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The global scale, distribution and growth of aviation: Implications for climate change

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Abstract

Prior to the COVID-19 crisis, global air transport demand was expected to triple between 2020 and 2050. The pandemic, which reduced global air travel significantly, provides an opportunity to discuss the scale, distribution and growth of aviation until 2018, also with a view to consider the climate change implications of a return to volume growth. Industry statistics, data provided by supranational organizations, and national surveys are evaluated to develop a pre-pandemic understanding of air transport demand at global, regional, national and individual scales. Results suggest that the share of the world's population travelling by air in 2018 was 11%, with at most 4% taking international flights. Data also supports that a minor share of air travelers is responsible for a large share of warming: The percentile of the most frequent fliers – at most 1% of the world population - likely accounts for more than half of the total emissions from passenger air travel. Individual users of private aircraft can contribute to emissions of up to 7,500 t CO2 per year. Findings are specifically relevant with regard to the insight that a large share of global aviation emissions is not covered by policy agreements.
The global scale, distribution and growth of aviation: implications for climate change
Please cite as:
Gössling, S. and Humpe, A. 2021. The global scale, distribution and growth of aviation:
Implications for climate change. Global Environmental
Change, https://doi.org/10.1016/j.gloenvcha.2020.102194
(free downloads available at Elsevier site)
Abstract
Prior to the COVID-19 crisis, global air transport demand was expected to triple between
2020 and 2050. The pandemic, which reduced global air travel significantly, provides an
opportunity to discuss the scale, distribution and growth of aviation until 2018, also with a
view to discuss the climate change implications of a return to volume growth. Industry
statistics, data provided by supranational organizations, and national surveys are evaluated to
develop a pre-pandemic understanding of air transport demand at global, regional, national
and individual scales. Results suggest that the share of the world’s population travelling by air
in 2018 was 11%, with just 2-4% taking international flights. Data also supports that a minor
share of air travelers is responsible for a large share of warming: The percentile of the most
frequent fliers – at most 1% of the world population - likely accounts for more than half of the
total emissions from passenger air travel. Individual users of private aircraft can contribute to
emissions of up to 7,500 t CO2 per year. Findings are specifically relevant with regard to the
insight that a large share of global aviation emissions is not covered by policy agreements.
Keywords: Aviation; climate policy; CORSIA; emission equity; emission gap; Paris
Agreement
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1. Introduction
Aviation is one of the most energy-intense forms of consumption, and has in the past been
characterized by strong growth, with estimates that emissions have increased by a factor 6.8
between 1960-2018 (Lee et al. 2020). Industry estimates prior to COVID-19 have suggested a
further tripling between 2020-2050 (ICAO 2016). By mid-2020, scheduled flights and
revenue passenger kilometers (RPK) had declined significantly (RPK by -50%; ICAO 2020a).
Industry has since then stated to expect a rebound (IATA 2020a), as witnessed after previous
crises including the global financial crisis in 2008 (IATA 2019). If aviation returns to a
volume growth trajectory, the sector will be in a growing conflict with global decarbonization
goals (Dubois et al. 2019; Larsson et al. 2019).
Against this background, the COVID-19 pandemic represents an opportunity to critically
discuss air transport and aviation climate governance (Dubois et al. 2019; Gössling 2020;
Larsson et al. 2018, 2019), based on patterns of air transport demand. Available data on air
transport distributions has remained scattered, but there is evidence of some countries and
individuals contributing disproportionally to emissions from air transport. Further analysis of
these distributions is warranted because of emerging debates of carbon inequality
(Chakravarty et al. 2009; Chancel and Piketty 2015; Hubacek et al. 2017; Ivanova and Wood
2020), as well as airlines and air transport advocates’ presentation of air travel as an
ubiquitous activity, in which a large share of the world population is involved (Gössling et al.
2019). This paper provides new insights on global, regional, national and individual scales of
analysis. It also discusses future growth trajectories under business-as-usual recovery
scenarios, and their implications for climate change.
2. Background
2.1 Who emits greenhouse gases?
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International mitigation agreements including the Kyoto Protocol and the Paris Agreement are
founded on ‘fairness’ principles, recognizing that averaged per capita contributions to
greenhouse gas emissions vary widely. Countries with high per capita emissions are expected
to make greater contributions to emission reductions (UNFCCC 2018a,b). Such ‘common but
differentiated’ mitigation principles generally omit the question of production (where?) versus
consumption (who?) (Hertwich and Peters 2009; Peters 2008), and they do not consider
differences in per capita emissions within countries (Girod and de Haan 2009; Munksgaard et
al. 2000). Chakravarty et al. (2009: 11884) were among the first to highlight this problem,
suggesting that principles for allocating mitigation responsibilities be based on those
generated by “individuals, rather than nations”. It is thus of interest to further study the
world’s “high-emitters”, i.e. individuals contributing disproportionally more to climate change
than the “average world citizen” (who emitted close to 5 t CO2 per capita and year in 2014;
World Bank 2020a).
Various national studies have confirmed that high emitters are found mostly among the highly
affluent (Büchs and Schnepf 2013; Gill and Moeller 2018; Irfany and Klasen 2016; Ummel
2014). Chancel and Piketty (2015) calculate that the top 10% emitters in the world account for
45% of global CO2-eq emissions, while the bottom 50% of emitters contributed 13% (see also
Hubacek et al. 2017). In a recent study of consumption in the European Union (EU), Ivanova
and Wood (2020) find that the top percentile of emitters is responsible for 27% emissions,
with the top 1% of emitters exceeding annual per capita emissions of 55 t CO2-eq. While
high-emitters live in all countries, Chancel and Piketty (2015) identify the top 1% of
wealthiest individuals in five countries as specifically relevant, with per capita emissions
exceeding 200 t CO2-eq per year. These high emitters are at home in the USA, with an
estimated 3.16 million people exceed average annual emissions of 318 t CO2-eq per person;
Luxemburg (10,000 individuals emitting 287 t CO2-eq/year each); Singapore (50,000
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individuals, 251 t CO2-eq/year); Saudi Arabia (290,000 individuals, 247 t CO2-eq/year); and
Canada (350,000 individuals, 204 t CO2-eq/year). In comparison, low emitters in many parts
of Africa emit a mere 0.1 t CO2 per year (World Bank 2020a).
While these studies indicate very significant differences in emissions between individuals, it
remains unclear how differences come into existence. Frequent movement, and in particular
access to private transportation, as well as multiple real estate ownership - often in different
continents (Beaverstock and Faulconbridge 2014) -, appear to be key determinants of carbon-
intense consumption. As affirmed by Girod and de Haan (2009: 5655) in a Swiss household
survey: “comparison of high and low emitters shows the main difference is that high emitters
spend a higher amount on mobility”.
2.2 Emission distributions and air travel
It is generally established that air transport is a highly energy and emission intense activity,
but there seem to exist diverse views on the distribution of demand. IATA (2018) affirms that
“the average [world] citizen flew […] once every 22 months”, giving associations of a normal
distribution of flight in which the whole world is involved. However, another industry view
holds that “less than 20 percent of the world’s population has ever taken a single flight […]”
(former Boeing CEO David Muilenburg; CNBC 2017). The latter would imply that the
distribution of air travel is skewed toward a relatively small number of travelers, and that
notions of “average world citizens” obscure that many people do not fly at all, while others
are very frequent fliers.
National surveys have established that air travelers are disproportionally wealthy (e.g.
Banister 2018; Carlsson-Kanyama and Lindén 1999), with repercussions for emissions. As
Ivanova and Wood (2020: 6) conclude, “air travel is the consumption category with the
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highest carbon contribution among the top emitters”. Korbetis et al. (2006) found that US-
households with incomes of US$75,000 or more emitted 13.74 t CO2 per year in transport
emissions, while households earning less than US$5,000 emitted 5.5 t CO2. This affects
distributions: In the UK, the 20% of the most frequent non-business travelers produced 60%
of related emissions, with the contribution by the highest income groups (>£40,000
person/year) being 3.5 times greater than that of the lowest income groups (<£10,000
person/year) (Brand and Boardman 2008; Brand and Preston 2010). Studies also established
that a share of business travelers may fly on an almost daily basis (Gössling et al. 2009), with
some individuals covering vast distances: Former US Secretary of State Hillary Clinton
reportedly flew 1,539,712 km, equivalent to more than 38 circumnavigations, in her four
years in office (The Atlantic 2013, referring to the US State Department). Much evidence thus
supports notions of highly skewed distributions in air transport demand, with significant
implications for climate change governance.
2.3 Climate policy and aviation
Averaged per capita emissions were the basis for the Kyoto Protocol (in 1997) and its
consideration of Annex I countries, as well as the Paris Agreement (in 2015), with the
expectation that high-emitting countries (on a per capita basis) make “fair and ambitious”
contributions to emission reductions (UNFCCC 2018a,b). The Kyoto Protocol exempted
international aviation and shipping from national contributions, due to their transborder and
over high seas character, and assigned responsibility for “limiting or reducing” emissions
from these sectors to the International Civil Aviation Organization (ICAO) and the World
Maritime Organization (WMO) (UNFCCC 2018a,b). This general distribution of
responsibilities has been maintained under the Paris Agreement, i.e. domestic aviation falls
under national mitigation targets, while international bunkers are addressed by ICAO (ibid.).
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An important omission of Kyoto Protocol and Paris Agreement is their focus on CO2 and
other long-lived greenhouse gases, ignoring aviation’s contribution to radiative forcing from
short-lived emissions such as nitrous oxides (NOx), or in the form of contrails or clouds (H2O)
(Lee et al. 2020). These non-CO2 emissions are not directly comparable with long-lived GHG,
but they do contribute to global warming (Lee and Sausen 2000). Non-CO2 warming is
expected to remain relevant in the short and medium-term future (Bock and Burkhardt 2019).
To account for non-CO2 warming, countries such Austria or Germany consider a warming
effect of non-CO2 that is comparable to CO2 in national assessments of aviation impacts
(Environment Agency Austria 2018; German Environment Agency 2018). In 2018, aviation
has been estimated to account for 2.4% of anthropogenic emissions of CO2 including land use
changes (Lee et al. 2020). There is an additional warming effect related to contrail cirrus and
NOx, which is larger than the warming from CO2, if calculated as net effective radiative
forcing. Lee et al. (2020: 2) conclude that aviation emissions are currently warming the
climate at approximately three times the rate of that associated with aviation CO2 emissions
alone”.
3. Method
Air transport demand is analyzed at global, regional, national and individual scales. Data is
presented for the situation prior to the COVID-19 pandemic, including scenarios for future
demand that are based on industry projections. COVID-19 challenges all assumptions in
principle, though industry expects a return to business-as-usual once the pandemic has passed
and the economy stabilizes. For example, IATA (2020b) suggested in April 2020 that 60% of
air travelers would “return to travel relatively quickly”. More informative are ICAO’s (2020b)
scenarios that show different possible pathways to recovery. The implication for scenarios
presented in the paper is that these could be delayed, even by several years, and that growth
may be slower than projected if demand adjusts downwards under longer periods. The
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scenarios remain useful, however, in that they illustrate where aviation growth is headed in
the longer run.
Global calculations of transport demand are based on data sources including Airbus (2019),
Boeing (2019), IATA (2019), World Bank (2020b), and UN DESA (2020). Data provided by
these sources is not always comparable. For example, IATA (2019) provides official passenger
statistics for the world and world regions, while the World Bank (2020b) makes available data
for 199 individual countries (based on ICAO data that is not publicly available). Limited
information is available on fuel use and emissions by subsector, i.e. commercial passenger
versus freight transport, private air travel, and military operations. The share of the global
population that is flying is calculated based on IATA (2019), UN DESA (2020) and national
surveys (USA: Airlines for America 2018; Germany: IFD Allensbach 2019; UK: Department
of Transport 2014; Taiwan: Tourism Bureau Taiwan 2019).
Regional flight demand is assessed on the basis of industry data (IATA 2019) as well as
extrapolations of industry growth expectations (Airbus 2019; Boeing 2019). Data is presented
for seven world regions (Africa, Asia-Pacific, Commonwealth of Independent States, Europe,
Latin America, Middle-East, North America, as well as the ‘Rest of the World’), and includes
RPK as well as emission estimates for 2018 and 2050.
National perspectives on air transport demand and fuel use are derived from IEA (2019a), and
UNFCCC (2020, for Annex I countries). Data is used to assess bunker fuel use
(domestic/international) in relation to national emissions, and to determine relationships
between GDP and transport demand. Nationally averaged transport demand measured in RPK
per capita is based on ICCT (2019a). Assessments of national transport demand need to
consider allocational issues (Larsson et al. 2018). Depending on allocation principle,
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differences can be significant. For example, in a calculation of distances flown by the
Swedish population, defined as the country’s residents (national and foreign), Larsson et al.
(2018) arrive at an average 5,800 km per person per year in the period 2010-2013. This
includes the distances flown by Swedish residents outside Sweden. In comparison, the ICCT
database suggests 3,350 RPK (in 2018) per Swedish citizen per year, based on a commercial
fuel allocation principle (ICCT 2019). Significant differences also arise out of inbound to
outbound ratios (Sun and Lin 2019). It is known that some countries are markets, while others
are destinations (UNWTO 2018), and allocation principles thus have significant implications
for results. Data in this paper is based on national fuel use (UNFCCC 2020), with the
implication that for countries with outbound to inbound ratios above 1, true fuel use and
emissions by these countries’ residents is underestimated.
Individual perspectives on transport demand are derived from airport surveys and national
travel surveys (UK Department for Transport 2014; Airlines for America 2018; Gössling et al.
2009, 2020; GRA Incorporated 2018), as well as assessments of fuel use and emissions for
private flight (Gössling 2019).
4. Distribution of air transport
4.1 Global emissions from aviation
Aviation fuel use includes commercial aviation (passengers/freight), private air transport, as
well as military flight. Estimates of global fuel use vary. Lee et al. (2009) concluded that
global emissions from aviation may have been in the order of 733 Mt CO2 in 2005. More
recent estimates presented by IATA (2018) suggest that civil aviation - including international
and domestic, passengers and freight - emitted 859 Mt CO2 in 2017. The International Energy
Agency (IEA 2019a) specifies that the world’s total aviation fuel demand was 310.56 Mt in
2017, about 60.4% of this for international aviation, and 39.6% for domestic aviation (table
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1). Together, commercial, private and military flight would thus have emitted 978 Mt CO2 in
2017 (IEA 2019a), of which, in comparison to IATA (2018) data, 87.8% would fall on
commercial aviation (Figure 1). Lee et al. (2020), also based on IEA data, extrapolate overall
aviation emissions to 1,034 Mt CO2 in 2018.
To differentiate non-commercial, i.e. military and private flight fuel use and emissions is
difficult, as there is no global data for military operations. It has been suggested that military
aircraft consumed 22% of US jet fuel in 2008 (Spicer et al. 2009), though a lower recent
estimate for the US in absolute numbers is 18.35 Mt CO2 (in 2017; Belcher et al. 2020). In a
global estimate for 2002, Eyers et al. (2004) concluded that global military operations
required 19.5 Mt of fuel, leading to emissions of 61 Mt CO2, or 11.1% of global emissions
from aviation. More recent data is not available, though given commercial air transport’s
strong growth over the past 20 years, it can be expected that the share of military operations in
total fuel use has declined. For an estimate, the current contribution of military flight to global
emissions from aviation is assumed to be 8% (Figure 1). This estimate is uncertain, but
highlights the importance of military flight in aviation emissions.
Data on private aviation is equally limited. The global business aviation market is estimated to
have included 22,295 jets, 14,241 turboprops, and 19,291 turbine helicopters in 2016
(AMSTAT Market Analysis 2018). Assuming an average of 400 hours of flight time per year
for the global fleet of private jets, with an estimate of a 1200 kg/hour fuel use (Gössling
2019), jet fuel burn was 10.7 Mt in 2016, corresponding to 33.7 Mt of CO2. Adding the fuel
use of turboprops and helicopters, overall emissions from private transport may be in the
order of 40 Mt CO2. This would suggest that private aviation accounts for about 4% of global
emissions from aviation (Figure 1).
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In summary, the estimate for 2018 is that global aviation burned approximately 320 Mt of
fuel, and emitted one Gt CO2, of which 88% fell on commercial aviation, 8% on military
operations, and 4% on private flight. For commercial aviation, fuel use can be further divided
into passenger transport (81%) and freight (19%) (ICCT 2019). The overall distribution is
shown in Figure 1.
71.00%
17.00%
8.00% 4.00%
Commercial
aviation:
passengers
Commercial
aviation: freight
Military Private
Figure 1: Global distribution of aviation fuel use
Source: Calculation based on Eyers et al. (2004), IATA (2019), ICCT (2019), IEA (2019a)
Fuel use and emissions associated with passenger transport are the focus of this paper.
According to IATA (2019), there were 4.378 billion passengers in 2018 (international and
domestic). This is not equivalent to trip numbers or individual travelers. Most air trips are
symmetrical, i.e. they will involve a departure as well as a return. Apart from an unknown
share of asymmetric trips (triangle flights, one-leg air trips), IATA (2019: 4) suggests that
close to 4 billion passengers flew origin-destination, while 400 million moved through a hub.
Assuming symmetric flight patterns, one trip through a hub will involve at least four
individual flights. As ten percent of all flights involve a transfer, 4.378 billion passengers
would thus represent a maximum of 1.99 billion trips. Compared to global population of
7.594 billion (UN DESA 2020), this means that the theoretical maximum share of the world
population that could have participated in air travel was 26.2% in 2018 (1.99 billion trips
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divided by 7.594 billion people, presupposing that each individual participates in exactly one
trip).
Demand is not evenly distributed throughout the world, however. Table 1 looks at
distributions between countries by income group, on the basis of World Bank (2020b)
statistics that consider 4.233 billion passengers in 217 countries. Comparing passenger
numbers to population and wealth levels, the number of flights averaged over the population
is 0.03 per person and year in low-income countries, 0.15 in lower middle-income countries,
0.49 in upper middle-income countries, and 2.02 in high income countries. The data suggests
that the theoretical maximum share of the population that could have participated in air travel
is 1.63% in low income countries, 7.51% in lower middle-income countries, 24.72% in upper
middle-income countries, and 100% in high income countries. Only the high income countries
reach 100%, because it is only in these countries that each individual in the population could
have participated in at least one trip.
Table 1: Theoretical maximum share of flying population
Population
2018
(million)*
Passengers 2018
(million)*
Passengers per
capita of the
population
Flying
population (%)
Maximum
flying
population
(million)
Low income 705 23 0.03 1.63 11
Lower middle 3,023 454 0.15 7.51 227
Upper middle 2,656 1,313 0.49 24.72 657
High income 1,210 2,442 2.02 100.00 1,210
Total 7,594 4,233 2,105
*Source: World Bank (2020b)
The ”theoretical maximum” assumes that each individual participates in exactly one trip per
year.
Distributions in Table 1 do not consider that there is a significant share of the population in
every country that does not fly, while some air travelers participate in one, two, or multiple
trips. For example, data for the USA suggests that 53% of the adult population do not fly
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(Airlines for America 2018). In Germany, 65% of the population do not fly (IFD Allensbach
2019), while this share is 66% in Taiwan (Tourism Bureau Taiwan 2019). In the UK, the non-
flying share of the population 16 years or older is 59% (DEFRA 2009). These national
surveys indicate that in high income countries, between 53-65% of the population will not fly
in a given year. The share of non-fliers is likely larger in low-income, lower-middle and
upper-middle income countries. For a conservative estimate, and given the lack of data for
lower income countries, Table 2 assumes that the share of the population participating in air
transport is 40% on global average (Table 2). The estimate is thus that the share of the world
population that flew in 2018 is 11.1% (845 million individual air travelers divided by a world
population of 7,594 million; Table 2).
Table 2: Share of flying population adjusted for non-flying share of population, 2018
Population
(million)*
Passengers
(million)*
Passengers per
capita of the
population
Flying
population
(%)
Flying population
(million)
Low income 705 23 0.03 0.7 4.9
Lower middle 3,023 454 0.15 3 90.7
Upper middle 2,656 1,313 0.49 10 265.6
High income 1,210 2,442 2.02 40 484.0
Total 7,594 4,233 845.2
Source: own calculations, based on World Bank (2020b)*. Flying population: The
share/number of the population/people in each income group that flies at least once per year.
The share of the global population participating in international air travel is even smaller, as a
significant share of all air travel takes place within countries. Domestic air travel included
2.566 billion passengers in 2018, out of this 590 million in the USA, 515 million in China,
and 116 million in India (IATA 2019). International air travel consequently only comprised
1.811 billion passengers, who are also more likely to move through hubs. On the basis of the
conservative assumption that one international trip comprises 2.2 flights (IATA 2019), some
823 million international trips were made in 2018. As trip numbers do not represent an equal
number of individual travelers, it is assumed, conservatively, that with a 60% non-flying
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population share, 823 million international trips would at most represent 329 million unique
air travelers, or 4.3% of the world population. As outlined, this is a conservative estimate. An
alternative way of calculating the share of the population participating in international air
travel is to divide the number of international trips by an average trip number per traveler. For
example, Airlines of America (2018) suggest that the average air traveler makes 5.3 trips per
year, with a relatively large share of travelers participating in only one or two trips, and a
rather small share accounting for large trip numbers (see also section 4.4). Applying the US
average of 5.3 trips as an indication of skewed demand, 823 million international trips
involved only 155 million unique air travelers, or 2% of the world population. Even though it
is unknown if US data is representative for air transport more generally, it can be estimated
that in 2018, only 2% to 4% of the world population participated in international air travel.
4.2 Regional distribution of flight
The uneven distribution of air transport demand on regional scales is illustrated in Table 3 and
Figure 2. Data suggests that a quarter (25.6%) of global air transport takes place in North
America, and another 22.7% in Europe (Table 3). The Asia-Pacific region accounts for 32.5%.
The remaining four regions, Africa, Commonwealth of Independent States (CIS), Latin
America and Middle East, plus all countries not included in the seven regions, together
account for 19.2%. Yet, these regions are home to a large share of humanity. Annual per capita
air transport demand illustrates these regional differences, varying between 5,967 RPK in
North America, 3,181 RPK in the Middle East and 2,867 RPK in Europe (Table 3). In all
other regions, and specifically Africa (123 RPK), air transport demand is significantly smaller.
Table 3: Regional distribution of transport demand and outlook to 2050
Region
Growth
rate per
year (%)
RPK 2018
(billion)
RPK share
2018 (%)
RPK 2050
(billion)
RPK
share
2050 (%)
RPK per
capita
2018
RPK per
capita
2050
Africa 5.35 157 1.8 833 2.4 123 335
Asia-Pacific 5.45 2,762 32.5 15,092 44.1 648 3,097
CIS 3.50 213 2.5 641 1.9 894 2,522
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329
Europe 3.45 1,934 22.7 5,727 16.7 2,867 8,616
Latin America 5.10 507 6.0 2,493 7.3 790 3,270
Middle-East 5.35 543 6.4 2,877 8.4 3,181 10,789
North America 3.10 2,174 25.6 5,774 16.9 5,967 13,580
Rest of world 4.28 212 2.5 811 2.4 - -
Average/Total 4.45 8,503 100 34,247 100
Source: own calculations based on Airbus (2019), Boeing (2019), ICCT (2019), UN DESA
(2020). RPK development to mid-century is based on industry growth expectations until 2038
(Airbus 2019, Boeing 2019), and extrapolated to 2050. As a result of COVID-19, it is
currently unclear whether this growth projection remains a likely scenario.
Table 3 also suggests that differences in individual air transport demand will become even
more pronounced in the future. According to industry expectations (Airbus 2019), the Asia-
Pacific region would account for 44% of air transport demand by mid-century, followed by
North America and Europe (both 17%) (Figure 2). The share of all other regions would be
22%. Even though the average per capita distance flown in Africa is expected to almost triple
to 335 RPK per capita, this is one tenth of the expectation for Asia-Pacific (3,097 RPK) or
Latin America (3,270 RPK), and 40 times less than North America (13,580 RPK). Although
Africa would account for 25.5% of the world population by 2050 (UN DESA 2020), it will
only represent 2.4% of global air transport demand. In comparison, North America would be
the home of 4.4% of the world’s population and 16.9% of its air transport demand. Overall, in
this post-COVID-19, “resumed growth” recovery scenario, air travel would grow from 8,503
billion RPK in 2018 to 34,247 billion RPK by mid-century, as a result of population and per
capita transport demand growth.
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2.49%
32.49%
1.85%
2.51%
22.75%
5.97%
6.38%
25.57%
2.37%
44.07%
2.43%
1.87%
16.72%
7.28%
8.40%
16.86%
Rest of world
Asia-Paci(c
Africa
CIS
Europe
Latin America
Middle-East
North America
Figure 2: Distribution of RPK by world region, 2018 and 2050
Table 4 translates growth in demand into emissions, in a scenario that considers sector-wide
efficiency gains of 1% per year, with a specific fuel use of 3.5 l per 100 RPK in 2018 (IEA
2019b; Peeters et al. 2016). Annual emissions from commercial passenger transport would
increase from 0.743 Gt CO2 in 2018 to 2.169 Gt CO2 by 2050. The contribution made by
world regions varies vastly, however, with averaged per capita contributions ranging between
21 kg CO2 per year in Africa to 860 kg CO2 per year in North America.
Table 4: Total and per capita emissions from commercial air passenger transport
Region
CO2 global
(Mt, 2018)
CO2 global
(Mt, 2050)
CO2 per capita
(kg, 2018)
CO2 per capita
(kg, 2050)
Africa 14 53 11 21
Asia-Pacific 241 956 57 196
CIS 19 41 78 160
Europe 169 363 250 546
Latin America 44 158 69 207
Middle-East 47 182 278 683
North America 190 366 521 860
Rest of world 19 51 n.a. n.a.
Average/Total 743 2.169
Source: own calculations based on Airbus (2019), Boeing (2019), ICCT (2019), UN DESA
(2019). Emission factors: 0.035 l fuel per RPK burns to 0.087 kg CO2 per RPK in 2018.
4.3 National perspectives on air transport demand
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National perspectives on air transport are important because they can illustrate differences
between countries, differences in domestic/international fuel use, developments in emission
growth, the relevance of aviation in comparison to overall national emissions, and
interrelationships of air transport demand and GDP. UNFCCC (2020) data shows that a
significant share of global emissions from air transport is emitted by a few countries, with
only 12 countries emitting more than 10 Mt of CO2 per year, and 25 countries emitting more
than 2 Mt CO2 (Figure 3). The USA alone emits more CO2 than the following 10 largest
consumers of aviation fuel combined. Two thirds of US emissions (67%) fall on domestic air
travel (161.5 Mt CO2, compared to 78.4 Mt CO2 used for international air transport). Other
countries, due to their size, have very small domestic emissions (Belgium, Netherlands, or
Switzerland).
Figure 3: Aviation fuel use in the 21 highest emitting Annex I countries
Source: UNFCCC (2020)
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UNFCCC (2020) data also shows that in most countries though not all emissions from
international aviation have grown significantly in the period 1990-2017. Emissions have
more than doubled in the United States (104%), the UK (118%), Czechia (105%), Sweden
(106%), Finland (108%), Canada (112%), Germany (141%), Austria (153%), Italy and
Norway (160%), Netherlands (161%), New Zealand (178%), or Ireland (184%). They tripled
in Australia (210%) and Spain (258%). The most significant growth was seen in Luxembourg
(336%), Iceland (423%) and Turkey (1,896%). A decline in emissions was recorded in
Belarus, Bulgaria, Kazakhstan, Lithuania, and Ukraine, as well as Croatia.
Further insights can be derived from the comparison of bunker fuel use (international and
domestic) in relation to national greenhouse gas emissions including international bunkers. In
28 of 43 Annex I countries, the share of emissions from air transport exceeded 2% of annual
greenhouse gas emissions in 2017 (Figure 4). For five countries, the share even exceeded
10%, including in Cyprus (10.1%), Switzerland (10.4%), Luxembourg (14.2%), Malta
(16.7%), and Iceland (19.9%). As the data represents a ratio, the comparison of 1990 and
2017 also confirms that in virtually all countries, emissions from aviation have grown faster
than those from the economy in general. Cyprus is the only country with a lower share of
aviation emissions in 2017 than in 1990.
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Figure 4: Domestic & international bunker fuel emissions as share of national total (%)
Source: UNFCCC (2020)
Figure 5 illustrates national differences in air transport demand on the basis of RPK and GDP
per capita relationships, confirming earlier insights that a higher average GDP is linked to air
transport demand. Data is based on bunker fuel use by ICCT (2019) for 105 countries, with
the lowest transport demand recorded in the Democratic Republic of Congo (23 RPK and a
GDP of US$562 per capita per year), and the maximum, more than 45,000 RPK and a GDP of
US$76,856 per capita and year in Iceland. It deserves to be mentioned that there are
considerable differences in income distribution within countries, and it is likely that a
correction of data for income inequality would yield a significantly higher correlation
between transport demand and GDP as a proxy of income.
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Figure 5: Interrelationships of RPK and GDP*
*logarithmic scale
Source: ICCT (2019), World Bank (2020b)
4.4 Individual air transport demand
Previous sections have determined that close to 90% of the world population does not fly in a
given year, and of those flying, shares of in between 11.0% to 26.5% have reported just one
trip per year (e.g. Airlines for America 2018; Gössling et al. 2020b). On the other side of the
flyer spectrum, very frequent fliers have reported to make 300 trips per year (i.e. some 600
flights), indicating near-daily air travel (Gössling et al. 2009). National transport studies rarely
investigate these distributions, as data collection is usually focused on passenger numbers
(standardized in the EU, for example, see regulation EC 437/2003; EU 2003). Available
surveys suggest that a minority of very frequent fliers is responsible for many flights. A
Swedish airport survey concluded that the 3.7% of the most frequent fliers accounted for
28.3% of all flights taken (Gössling et al. 2009), while in a study representative of adults in
Germany, 10.9% of the sample were responsible for 28.8% of all flights (Gössling et al.
2020b). Figure 6 illustrates the overall distribution of air transport for the USA, showing that
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while more than half of adults did not fly in 2018, the most frequent fliers (6 flights or more),
just 12% of adults, accounted for 68% of all flights taken.
Figure 6: Air transport demand distribution in the USA
Source: based on ICCT (2019)
Figure 7 illustrates this relationship for different countries (UK, USA and Germany) as well as
two airports (Gothenburg and San Francisco). Surveys suggest that among commercial air
travelers, the most frequent 10% of fliers may account for 30-50% of all flights taken. The
share of the fuel used by these air travelers is likely higher, as more frequent fliers will more
often travel business or first class (Gössling and Nilsson 2010). For example, The World Bank
(2013) estimates that 70% of staff travel is on premium classes, which the World Bank (ibid.)
estimates to have a three times (business) and nine times (first class) larger carbon footprint
than economy class. The energy demand for people to fly in private First Class Suites, as
offered by Singapore Airlines or Ethiad, is even greater, with floor spaces of up to 5.8 m2 per
guest (11.6m2 per suite; Mainlymiles 2018). Larger toilets and additional aisle space make it
likely that first class suites require significantly more fuel than first class flights. The ICCT
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(2020) estimates that the carbon footprint of flying business class, first class, or in a large
suite is 5.3, 9.2 or 14.8 times larger than for flying in economy class.
In its A380 cabin layout, Singapore Airlines can transport 471 passengers, with 12 first class
suites requiring about the same space as 60 business class seats (Flightglobal 2007). Together,
these two classes (72 passengers) require the same space as 399 passengers in economy. This
would suggest that premium flight classes require an average 5.5 greater energy demand than
economy class seats. Even though aircraft layouts vary, a global 15% share of premium class
seats that on average require 5 times more energy than an economy class seat would mean that
premium class flights account for 40% of energy use, and economy flights (85% of seats) for
60%. Assuming further, conservatively, that the 10% of the most frequent fliers take 40% of
all flights, including all those available in premium classes, the estimate is that the most
frequent flier percentile accounts for 55% of energy use and emissions from commercial
passenger transport. Given that at most 11% of the world population participate in air travel,
this also means that 1% of the world population is responsible for 50% of emissions from all
air travel.
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Figure 7: Air transport demand distribution*
*broken lines: airport surveys
Source: UK Department for Transport (2014); Airlines for America (2018); Gössling et al.
(2009); GRA Incorporated (2018)
Finally, private air travel is the most energy-intense form of flight. Emissions can be
determined on the basis of hours of flight and fuel use per hour (Gössling 2019). While
private jet membership programs report average annual operation times of up to 1,090 hours
per aircraft (Private Jet Card Comparisons 2020), privately owned aircraft may be used at
lower levels of between 200-350 hours/year, with an average fuel use of about 1200 kg/hour
(Gössling 2019). Importantly, private aircraft may also be made available to friends, relatives
or business partners, which will add hours of operation. It has been documented that private
air travel can exceed fuel use of 500 t (or about 1500 t CO2) per capita per year (ibid.). Again,
this can be seen in the context of 75% of private jets worldwide being registered in the USA
(Forbes 2017). Where larger aircraft are involved, such as the US president’s Air Force Ones
(two Boeing 747-200B; Whitehouse 2020) or the Boeing 767 reportedly owned by Russian
oligarch Roman Abramovich (Aircraftcompare 2020), fuel consumption will increase
significantly. As an example, to cover a distance of about 8,200 km, a B744 (with a seat
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capacity similar to the Boeing 747-200), requires in excess of 97 t of fuel (Park and Kelly
2014). To cover a distance of 200,000 km per year (cf. Gössling 2019) will entail fuel use in
the order of 2,365 t, and result in emissions of 7,450 t CO2. Note that actual fuel use will be
influenced by flight distances, as shorter flights (high energy use for take-off) and longer
flights (additional weight of fuel carried) are characterized by higher specific fuel burn.
5. Discussion
Two major insights emerge from the analysis of global, regional, national and individual
patterns of air transport demand. First, a large share of emissions is unaccounted for in global
mitigation plans for aviation, which under Kyoto Protocol and Paris Agreement focus on
commercial international bunker fuels, and CO2 alone. Domestic commercial and private fuel
use is a responsibility of nation states, but several key emitting countries have shown limited
ambition to curb these emissions, or even formally rejected responsibility (UNFCCC 2017).
Military flight remains unaddressed, as well as a large share of private flight with smaller
aircraft.
This highlights that aviation’s contribution to global warming is only partially covered by
climate policies, which currently address international bunkers from commercial aviation (505
Mt CO2) and domestic emissions in countries joining the Paris Agreement (182 Mt CO2). Not
covered are domestic emissions in the USA (161 Mt CO2), military flight (80 Mt CO2), private
aviation (40 Mt CO2) as well as non-CO2 radiative forcing from all aviation.
In all countries that remain signatories to the UNFCCC Paris Agreement, domestic aviation
falls under these States’ NDCs. International bunkers fall under the remit of the ICAO. As a
caveat, national aviation CO2 emissions are theoretically covered by climate policies, but this
does not necessarily mean they will be addressed in mitigation schemes. Military flight as
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well as private international flight would fall, at least partially, under Nationally Determined
Contributions (NDCs) under the Paris Agreement. However, in practice countries do not
report fuel use for these sectors. A large share of military aviation and private flight take place
in the USA, a country that also stands for more commercial air transport emissions than the
next ten major contributors combined (Figure 3), yet has rejected any formal responsibility for
emissions. Including domestic, military and private air travel, the overall emission gap from
aviation is considerably larger than currently anticipated (Healy 2017). It will continue to
grow if the aviation sector rebounds and resumes its pre-COVID growth trajectory, raising
urgent questions regarding climate governance for aviation.
With regard to the second major insight of this research, a major share of aviation emissions is
generated by a very small share of very high emitters who are geographically located in a few
countries. These frequent air travelers are very wealthy individuals, and the effect of market-
based measures on reducing their emissions is debatable, specifically in regard to industry
plans for mitigation. The international aviation industry’s Carbon Offsetting Scheme for
International Aviation (CORSIA) is designed to offset emissions from international
commercial aviation at a low cost, and hence unlikely to slow down fuel consumption and
emission growth (Warnecke et al. 2019). This is also true for the EU ETS for aviation
(Efthymiou and Papatheodorou 2019). None of the schemes addresses private flight. Given
the future cost of climate change (Tol 2018; DeFries et al. 2019), the absence of markets for
aviation’s negative environmental externalities represents a major subsidy to the most
affluent. As half of aviation’s (non-CO2) warming remains unaddressed, together with close to
one Gt CO2 per year under CORSIA’s carbon neutral growth proposition, the value of this
subsidy to global aviation is, at a minimum carbon cost of US$50 per ton (cf. Rockström et al.
2017), in the order of US$100 billion per year (at US$50 per ton of CO 2 multiplied by one Gt
CO2 and weighted by a factor two as a conservative approximation of non-CO2 effects).
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This highlights the need to scrutinize the sector, and in particular the super emitters, i.e. the
10% of the most frequent fliers emitting more than half of global CO2 emissions from
commercial air travel, as well as the users of private aircraft who cause emissions of up to
7,500 t CO2 per year. Adding air transport’s non-CO2 warming effects, super emitters may
contribute to global warming at a rate 225,000 times higher than the global poor (0.1 t CO2
per person per year). This calculation is based on emissions of 7,500 CO2 per year and an
approximation of a warming effect three times the rate of CO2. It does not include the
importance of multiple housing, the energy required by other transport modes such as
superyachts and helicopters (Harding 2019; Superyachts 2020), or the energy to produce and
the infrastructure to operate these. Notably, a future intensification of energy-use among the
very affluent may be triggered by emerging opportunities for space tourism (Spector et al.
2020).
Chancel and Piketty (2015) highlighted the carbon importance of the lifestyles of the most
affluent individuals in the USA, with an average annual income purchasing power parity of
€542,000 in 2013. These 3.16 million individuals - or 0.04% of the world populationwere
calculated to contribute to emissions exceeding 1 Gt CO2 (3.6% of the global total). As this
research shows, a significant share of these emissions is likely represented by transportation.
A key question is thus how continued growth in GDP and concentration of wealth will affect
emission growth. Notably, this is a distributional issue that is relevant for the wider population
of air travelers: As Banister (2018) highlights, the opportunity to fly does not change the share
of the population flying, rather than the intensity of flight activity among those already flying.
In the current policy domain, economic instruments have aimed for market efficiency, i.e.
least cost solutions delivered through the EU ETS (Maertens et al. 2019) or CORSIA
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(Scheelhaase et al. 2018; Warnecke et al. 2019). These are inappropriate for a sector in which
the distribution of air transport demand and associated emissions is more highly skewed than
in other areas of consumption. From a market-based viewpoint, a modest increase in the cost
of air travel will not affect business travelers (Falk and Hagsten 2019), who are causing
disproportionally high emissions. Yet, as the data presented in this paper suggests, halving the
flight activity of the percentile of the most frequent fliers would reduce emissions from
commercial passenger transport by more than 25%. These insights confirm the need to
develop more complex transition policies for aviation (Lyle 2018; Larsson et al. 2019).
Industry projections (Airbus 2019; Boeing 2019) as well as scenarios of GDP growth (World
Bank 2020b) and the low cost of fuel (Bloomberg 2020) support an expectation of continued
growth in global air transport, much of this in domestic markets (IATA 2019). The COVID-19
pandemic currently delays growth trajectories. To help global aviation to recover, IATA
(2020a) has asked for “immediate relief measures” including direct financial aid, loans, and
tax relief; in a situation in which an estimated US$100 billion in State aid have already been
allocated to airlines (Gössling 2020), adding to the carbon subsidy of US$100 billion per year
calculated in this paper. At the same time, IATA has called on ICAO to postpone CORSIA
(Euractiv 2020). These findings should raise a wide range of questions regarding the
economic foundations of air transport, the distribution of aviation’s cost and benefits, and the
efficiency of climate policies to resolve the sector’s interference with the climate system
(Gössling 2020).
Conclusions
This paper systematically reviewed air transport demand on global, regional, national and
individual scales. Results support two insights of key relevance for climate change, i.e. the
large share of overall emissions from aviation not covered by climate policies - notably in
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light of evidence that existing climate policies for aviation are inadequate -; as well as the
significant concentration of air transport demand among a small share of affluent frequent
fliers. Both highlight the lack of and need for aviation climate governance possibly at
national and regional scales to tackle emissions from aviation. The ongoing COVID-19
pandemic represents an opportunity to rethink aviation in terms of demand distributions, air
transport wants and needs (private aircraft, first class suites), as well as aviation’s growth
trajectory under recovery scenarios and the sector’s growing interference with mitigation
goals.
Results also underscore the need for further research to better understand a wide range of
interrelationships, such as the distribution of air transport demand under different allocational
principles, and on the basis of revenue passenger kilometers rather than trip numbers; general
interrelationships of GDP growth and wealth concentration with the energy intensity of air
transport demand; or the quantification of subsidies forwarded to air travelers in current
policy regimes. There is also a limited understanding of military aviation’s interference with
climate goals. These will provide important further input for air transport governance, i.e. the
design of transition policies that align the sector with low-carbon economy goals.
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... The considerable contribution of CO 2 emissions of aviation reached 1.034 Gt in 2019 ). This includes commercial passenger flights (71% of emissions), private passenger flights (4%), freight (17%), and military flights (8%) (Gössling and Humpe 2020). Domestic flights represent 39.6% of fuel and emissions, and international flights 60.4% (Gössling and Humpe 2020). ...
... This includes commercial passenger flights (71% of emissions), private passenger flights (4%), freight (17%), and military flights (8%) (Gössling and Humpe 2020). Domestic flights represent 39.6% of fuel and emissions, and international flights 60.4% (Gössling and Humpe 2020). Aviation's climate impact could actually be three times larger than measured by CO 2 emissions alone, due to the multiple effects of burning kerosene at high altitudes . ...
... Plans by airlines and their organizations such as IATA could be seen as wishful thinking (Beevor and Alexander 2022) given their reliance on "sustainable" fuels. Scientific literature quantifies in detail aviation's past and current impact Gössling and Humpe 2020) and makes projections about possible futures (Klöwer et al. 2021), without suggesting how net zero impact could be achieved. Country long-term climate plans, even well-written plans (Swiss Federal Council 2021), may simply suggest that climate-neutral fuels would solve the problem, without much further analysis. ...
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... However, aviation is a fast-growing high-energy sector coined by a great degree of unsustainability as it makes substantial contributions to anthropogenic climate change (Paddon, 2022). Despite a seemingly small global annual contribution of 2.4% CO 2 emissions (Klöwer et al., 2021), the current global share of CO 2 emissions from commercial flight activities is estimated at 5-8% and total emissions (from commercial aviation) are projected to triple by 2050 (Gössling & Humpe, 2020;Paddon, 2022). Klöwer et al. (2021) estimate that aviation has contributed roughly 4% to observed human-induced global warming to date. ...
... Klöwer et al. (2021) estimate that aviation has contributed roughly 4% to observed human-induced global warming to date. According to Gössling and Humpe (2020), while less than 5% of the world population is flying internationally, 1% of the world population accounts for about 50% of CO 2 emissions from commercial flights. Noticeably, throughout recent years, aviation has started to play an increasingly central role in the political and societal discourse regarding climate change and sustainability. ...
... (Haygood, 2021). GA is the smallest niche in aviation accounting for "only" 4% of the global aviation fuel use compared to military aviation (8%), commercial aviation (freight) (17%), and commercial aviation (passengers) (71%) as depicted in Figure 1 (Gössling & Humpe, 2020). Switzerland features one of the most densely populated airspaces in entire Europe featuring more than 1.1m flight movements in 2020 (24% less compared to pre-Covid19) of which 84% were GA flight movements, according to the Federal Statistical Office (FSO, 2021). ...
Thesis
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Whereas commercial aviation is attempting to achieve the reduction of its substantial carbon footprint, general aviation’s (GA) climate change contribution is negligibly small, which is why the sector is facing other sustainability challenges mainly entailing the operation of dated technology and aircraft, increasing regulatory constraints, rising costs, noise emissions, and popular discontent, as well as remaining the last mobility sector in the world to still use leaded fuels. Throughout recent years, there have been remarkable sustainability trends in GA as well as heightened efforts to improve its emissions profile (noise, pollutants, CO2) and environmental reputation, for instance by the increased use of electric aircraft, especially for private pilot training. From a sociotechnical perspective, this mixed-methods study highlights current sustainability challenges and trends in GA as well as potential pathways towards more sustainable GA and private pilot training. Eight in-depth semi-structured interviews with Swiss and international GA stakeholders were complemented with a bilingual representative quantitative online survey (N=427) among Swiss GA stakeholders, a comparative CO2 analysis showing the emissions advantages and feasibility limits of supplementing private pilot training with lessons using electric aircraft, as well as participant observation. The data show that most Swiss GA stakeholders have increased environmental awareness and are concerned about sustainability and the environment both, in flight and other activities. Although the majority advocates for sustainable development in GA there are not one but many challenges and obstacles to a more sustainable GA. The largest challenges are the abatement of noise emissions and the facilitation of the leaded aviation gasoline (AVGAS 100LL) phaseout. The most pertinent obstacles towards sustainable GA innovation are said to be bureaucracy, overregulation and reluctance in the civil aviation authorities, high costs, averseness to risk and innovation, as well as a trend of decline in GA activity due to continuous demographic change. No single sustainability pathway but rather a mix of immediate and long-term sustainability measures was identified. Despite its current limitations, electric aviation proves to be one of the most feasible pathways to sustainable private pilot training. For more sustainable GA, the use of more fuel-efficient planes and available unleaded fuels, propeller, and muffler retrofits, as well as is feasible short- and midterm measures. In the long run, electric and hybrid aviation as well as bio- and synfuels are likely to become attractive options for GA. The study shows the importance of sustainable development in GA and private pilot training, not because it will majorly contribute to climate change mitigation, but because it will ensure the improvement of its negative environmental reputation and societal acceptance, which will be vital to ensuring the survival of the GA sector.
... Between 1960 and 2018, the sector grew by a factor of 6.8 to an estimated total of 1034 Mt CO 2 (Lee et al., 2021). An estimated 75% of this fall on commercial passenger transport, including a 4% share of private aviation (Gössling & Humpe, 2020). Further growth is expected in the sector's post-COVID rebound and longer-term developments: Industry expects that aviation will double or even triple to 2050 (ICAO, 2020). ...
... Further growth is expected in the sector's post-COVID rebound and longer-term developments: Industry expects that aviation will double or even triple to 2050 (ICAO, 2020). Apart from its central role in emission growth, aviation is also of relevance in the context of responsibilities for mitigation, as only a small share of its emissions is covered by existing legal frameworks (Gössling & Humpe, 2020). Tourism is also poised to grow as an overall system. ...
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... This demonstrates the difficulties in persuading both developed-and developing-nations airlines to adhere to the same targets (FT, 2021). A study by Gössling and Humpe (2020) demonstrated that just 1% of the global population accounts for 50% of CO 2 from commercial aviation. Thus, in tackling the crisis, attention needs to be directed towards this group to pay for the cost of emissions. ...
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... Often this is compensated by recruiting new collaborators into the collaborations which are geographically more dispersed with less means to travel regularly to the experiments. At the same time, travel might become more sparsely available, given immense effort to reduce carbon emissions to limit climate change [4,5]. ...
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