Environmental effects of aviation

Aircraft engines produce gases, noise, and particulates from fossil fuel combustion, raising environmental concerns over their global effects and their effects on local air quality.^[2]Jet airliners contribute to climate change by emitting carbon dioxide (CO₂), the best understood greenhouse gas, and, with less scientific understanding, nitrogen oxides, contrails and particulates. Their radiative forcing is estimated at 1.3–1.4 that of CO₂ alone, excluding induced cirrus cloud with a very low level of scientific understanding. In 2018, global commercial operations generated 2.4% of all CO₂ emissions.^[3]

Between 1940 and 2018, aviation CO₂ emissions grew from 0.7% to 2.65% of all CO₂ emissions.^[1]

Jet airliners have become 70% more fuel efficient between 1967 and 2007, and CO₂ emissions per revenue ton-kilometer (RTK) in 2018 were 47% of those in 1990. In 2018, CO₂ emissions averaged 88 grams of CO₂ per revenue passenger per km. While the aviation industry is more fuel efficient, overall emissions have risen as the volume of air travel has increased. By 2020, aviation emissions were 70% higher than in 2005 and they could grow by 300% by 2050.^[4]

Aircraft noise pollution disrupts sleep, children's education and could increase cardiovascular risk. Airports can generate water pollution due to their extensive handling of jet fuel and deicing chemicals if not contained, contaminating nearby water bodies. Aviation activities emit ozone and ultrafine particles, both of which are health hazards. Piston engines used in general aviation burn Avgas, releasing toxic lead.

Aviation's environmental footprint can be reduced by better fuel economy in aircraft, or air traffic control and flight routes can be optimized to lower non-CO₂ effects on climate from NO
_x, particulates or contrails. Aviation biofuel, emissions trading and carbon offsetting, part of the ICAO's CORSIA, can lower CO₂ emissions. Aviation usage can be lowered by short-haul flight bans, train connections, personal choices and aviation taxation and subsidies. Fuel-powered aircraft may be replaced by hybrid electric aircraft and electric aircraft or by hydrogen-powered aircraft. Since 2021, the IATA members plan net-zero carbon emissions by 2050, followed by the ICAO in 2022.

Climate change

Factors

 

Radiative forcings from aviation emissions estimated in 2020^[1]

See also: radiative forcing

Airplanes emit gases (carbon dioxide, water vapor, nitrogen oxides or carbon monoxide − bonding with oxygen to become CO₂ upon release) and atmospheric particulates (incompletely burned hydrocarbons, sulfur oxides, black carbon), interacting among themselves and with the atmosphere.^[5] While the main greenhouse gas emission from powered aircraft is CO₂, jet airliners contribute to climate change in four ways as they fly in the tropopause:^[6]

Carbon dioxide (CO₂)

CO₂ emissions are the most significant and best understood contribution to climate change.^[7] The effects of CO₂ emissions are similar regardless of altitude. Airport ground vehicles, those used by passengers and staff to access airports, emissions generated by airport construction and aircraft manufacturing also contribute to the greenhouse gas emissions from the aviation industry.^[8]

Nitrogen oxides (NO
_x, nitric oxide and nitrogen dioxide)

In the tropopause, emissions of NO
_x favor ozone (O
₃) formation in the upper troposphere. At altitudes from 8 to 13 km (26,000 to 43,000 ft), NO
_x emissions result in greater concentrations of O
₃ than surface NO
_x emissions and these in turn have a greater global warming effect. The effect of O
₃ surface concentrations are regional and local, but it becomes well mixed globally at mid and upper tropospheric levels.^[9] NO
_x emissions also reduce ambient levels of methane, another greenhouse gas, resulting in a climate cooling effect, though not offsetting the O
₃ forming effect. Aircraft sulfur and water emissions in the stratosphere tend to deplete O
₃, partially offsetting the NO
_x-induced O
₃ increases, although these effects have not been quantified.^[10] Light aircraft and small commuter aircraft fly lower in the troposphere, not in the tropopause.

 

Contrails and cirrus clouds

Contrails and cirrus clouds

Fuel burning produces water vapor, which condenses at high altitude, under cold and humid conditions, into visible line clouds: condensation trails (contrails). They are thought to have a global warming effect, though less significant than CO₂ emissions.^[11] Contrails are uncommon from lower-altitude aircraft. Cirrus clouds can develop after the formation of persistent contrails and can have an additional global warming effect.^[12] Their global warming contribution is uncertain and estimating aviation's overall contribution often excludes cirrus cloud enhancement.^[7]

Particulates

Compared with other emissions, sulfate and soot particles have a smaller direct effect: sulfate particles have a cooling effect and reflect radiation, while soot has a warming effect and absorbs heat, while the clouds' properties and formation are influenced by particles.^[13] Contrails and cirrus clouds evolving from particles may have a greater radiative forcing effect than CO₂ emissions.^[14] As soot particles are large enough to serve as condensation nuclei, they are thought to cause the most contrail formation. Soot production may be decreased by reducing the aromatic compound of jet fuel.^[15][16][17]

In 1999, the IPCC estimated aviation's radiative forcing in 1992 to be 2.7 (2 to 4) times that of CO₂ alone − excluding the potential effect of cirrus cloud enhancement.^[6] This was updated for 2000, with aviation's radiative forcing estimated at 47.8 mW/m², 1.9 times the effect of CO₂ emissions alone, 25.3 mW/m².^[7]

In 2005, research by David S. Lee, et al., published in the scientific journal Atmospheric Environment estimated the cumulative radiative forcing effect of aviation at 55 mW/m², which is twice the 28 mW/m² radiative forcing effect of its CO₂ emissions alone, excluding induced cirrus cloud, with a very low level of scientific understanding.^[18] In 2012, research from Chalmers university estimated this weighting factor at 1.3–1.4 if aviation induced cirrus is not included, 1.7–1.8 if they are included (within a range of 1.3–2.9).^[19]

Uncertainties remain on the NO_x–O₃–CH₄ interactions, aviation-produced contrails formation, the effects of soot aerosols on cirrus clouds and measuring non-CO₂ radiative forcing.^[5]

In 2018, CO₂ represented 34.3 mW/m² of aviation's effective radiative forcing (ERF, on the surface), with a high confidence level (± 6 mW/m²), NO_x 17.5 mW/m² with a low confidence level (± 14) and contrail cirrus 57.4 mW/m², also with a low confidence level (± 40).^[1] All factors combined represented 43.5 mW/m² (1.27 that of CO₂ alone) excluding contrail cirrus and 101 mW/m² (±45) including them, 3.5% of the anthropogenic ERF of 2290 mW/m² (± 1100).^[1]

Volume

By 2018, airline traffic reached 4.3 billion passengers with 37.8 million departures, an average of 114 passengers per flight and 8.26 trillion RPKs, an average journey of 1,920 km (1,040 nmi), according to ICAO.^[20] The traffic was experiencing continuous growth, doubling every 15 years, despite external shocks − a 4.3% average yearly growth and Airbus forecasts expect the growth to continue.^[21] While the aviation industry is more fuel efficient, halving the amount of fuel burned per flight compared to 1990 through technological advancement and operations improvements, overall emissions have risen as the volume of air travel has increased.^[22] Between 1960 and 2018, RPKs increased from 109 to 8,269 billion.^[1]

In 1992, aircraft emissions represented 2% of all man-made CO₂ emissions, having accumulated a little more than 1% of the total man-made CO₂ increase over 50 years.^[10] By 2015, aviation accounted for 2.5% of global CO₂ emissions.^[23] In 2018, global commercial operations emitted 918 million tonnes (Mt) of CO₂, 2.4% of all CO₂ emissions: 747 Mt for passenger transport and 171 Mt for freight operations.^[3] Between 1960 and 2018, CO₂ emissions increased 6.8 times from 152 to 1,034 million tonnes per year.^[1] Emissions from flights rose by 32% between 2013 and 2018.^[24]

 

Aviation GHG emissions within the European Economic Area for the EU ETS, showing the top 10 emitters (2013–2019).^[25]

Between 1990 and 2006, greenhouse gas emissions from aviation increased by 87% in the European Union.^[26] In 2010, about 60% of aviation emissions came from international flights, which are outside the emission reduction targets of the Kyoto Protocol.^[27] International flights are not covered by the Paris Agreement, either, to avoid a patchwork of individual country regulations. That agreement was adopted by the International Civil Aviation Organization, however, capping airlines carbon emissions to the year 2020 level, while allowing airlines to buy carbon credits from other industries and projects.^[28]

In 1992, aircraft radiative forcing was estimated by the IPCC at 3.5% of the total man-made radiative forcing.^[29]

Per passenger

 

Between 1950 and 2018, efficiency per passenger grew from 0.4 to 8.2 RPK per kg of CO₂.^[1]

See also: fuel economy in aircraft

As it accounts for a large share of their costs, 28% by 2007, airlines have a strong incentive to lower their fuel consumption, reducing their environmental footprint.^[30] Jet airliners have become 70% more fuel efficient between 1967 and 2007.^[30] Jetliner fuel efficiency improves continuously, 40% of the improvement come from engines and 30% from airframes.^[31] Efficiency gains were larger early in the jet age than later, with a 55–67% gain from 1960 to 1980 and a 20–26% gain from 1980 to 2000.^[32]

The average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction of 1.3% with variable reduction rate.^[33] By 2018, CO₂ emissions per revenue ton-kilometer (RTK) were more than halved compared to 1990, at 47%.^[34] The aviation energy intensity went from 21.2 to 12.3 MJ/RTK between 2000 and 2019, a 42% reduction.^[35]

In 2018, CO₂ emissions totalled 747 million tonnes for passenger transport, for 8.5 trillion revenue passenger kilometres (RPK), giving an average of 88 gram CO₂ per RPK.^[3] The UK's Department for BEIS calculate a long-haul flight release 102g of CO₂ per passenger kilometre, and 254g of CO₂ equivalent, including non-CO₂ greenhouse gas emissions, water vapor etc.; for a domestic flight in Britain.^[24]

The ICAO targets a 2% efficiency improvement per year between 2013 and 2050, while the IATA targets 1.5% for 2009–2020 and to cut net CO₂ emissions in half by 2050 relative to 2005.^[35]

Evolution

In 1999, the IPCC estimated aviation's radiative forcing may represent 190 mW/m² or 5% of the total man-made radiative forcing in 2050, with the uncertainty ranging from 100 to 500 mW/m².^[36] If other industries achieve significant reductions in greenhouse gas emissions over time, aviation's share, as a proportion of the remaining emissions, could rise.

Alice Bows-Larkin estimated that the annual global CO₂ emissions budget would be entirely consumed by aviation emissions to keep the climate change temperature increase below 2 °C by mid-century.^[37] Given that growth projections indicate that aviation will generate 15% of global CO₂ emissions, even with the most advanced technology forecast, she estimated that to hold the risks of dangerous climate change to under 50% by 2050 would exceed the entire carbon budget in conventional scenarios.^[38]

In 2013, the National Center for Atmospheric Science at the University of Reading forecast that increasing CO₂ levels will result in a significant increase in in-flight turbulence experienced by transatlantic airline flights by the middle of the 21st century.^[39]

Aviation CO₂ emissions grow despite efficiency innovations to aircraft, powerplants and flight operations.^[40][41] Air travel continue to grow.^[42][43]

In 2015, the Center for Biological Diversity estimated that aircraft could generate 43 Gt of carbon dioxide emissions through 2050, consuming almost 5% of the remaining global carbon budget. Without regulation, global aviation emissions may triple by mid-century and could emit more than 3 Gt of carbon annually under a high-growth, business-as-usual scenario. Many countries have pledged emissions reductions for the Paris Agreement, but the sum of these efforts and pledges remains insufficient and not addressing airplane pollution would be a failure despite technological and operational advancements.^[44]

The International Energy Agency projects aviation share of global CO₂ emissions may grow from 2.5% in 2019 to 3.5% by 2030.^[45]

By 2020, global international aviation emissions were around 70% higher than in 2005 and the ICAO forecasts they could grow by over further 300% by 2050 in the absence of additional measures.^[4]

By 2050, aviation's negative effects on climate could be decreased by a 2% increase in fuel efficiency and a decrease in NO_x emissions, due to advanced aircraft technologies, operational procedures and renewable alternative fuels decreasing radiative forcing due to sulfate aerosol and black carbon.^[5]

Noise

Main article: Aircraft noise pollution

 

Noise map of Berlin Tegel Airport

Air traffic causes aircraft noise, which disrupts sleep, adversely affects children's school performance and could increase cardiovascular risk for airport neighbours.^[46] Sleep disruption can be reduced by banning or restricting flying at night, but disturbance progressively decreases and legislation differs across countries.^[46]

The ICAO Chapter 14 noise standard applies for aeroplanes submitted for certification after 31 December 2017, and after 31 December 2020 for aircraft below 55 t (121,000 lb), 7 EPNdB (cumulative) quieter than Chapter4.^[47] The FAA Stage 5 noise standards are equivalent.^[48] Higher bypass ratio engines produce less noise. The PW1000G is presented as 75% quieter than previous engines.^[49] Serrated edges or 'chevrons' on the back of the nacelle reduce noise.^[50]

A Continuous Descent Approach (CDA) is quieter as less noise is produced while the engines are near idle power.^[51] CDA can reduce noise on the ground by ~1–5 dB per flight.^[52]

Water pollution

 

Excess aircraft deicing fluid may contaminate nearby water bodies

Airports can generate significant water pollution due to their extensive use and handling of jet fuel, lubricants and other chemicals. Chemical spills can be mitigated or prevented by spill containment structures and clean-up equipment such as vacuum trucks, portable berms and absorbents.^[53]

Deicing fluids used in cold weather can pollute water, as most of them fall to the ground and surface runoff can carry them to nearby streams, rivers or coastal waters.^[54]: 101 Deicing fluids are based on ethylene glycol or propylene glycol.^[54]: 4 Airports use pavement deicers on paved surfaces including runways and taxiways, which may contain potassium acetate, glycol compounds, sodium acetate, urea or other chemicals.^[54]: 42

During degradation in surface waters, ethylene and propylene glycol exert high levels of biochemical oxygen demand, consuming oxygen needed by aquatic life. Microbial populations decomposing propylene glycol consume large quantities of dissolved oxygen (DO) in the water column.^{[55]: 2–23} Fish, macroinvertebrates and other aquatic organisms need sufficient dissolved oxygen levels in surface waters. Low oxygen concentrations reduce usable aquatic habitat because organisms die if they cannot move to areas with sufficient oxygen levels. Bottom feeder populations can be reduced or eliminated by low DO levels, changing a community's species profile or altering critical food-web interactions.^{[55]: 2–30}

Glycol-based deicing fluids are toxic to humans and other mammals.^[56][57] Research into non-toxic alternative deicing fluids is ongoing.^[56]

See also: Aircraft deicing fluid

Air pollution

See also: Air pollution and Avgas § environmental regulation

Aviation is the main human source of ozone, a respiratory health hazard, causing an estimated 6,800 premature deaths per year.^[58]

Aircraft engines emit ultrafine particles (UFPs) in and near airports, as does ground support equipment. During takeoff, 3 to 50 × 10¹⁵ particles were measured per kg of fuel burned,^[59] while significant differences are observed depending on the engine.^[60] Other estimates include 4 to 200 × 10¹⁵ particles for 0.1–0.7 gram,^[61] or 14 to 710 × 10¹⁵ particles,^[62] or 0.1–10 × 10¹⁵ black carbon particles for 0.046–0.941 g.^[63]

In the United States, 167,000 piston aircraft engines, representing three-quarters of private airplanes, burn Avgas, releasing lead into the air.^[64] The Environmental Protection Agency estimated this released 34,000 tons of lead into the atmosphere between 1970 and 2007.^[65] The Federal Aviation Administration recognizes inhaled or ingested lead leads to adverse effects on the nervous system, red blood cells, and cardiovascular and immune systems. Lead exposure in infants and young children may contribute to behavioral and learning problems and lower IQ.^[66]

Mitigation

See also: Climate change mitigation

Aviation's environmental footprint can be mitigated by reducing air travel, optimizing flight routes, capping emissions, restricting short-distance flights, increasing taxation and decreasing subsidies to the aviation industry. Technological innovation could also mitigate damage to the environment and climate, for example, through the development of electric aircraft, biofuels, and increased fuel efficiency.

In 2016, the International Civil Aviation Organization (ICAO) committed to improve aviation fuel efficiency by 2% per year and to keeping the carbon emissions from 2020 onwards at the same level as those from 2010.^[67] To achieve these goals, multiple measures were identified: more fuel-efficient aircraft technology; development and deployment of sustainable aviation fuels (SAFs); improved air traffic management (ATM); market-based measures like emission trading, levies, and carbon offsetting,^[67] the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).^[68]

In December 2020, the UK Climate Change Committee said that: "Mitigation options considered include demand management, improvements in aircraft efficiency (including use of hybrid electric aircraft), and use of sustainable aviation fuels (biofuels, biowaste to jet and synthetic jet fuels) to displace fossil jet fuel."^[69]

In February 2021, Europe's aviation sector unveiled its Destination 2050 sustainability initiative towards zero CO₂ emissions by 2050:

• aircraft technology improvements for 37% emission reductions;
• SAFs for 34%;
• economic measures for 8%;
• ATM and operations improvements for 6%;

while air traffic should grow by 1.4% per year between 2018 and 2050.^[70] The initiative is led by ACI Europe, ASD Europe, A4E, CANSO and ERA.^[70] This would apply to flights within and departing the European single market and the UK.^[70]

In October 2021, the IATA committed to net-zero carbon emissions by 2050.^[71] In 2022, the ICAO agreed to support a net-zero carbon emission target for 2050.^[72]

The aviation sector could be decarbonized by 2050 with moderate demand growth, continuous efficiency improvements, new short-haul engines, higher SAF production and CO₂ removal to compensate for non-CO₂ forcing.^[73] With constant air transport demand and aircraft efficiency, decarbonizing aviation would require nearly five times the 2019 worldwide biofuel production, competing with other hard-to-decarbonize sectors, and 0.2 to 3.4 Gt of CO₂ removal to compensate for non-CO₂ forcing.^[73] Carbon offsets would be preferred if carbon credits are less expensive than SAFs, but they may be unreliable, while specific routing could avoid contrails.^[73] As of 2023, fuel represents 20-30% of the airlines' operating costs, while SAF is 2–4 times more expensive than fossil jet fuel.^[73] Projected cost decreases of green hydrogen and carbon capture could make synthetic fuels more affordable, and lower feedstock costs and higher conversion efficiencies would help FT and HEFA biofuels.^[73] Policy incentives like cleaner aviation fuel tax credits and low-carbon fuel standards could induce improvements, and carbon pricing could render SAFs more competitive, accelerating their deployment and reducing their costs through learning and economies of scale.^[73]

According to a 2023 Royal Society study, reaching net zero would need replacing fossil aviation fuel with a low or zero carbon energy source, as battery technologies are unlikely to give enough specific energy.^[74]Biofuels can be introduced quickly and with little aircraft modification, but are restricted by scale and feedstock availability, and few are low-carbon.^[74] Producing enough renewable electricity to produce green hydrogen would be a costly challenge and would need substantial aircraft and infrastructure modification.^[74]Synthetic fuels would need with little aircraft modification, but necessitates green hydrogen feedstock and large scale direct CO₂ air capture at high costs.^[74] Low-carbon Ammonia would also need costly green hydrogen at scale, and would need substantial aircraft and infrastructure modifications.^[74]

In its Sixth Assessment Report, the IPCC notes that sustainable biofuels, low-emissions hydrogen, and derivatives (including ammonia and synthetic fuels) can support mitigation of CO₂ emissions but some hard-to-abate residual GHG emissions remain and would need to be counterbalanced by deployment of carbon dioxide removal methods.^[75] On 29 March 2003, during a Senate hearing, hydrogen propulsion proponents like ZeroAvia or Universal Hydrogen bemoaned the incumbents like GE Aerospace or Boeing were supporting sustainable aviation fuel (SAF) because it does not require major changes to existing infrastructure.^[76]

An April 2023 report of the Sustainable Aero Lab estimate current in-production aircraft will be the vast majority of the 2050 fleet as electric aircraft will not have enough range and hydrogen aircraft will not be available soon enough : the main decarbonisation drivers will be SAF ; replacing regional jets with turboprop aircraft ; and incentives to replace older jets with new generation ones.^[77]

Technology improvements

Electric aircraft

 

The Velis Electro was the first type certificated electric aircraft on 10 June 2020.

Main articles: Electric aircraft and Hybrid electric aircraft

Electric aircraft operations do not produce any emissions and electricity can be generated by renewable energy. Lithium-ion batteries including packaging and accessories gives a 160 Wh/kg energy density while aviation fuel gives 12,500 Wh/kg.^[78] As electric machines and converters are more efficient, their shaft power available is closer to 145 Wh/kg of battery while a gas turbine gives 6,545 Wh/kg of fuel: a 45:1 ratio.^[79] For Collins Aerospace, this 1:50 ratio forbids electric propulsion for long-range aircraft.^[80] By November 2019, the German Aerospace Center estimated large electric planes could be available by 2040.^[81] Large, long-haul aircraft are unlikely to become electric before 2070 or within the 21st century, whilst smaller aircraft can be electrified.^[82] As of May 2020, the largest electric airplane was a modified Cessna 208B Caravan.

For the UK's Committee on Climate Change (CCC), huge technology shifts are uncertain, but consultancy Roland Berger points to 80 new electric aircraft programmes in 2016–2018, all-electric for the smaller two-thirds and hybrid for larger aircraft, with forecast commercial service dates in the early 2030s on short-haul routes like London to Paris, with all-electric aircraft not expected before 2045.^[83] Berger predicts a 24% CO₂ share for aviation by 2050 if fuel efficiency improves by 1% per year and if there are no electric or hybrid aircraft, dropping to 3–6% if 10-year-old aircraft are replaced by electric or hybrid aircraft due to regulatory constraints, starting in 2030, to reach 70% of the 2050 fleet.^[83] This would greatly reduce the value of the existing fleet of aircraft, however.^[83] Limits to the supply of battery cells could hamper their aviation adoption, as they compete with other industries like electric vehicles. Lithium-ion batteries have proven fragile and fire-prone and their capacity deteriorates with age. However, alternatives are being pursued, such as sodium-ion batteries.^[83]

Hydrogen-powered aircraft

Main article: Hydrogen-powered aircraft

In 2020, Airbus unveiled liquid-hydrogen-powered aircraft concepts as zero-emissions airliners, poised for 2035.^[84] Aviation, like industrial processes that cannot be electrified, could use primarily Hydrogen-based fuel.^[85]

A 2020 study by the EU Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings found that hydrogen could power aircraft by 2035 for short-range aircraft.^[86] A short-range aircraft (< 2,000 km, 1,100 nmi) with hybrid Fuel cell/Turbines could reduce climate impact by 70-80% for a 20-30% additional cost, a medium-range airliner with H₂ turbines could have a 50-60% reduced climate impact for a 30-40% overcost, and a long-range aircraft (> 7,000 km, 3,800 nmi) also with H₂ turbines could reduce climate impact by 40-50% for a 40-50% additional cost.^[86] Research and development would be required, in aircraft technology and into hydrogen infrastructure, regulations and certification standards.^[86]

Sustainable aviation fuels (SAF)

Main article: Aviation biofuel

 

Refueling an Airbus A320 with biofuel in 2011

An aviation biofuel (also known as bio-jet fuel^[87] or bio-aviation fuel (BAF);^[88]) is a biofuel used to power aircraft and is said to be a sustainable aviation fuel (SAF). The International Air Transport Association (IATA) considers it a key element in reducing the carbon footprint within the environmental impact of aviation.^[89] Aviation biofuel could help decarbonize medium and long-haul air travel generating most emissions, and could extend the life of older aircraft types by lowering their carbon footprint. The jargon synthetic paraffinic kerosene (SPK) refers to any non-petroleum-based fuel designed to replace kerosene jet fuel, which is often, but not always, made from biomass.

Biofuels are biomass-derived fuels from plants, animals, or waste; depending on which type of biomass is used, they could lower CO₂ emissions by 20–98% compared to conventional jet fuel.^[90] The first test flight using blended biofuel was in 2008, and in 2011 blended fuels with 50% biofuels were allowed on commercial flights. In 2019, the IATA was aiming for a 2% penetration by 2025.

Aviation biofuel can be produced from plant or animal sources such as Jatropha, algae, tallows, waste oils, palm oil, Babassu, and Camelina (bio-SPK); from solid biomass using pyrolysis processed with a Fischer–Tropsch process (FT-SPK); with an alcohol-to-jet (ATJ) process from waste fermentation; or from synthetic biology through a solar reactor. Small piston engines can be modified to burn ethanol.

Sustainable biofuels do not compete with food crops, prime agricultural land, natural forest or fresh water.^{[further explanation needed]} They are an alternative to electrofuels.^[91] Sustainable aviation fuel is certified as being sustainable by a third-party organisation.

Electrofuels (e-fuels)

The Potsdam Institute for Climate Impact Research reported a €800–1,200 mitigation cost per ton of CO₂ for hydrogen-based e-fuels.^[92] Those could be reduced to €20–270 per ton of CO₂ in 2050, but maybe not early enough to replace fossil fuels.^[92]Climate policies could bear the risk of e-fuel uncertain availability, and Hydrogen and e-fuels may be prioritised when direct electrification is inaccessible.^[92]

Reducing air travel

Main article: Air travel demand reduction

 

UK air travel by income quintile through time^[93]

 

Global distribution of aviation fuel use^[94]

Aviation is one of three sectors identified in a study where "demand-side options" can have a large effect in "reaching SDS levels".^[95] According to a study, the attainment of the 1.5–2°C global temperature goal necessitates substantial demand reductions in the critical sectors of aviation, shipping, road freight, and industry, should large-scale negative emissions not be realized.^[96] According to the IMAGE model used to project scenarios aimed at limiting global temperature increases to 1.5°C and 2°C, it is suggested that achieving deep decarbonization within the aviation sector within the specified timeframe is contingent upon a reduction in air travel in certain markets.^[96] The decreases in carbon intensity of aviation energy in net-zero scenarios "are heavily dependent on projected changes in aviation demand and energy intensity".^[97] The significant challenges of sustainable aviation fuel expansion, including food security, local community impacts, and land use issues, underscore the importance of simultaneous demand reduction efforts.^[97] For instance, according to a report by the Royal Society, to produce enough biofuel to supply the UK's aviation industry would require using half of Britain's farming land which would put major pressures on food supplies.^[98][99]

Tourism is projected to generate up to 40% of total global CO₂ emissions by 2050.^[100] Of climate change mitigation consumption options investigated by a review, the consumption options with "the highest mitigation potential advocate reduction in car and air travel".^[101] A study projected a potential reduction of "transport direct CO₂ emissions by around 50% in the end of the century compared to the baseline" via combined behavioral factors.^[102]

Measures

 

The Taiwan High Speed Rail in 2007

According to the IPCC Sixth Assessment Report, "the greatest Avoid potential" in demand-side mitigation, which consists of Avoid-Shift-Improve (ASI) options, "comes from reducing long-haul aviation and providing short-distance low-carbon urban infrastructure".^[103] It lists the following related mobility measures:^[103]

• Avoid: integrate transport & land use planning, tele-working, fewer long-haul flights, local holidays^[103]
• Shift: from air travel to high-speed rail^[103]

It found that socio-cultural factors promoting a preference for train travel over long-haul flights have the potential to reduce aviation greenhouse gas emissions by 10% to 40% by 2050.^[103]

The ICCT estimates that 3% of the global population take regular flights.^[24] Stefan Gössling of the Western Norway Research Institute estimates 1% of the world population emits half of commercial aviation's CO₂, while close to 90% does not fly in a given year.^[104]

 

Per capita emissions from domestic and international flights

In early 2022, the European Investment Bank published the results of its 2021–2022 Climate Survey, showing that 52% of Europeans under 30, 37% of people between 30 and 64 and 25% for people aged 65 and above plan to travel by air for their summer holidays in 2022; and 27% of those under 30, 17% for people aged 30–64 and 12% for people aged 65 and above plan to travel by air to a faraway destination.^[105]

Short-haul flight ban

Main article: Short-haul flight ban

A short-haul flight ban is a prohibition imposed by governments on airlines to establish and maintain a flight connection over a certain distance, or by organisations or companies on their employees for business travel using existing flight connections over a certain distance, in order to mitigate the environmental impact of aviation (most notably to reduce anthropogenic greenhouse gas emissions which is the leading cause of climate change). In the 21st century, several governments, organisations and companies have imposed restrictions and even prohibitions on short-haul flights, stimulating or pressuring travellers to opt for more environmentally friendly means of transportation, especially trains.^[106]

Flight shame

In Sweden the concept of "flight shame" or "flygskam" has been cited as a cause of falling air travel.^[107] Swedish rail company SJ AB reports that twice as many Swedish people chose to travel by train instead of by air in summer 2019 compared with the previous year.^[108] Swedish airports operator Swedavia reported 4% fewer passengers across its 10 airports in 2019 compared to the previous year: a 9% drop for domestic passengers and 2% for international passengers.^[109]

Personal allowances

Climate change mitigation can be backed by Personal carbon allowances (PCAs) where all adults receive "an equal, tradable carbon allowance that reduces over time in line with national targets."^{[110][111][112][excessive citations]} Everyone would have a share of allowed carbon emissions and would need to trade further emissions allowances.^{[113][importance?]} An alternative would be rationing everyone's flights: an "individual cap on air travel, that people can trade with each other".^[114]

Economic measures

Emissions trading

 

CO₂ price in the European Union Emission Trading Scheme

ICAO has endorsed emissions trading to reduce aviation CO₂ emission, guidelines were to be presented to the 2007 ICAO Assembly.^[115] Within the European Union, the European Commission has included aviation in the European Union Emissions Trading Scheme operated since 2012, capping airline emissions, providing incentives to lower emissions through more efficient technology or to buy carbon credits from other companies.^[116][117] The Centre for Aviation, Transport and Environment at Manchester Metropolitan University estimates the only way to lower emissions is to put a price on carbon and to use market-based measures like the EU ETS.^[118]

Taxation and subsidies

Main article: Aviation taxation and subsidies

Financial measures can discourage airline passengers and promote other transportation modes and motivates airlines to improve fuel efficiency. Aviation taxation include:

• air passenger taxes, paid by passengers for environmental reasons, may be variable by distance and include domestic flights;
• departure taxes, paid by passengers leaving the country, sometimes also applies outside aviation;
• jet fuel taxes, paid by airlines for the consumed jet fuel. Jet fuel taxation is applied in the United States, but banned in the European Union.

Consumer behavior can be influenced by cutting subsidies for unsustainable aviation and subsidising the development of sustainable alternatives. By September–October 2019, a carbon tax on flights would be supported by 72% of the EU citizens, in a poll conducted for the European Investment Bank.^[119]

Aviation taxation could reflect all its external costs and could be included in an emissions trading scheme.^[120] International aviation emissions escaped international regulation until the ICAO triennial conference in 2016 agreed on the CORSIA offset scheme.^[121] Due to low or nonexistent taxes on aviation fuel, air travel has a competitive advantage over other transportation modes.^[122][123]

Carbon offsetting

 

Money generated by carbon offsets from airlines often go to fund green-energy projects such as wind farms.

A carbon offset is a means of compensating aviation emissions by saving enough carbon or absorbing carbon back into plants through photosynthesis (for example, by planting trees through reforestation or afforestation) to balance the carbon emitted by a particular action.

However, carbon credits permanence and additionality can be questionable.^[73] More than 90% of rainforest offset credits certified by Verra's Verified Carbon Standard may not represent genuine carbon reductions.^[124]

Consumer option

Some airlines offer carbon offsets to passengers to cover the emissions created by their flight, invested in green technology such as renewable energy and research into future technology. Airlines offering carbon offsets include British Airways,^[125] Continental Airlines,^[126][127] easyJet,;^[128] and also Air Canada, Air New Zealand, Delta Air Lines, Emirates Airlines, Gulf Air, Jetstar, Lufthansa, Qantas, United Airlines and Virgin Australia.^[129] Consumers can also purchase offsets on the individual market. There are certification standards for these,^[130] including the Gold Standard^[131] and the Green-e.^[132]

National carbon budgets

In UK, transportation replaced power generation as the largest emissions source. This includes aviation's 4% contribution. This is expected to expand until 2050 and passenger demand may need to be reduced.^[83] For the UK Committee on Climate Change (CCC), the UK target of an 80% reduction from 1990 to 2050 was still achievable from 2019, but the committee suggests that the Paris Agreement should tighten its emission targets.^[83] Their position is that emissions in problematic sectors, like aviation, should be offset by greenhouse gas removal, carbon capture and storage and reforestation.^[83] The UK will include international aviation and shipping in their carbon budgets and hopes other countries will too.^[133]

See also: § Personal carbon allowances

Airline offsets

Some airlines have been carbon-neutral like Costa Rican Nature Air,^[134] or claim to be, like Canadian Harbour Air Seaplanes.^[135] Long-haul low-cost venture Fly POP aims to be carbon neutral.^[136]

In 2019, Air France announced it would offset CO₂ emissions on its 450 daily domestic flights, that carry 57,000 passengers, from January 2020, through certified projects. The company will also offer its customers the option to voluntarily compensate for all their flights and aims to reduce its emissions by 50% per pax/km by 2030, compared to 2005.^[137]

Starting in November 2019, UK budget carrier EasyJet decided to offset carbon emissions for all its flights, through investments in atmospheric carbon reduction projects. It claims to be the first major operator to be carbon neutral, at a cost of £25 million for its 2019–20 financial year. Its CO₂ emissions were 77 g per passenger in its 2018–19 financial year, down from 78.4 g the previous year.^[138]

From January 2020, British Airways began offsetting its 75 daily domestic flights emissions through carbon-reduction project investments. The airline seeks to become carbon neutral by 2050 with fuel-efficient aircraft, sustainable fuels and operational changes. Passengers flying overseas can offset their flights for £1 to Madrid in economy or £15 to New York in business-class.^[139]

US low-cost carrier JetBlue planned to use offsets for its emissions from domestic flights starting in July 2020, the first major US airline to do so. It also plans to use sustainable aviation fuel made from waste by Finnish refiner Neste starting in mid-2020.^[140] In August 2020, JetBlue became entirely carbon-neutral for its U.S. domestic flights, using efficiency improvements and carbon offsets.^[141] Delta Air Lines pledged to do the same within ten years.^[142]

To become carbon neutral by 2050, United Airlines invests to build in the US the largest carbon capture and storage facility through the company 1PointFive, jointly owned by Occidental Petroleum and Rusheen Capital Management, with Carbon Engineering technology, aiming for nearly 10% offsets.^[143]

Air traffic management improvements

 

Improved Air Traffic Control would allow more direct routes

An improved air traffic management system, with more direct routes than suboptimal air corridors and optimized cruising altitudes, would allow airlines to reduce their emissions by up to 18%.^[30] In the European Union, a Single European Sky has been proposed since 1999 to avoid overlapping airspace restrictions between EU countries and to reduce emissions.^[144] By 2007, 12 million tons of CO₂ emissions per year were caused by the lack of a Single European Sky.^[30] As of September 2020, the Single European Sky has still not been completely achieved, costing 6 billion euros in delays and causing 11.6 million tonnes of excess CO₂ emissions.^[145]

Operations improvements

 

Economic cost and climate influence relation for transatlantic traffic

Non-CO₂ emissions

Besides carbon dioxide, aviation produces nitrogen oxides (NO
_x), particulates, unburned hydrocarbons (UHC) and contrails. Flight routes can be optimized: modelling CO₂, H
₂O and NO
_x effects of transatlantic flights in winter shows westbound flights climate forcing can be lowered by up to 60% and ~25% for jet stream-following eastbound flights, costing 10–15% more due to longer distances and lower altitudes consuming more fuel, but 0.5% costs increase can reduce climate forcing by up to 25%.^[146] A 2000 feet (~600 m) lower cruise altitude than the optimal altitude has a 21% lower radiative forcing, while a 2000 feet higher cruise altitude 9% higher radiative forcing.^[147]

Nitrogen oxides (NO
_x)

As designers work to reduce NO
_x emissions from jet engines, they fell by over 40% between 1997 and 2003.^[50] Cruising at a 2,000 ft (610 m) lower altitude could reduce NO
_x-caused radiative forcing from 5 mW/m² to ~3 mW/m².^[148]

Particulates

Modern engines are designed so that no smoke is produced at any point in the flight while particulates and smoke were a problem with early jet engines at high power settings.^[50]

Unburned hydrocarbons (UHC)

Produced by incomplete combustion, more unburned hydrocarbons are produced with low compressor pressures and/or relatively low combustor temperatures, they have been eliminated in modern jet engines through improved design and technology, like particulates.^[50]

Contrails

Contrail formation would be reduced by lowering the cruise altitude with slightly increased flight times, but this would be limited by airspace capacity, especially in Europe and North America, and increased fuel burn due to lower efficiency at lower altitudes, increasing CO₂ emissions by 4%.^[149] Contrail radiative forcing could be minimized by schedules: night flights cause 60–80% of the forcing for only 25% of the air traffic, while winter flights contribute half of the forcing for only 22% of the air traffic.^[150] As 2% of flights are responsible for 80% of contrail radiative forcing, changing a flight altitude by 2,000 ft (610 m) to avoid high humidity for 1.7% of flights would reduce contrail formation by 59%.^[151]

See also

• Aviation Environment Federation, UK concerned organization
• Construction of solar photovoltaic arrays on airport roofs to offset their electricity use
• Energy efficiency in transport
• European Green Deal
• Environmental effects of aviation in the United Kingdom
• Environmental effects of transport
• Flying Matters, UK former pro-aviation coalition
• Health hazards of air travel
• Individual action on climate change
• Plane Mad, Irish concerned action group

References

1. D. S. Lee; et al. (2021), "The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018", Atmospheric Environment, 244: 117834, Bibcode:2021AtmEn.24417834L, doi:10.1016/j.atmosenv.2020.117834, PMC 7468346, PMID 32895604
2. "Aircraft Engine Emissions". International Civil Aviation Organization.
3. Brandon Graver; Kevin Zhang; Dan Rutherford (September 2019). "CO₂ emissions from commercial aviation, 2018" (PDF). International Council on Clean Transportation.
4. "Reducing emissions from aviation". Climate Action. European Commission. 23 November 2016.
5. Brasseur, Guy P.; Gupta, Mohan; et al. (April 2016). "Impact of aviation on climate". Bulletin of the American Meteorological Society. FAA's ACCRI Phase II. 97 (4): 561–583. doi:10.1175/BAMS-D-13-00089.1. hdl:1721.1/109270.
6. Joyce E. Penner; et al. (1999). Aviation and the Global Atmosphere. IPCC. Bibcode:1999aga..book.....P.
7. Sausen, Robert; et al. (August 2005). "Aviation radiative forcing in 2000: an update on IPCC" (PDF). Meteorologische Zeitschrift. Gebrüder Borntraeger. 14 (4): 555–561. doi:10.1127/0941-2948/2005/0049.
8. Horvath A, Chester M (1 December 2008), Environmental Life-cycle Assessment of Passenger Transportation An Energy, Greenhouse Gas and Criteria Pollutant Inventory of Rail and Air Transportation, University of California Transportation Center, UC Berkeley
9. Derwent, Richard; Collins, William; et al. (1 October 2002), "Global Ozone Concentrations and Regional Air Quality", Environmental Science & Technology, 36 (19): 379A–382A, doi:10.1021/es022419q, PMID 12380066
10. Joyce E. Penner; et al. (1999). "What are the Current and Future Impacts of Subsonic Aviation on Radiative Forcing and UV Radiation?". Aviation and the Global Atmosphere. IPCC. Bibcode:1999aga..book.....P.
11. (PDF), Climate Change 2007: The Physical Science Basis, Intergovernmental Panel on Climate Change, February 2007, archived from the original (PDF) on 14 November 2007
12. Le Page, Michael (27 June 2019). "It turns out planes are even worse for the climate than we thought". New Scientist.
13. "Questions & Answers on Aviation & Climate Change". Press corner. European Commission. 27 September 2005.
14. Kärcher, B. (2016). "The importance of contrail ice formation for mitigating the climate impact of aviation". Journal of Geophysical Research: Atmospheres. 121 (7): 3497–3505. Bibcode:2016JGRD..121.3497K. doi:10.1002/2015JD024696.
15. Corporan, E.; et al. (2007). "Emissions characteristics of a turbine engine and research combustor burning a Fischer–Tropsch jet fuel". Energy & Fuels. 21 (5): 2615–2626. doi:10.1021/ef070015j.
16. Lobo, P.; Hagen, D.E.; Whitefield, P.D. (2011). "Comparison of PM emissions from a commercial jet engine burning conventional, biomass, and Fischer–Tropsch fuels". Environmental Science & Technology. 45 (24): 10744–10749. Bibcode:2011EnST...4510744L. doi:10.1021/es201902e. PMID 22043875.
17. Moore, R.H.; et al. (2017). "Biofuel blending reduces particle emissions from aircraft engines at cruise conditions" (PDF). Nature. 543 (7645): 411–415. Bibcode:2017Natur.543..411M. doi:10.1038/nature21420. PMC 8025803. PMID 28300096.
18. David S. Lee; et al. (July 2009). "Aviation and global climate change in the 21st century" (PDF). Atmospheric Environment. 43 (22–23): 3520–3537. Bibcode:2009AtmEn..43.3520L. doi:10.1016/j.atmosenv.2009.04.024. PMC 7185790. PMID 32362760.
19. Azar, Christian; Johansson, Daniel J. A. (April 2012). "Valuing the non-CO₂ climate impacts of aviation". Climatic Change. 111 (3–4): 559–579. Bibcode:2012ClCh..111..559A. doi:10.1007/s10584-011-0168-8.
20. "The World of Air Transport in 2018". ICAO.
21. "Global Market Forecast" (PDF). Airbus. 2019.
22. "Aviation industry reducing its environmental footprint". Aviation Benefits.
23. CO₂ emissions from fuel combustion: detailed estimates, IEA, 2014 and "International Energy Statistics", www.eia.gov, EIA, 2015 {{citation}}: Missing or empty |url= (help) via Schäfer, Andreas W.; Evans, Antony D.; Reynolds, Tom G.; Dray, Lynnette (2016). "Costs of mitigating CO₂ emissions from passenger aircraft" (PDF). Nature Climate Change. 6 (4): 412–417. Bibcode:2016NatCC...6..412S. doi:10.1038/nclimate2865.
24. Timperley, Jocelyn (19 February 2020). "Should we give up flying for the sake of the climate?". BBC.
25. EEA Report No 19/2020, EEA, 2021, p. 24
26. "Climate change: Commission proposes bringing air transport into EU Emissions Trading Scheme" (Press release). EU Commission. 20 December 2006.
27. Owen, Bethan; Lee, David S.; Lim, Ling (2010). "Flying into the Future: Aviation Emissions Scenarios to 2050". Environmental Science & Technology. 44 (7): 2255–2260. Bibcode:2010EnST...44.2255O. doi:10.1021/es902530z. PMID 20225840.
28. Lowy, Joan (7 October 2016). "UN agreement reached on aircraft climate-change emissions". Associated Press.
29. Joyce E. Penner; et al. (1999). "Summary for Policymakers". What are the Overall Climate Effects of Subsonic Aircraft?. IPCC.
30. Giovanni Bisignani, CEO of the IATA (20 September 2007). "Opinion: Aviation and global warming". The New York Times.
31. Joyce E. Penner; et al. (1999), "9.2.2. Developments in Technology", Special Report on Aviation and the Global Atmosphere, IPCC
32. Peeters, P. M.; et al. (November 2005). "Fuel efficiency of commercial aircraft" (PDF). Netherlands National Aerospace Laboratory. An overview of historical and future trends
33. Anastasia Kharina; Daniel Rutherford (August 2015), Fuel efficiency trends for new commercial jet aircraft: 1960 to 2014 (PDF), ICCT
34. Fuel Fact Sheet (PDF), IATA, December 2019
35. Aviation report, International Energy Agency, 2020
36. Joyce E. Penner; et al. (1999). "Potential Climate Change from Aviation". The Role of Aircraft in Climate Change-Evaluation of Sample Scenarios. IPCC.
37. Bows, A.; et al. (2009), "5", Aviation and Climate Change: Lessons for European Policy, Routledge, p. 146
38. Alice Bows-Larkin (August 2010), "Aviation and climate change: confronting the challenge", Aeronautical Journal, 114 (1158): 459–468, doi:10.1017/S000192400000395X, S2CID 233361436
39. Paul D. Williams; Manoj M. Joshi (8 April 2013). "Intensification of winter transatlantic aviation turbulence in response to climate change". Nature Climate Change. 3 (7): 644. Bibcode:2013NatCC...3..644W. doi:10.1038/nclimate1866.
40. Bows-Larkin, A.; et al. (2016), "Aviation and Climate Change – The Continuing Challenge", Encyclopedia of aerospace engineering, Fig. 7
41. Timmis, A.; et al. (2014). "Environmental impact assessment of aviation emission reduction through the implementation of composite materials". Int J Life Cycle Assess (Submitted manuscript). 20 (2): 233–243. doi:10.1007/s11367-014-0824-0. S2CID 55899619.
42. (PDF), Boeing, 2014, archived from the original (PDF) on 15 October 2014
43. , Airbus, 2015, archived from the original on 15 January 2013
44. Paradee, Vera (December 2015). Up in the air: how airplane carbon pollution jeopardizes global climate goals (PDF). Center for Biological Diversity (Report). Tucson, AZ.
    • "New Report: Airplane Pollution Jeopardizes Paris Climate Goals". Center for Biological Diversity (Press release). 2 December 2015.
45. Pharoah Le Feuvre (18 March 2019). "Are aviation biofuels ready for take off?". International Energy Agency.
46. Basner, Mathias; et al. (2017). "Aviation Noise Impacts: State of the Science". Noise & Health. 19 (87): 41–50. doi:10.4103/nah.NAH_104_16 (inactive 31 January 2024). PMC 5437751. PMID 29192612.{{cite journal}}: CS1 maint: DOI inactive as of January 2024 (link)
47. "Reduction of Noise at Source". ICAO.
48. "Aircraft Noise Levels and Stages". FAA. 1 July 2020.
49. Peter Coy (15 October 2015). "The Little Gear That Could Reshape the Jet Engine". Bloomberg.
50. Rolls-Royce (1996). The Jet Engine. Rolls-Royce. ISBN 0-902121-2-35.
51. (PDF), UK Civil Aviation Authority, archived from the original (PDF) on 9 November 2008
52. "European Joint Industry CDA Action Plan". Eurocontrol. 2009.
53. Sector S: Vehicle Maintenance Areas, Equipment Cleaning Areas, or Deicing Areas Located at Air Transportation Facilities (Report). Industrial Stormwater Fact Sheet Series. Washington, D.C.: U.S. Environmental Protection Agency (EPA). December 2006. EPA-833-F-06-034.
54. Technical Development Document for the Final Effluent Limitations Guidelines and New Source Performance Standards for the Airport Deicing Category (Report). EPA. April 2012. EPA-821-R-12-005.
55. Environmental Impact and Benefit Assessment for the Final Effluent Limitation Guidelines and Standards for the Airport Deicing Category (Report). EPA. April 2012. EPA-821-R-12-003.
56. Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics. U.S. Federal Aviation Administration. April 2010. doi:10.17226/14370. ISBN 978-0-309-11832-3.
57. (PDF). SAE International. 13 June 2011. Archived from the original (PDF) on 2 February 2013.
58. Eastham, Sebastian D.; Barrett, Steven R. H. (1 November 2016). "Aviation-attributable ozone as a driver for changes in mortality related to air quality and skin cancer". Atmospheric Environment. 144: 17–23. Bibcode:2016AtmEn.144...17E. doi:10.1016/j.atmosenv.2016.08.040. ISSN 1352-2310.
59. Herndon, S.C.; et al. (2005). "Particulate Emissions from in-use Commercial Aircraft". Aerosol Science and Technology. 39 (8): 799–809. Bibcode:2005AerST..39..799H. doi:10.1080/02786820500247363.
60. Herdon, S.C.; et al. (2008). "Commercial Aircraft Engine Emissions Characterization of in-Use Aircraft at Hartsfield-Jackson Atlanta International Airport". Environmental Science & Technology. 42 (6): 1877–1883. Bibcode:2008EnST...42.1877H. doi:10.1021/es072029+. PMID 18409607.
61. Lobo, P.; Hagen, D.E.; Whitefield, P.D. (2012). "Measurement and analysis of aircraft engine PM emissions downwind of an active runway at the Oakland International Airport". Atmospheric Environment. 61: 114–123. Bibcode:2012AtmEn..61..114L. doi:10.1016/j.atmosenv.2012.07.028.
62. Klapmeyer, M.E.; Marr, L.C. (2012). "CO₂, NO_x, and Particle Emissions from Aircraft and Support Activities at a Regional Airport". Environmental Science & Technology. 46 (20): 10974–10981. Bibcode:2012EnST...4610974K. doi:10.1021/es302346x. PMID 22963581.
63. Moore, R.H.; et al. (2017). "Take-off engine particle emission indices for in-service aircraft at Los Angeles International Airport". Scientific Data. 4: 170198. Bibcode:2017NatSD...470198M. doi:10.1038/sdata.2017.198. PMC 5744856. PMID 29257135.
64. "Leaded Fuel Is a Thing of the Past—Unless You Fly a Private Plane". Mother Jones. 10 January 2013.
65. "Lead-free airplane fuel testing is in progress at Lewis" (Press release). Lewis University. 18 July 2011.
66. "Fact Sheet – Leaded Aviation Fuel and the Environment". FAA. 20 November 2019.
67. "Sustainable Aviation Fuels Guide" (PDF). ICAO. December 2018.
68. "Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA)". ICAO.
69. "The Sixth Carbon Budget: Aviation" (PDF).
70. "Europe's aviation sector launches ambitious plan to reach net zero CO₂ emissions by 2050" (PDF) (Press release). Destination 2050. 11 February 2021.
71. "Net-Zero Carbon Emissions by 2050" (Press release). IATA. 4 October 2021.
72. "Climate change: World aviation agrees 'aspirational' net zero plan". BBC News. 7 October 2022.
73. Bergero, Candelaria; et al. (30 January 2023). "Pathways to net-zero emissions from aviation". Nature Sustainability. 6 (4): 404–414. Bibcode:2023NatSu...6..404B. doi:10.1038/s41893-022-01046-9. S2CID 256449498.
74. Net zero aviation fuels – resource requirements and environmental impacts (PDF). The Royal Society. February 2023.
75. Lewis Harper (22 March 2023). "Carbon removal 'a necessity' for aviation to reach net-zero emissions: IPCC report". FlightGlobal.
76. Jon Hemmerdinger (30 March 2023). "US aerospace leaders disagree on best path to 'net-zero' carbon emissions". FlightGlobal.
77. "Bridging the Gap to 2050 - How to Decarbonize Aviation Faster With Today's Technologies". Sustainable Aviation Lab GmbH. Hamburg Investment and Development Bank. April 2023.
78. Philip E. Ross (1 June 2018). "Hybrid Electric Airliners Will Cut Emissions—and Noise". IEEE Spectrum.
79. Bjorn Fehrm (30 June 2017). "Bjorn's Corner: Electric aircraft". Leeham.
80. Paul Seidenman (10 January 2019). "How Batteries Need To Develop To Match Jet Fuel". Aviation Week Network.
81. "Don't Expect To See Large Electric Planes Until At Least 2040". Simple Flying. 28 November 2019.
82. Chris Baraniuk (18 June 2020). "The largest electric plane ever to fly". Future Planet. BBC.
83. Kerry Reals (7 January 2019). "Don't count on technology to save us". Flightglobal. Retrieved 20 October 2020.
84. Guy Norris (4 February 2021). "Boeing Moves Forward With Airbus A321XLR-Competitor Plan". Aviation Week.
85. "Hydrogen instead of electrification? Potentials and risks for climate targets" (Press release). Potsdam Institute for Climate Impact Research. 6 May 2021.
86. Hydrogen-powered aviation (PDF) (Report). EU Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings. May 2020.
87. "Sustainable aviation fuel market demand drives new product launches". Investable Universe. 4 December 2020. Retrieved 12 December 2022. Note: Investable Universe>About
88. Doliente, Stephen S.; et al. (10 July 2020). "Bio-aviation Fuel: A Comprehensive Review and Analysis of the Supply Chain Components" (PDF). Frontiers in Energy Research. 8. doi:10.3389/fenrg.2020.00110.
89. "Developing Sustainable Aviation Fuel (SAF)". IATA.
90. Bauen, Ausilio; Howes, Jo; Bertuccioli, Luca; Chudziak, Claire (August 2009). "Review of the potential for biofuels in aviation". CiteSeerX 10.1.1.170.8750.
91. Mark Pilling (25 March 2021). "How sustainable fuel will help power aviation's green revolution". Flight Global.
92. Ueckerdt, Falko; et al. (6 May 2021). (Potsdam Institute for Climate Impact Research). "Potential and risks of hydrogen-based e-fuels in climate change mitigation". Nature Climate Change. 11 (5): 384. Bibcode:2021NatCC..11..384U. doi:10.1038/s41558-021-01032-7. S2CID 233876615.
93. Fouquet, Roger; O'Garra, Tanya (1 December 2022). "In pursuit of progressive and effective climate policies: Comparing an air travel carbon tax and a frequent flyer levy". Energy Policy. 171: 113278. doi:10.1016/j.enpol.2022.113278. ISSN 0301-4215.
94. Gössling, Stefan; Humpe, Andreas (1 November 2020). "The global scale, distribution and growth of aviation: Implications for climate change". Global Environmental Change. 65: 102194. doi:10.1016/j.gloenvcha.2020.102194. ISSN 0959-3780. PMC 9900393. PMID 36777089.
95. Creutzig, Felix; Niamir, Leila; Bai, Xuemei; Callaghan, Max; Cullen, Jonathan; Díaz-José, Julio; Figueroa, Maria; Grubler, Arnulf; Lamb, William F.; Leip, Adrian; Masanet, Eric; Mata, Érika; Mattauch, Linus; Minx, Jan C.; Mirasgedis, Sebastian; Mulugetta, Yacob; Nugroho, Sudarmanto Budi; Pathak, Minal; Perkins, Patricia; Roy, Joyashree; de la Rue du Can, Stephane; Saheb, Yamina; Some, Shreya; Steg, Linda; Steinberger, Julia; Ürge-Vorsatz, Diana (January 2022). "Demand-side solutions to climate change mitigation consistent with high levels of well-being". Nature Climate Change. 12 (1): 36–46. Bibcode:2022NatCC..12...36C. doi:10.1038/s41558-021-01219-y. ISSN 1758-6798. S2CID 234275540.
96. Sharmina, M.; Edelenbosch, O. Y.; Wilson, C.; Freeman, R.; Gernaat, D. E. H. J.; Gilbert, P.; Larkin, A.; Littleton, E. W.; Traut, M.; van Vuuren, D. P.; Vaughan, N. E.; Wood, F. R.; Le Quéré, C. (21 April 2021). "Decarbonising the critical sectors of aviation, shipping, road freight and industry to limit warming to 1.5–2°C". Climate Policy. 21 (4): 455–474. Bibcode:2021CliPo..21..455S. doi:10.1080/14693062.2020.1831430. ISSN 1469-3062. S2CID 226330972.
97. Bergero, Candelaria; Gosnell, Greer; Gielen, Dolf; Kang, Seungwoo; Bazilian, Morgan; Davis, Steven J. (30 January 2023). "Pathways to net-zero emissions from aviation". Nature Sustainability. 6 (4): 404–414. Bibcode:2023NatSu...6..404B. doi:10.1038/s41893-022-01046-9. ISSN 2398-9629. S2CID 256449498.
98. "Green flights not in easy reach, warn scientists". BBC News. 28 February 2023. Retrieved 3 March 2023.
99. "UK net zero aviation ambitions must resolve resource and research questions around alternatives to jet fuel | Royal Society". royalsociety.org. Retrieved 3 March 2023.
100. Higham, James; Cohen, Scott A.; Cavaliere, Christina T.; Reis, Arianne; Finkler, Wiebke (16 January 2016). "Climate change, tourist air travel and radical emissions reduction". Journal of Cleaner Production. 111: 336–347. doi:10.1016/j.jclepro.2014.10.100. ISSN 0959-6526.
101. Ivanova, Diana; Barrett, John; Wiedenhofer, Dominik; Macura, Biljana; Callaghan, Max; Creutzig, Felix (1 September 2020). "Quantifying the potential for climate change mitigation of consumption options". Environmental Research Letters. 15 (9): 093001. Bibcode:2020ERL....15i3001I. doi:10.1088/1748-9326/ab8589.
102. Girod, Bastien; van Vuuren, Detlef P.; de Vries, Bert (1 April 2013). "Influence of travel behavior on global CO₂ emissions". Transportation Research Part A: Policy and Practice. 50: 183–197. doi:10.1016/j.tra.2013.01.046. hdl:1874/386161. ISSN 0965-8564. S2CID 154332068.
103. Creutzig, F.; Roy, J.; Devine-Wright, P.; Díaz-José, J.; et al. (2022). "Chapter 5: Demand, services and social aspects of mitigation" (PDF). IPCC AR6 WG3 2022. pp. 752–943. doi:10.1017/9781009157926.007. hdl:20.500.11937/88566.
104. Stefan Gössling (November 2020). "The global scale, distribution and growth of aviation: Implications for climate change". Global Environmental Change. 65. doi:10.1016/j.gloenvcha.2020.102194. PMC 9900393. PMID 36777089. S2CID 228984718.
105. "2021–2022 EIB Climate Survey, part 2 of 3: Shopping for a new car? Most Europeans say they will opt for hybrid or electric". European Investment Bank. 22 March 2022.
106. Matthias Wabl and Christopher Jasper (9 June 2020). "Airline bailouts point to greener travel—and higher fares". BNN Bloomberg. Retrieved 13 June 2020.
107. Haines, Gavin (31 May 2019). "Is Sweden's 'flight shame' movement dampening demand for air travel?". The Daily Telegraph. Retrieved 1 June 2019 – via www.telegraph.co.uk.
108. Kerry Reals (6 September 2019). "'Flight shaming' is changing the face of travel". Flightglobal.
109. "'Flight shame' a factor in Swedish traffic decline". Flightglobal. 10 January 2020.
110. Fuso Nerini, Francesco; et al. (16 August 2021). "Personal carbon allowances revisited". Nature Sustainability. 4 (12): 1025–1031. Bibcode:2021NatSu...4.1025F. doi:10.1038/s41893-021-00756-w. S2CID 237101457.
111. "Pandemic and digitalization set stage for revival of a cast-off idea: Personal carbon allowances". phys.org. 16 August 2021.
112. "Opinion: We Need Cap-and-Trade For Individuals As Well As Companies". Bloomberg. 25 August 2021.
113. "How personal carbon allowances can help normal people fight climate change". Popular Science. 28 August 2021.
114. Sodha, Sonia (9 May 2018). "Opinion: A radical way to cut emissions – ration everyone's flights". The Guardian.
115. "International Civil Aviation Day calls for the greening of aviation" (PDF) (Press release). ICAO. 30 November 2005.
116. Reducing the Climate Change Impact of Aviation (PDF), European Commission, 2005
117. "Climate change: Commission proposes bringing air transport into EU Emissions Trading Scheme" (Press release). European Commission. 20 December 2006.
118. Lee, D.; et al. (2013), Bridging the aviation CO₂ emissions gap: why emissions trading is needed, Centre for Aviation, Transport and the Environment
119. Kate Abnett (10 March 2020). "Ban short-haul flights for climate? In EU poll 62% say yes". Reuters.
120. ICF Consulting (1 February 2006). "Including Aviation into the EU ETS: Impact on EU allowance prices" (PDF).
121. "Resolution A39-3: Consolidated statement of continuing ICAO policies and practices related to environmental protection – Global Market-based Measure (MBM) scheme" (PDF). ICAO. 15 February 2019.
122. "Study: Aviation tax breaks cost EU states €39 billion a year". euractiv. 25 July 2013.
123. "EU governments miss out on up to €39bn a year due to aviation's tax breaks". Transport and Environment. 24 July 2013.
124. Greenfield, Patrick (18 January 2023). "Revealed: more than 90% of rainforest carbon offsets by biggest certifier are worthless, analysis shows". The Guardian. from the original on 14 February 2023.
125. British Airways Carbon Offset Programme, British Airways, retrieved 2 May 2010
126. , Continental Airlines, archived from the original on 2 March 2012, retrieved 2 May 2010
127. , Bloomberg, archived from the original on 28 March 2008, retrieved 2 May 2010
128. easyJet Carbon Offset Programme, easyJet, retrieved 2 May 2010
129. 11 Airlines That Offer Carbon Offset Programs
130. How to Buy Carbon Offsets(subscription required)
131. The Gold Standard
132. Find Green-e Certified Carbon Offsets
133. "UK to include aviation in carbon emissions targets". CAPA - Centre for Aviation. 27 April 2021.
134. "Carbon neutral airline gets on board UN scheme to cut greenhouse gas emissions". UN News. 20 November 2008.
135. "Corporate Responsibility > Going Green". Harbour Air.
136. "flypop plans to be first international carbon-neutral airline" (Press release). flypop. 17 July 2019.
137. "Air France to proactively offset 100% of CO₂ emissions on its domestic flights as of January 1st, 2020" (Press release). Air France. 1 October 2019.
138. David Kaminski-Morrow (19 November 2019). "EasyJet to offset carbon emissions across whole network". Flightglobal.
139. "BA begins offsetting domestic flight emissions". Flightglobal. 3 January 2020.
140. Pilar Wolfsteller (6 January 2020). "JetBlue to be first major US airline to offset all emissions from domestic flights". Flightglobal.
141. "All JetBlue Flights Are Now Carbon Neutral Within The US". simpleflying.
142. "Delta burns tons of jet fuel - but says it's on track to be carbon neutral. What?". CNN. 14 February 2020.
143. Jon Hemmerdinger (10 December 2020). "United to invest in 'direct air capture' as it makes 2050 carbon-neutral pledge". Flightglobal.
144. Crespo, Daniel Calleja; de Leon, Pablo Mendes (2011). Achieving the Single European Sky: Goals and Challenges. Alphen aan de Rijn: Kluwer Law International. pp. 4–5. ISBN 978-90-411-3730-2.
145. Sam Morgan (22 September 2020). "Corona-crisis and Brexit boost EU air traffic reform hopes". Euractiv.
146. Volker Grewe; et al. (September 2014). "Reduction of the air traffic's contribution to climate change: A REACT4C case study". Atmospheric Environment. 94: 616. Bibcode:2014AtmEn..94..616G. doi:10.1016/j.atmosenv.2014.05.059.
147. Matthes, Sigrun; et al. (31 January 2021). (Deutsches Zentrum für Luft- und Raumfahrt). "Mitigation of Non-CO₂ Aviation's Climate Impact by Changing Cruise Altitudes". Aerospace. 8 (2): 36. Bibcode:2021Aeros...8...36M. doi:10.3390/aerospace8020036. hdl:10852/92624.
148. Ole Amund Søvde; et al. (October 2014). "Aircraft emission mitigation by changing route altitude: A multi-model estimate of aircraft NOx emission impact on O
     ₃ photochemistry". Atmospheric Environment. 95: 468. Bibcode:2014AtmEn..95..468S. doi:10.1016/j.atmosenv.2014.06.049.
149. Williams, Victoria; et al. (November 2002). "Reducing the climate change impacts of aviation by restricting cruise altitudes". Transportation Research Part D: Transport and Environment. 7 (6): 451–464. Bibcode:2002EGSGA..27.1331W. doi:10.1016/S1361-9209(02)00013-5.
150. Nicola Stuber; et al. (15 June 2006). "The importance of the diurnal and annual cycle of air traffic for contrail radiative forcing". Nature. 441 (7095): 864–867. Bibcode:2006Natur.441..864S. doi:10.1038/nature04877. PMID 16778887. S2CID 4348401.
151. Caroline Brogan (12 February 2020). "Small altitude changes could cut contrail impact of flights by up to 59 per cent". Imperial College.

Works cited

• IPCC (2022). Shukla, P.R.; Skea, J.; Slade, R.; Al Khourdajie, A.; et al. (eds.). Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.

Further reading

Institutional

• "Aviation Emissions, Impacts & Mitigation: A Primer" (PDF). FAA Office of Environment and Energy. January 2015.
• (PDF). Advisory Council for Aviation Research and Innovation in Europe. 2017.
• (PDF). EASA. 2019.
• "Environmental Report". ICAO. 2019.

Concerns

• "airportwatch.org.uk". AirportWatch. oppose any expansion of aviation and airports likely to damage the human or natural environment, and to promote an aviation policy for the UK which is in full accordance with the principles of sustainable development

Industry

• "Aviation: Benefits Beyond Borders". Air Transport Action Group. information on the many industry measures underway to limit the impact of aviation on the environment
• "sustainableaviation.co.uk". Sustainable Aviation. collective approach of UK aviation to tackling the challenge of ensuring a sustainable future
• "The aviation sector's climate action framework" (PDF). Air Transport Action Group. November 2015.
• "Making Net-Zero Aviation Possible" (PDF). Mission Possible Partnership. July 2022. An industry-backed, 1.5°C-aligned transition strategy

Research

• "Aviation Sustainability Center". Washington State University and the Massachusetts Institute of Technology.
• "Laboratory for Aviation and the Environment". Massachusetts Institute of Technology.
• "Partnership for Air Transportation Noise and Emissions Reduction". Massachusetts Institute of Technology.
• "Sustainable Sky Institute". Sustainable Sky Institute.

Studies

• Kivits, Robbert; Charles, Michael B.; Ryan, Neal (2010). "A post-carbon aviation future: Airports and the transition to a cleaner aviation sector". Futures. 42 (3): 199–211. doi:10.1016/j.futures.2009.11.005.
• The Heinrich Böll Foundation and the Airbus Group (May 2016). "Aloft - An Inflight Review" (PDF).
• Antoine Gelain (10 August 2016). "Opinion: The Uncomfortable Truth About Aviation Emissions". Aviation Week & Space Technology.
• "Tracking report: Aviation". International Energy Agency. June 2020.
• Hannah Ritchie (22 October 2020). "Climate change and flying: what share of global CO₂ emissions come from aviation?". Our World in Data.
• "The aviation industry wants to be net zero—but not soon". The Economist. 14 May 2023.