparable effect to that of all other pollutants emitted by the flight added together (effective CO2 emissions)”. Therefore, the calculator’s final output is expressed in carbon dioxide.

At the same time, the production of pollutants by air traffic is three times higher than that of carbon emissions alone, due to the high altitude in which they are released. To be able to compare the effects on the environment resulting from CO2 production at high altitude with the effects of CO2 production on the ground (as produced by railways or cars), the calculator multiplies by a factor 3 all carbon emissions produced during a flight at over 9 kms to correctly render the flight’s climate impact in CO2. Carbon emissions emitted at altitudes of less than 9 kms are not submitted to any alterations and are directly included in the flight’s carbon footprint. The “atmosfair Flight Emissions Calculator” explains how this is a “conservative, quantitative–qualitative average value based on two metrics (RFI and GWP) and their bandwidths. Both metrics present the same numerical value, whereby the higher-value GWP even has a smaller bandwidth. This actual value of 3 is exactly in the middle of the old IPCC bandwidth of the RFI, which was indicated to be 2–4 by the IPCC in 1999”. The validity of this assumption has been confirmed both by Lee et al. (2021) and by the European Commission (2020) and EASA, which state “the CO2-warming-equivalent emissions based on this method indicate that aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO2emissions alone”.

More information on the atmosfair calculator can be found at the following address: https://www.atmosfair.de/en/offset/flight/.

As the fuel consumption and therefore the carbon dioxide production varies between which aircraft is being analysed, the study took the Airbus A320 as an aircraft model. In fact, as far as the five largest airlines companies in Europe are concerned, the Airbus A320 is the most common aircraft with more than 600 operating units. Furthermore, according to the Centre for aviation’s forecast, the Airbus A320 NEO leads the orders for narrowbodied aircrafts in Europe, with 1.058 aircrafts ordered (CAPA 2018).Footnote 4 The largest airline companies in Europe, together with the number of passengers carried globally in 2017 and the most common aircraft in their fleet are shown in the following table. (Table 2).

Table 2 Most common aircraft by airline company
Full size table

The second most common aircraft is the Boeing 737–800 with 450 units and 611 orders for its variants for the future fleets in Europe. The airline company with more Boeing 737–800 in its fleet is Ryanair.

The overall amount of carbon dioxide production between the two aircrafts does not change dramatically. However, the Airbus is slightly less efficient on distances below 340 km, while its greater efficiency on the Boeing is noticeable starting from 360 km. Furthermore, the difference in carbon dioxide production between the two aircrafts increases steadily from the 420 km threshold onwards. A short overview of the differences in carbon dioxide production between the Airbus A320 and Boeing 737–800 with regard to the route distances is provided below. The data has been extrapolated from the Atmosfair calculator (Table 3).

Table 3 Differences in CO2 production between airbus A320 and Boeing 737–800 per passenger
Full size table

Furthermore, in order to be able to estimate the feasibility of shifting means of transport from air carriers to the rail network, the distances between city centres have been calculated with the online software “Maps” from Google. Three steps have characterized the approach to distance measurement: first, the distance in a straight line between the two cities has been measured, then the distance between such cities has been measured on the already existing railway network. Lastly, those routes which exceed the threshold of the 800 kms on the rail network have been compared with the same route on the existing road network and have been considered in the study in case the distance on the road network was less than 800 km. Ultimately, those routes which are no longer than 800 km on the existing rail network have been classified as “short-distance route”, while those which exceed the threshold of 800 km on the existing rail network but are no longer than 800 km on the existing road network have been classified as “medium-distance route”. These last routes were included in this study in order to evaluate, in terms of CO2 savings, the results arising from an enhanced rail network. Routes longer than 800 km on the road network have not been selected for the study. A short explanation of the selection process is shown in the following (Table 4).

Table 4 Selection process of the suitable routes
Full size table

All the routes, distances, passengers and estimated carbon dioxide production can be found in the Annex section.

Lastly, this study takes into consideration the basis set by Prussi and Lonza (2018),Footnote 5 which identify an annual passenger increment of 3.5%. It also applies the so-called high-rail scenario, in which 25% of the expected aviation passenger growth is shifted to High Speed Rail (hereinafter “HSR”) service. A shift of 25% of the expected passengers from air to rail transport would allow a 20% greenhouse gas emission saving. Prussi and Lonza (2018) identified a 20% saving only from analysed routes within five European countries. This study employs the same result in CO2 saving on an EU-wide analysis. The reason behind accepting this value for the routes and countries other than the originally analysed, is based upon the estimation that a shift in 25% of the expected passenger increment is not an ambitious-enough target for the European transport sector at this time.

7 Analysis of Results Through Comparisons

The following table includes the ten routes with higher CO2 impact in Europe. It is possible to notice, interestingly, the prevalence of national routes amongst the top 10 most environmentally harmful. While only two of the 10 routes are international (London—Amsterdam and London—Frankfurt), the remaining eight routes are within the borders of different European countries. Of these, Germany is the country with the highest number of national routes (three), followed by France with two (one of which is the most polluting route in the EU) and The United Kingdom, Spain, and Italy, with one national route each (Table 5).

Table 5 Ten most environmentally harmful routes in Europe
Full size table

Overall, in 2017, the passengers that flew between major European cities on routes which do not exceed the 800 km threshold on the rail network have been 78.3 million. The estimated carbon dioxide equivalent production resulting from these movements was 7.62 MT.

Combining both short and medium distance flights, the total amount of carbon dioxide equivalent produced in 2017 within these routes alone is 9.2 MT. It is an impressive amount of carbon dioxide, especially when considered that it results from short flights within the major cities in the European Union alone. According to the European Environment Agency (EEA 2019),Footnote 6 in 2017, the CO2 equivalent production in the EU amounted to 4.483 MT. Therefore, if we take into consideration the data resulting from this study, it is possible to notice that the 175 analysed routes accounted for more than 0,21% of the total CO2 equivalent production within the European Union. If only the 144 routes which have been classified as short-distance routes were taken into account, the carbon dioxide equivalent production would still reach a 0,17% of the total European production.

As highlighted by Eurostat (2019),Footnote 7 the transport sector represents 25% of the carbon dioxide equivalent total production within the European Union with 1.120 MT of carbon dioxide, second only to fuel combustion without transport. Followed by agriculture (10%), industrial processes and product use (8%) and waste management (3%). The carbon dioxide equivalent production in the 175 routes analysed in this study, therefore, accounted for 0,82% of the total transport sector emissions.

According to the data reported by the European Member States to the UN Framework Convention on Climate Change (EASA 2019),Footnote 8 the total carbon dioxide emissions of all flights departing from EU28 and EFTA in 2017 have been 163 MT. Those routes which are classified as short distance in this study, therefore, amounted to 4.67% of the total production. Including into this evaluation also the medium distance routes, 5.64% of the total CO2 production to and from European airports has been produced on the routes analysed in this study. These figures might seem irrelevant to consider in the big scheme of things, but it is worth remembering that, as a reference, the EU greenhouse gas emission in 2016 decreased by 0.4% compared with 2015 and later increased again in 2017 by 0.6% compared to 2016, according to preliminary data.Footnote 9 So far then the EU target of reducing greenhouse gas emission by 20% compared to the 1990 levels looks within reach, even if by a narrow margin. However, as set in the 2030 climate and energy policy framework, a binding target of at least 40% cut in greenhouse gas emissions compared with 1990 levels have been determined in 2014, and the possibility of achieving a 0.17% cut in emission by enhancing the rail network on routes shorter than 800 km alone should be fully considered (Graph 1).

Graph 1
figure 1

Share of analysed routes on EU CO2 production

Full size image

Building upon the contribution from Prussi and Lonza, this study considers the possible CO2 emission savings resulting from shifting 25% of the expected aviation passenger growth to HSR service, in a so-called “high-rail” scenario. Although a total transferability scenario would be highly preferable, at the same time it is also extremely unlikely. Therefore, an achievable target for the reduction of carbon dioxide production must be considered, in order to better identify the steps to undertake towards a sustainable future for the sector.

Prussi and Lonza identify a 20% saving in CO2 emissions by shifting 25% of the expected passenger growth to the rail sector. As they also identify an annual passenger increment of 3.5%, this study builds upon this projection employing the collected data. As a result, the estimated saving of carbon dioxide equivalent on the 175 routes analysed would have been of around 1.84 MT CO2, lowering the emission production from 9.2 MT to 7.36. If such a trend were to be implemented systematically, the CO2 saving on these routes by 2019 could have been of an additional 1.47MT. Such a saving would have allowed the analysed routes to decrease their share in the European CO2 production resulting from the transport sector from 0.82% to a hypothetical 0.53%. Since 31 of these 175 routes need investments in the rail sector to be competitive with the air transport, enhancement of the network should be considered as an alternative way of cutting CO2 emission. Furthermore, investments in the current rail network would enlarge the possibility for shifting mean of transport for more end-users even on routes longer than the one analysed in this study. However, it should be noted that the current contribution does not include a detailed calculation of the costs, both in monetary terms and CO2 production, necessary for the railway infrastructure to accommodate the forecasted modal shift of the passengers.

If 25% of the expected passenger increment on other routes which sits outside the scope of this study were to be substituted with rail transport as well, the saving would be even greater. To give a reference, if the four routes between the five most populous cities which are less than 1500 km long on the rail network were taken into consideration—see in the following table—the production of carbon dioxide equivalent would have been 1.55 MT. In the case of a high-rail scenario, the possible saving on these routes would have been 0.31 MT. These four routes alone would have saved almost one-sixth of all the other 175 routes combined during the year 2018 alone. If both these four high-traffic routes and the previously analysed ones were combined, the total CO2 production in 2017 would amount to 10.69 MT: 0,95% of the entire greenhouse gas production from the transport sector in the EU. The possible saving in a high-rail scenario from these routes alone could have reached 2.14 MT of CO2 (Table 6).

Table 6 CO2 production on four routes between the five most populous cities in EU
Full size table

On the other hand, however, what did happen as a result of a lack of policies able to alter the CO2 emission rate? Considering an annual passenger increment of 3.5% on the 175 routes analysed in this study, and not considering the eventual CO2 production saving from the newest technologies in the air transport field, the results are dangerous. In the first year, the CO2 emissions increased by 14.24%, with a total carbon dioxide equivalent production of 10.51 MT, from the 9.2 of 2017. By 2019, assuming that a stable passenger increment of + 3,5% remained, the CO2 emissions reached 11.71 MT. Furthermore, this growth does take into account only the production resulting from the greater number of flights per se, without considering the emission from infrastructure investments (Graph 2).

Graph 2
figure 2

Effects of sustainability-driven policies on CO2 emissions

Full size image

On the four high-traffic routes alone, in 2019, CO2 emissions reached 1.66 MT, with an increment of 7.1% over the 1.55 MT resulting from 2017. If this growth is not to be corrected timely, the transport sector contribution to the achieving of the 2030 objectives would not only be limited, but even harmful.

8 Lessons Learnt

In conclusion, this study highlights the influence of airlines on the GHG emissions resulting from the European transport sector. More importantly, it also analyses to what extent it would be possible to lower these emissions by shifting a relatively small percentage of passengers to railways.

We recognise it is vital to safeguard environmental protection and mobility necessity at the same time, thus this study underlined the importance of actively promoting a shift from transport modes which are not environmentally sustainable anymore to transport modes which are ecologically friendly and can play a great role in tomorrow’s mobility.

Enhancement of the rail network, a change of mindset in the end-users regarding air transportation and sustainability-driven policies could start a ripple effect in the entire transport sector. Given the fact that since 1990 the emission levels from this sector constantly increased, a change of paradigm together with a re-consideration of different modes of transport is necessary.

This study does not address the question regarding which airline does produce more of the carbon dioxide equivalent on the analysed routes. However, it should be mentioned that in April 2019 Ryanair, according to data from the EU Emissions Trading System statistics,Footnote 10 has become the only airline to be included in a list of Europe's top 10 polluters. According to the data, Ryanair's carbon dioxide emissions rose by 6.9% in 2018. The news produced quite a clamour since it has been the first time a company that does not run a coal power plant has entered in the top 10. Indeed, Ryanair has been identified as one of the top polluters, rather than Lufthansa, which has been the largest airline in Europe in number of passengers carried globally in 2017, or IAG which currently is the third airline in Europe. In response to the public opinion, the company stated that Ryanair is “Europe's greenest and cleanest airline". Furthermore, from June 2019 the company became the “first EU airline to release monthly CO2 emissions statistics, which show an average of 66 g CO2 per passenger/km in May 2019”. However, this “new transparent course” should not be misleading. In fact, a quick look at the data given by the two major companies will allow noticing that albeit Lufthansa carried more people in 2017 than Ryanair (130.04 versus 128.77 million), the difference in number and length of their respective routes is stark. While Lufthansa (2017) connects 288 airports worldwide,Footnote 11 Ryanair (2019) flies to 210 which are all located within Europe, North Africa—where it has nine destinations—and the middle east—with four destinations.Footnote 12 Thus, Ryanair’s statement claiming to have “the lowest CO2 emissions per kilometre travelled than any other airline”, might be correct but certainly is ambiguous. As such, the fact that 14.1 million people flew with the company in May 2019 alone, according to Ryanair figures, should be highlighted. As already noted earlier in the “methodology” section, Ryanair is the leading company in Europe for Boeing 737–800 presence in its fleet, which presents a higher environmental footprint than the Airbus counterpart from routes longer than 420 km. As a Boeing 737–800 can seat up to 189 passengers, even by taking into account an unrealistic full load scenario through an entire month, in May alone 74.603 flights took off, on average more than 2.406 flights per day.

The medium-term sustainability of these numbers must be addressed by further researches.

9 Conclusions

This study showed that the share of the short and medium-distance airline flights in the GHG emissions from the European transport sector is not negligible.

The analysis of the short-distance routes alone shows that 78.3 million passengers travelled between major European cities, while the estimated cost of these movements was 7.62 MT of CO2. These routes alone accounted for 4.67% of the total production carbon dioxide emissions of all flights departing from EU28 and EFTA in 2017, while if the medium-distance routes are also included, the 175 routes are expected to have produced 5.64% of the total CO2 production to and from EU28 and EFTA airports.

In 2017, the flights on the 175 analysed short and medium-distance routes carried an estimated 90.56 million passengers and produced 9.2 MT CO2. As a result, these analysed routes accounted for more than 0.21% of the total CO2 production within the European Union.

The introduction of sustainability-driven policies would have allowed the European transport sector to reduce the share of the analysed routes from 0.82% of the European transport CO2 production to a hypothetical 0.53%, while ensuring the service without complication for the end-users. In case these policies were implemented as to shift 25% of the expected passenger growth from the air sector to railways on the 175 routes, it would have been possible for the European transport sector to save 1.84 MT of CO2, lowering the emission production from 9.2 MT to 7.36.

Keeping in mind that the existing capacity of the European railway system might not be able to accommodate the passenger shift outlined in this contribution, it is nevertheless important to recognise the importance of airlines share in the transport sector CO2 emissions. While further investments will be necessary to expand the rail network accordingly, the advantage of the sector in terms of GHG emissions over air transportation is undisputable.

10 Reflections Beyond—Policy Recommendations

Given the magnitude of the CO2 values resulting from air passengers transport, we believe it is time to implement effective policies addressing climate challenge, especially regarding the transport sector. The urgency of these policies is evident when considering the aftermath of the Coronavirus crisis. The pandemic had profound effects on the global air transport sector and on European airlines, which have been forced to accept bailout packages from the respective home governments. Although these bailouts are not expected to focus on the environmental damage airlines pose but rather on economic and societal aspects, the aspect of green mobility still influences key policymakers. The development of significant state bailouts can give governments a rare chance to shift transport away from planes to the greener rail sector. In particular, the decision by Austrian Airlines to replace the air transportation on the Vienna—Salzburg route with train service to meet environmental requirements in the recently accepted government bailout package is noteworthy. This development will enhance railway performance by allowing travellers to choose amongst 31 trains between the two domestic cities instead of the previous three rail connections per day. However, the significance of government bailouts might be lower, as in the case of KLM. In this instance, the bailout package requires the general objective of reducing CO2 emissions per passenger per kilometre by −50% in 2030 compared to 2005. Such a target not only was already set by KLM itself in 2019 but it also only influences the efficiency levels, thus allowing unlimited passengers growth.

Ultimately, scientific research serves as the compass for environmental policy, and legislation can deliver the forward momentum. A re-evaluation of air mobility services is necessary for the European Union not only to cope with the crisis triggered by the COVID-19 pandemic but also to achieve a long-term vision arising from commitments in international cooperation. In particular, this study shows how the nature of air transportation and its constant increase in passengers share hinder the process of reaching the objectives identified by the UN SDGs 12 “Ensure sustainable consumption and production patterns” and 13 “Take urgent action to combat climate change and its impacts”.

SDG 12 highlights the following target: “rationalize inefficient fossil-fuel subsidies that encourage wasteful consumption by removing market distortions, in accordance with national circumstances, including by restructuring taxation and phasing out those harmful subsidies, where they exist, to reflect their environmental impacts, taking fully into account the specific needs and conditions of developing countries and minimizing the possible adverse impacts on their development in a manner that protects the poor and the affected communities”. It is clear that, in light of this objective, the pre-COVID-19 situation vis a vis CO2 emission by airlines cannot be restored. The low level of taxation that the air transportation sector benefited from actively pushed forward the trend of high CO2 emissions. A fairer, more level playing field amongst transport modes is, therefore, necessary to reduce the emissions from the transport sector to reach this Sustainable Development Goal. Furthermore, SDG 13 underlines the target of “integrate climate change measures into national policies, strategies and planning”. In this context, the continued growth of air transport, and thus emissions, indicates how national policies have failed in containing the growth of GHG emissions through selected mobility services. Despite its impact on the environment, air transportation has been at least condoned—if not actively promoted—by national measures sacrificing the environment on behalf of economic growth. Sustained steps towards the achievement of these two SDGs by European leaders would not only be further evidence that railways can accommodate the needs for environmental protection and high levels of mobility better than air transportation but would also firmly establish the EU as global leader in transportation and environmental policies.

In line with these objectives, policymakers should consider the development of ad-hoc financial measures for big polluters such as airlines. In particular, measures which might be introduced to curb CO2 emissions from the air sector could be either taxes on jet fuel, or rather distance-based air passenger taxes or again an increased ticket prices with the aim to reduce demand for air travel and thus reduce emissions. However, the effectiveness of any carbon tax on airlines depends on the reinvestment of income within the transport sector. As the purpose is not taxation per se but rather development of green mobility, policymakers should consider curbing financial support from environmentally harmful travel modes to more eco-friendly options.

Other options, which however should be investigated regarding their possible outcome, could include a quota obligation for biofuels or mandatory electric vehicles for the airport infrastructure. Further studies must examine the results, costs and opportunities of alternative sustainability-oriented policies.

Following the European Union aim to reduce carbon dioxide emissions substantially, the EU climate action strategy requires a change of paradigm in approaching transportation and mobility: the 2030 targets require efforts beyond the currently implemented measures. The transport sector, in particular, cannot continue its path of steadily increasing emissions, since 1990. The need to meet sustainability targets has to lead to a reconsideration of different modes of transport where the railways might play a key role in the mobility’s ‘promising’ future. The EU cannot afford to maintain the current course of action in respect to air transport regulations and taxations within its member states if it wants to lead the global change towards an ecologically sustainable future.

11 Avenues for Future Work

In the context of the existing literature, this study aimed at starting a debate over the need for research focusing on CO2 emissions from for EU-wide sectors. As this contribution does not focus on infrastructure development but rather on operations, further research might consider the costs in terms of monetary expenses and CO2 emissions resulting from enhancement of the infrastructure network for the European transport sector on a continental scale. At the same time, further studies will need to provide a detailed evaluation of the feasibility for the railway system to adapt to the passenger shift outlined in this contribution, together with a detailed evaluation for such a shift.

Lastly, this study wanted to fill in the current lack of cross-sectoral analysis by providing a novel contribution. Further researches might focus on the comparison and analysis of other transport solutions and their CO2 share within the Union. Greater emphasis, we argue, must be placed on the analysis of transport and economic policies in light of CO2 emission and the 2030 target.