:Environmental impact of aviation

File:CO2 emissions fraction of Aviation (%).png grew from 0.7% to 2.65% of all {{CO2}} emissions]]

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.{{cite web | url=https://www.icao.int/environmental-protection/pages/aircraft-engine-emissions.aspx | title=Aircraft Engine Emissions | publisher=International Civil Aviation Organization | access-date=23 October 2020 | archive-date=27 July 2019 | archive-url=https://web.archive.org/web/20190727040541/https://www.icao.int/environmental-protection/Pages/aircraft-engine-emissions.aspx | url-status=live}}

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.

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.

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 {{chem|N|O|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 =

File:Aviation Effective Radiative Forcing components, 2018 (mW per m²).svgs from aviation emissions, estimated in 2020]]

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.{{cite journal | last1=Brasseur | first1=Guy P. | last2=Gupta | first2=Mohan | last3=Anderson | first3=Bruce E. | last4=Balasubramanian | first4=Sathya | last5=Barrett | first5=Steven | last6=Duda | first6=David | last7=Fleming | first7=Gregg | last8=Forster | first8=Piers M. | last9=Fuglestvedt | first9=Jan | last10=Gettelman | first10=Andrew | last11=Halthore | first11=Rangasayi N. | last12=Jacob | first12=S. Daniel | last13=Jacobson | first13=Mark Z. | last14=Khodayari | first14=Arezoo | last15=Liou | first15=Kuo-Nan | last16=Lund | first16=Marianne T. | last17=Miake-Lye | first17=Richard C. | last18=Minnis | first18=Patrick | last19=Olsen | first19=Seth | last20=Penner | first20=Joyce E. | last21=Prinn | first21=Ronald | last22=Schumann | first22=Ulrich | last23=Selkirk | first23=Henry B. | last24=Sokolov | first24=Andrei | last25=Unger | first25=Nadine | last26=Wolfe | first26=Philip | last27=Wong | first27=Hsi-Wu | last28=Wuebbles | first28=Donald W. | last29=Yi | first29=Bingqi | last30=Yang | first30=Ping | last31=Zhou | first31=Cheng | date=1 April 2016 | title=Impact of Aviation on Climate: FAA's Aviation Climate Change Research Initiative (ACCRI) Phase II | journal=Bulletin of the American Meteorological Society | publisher=American Meteorological Society | volume=97 | issue=4 | pages=561–583 | doi=10.1175/bams-d-13-00089.1 | doi-access=free | hdl=1721.1/109270 | hdl-access=free}}

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:{{cite book | url=https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=0 | title=Aviation and the Global Atmosphere | publisher=IPCC | author=Joyce E. Penner | author-link=Joyce E. Penner | display-authors=etal | date=1999 | bibcode=1999aga..book.....P | access-date=20 October 2020 | archive-date=7 June 2023 | archive-url=https://web.archive.org/web/20230607191315/https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=0 | url-status=live}}

; Carbon dioxide ({{CO2}})

: {{CO2}} emissions are the most significant and best understood contribution to climate change.{{cite journal | last1=Sausen | first1=Robert | last2=Isaksen | first2=Ivar | last3=Grewe | first3=Volker | last4=Hauglustaine | first4=Didier | last5=Lee | first5=David S. | last6=Myhre | first6=Gunnar | last7=Köhler | first7=Marcus O. | last8=Pitari | first8=Giovanni | last9=Schumann | first9=Ulrich | last10=Stordal | first10=Frode | last11=Zerefos | first11=Christos | date=August 2005 | title=Aviation radiative forcing in 2000: An update on IPCC (1999) | journal=Meteorologische Zeitschrift | publisher=Gebrüder Borntraeger Verlagsbuchhandlung | volume=14 | issue=4 | pages=555–561 | doi=10.1127/0941-2948/2005/0049 | doi-access=free | url=https://www.schweizerbart.de/content/papers/download/54291 }} 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.{{cite report | vauthors=Horvath A, Chester M | date=2008-12-01 | url=http://escholarship.org/uc/item/6m5865v5.pdf;origin=repeccitec | title=Environmental Life-cycle Assessment of Passenger Transportation An Energy, Greenhouse Gas and Criteria Pollutant Inventory of Rail and Air Transportation | publisher=University of California Transportation Center, UC Berkeley | access-date=27 January 2011 | archive-date=5 July 2017 | archive-url=https://web.archive.org/web/20170705135840/http://escholarship.org/uc/item/6m5865v5.pdf;origin=repeccitec | url-status=live}}

; Nitrogen oxides ({{chem|N|O|x}}, nitric oxide and nitrogen dioxide)

: In the tropopause, emissions of {{chem|N|O|x}} favor ozone ({{chem|O|3}}) formation in the upper troposphere. At altitudes from {{cvt|8|to|13|km|ft}}, {{chem|N|O|x}} emissions result in greater concentrations of {{chem|O|3}} than surface {{chem|N|O|x}} emissions and these in turn have a greater global warming effect. The effect of {{chem|O|3}} surface concentrations are regional and local, but it becomes well mixed globally at mid and upper tropospheric levels.{{cite journal | last1=Derwent | first1=Richard | last2=Collins | first2=William | last3=Johnson | first3=Colin | last4=Stevenson | first4=David | date=1 October 2002 | title=Global Ozone Concentrations and Regional Air Quality | journal=Environmental Science & Technology | publisher=American Chemical Society | volume=36 | issue=19 | doi=10.1021/es022419q | doi-access=free | pmid=12380066 | pages=379A–382A}} {{chem|N|O|x}} emissions also reduce ambient levels of methane, another greenhouse gas, resulting in a climate cooling effect, though not offsetting the {{chem|O|3}} forming effect. Aircraft sulfur and water emissions in the stratosphere tend to deplete {{chem|O|3}}, partially offsetting the {{chem|N|O|x}}-induced {{chem|O|3}} increases, although these effects have not been quantified. Light aircraft and small commuter aircraft fly lower in the troposphere, not in the tropopause.

File:Contrails.jpg 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.{{cite report | url=http://www.ipcc.ch/SPM2feb07.pdf | date=February 2007 | title=Climate Change 2007: The Physical Science Basis | at=Summary for Policymakers | publisher=Intergovernmental Panel on Climate Change | archive-url=https://web.archive.org/web/20071114144734/http://www.ipcc.ch/SPM2feb07.pdf | archive-date=14 November 2007}} 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.{{Cite web | url=https://www.newscientist.com/article/2207886-it-turns-out-planes-are-even-worse-for-the-climate-than-we-thought/ | title=It turns out planes are even worse for the climate than we thought | last=Le Page | first=Michael | work=New Scientist | date=27 June 2019 | access-date=5 July 2019 | archive-date=5 July 2019 | archive-url=https://web.archive.org/web/20190705102129/https://www.newscientist.com/article/2207886-it-turns-out-planes-are-even-worse-for-the-climate-than-we-thought/ | url-status=live}} Their global warming contribution is uncertain and estimating aviation's overall contribution often excludes cirrus cloud enhancement.

; 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.{{cite web | title=Questions & Answers on Aviation & Climate Change | publisher=European Commission | date=27 September 2005 | url=https://ec.europa.eu/commission/presscorner/detail/en/MEMO_05_341 | work=Press corner | access-date=23 October 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105753/https://ec.europa.eu/commission/presscorner/detail/en/MEMO_05_341 | url-status=live}} Contrails and cirrus clouds evolving from particles may have a greater radiative forcing effect than {{CO2}} emissions.{{cite journal | last1=Kärcher | first1=B. | title=The importance of contrail ice formation for mitigating the climate impact of aviation | journal=Journal of Geophysical Research: Atmospheres | date=2016 | volume=121 | issue=7 | pages=3497–3505 | doi=10.1002/2015JD024696 | bibcode=2016JGRD..121.3497K | doi-access=free}} 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.{{cite journal | last1=Corporan | first1=Edwin | last2=DeWitt | first2=Matthew J. | last3=Belovich | first3=Vincent | last4=Pawlik | first4=Robert | last5=Lynch | first5=Amy C. | last6=Gord | first6=James R. | last7=Meyer | first7=Terrence R. | date=17 July 2007 | title=Emissions characteristics of a turbine engine and research combustor burning a Fischer–Tropsch jet fuel | journal=Energy & Fuels | publisher=American Chemical Society | volume=21 | issue=5 | pages=2615–2626 | issn=0887-0624 | doi=10.1021/ef070015j}}{{cite journal | last1=Lobo | first1=Prem | last2=Hagen | first2=Donald E. | last3=Whitefield | first3=Philip D. | date=15 November 2011 | title=Comparison of PM emissions from a commercial jet engine burning conventional, biomass, and Fischer–Tropsch fuels | journal=Environmental Science & Technology | publisher=American Chemical Society | volume=45 | issue=24 | pages=10744–10749 | issn=0013-936X | doi=10.1021/es201902e | pmid=22043875 | bibcode=2011EnST...4510744L}}{{cite journal | last1=Moore | first1=Richard H. | last2=Thornhill | first2=Kenneth L. | last3=Weinzierl | first3=Bernadett | last4=Sauer | first4=Daniel | last5=D'Ascoli | first5=Eugenio | last6=Kim | first6=Jin | last7=Lichtenstern | first7=Michael | last8=Scheibe | first8=Monika | last9=Beaton | first9=Brian | last10=Beyersdorf | first10=Andreas J. | last11=Barrick | first11=John | last12=Bulzan | first12=Dan | last13=Corr | first13=Chelsea A. | last14=Crosbie | first14=Ewan | last15=Jurkat | first15=Tina | last16=Martin | first16=Robert | last17=Riddick | first17=Dean | last18=Shook | first18=Michael | last19=Slover | first19=Gregory | last20=Voigt | first20=Christiane | last21=White | first21=Robert | last22=Winstead | first22=Edward | last23=Yasky | first23=Richard | last24=Ziemba | first24=Luke D. | last25=Brown | first25=Anthony | last26=Schlager | first26=Hans | last27=Anderson | first27=Bruce E. | year=2017 | title=Biofuel blending reduces particle emissions from aircraft engines at cruise conditions | journal=Nature | publisher=Springer | volume=543 | issue=7645 | pages=411–415 | issn=0028-0836 | doi=10.1038/nature21420 | doi-access=free | pmid=28300096 | pmc=8025803 | bibcode=2017Natur.543..411M | url=https://elib.dlr.de/112943/1/Moore_et_al_Nature_2017.pdf | access-date=4 July 2019 | archive-date=27 April 2019 | archive-url=https://web.archive.org/web/20190427124937/https://elib.dlr.de/112943/1/Moore_et_al_Nature_2017.pdf | url-status=live}}

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.

This was updated for 2000, with aviation's radiative forcing estimated at 47.8 mW/m², {{#expr:47.8/25.3round1}} times the effect of {{CO2}} emissions alone, 25.3 mW/m².

In 2005, research by David S. Lee, et al., published in the scientific journal Atmospheric Environment estimated the cumulative radiative forcing effect of aviation as 55 mW/m², which is twice the 28 mW/m² radiative forcing effect of the cumulative {{CO2}} emissions alone, excluding induced cirrus clouds.{{cite journal | last1=Lee | first1=David S. | last2=Fahey | first2=David W. | last3=Forster | first3=Piers M. | last4=Newton | first4=Peter J. | last5=Wit | first5=Ron C.N. | last6=Lim | first6=Ling L. | last7=Owen | first7=Bethan | last8=Sausen | first8=Robert | date=July 2009 | title=Aviation and global climate change in the 21st century | journal=Atmospheric Environment | publisher=Elsevier BV | volume=43 | issue=22 | pages=3520–3537 | doi=10.1016/j.atmosenv.2009.04.024 | doi-access=free | pmid=32362760 | pmc=7185790 | bibcode=2009AtmEn..43.3520L | url=https://elib.dlr.de/59761/1/lee.pdf | access-date=28 October 2020 | archive-date=4 July 2023 | archive-url=https://web.archive.org/web/20230704001335/https://elib.dlr.de/59761/1/lee.pdf | url-status=live}}

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).{{cite journal | last1=Azar | first1=Christian | last2=Johansson | first2=Daniel J. A. | title=Valuing the non-CO₂ climate impacts of aviation | journal=Climatic Change | date=April 2012 | volume=111 | issue=3–4 | pages=559–579 | doi=10.1007/s10584-011-0168-8 | bibcode=2012ClCh..111..559A | doi-access=free}} This ratio depends on how aviation activity grows. If the growth is exponential then the ratio is constant. But if the growth stops, the ratio will go down because the {{CO2}} in the atmosphere due to aviation will continue to go up, whereas the other effects will stagnate.

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.

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), {{NOx}} 17.5 mW/m² with a low confidence level (± 14) and contrail cirrus 57.4 mW/m², also with a low confidence level (± 40).

All factors combined represented 43.5 mW/m² ({{#expr:43.5/34.3round2}} 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).{{cite journal | last1=Lee | first1=D. S. | last2=Fahey | first2=D. W. | last3=Skowron | first3=A. | last4=Allen | first4=M. R. | last5=Burkhardt | first5=U. | last6=Chen | first6=Q. | last7=Doherty | first7=S. J. | last8=Freeman | first8=S. | last9=Forster | first9=P. M. | last10=Fuglestvedt | first10=J. | last11=Gettelman | first11=A. | last12=De León | first12=R. R. | last13=Lim | first13=L. L. | last14=Lund | first14=M. T. | last15=Millar | first15=R. J. | last16=Owen | first16=B. | last17=Penner | first17=J. E. | last18=Pitari | first18=G. | last19=Prather | first19=M. J. | last20=Sausen | first20=R. | last21=Wilcox | first21=L. J. | year=2021 | title=The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018 | journal=Atmospheric Environment | publisher=Elsevier | volume=244 | page=117834 | doi=10.1016/j.atmosenv.2020.117834 | doi-access=free | pmid=32895604 | pmc=7468346 | bibcode=2021AtmEn.24417834L}} Again, it must be remembered that the effect of {{CO2}} accumulates from year to year, unlike the effect of contrails and cirrus clouds.

= Volume =

By 2018, airline traffic reached 4.3 billion passengers with 37.8 million departures, an average of {{#expr:4300/37.8round0}} passengers per flight and 8.26 trillion RPKs, an average journey of {{cvt|{{#expr:8258/4.3round0}}|km|nmi}}, according to ICAO.{{cite news | url=https://www.icao.int/annual-report-2018/Pages/the-world-of-air-transport-in-2018.aspx | title=The World of Air Transport in 2018 | publisher=ICAO | access-date=20 October 2020 | archive-date=19 July 2023 | archive-url=https://web.archive.org/web/20230719062837/https://www.icao.int/annual-report-2018/Pages/the-world-of-air-transport-in-2018.aspx | url-status=live}}

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.{{cite web | url=https://www.airbus.com/sites/g/files/jlcbta136/files/2021-07/GMF-2019-2038-Airbus-Commercial-Aircraft-book.pdf | title=Global Market Forecast | website=Airbus | date=2019 | access-date=4 October 2022 | archive-date=26 March 2023 | archive-url=https://web.archive.org/web/20230326045318/https://www.airbus.com/sites/g/files/jlcbta136/files/2021-07/GMF-2019-2038-Airbus-Commercial-Aircraft-book.pdf | url-status=live}}

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.{{cite web | url=https://aviationbenefits.org/environmental-efficiency/climate-action | title=Aviation industry reducing its environmental footprint | website=Aviation Benefits | access-date=23 October 2020 | archive-date=13 June 2008 | archive-url=https://web.archive.org/web/20080613081504/http://www.enviro.aero/Impactofflying.aspx | url-status=live}}

Between 1960 and 2018, RPKs increased from 109 to 8,269 billion.

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.{{cite book | section-url=https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=6 | section=What are the Current and Future Impacts of Subsonic Aviation on Radiative Forcing and UV Radiation? | title=Aviation and the Global Atmosphere | author=Joyce E. Penner | author-link=Joyce E. Penner | display-authors=etal | publisher=IPCC | date=1999 | bibcode=1999aga..book.....P | access-date=20 October 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105752/https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=6 | url-status=live}}

By 2015, aviation accounted for 2.5% of global {{CO2}} emissions.{{cite report | publisher=IEA | title=CO₂ emissions from fuel combustion: detailed estimates | year=2014}} and {{cite report | publisher=EIA | title=International Energy Statistics | website=www.eia.gov | date=2015}} via {{Cite journal | doi=10.1038/nclimate2865 | title=Costs of mitigating CO₂ emissions from passenger aircraft | journal=Nature Climate Change | volume=6 | issue=4 | pages=412–417 | year=2016 | last1=Schäfer | first1=Andreas W. | last2=Evans | first2=Antony D. | last3=Reynolds | first3=Tom G. | last4=Dray | first4=Lynnette | bibcode=2016NatCC...6..412S | url=http://discovery.ucl.ac.uk/1477564/1/Schafer_NCLIM%28accpt%29.pdf | access-date=18 October 2020 | archive-date=23 July 2018 | archive-url=https://web.archive.org/web/20180723094918/http://discovery.ucl.ac.uk/1477564/1/Schafer_NCLIM(accpt).pdf | url-status=live}}

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.{{cite web | url=https://theicct.org/sites/default/files/publications/ICCT_CO2-commercl-aviation-2018_20190918.pdf | title=CO₂ emissions from commercial aviation, 2018 | author=Brandon Graver | author2=Kevin Zhang | author3=Dan Rutherford | date=September 2019 | publisher=International Council on Clean Transportation | access-date=10 January 2020 | archive-date=20 November 2019 | archive-url=https://web.archive.org/web/20191120065456/https://theicct.org/sites/default/files/publications/ICCT_CO2-commercl-aviation-2018_20190918.pdf | url-status=live}}

Between 1960 and 2018, {{CO2}} emissions increased 6.8 times from {{#expr:1034/6.8round0}} to 1,034 million tonnes per year.

Emissions from flights rose by 32% between 2013 and 2018.

File:Aviation GHG emissions in the EU ETS and the top 10 emitters in aviation 2013-2019-en.svg, showing the top 10 emitters (2013–2019).{{cite report | publisher=EEA | title=EEA Report No 19/2020 | page=24 | year=2021 | url=https://www.eea.europa.eu/ds_resolveuid/1d491124b59a4f5099b5d13ac707eee9}}]]

Between 1990 and 2006, greenhouse gas emissions from aviation increased by 87% in the European Union.{{cite press release | title=Climate change: Commission proposes bringing air transport into EU Emissions Trading Scheme | publisher=EU Commission | date=20 December 2006 | url=http://europa.eu/rapid/pressReleasesAction.do?reference=IP/06/1862 | access-date=3 January 2008 | archive-date=19 May 2011 | archive-url=https://web.archive.org/web/20110519102426/http://europa.eu/rapid/pressReleasesAction.do?reference=IP/06/1862 | url-status=live}}

In 2010, about 60% of aviation emissions came from international flights, which are outside the emission reduction targets of the Kyoto Protocol.{{Cite journal | doi=10.1021/es902530z | title=Flying into the Future: Aviation Emissions Scenarios to 2050 | journal=Environmental Science & Technology | volume=44 | issue=7 | pages=2255–2260 | year=2010 | last1=Owen | first1=Bethan | last2=Lee | first2=David S. | last3=Lim | first3=Ling | pmid=20225840 | bibcode=2010EnST...44.2255O | doi-access=free}} 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.{{Cite news | url=https://apnews.com/article/6be5cb930f7b4ecbb24ec79219a74225 | title=UN agreement reached on aircraft climate-change emissions | last=Lowy | first=Joan | date=2016-10-07 | work=Associated Press | access-date=20 October 2020 | archive-date=24 December 2022 | archive-url=https://web.archive.org/web/20221224003137/https://apnews.com/article/6be5cb930f7b4ecbb24ec79219a74225 | url-status=live}}

In 1992, aircraft radiative forcing was estimated by the IPCC at 3.5% of the total man-made radiative forcing.{{cite book | url=https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=8 | title=What are the Overall Climate Effects of Subsonic Aircraft? | chapter=Summary for Policymakers | author=Joyce E. Penner | display-authors=etal | publisher=IPCC | date=1999 | access-date=20 October 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105802/https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=8 | url-status=live}}

= Per passenger =

File:Aviation Efficiency (RPK per kg CO2).svg

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.{{cite news | title=Opinion: Aviation and global warming | newspaper=The New York Times | date=Sep 20, 2007 | url=https://www.nytimes.com/2007/09/20/opinion/20iht-edbisi.1.7583290.html | author=Giovanni Bisignani, CEO of the IATA | access-date=18 October 2020 | archive-date=21 April 2020 | archive-url=https://web.archive.org/web/20200421174310/https://www.nytimes.com/2007/09/20/opinion/20iht-edbisi.1.7583290.html | url-status=live}}

Jet airliners have become 70% more fuel efficient between 1967 and 2007.

Jetliner fuel efficiency improves continuously, 40% of the improvement come from engines and 30% from airframes.{{cite book | chapter-url=https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=133 | title=Special Report on Aviation and the Global Atmosphere | chapter=9.2.2. Developments in Technology | author=Joyce E. Penner | display-authors=etal | date=1999 | publisher=IPCC | access-date=26 November 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105758/https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=133 | url-status=live}}

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.{{cite web | last1=Peeters | first1=P. M. | display-authors=etal | date=November 2005 | url=http://www.transportenvironment.org/sites/te/files/media/2005-12_nlr_aviation_fuel_efficiency.pdf | title=Fuel efficiency of commercial aircraft | quote=An overview of historical and future trends | publisher=Netherlands National Aerospace Laboratory | access-date=21 November 2020 | archive-date=19 January 2018 | archive-url=https://web.archive.org/web/20180119183636/http://www.transportenvironment.org/sites/te/files/media/2005-12_nlr_aviation_fuel_efficiency.pdf | url-status=dead}}

The average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction of 1.3% with variable reduction rate.{{cite report | url=https://theicct.org/sites/default/files/publications/ICCT_Aircraft-FE-Trends_20150902.pdf | title=Fuel efficiency trends for new commercial jet aircraft: 1960 to 2014 | author1=Anastasia Kharina | author2=Daniel Rutherford | publisher=ICCT | date=Aug 2015 | access-date=26 November 2020 | archive-date=4 June 2023 | archive-url=https://web.archive.org/web/20230604032057/https://theicct.org/sites/default/files/publications/ICCT_Aircraft-FE-Trends_20150902.pdf | url-status=live}}

By 2018, {{CO2}} emissions per revenue ton-kilometer (RTK) were more than halved compared to 1990, at 47%.{{cite web | url=https://www.iata.org/contentassets/25e5377cf53c4e48bbaa49d252f3ab03/fact-sheet-fuel.pdf | title=Fuel Fact Sheet | publisher=IATA | date=December 2019 | access-date=8 November 2022 | archive-date=8 November 2022 | archive-url=https://web.archive.org/web/20221108151528/https://www.iata.org/contentassets/25e5377cf53c4e48bbaa49d252f3ab03/fact-sheet-fuel.pdf | url-status=live}}

The aviation energy intensity went from 21.2 to 12.3 MJ/RTK between 2000 and 2019, a {{#expr:(1-12.3/21.2)*100round0}}% reduction.

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.

The UK's Department for {{abbr|BEIS|Business, Energy and Industrial Strategy}} calculate a long-haul flight release 102 g of {{CO2}} per passenger kilometre, and 254 g of {{CO2}} equivalent, including non-CO₂ greenhouse gas emissions, water vapor etc.; for a domestic flight in Britain.{{Cite web | last=Timperley | first=Jocelyn | title=Should we give up flying for the sake of the climate? | url=https://www.bbc.com/future/article/20200218-climate-change-how-to-cut-your-carbon-emissions-when-flying | date=19 February 2020 | website=BBC | access-date=28 November 2021 | archive-date=22 September 2023 | archive-url=https://web.archive.org/web/20230922064440/https://www.bbc.com/future/article/20200218-climate-change-how-to-cut-your-carbon-emissions-when-flying | url-status=live}}

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.{{cite report | url=https://www.iea.org/reports/aviation | title=Aviation report | publisher=International Energy Agency | date=2020 | access-date=20 October 2020 | archive-date=6 July 2023 | archive-url=https://web.archive.org/web/20230706035309/https://www.iea.org/reports/aviation | url-status=live}}

= 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.{{cite book | url=https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=83 | title=The Role of Aircraft in Climate Change-Evaluation of Sample Scenarios | chapter=Potential Climate Change from Aviation | publisher=IPCC | author=Joyce E. Penner | display-authors=etal | date=1999 | access-date=21 October 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105753/https://archive.ipcc.ch/ipccreports/sres/aviation/index.php?idp=83 | url-status=live}} 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|link=}} emissions budget would be entirely consumed by aviation emissions to keep the climate change temperature increase below 2 °C by mid-century.{{cite book | last=Bows | first=A. | display-authors=etal | year=2009 | chapter-url=https://www.routledge.com/Aviation-and-Climate-Change-Lessons-for-European-Policy/Bows-Anderson-Upham/p/book/9780415897693 | title=Aviation and Climate Change: Lessons for European Policy | publisher=Routledge | page=146 | chapter=5 | access-date=9 June 2016 | archive-date=16 August 2016 | archive-url=https://web.archive.org/web/20160816135100/https://www.routledge.com/Aviation-and-Climate-Change-Lessons-for-European-Policy/Bows-Anderson-Upham/p/book/9780415897693 | url-status=live}} 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.{{cite journal | author=Alice Bows-Larkin | date=August 2010 | url=http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10106917&fileId=S000192400000395X | title=Aviation and climate change: confronting the challenge | journal=Aeronautical Journal | volume=114 | issue=1158 | pages=459–468 | doi=10.1017/S000192400000395X | s2cid=233361436 | access-date=18 October 2020 | archive-date=2 June 2020 | archive-url=https://web.archive.org/web/20200602164708/https://www.cambridge.org/core/redirect-support/ | url-status=live}}

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.{{cite journal | url=https://www.nature.com/articles/nclimate1866 | date=8 April 2013 | title=Intensification of winter transatlantic aviation turbulence in response to climate change | author=Paul D. Williams | author2=Manoj M. Joshi | journal=Nature Climate Change | volume=3 | issue=7 | page=644 | doi=10.1038/nclimate1866 | bibcode=2013NatCC...3..644W | access-date=21 October 2020 | archive-date=9 June 2023 | archive-url=https://web.archive.org/web/20230609064145/https://www.nature.com/articles/nclimate1866 | url-status=live}} This prediction is supported by data showing that incidents of severe turbulence increased by 55% between 1979 and 2020, attributed to changes in wind velocity at high altitudes.{{Cite news | last1=Topham | first1=Gwyn | last2=correspondent | first2=Gwyn Topham Transport | date=2024-05-21 | title=What causes air turbulence and is the climate crisis making it worse? | url=https://www.theguardian.com/business/article/2024/may/21/what-causes-air-turbulence-and-how-worried-should-passengers-be | access-date=2024-05-28 | work=The Guardian | language=en-GB | issn=0261-3077 | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014849/https://www.theguardian.com/business/article/2024/may/21/what-causes-air-turbulence-and-how-worried-should-passengers-be | url-status=live}}

Aviation {{CO2}} emissions grow despite efficiency innovations to aircraft, powerplants and flight operations.{{cite encyclopedia | last=Bows-Larkin | first=A. | display-authors=etal | year=2016 | article-url=https://www.researchgate.net/publication/303446744 | article=Aviation and Climate Change – The Continuing Challenge | encyclopedia=Encyclopedia of aerospace engineering | at=Fig. 7}}{{cite journal | last1=Timmis | first1=A. | display-authors=etal | year=2014 | title=Environmental impact assessment of aviation emission reduction through the implementation of composite materials | journal=Int J Life Cycle Assess | volume=20 | issue=2 | pages=233–243 | doi=10.1007/s11367-014-0824-0 | s2cid=55899619 | url=https://dspace.lboro.ac.uk/2134/21192 | type=Submitted manuscript | access-date=20 October 2018 | archive-date=28 January 2020 | archive-url=https://web.archive.org/web/20200128181450/https://repository.lboro.ac.uk/articles/Environmental_impact_assessment_of_aviation_emission_reduction_through_the_implementation_of_composite_materials/9450170 | url-status=live}}

Air travel continue to grow.{{cite report | publisher=Boeing | year=2014 | url=http://www.boeing.com/assets/pdf/commercial/cmo/pdf/Boeing_Current_Market_Outlook_2014.pdf | title=Current Market Outlook, 2014–2033 | archive-url=https://web.archive.org/web/20141015114919/http://www.boeing.com/assets/pdf/commercial/cmo/pdf/Boeing_Current_Market_Outlook_2014.pdf | archive-date=15 October 2014}}{{cite web | publisher=Airbus | year=2015 | title=Flying by Numbers: Global Market Forecast 2015–2034 | url=http://www.airbus.com/company/market/forecast/?eID=maglisting_push&tx_maglisting_pi1%5BdocID%5D=89373 | archive-url=https://web.archive.org/web/20151115060157/http://www.airbus.com/company/market/forecast/?eID=maglisting_push&tx_maglisting_pi1%5BdocID%5D=89373 | archive-date=2015-11-15}}

In 2015, the Center for Biological Diversity estimated that aircraft could generate {{val|43|ul=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 {{val|3|u=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.{{cite report | first=Vera | last=Paradee | title=Up in the air: how airplane carbon pollution jeopardizes global climate goals | date=December 2015 | website=Center for Biological Diversity | location=Tucson, AZ | url=https://www.biologicaldiversity.org/programs/climate_law_institute/transportation_and_global_warming/airplane_emissions/pdfs/Airplane_Pollution_Report_December2015.pdf | access-date=17 October 2016 | archive-date=20 January 2018 | archive-url=https://web.archive.org/web/20180120002942/http://www.biologicaldiversity.org/programs/climate_law_institute/transportation_and_global_warming/airplane_emissions/pdfs/Airplane_Pollution_Report_December2015.pdf | url-status=live}}

{{cite press release | date=December 2, 2015 | title=New Report: Airplane Pollution Jeopardizes Paris Climate Goals | url=https://www.biologicaldiversity.org/news/press_releases/2015/airplane-emissions-12-02-2015.html | website=Center for Biological Diversity | access-date=17 October 2016 | archive-date=16 December 2015 | archive-url=https://web.archive.org/web/20151216014614/http://www.biologicaldiversity.org/news/press_releases/2015/airplane-emissions-12-02-2015.html | url-status=live}}

The International Energy Agency projects aviation share of global {{CO2}} emissions may grow from 2.5% in 2019 to 3.5% by 2030.{{cite news | url=https://www.iea.org/commentaries/are-aviation-biofuels-ready-for-take-off | title=Are aviation biofuels ready for take off? | author=Pharoah Le Feuvre | date=18 March 2019 | publisher=International Energy Agency | access-date=11 December 2020 | archive-date=17 September 2023 | archive-url=https://web.archive.org/web/20230917075804/https://www.iea.org/commentaries/are-aviation-biofuels-ready-for-take-off | url-status=live}}

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.{{Cite web | url=https://ec.europa.eu/clima/policies/transport/aviation_en | title=Reducing emissions from aviation | website=Climate Action | date=23 November 2016 | publisher=European Commission | access-date=1 June 2019 | archive-date=22 June 2018 | archive-url=https://web.archive.org/web/20180622053225/https://ec.europa.eu/clima/policies/transport/aviation_en | url-status=live}}

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

Noise

File:Lärmkarte Flughafen Berlin-Tegel.png 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.{{Cite journal | last=Basner | first=Mathias | display-authors=etal | date=2017 | title=Aviation Noise Impacts: State of the Science | journal=Noise & Health | volume=19 | issue=87 | pages=41–50 | doi=10.4103/nah.NAH_104_16 | doi-broken-date=1 November 2024 | doi-access=free | pmid=29192612 | pmc=5437751}} Sleep disruption can be reduced by banning or restricting flying at night, but disturbance progressively decreases and legislation differs across countries.

The ICAO Chapter 14 noise standard applies for aeroplanes submitted for certification after 31 December 2017, and after 31 December 2020 for aircraft below {{cvt|55|t|lb}}, 7 EPNdB (cumulative) quieter than Chapter4.{{cite web | url=https://www.icao.int/environmental-protection/pages/reduction-of-noise-at-source.aspx | title=Reduction of Noise at Source | publisher=ICAO | access-date=4 February 2021 | archive-date=1 June 2023 | archive-url=https://web.archive.org/web/20230601164511/https://www.icao.int/environmental-protection/pages/reduction-of-noise-at-source.aspx | url-status=live}} The FAA Stage 5 noise standards are equivalent.{{cite web | url=https://www.faa.gov/noise/levels/ | title=Aircraft Noise Levels and Stages | date=July 1, 2020 | publisher=FAA | access-date=6 February 2021 | archive-date=30 March 2023 | archive-url=https://web.archive.org/web/20230330184234/https://www.faa.gov/noise/levels | url-status=live}} Higher bypass ratio engines produce less noise. The PW1000G is presented as 75% quieter than previous engines.{{Cite news | title=The Little Gear That Could Reshape the Jet Engine | url=https://www.bloomberg.com/news/articles/2015-10-15/pratt-s-purepower-gtf-jet-engine-innovation-took-almost-30-years | work=Bloomberg | date=October 15, 2015 | author=Peter Coy | access-date=25 November 2020 | archive-date=15 October 2015 | archive-url=https://web.archive.org/web/20151015220739/https://www.bloomberg.com/news/articles/2015-10-15/pratt-s-purepower-gtf-jet-engine-innovation-took-almost-30-years | url-status=live}} Serrated edges or 'chevrons' on the back of the nacelle reduce noise.

A Continuous Descent Approach (CDA) is quieter as less noise is produced while the engines are near idle power.{{cite web | title=Basic Principles of the Continuous Descent Approach (CDA) for the Non-Aviation Community | publisher=UK Civil Aviation Authority | url=http://www.caa.co.uk/docs/68/Basic_Principles_CDA.pdf | archive-url=https://web.archive.org/web/20081109085133/http://www.caa.co.uk/docs/68/Basic_Principles_CDA.pdf | archive-date=2008-11-09}} CDA can reduce noise on the ground by ~1–5 dB per flight.{{cite web | url=https://www.eurocontrol.int/archive_download/all/node/10813 | title=European Joint Industry CDA Action Plan | publisher=Eurocontrol | date=2009 | access-date=25 November 2020 | archive-date=16 March 2021 | archive-url=https://web.archive.org/web/20210316213719/https://www.eurocontrol.int/archive_download/all/node/10813 | url-status=live}}

Water pollution

File:A U.S. Army C-37B aircraft transporting Army Chief of Staff Gen. Raymond T. Odierno, gets de-iced before it departs Joint Base Elmendorf-Richardson, Alaska.jpg 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.{{cite web | date=December 2006 | title=Sector S: Vehicle Maintenance Areas, Equipment Cleaning Areas, or Deicing Areas Located at Air Transportation Facilities | series=Industrial Stormwater Fact Sheet Series | url=https://www.epa.gov/sites/default/files/2016-04/documents/sector_s_airtransmaint.pdf | publisher=U.S. Environmental Protection Agency (EPA) | location=Washington, D.C. | id=EPA-833-F-06-034 | access-date=4 February 2017}}

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.{{rp|101}} Deicing fluids are based on ethylene glycol or propylene glycol.{{rp|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.{{Cite web | date=April 2012 | title=Technical Development Document for the Final Effluent Limitations Guidelines and New Source Performance Standards for the Airport Deicing Category | url=https://www.epa.gov/sites/default/files/2015-06/documents/airport-deicing-tdd-final-2012.pdf | publisher=EPA | id=EPA-821-R-12-005 | access-date=4 February 2017}}{{rp|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.{{rp|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.{{Cite web | date=April 2012 | title=Environmental Impact and Benefit Assessment for the Final Effluent Limitation Guidelines and Standards for the Airport Deicing Category | url=https://www.epa.gov/eg/airport-deicing-effluent-guidelines-documents | publisher=EPA | id=EPA-821-R-12-003 | access-date=4 February 2017 | archive-date=22 September 2017 | archive-url=https://web.archive.org/web/20170922095914/https://www.epa.gov/eg/airport-deicing-effluent-guidelines-documents | url-status=live}}{{rp|2–30}}

Glycol-based deicing fluids are toxic to humans and other mammals.{{cite book | publisher=U.S. Federal Aviation Administration | date=April 2010 | url=https://nap.nationalacademies.org/read/14370/chapter/1 | doi=10.17226/14370 | isbn=978-0-309-11832-3 | title=Alternative Aircraft and Pavement Deicers and Anti-Icing Formulations with Improved Environmental Characteristics}}{{cite web | publisher=SAE International | date=June 13, 2011 | title=Issues and Testing of Non-Glycol Aircraft Ground Deicing Fluids | url=http://www.uqac.ca/amil/en/publications/papers/2009-2012/2011-38-0058.pdf | archive-url=https://web.archive.org/web/20130202231949if_/http://www.uqac.ca/amil/en/publications/papers/2009-2012/2011-38-0058.pdf | archive-date=2013-02-02}} Research into non-toxic alternative deicing fluids is ongoing.

Air pollution

Aviation is the main human source of ozone, a respiratory health hazard, causing an estimated 6,800 premature deaths per year.{{Cite journal | last1=Eastham | first1=Sebastian D. | last2=Barrett | first2=Steven R. H. | date=2016-11-01 | title=Aviation-attributable ozone as a driver for changes in mortality related to air quality and skin cancer | url=http://www.sciencedirect.com/science/article/pii/S1352231016306331 | journal=Atmospheric Environment | language=en | volume=144 | pages=17–23 | doi=10.1016/j.atmosenv.2016.08.040 | bibcode=2016AtmEn.144...17E | issn=1352-2310 | url-access=subscription}}

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,{{cite journal | last1=Herndon | first1=S.C. | display-authors=etal | title=Particulate Emissions from in-use Commercial Aircraft | journal=Aerosol Science and Technology | date=2005 | volume=39 | issue=8 | pages=799–809 | doi=10.1080/02786820500247363 | bibcode=2005AerST..39..799H | doi-access=free}} while significant differences are observed depending on the engine.{{cite journal | last1=Herdon | first1=S.C. | display-authors=etal | title=Commercial Aircraft Engine Emissions Characterization of in-Use Aircraft at Hartsfield-Jackson Atlanta International Airport | journal=Environmental Science & Technology | date=2008 | volume=42 | issue=6 | pages=1877–1883 | doi=10.1021/es072029+ | pmid=18409607 | bibcode=2008EnST...42.1877H}} Other estimates include 4 to 200 × 10¹⁵ particles for 0.1–0.7 gram,{{cite journal | last1=Lobo | first1=P. | last2=Hagen | first2=D.E. | last3=Whitefield | first3=P.D. | title=Measurement and analysis of aircraft engine PM emissions downwind of an active runway at the Oakland International Airport | journal=Atmospheric Environment | date=2012 | volume=61 | pages=114–123 | doi=10.1016/j.atmosenv.2012.07.028 | bibcode=2012AtmEn..61..114L}} or 14 to 710 × 10¹⁵ particles,{{cite journal | last1=Klapmeyer | first1=M.E. | last2=Marr | first2=L.C. | author-link2=Linsey Marr | title=CO₂, NO_x, and Particle Emissions from Aircraft and Support Activities at a Regional Airport | journal=Environmental Science & Technology | date=2012 | volume=46 | issue=20 | pages=10974–10981 | doi=10.1021/es302346x | pmid=22963581 | bibcode=2012EnST...4610974K}} or 0.1–10 × 10¹⁵ black carbon particles for 0.046–0.941 g.{{cite journal | last1=Moore | first1=R.H. | display-authors=etal | title=Take-off engine particle emission indices for in-service aircraft at Los Angeles International Airport | journal=Scientific Data | date=2017 | volume=4 | issue=1 | doi=10.1038/sdata.2017.198 | page=170198 | pmid=29257135 | pmc=5744856 | bibcode=2017NatSD...470198M}}

In the United States, 167,000 piston aircraft engines, representing three-quarters of private airplanes, burn Avgas, releasing lead into the air.{{Cite news | url=https://www.motherjones.com/politics/2013/01/private-planes-still-use-leaded-gasoline/ | title=Leaded Fuel Is a Thing of the Past—Unless You Fly a Private Plane | work=Mother Jones | date=Jan 10, 2013 | language=en | access-date=25 November 2020 | archive-date=17 June 2023 | archive-url=https://web.archive.org/web/20230617141416/https://www.motherjones.com/politics/2013/01/private-planes-still-use-leaded-gasoline/ | url-status=live}} The Environmental Protection Agency estimated this released 34,000 tons of lead into the atmosphere between 1970 and 2007.{{Cite press release | url=https://www.lewisu.edu/news/Newsarticle.htm?PArticleID=8686 | title=Lead-free airplane fuel testing is in progress at Lewis | publisher=Lewis University | date=July 18, 2011 | access-date=25 November 2020 | archive-date=23 December 2022 | archive-url=https://web.archive.org/web/20221223233017/https://www.lewisu.edu/news/Newsarticle.htm?PArticleID=8686 | url-status=live}} 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.{{Cite web | url=https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=14754 | title=Fact Sheet – Leaded Aviation Fuel and the Environment | publisher=FAA | language=en-us | date=November 20, 2019 | access-date=21 May 2017 | archive-date=30 August 2021 | archive-url=https://web.archive.org/web/20210830183606/https://www.faa.gov/news/fact_sheets/news_story.cfm?newsId=14754 | url-status=live}}

Private jet travel

A 2024 study published in Communications Earth & Environment revealed that carbon dioxide emissions from private jet travel surged to 15.6 million tonnes in 2023, a 46% increase compared to 2019. Despite serving only 256,000 individuals—approximately 0.003% of the global population—the industry contributes significantly to greenhouse gas emissions.{{cite web | title=Private jet carbon emissions soar 46%: Study | website=Phys.org | date=2024-11-10 | url=https://phys.org/news/2024-11-private-jet-carbon-emissions-soar.html | access-date=2024-11-11}}

The research further highlights that nearly half of these flights covered distances shorter than 500 kilometers. Moreover, many flights involved empty legs, where aircraft traveled without passengers, often for repositioning or ferry flights.

The private jet industry is poised for further growth, with projections indicating a 33% increase in the global fleet to 26,000 aircraft by 2033.

Mitigation

{{See also|Air travel demand reduction|Climate change mitigation|Electric aircraft|Hydrogen-powered aircraft|Ram air turbine|Solar-powered aircraft}}

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.

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,{{Cite web | url=https://www.icao.int/environmental-protection/Documents/Sustainable%20Aviation%20Fuels%20Guide_100519.pdf | title=Sustainable Aviation Fuels Guide | publisher=ICAO | date=Dec 2018 | access-date=6 December 2020 | archive-date=25 December 2022 | archive-url=https://web.archive.org/web/20221225205602/https://www.icao.int/environmental-protection/Documents/Sustainable%20Aviation%20Fuels%20Guide_100519.pdf | url-status=live}} the Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA).{{Cite web | url=https://www.icao.int/environmental-protection/CORSIA/Pages/default.aspx | title=Carbon Offsetting and Reduction Scheme for International Aviation (CORSIA) | publisher=ICAO | access-date=6 December 2020 | archive-date=18 February 2020 | archive-url=https://web.archive.org/web/20200218173909/https://www.icao.int/environmental-protection/CORSIA/Pages/default.aspx | url-status=live}}

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."{{Cite web | title=The Sixth Carbon Budget: Aviation | url=https://www.theccc.org.uk/wp-content/uploads/2020/12/Sector-summary-Aviation.pdf | access-date=21 May 2021 | archive-date=19 March 2023 | archive-url=https://web.archive.org/web/20230319061812/https://www.theccc.org.uk/wp-content/uploads/2020/12/Sector-summary-Aviation.pdf | url-status=live}}

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.

The initiative is led by ACI Europe, ASD Europe, A4E, CANSO and ERA.{{cite press release | url=https://www.destination2050.eu/wp-content/uploads/2021/02/European-Aviation-Launches-Net-Zero-Emissions-Flightpath-11FEB20217-1.pdf | title=Europe's aviation sector launches ambitious plan to reach net zero CO₂ emissions by 2050 | date=11 February 2021 | publisher=Destination 2050 | access-date=13 February 2021 | archive-date=12 August 2022 | archive-url=https://web.archive.org/web/20220812185726/https://www.destination2050.eu/wp-content/uploads/2021/02/European-Aviation-Launches-Net-Zero-Emissions-Flightpath-11FEB20217-1.pdf | url-status=live}}

This would apply to flights within and departing the European single market and the UK.

In October 2021, the IATA committed to net-zero carbon emissions by 2050.{{Cite press release | title=Net-Zero Carbon Emissions by 2050 | url=https://www.iata.org/en/pressroom/pressroom-archive/2021-releases/2021-10-04-03/ | date=4 October 2021 | publisher=IATA | access-date=1 February 2023 | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014823/https://www.iata.org/en/pressroom/pressroom-archive/2021-releases/2021-10-04-03/ | url-status=live}} In 2022, the ICAO agreed to support a net-zero carbon emission target for 2050.{{Cite news | date=2022-10-07 | title=Climate change: World aviation agrees 'aspirational' net zero plan | language=en-GB | work=BBC News | url=https://www.bbc.com/news/science-environment-63165607 | access-date=31 January 2023 | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014824/https://www.bbc.com/news/science-environment-63165607 | url-status=live}}

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.

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.

Carbon offsets would be preferred if carbon credits are less expensive than SAFs, but they may be unreliable, while specific routing could avoid contrails.

As of 2023, fuel represents 20–30% of the airlines' operating costs, while SAF is 2–4 times more expensive than fossil jet fuel.

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.

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.{{cite journal | last1=Bergero | first1=Candelaria | display-authors=etal | title=Pathways to net-zero emissions from aviation | journal=Nature Sustainability | date=30 January 2023 | volume=6 | issue=4 | pages=404–414 | doi=10.1038/s41893-022-01046-9 | s2cid=256449498 | doi-access=free | bibcode=2023NatSu...6..404B}}

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.

Biofuels can be introduced quickly and with little aircraft modification, but are restricted by scale and feedstock availability, and few are low-carbon.

Producing enough renewable electricity to produce green hydrogen would be a costly challenge and would need substantial aircraft and infrastructure modification.

Synthetic fuels would need little aircraft modification, but necessitates green hydrogen feedstock and large scale direct {{CO2}} air capture at high costs.

Low-carbon Ammonia would also need costly green hydrogen at scale, and would need substantial aircraft and infrastructure modifications.{{cite book | title=Net zero aviation fuels – resource requirements and environmental impacts | date=February 2023 | publisher=The Royal Society | url=https://royalsociety.org/-/media/policy/projects/net-zero-aviation/net-zero-aviation-fuels-policy-briefing.pdf | access-date=1 March 2023 | archive-date=28 February 2023 | archive-url=https://web.archive.org/web/20230228180830/https://royalsociety.org/-/media/policy/projects/net-zero-aviation/net-zero-aviation-fuels-policy-briefing.pdf | url-status=live}}

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 {{abbr|GHG|greenhous gases}} emissions remain and would need to be counterbalanced by deployment of carbon dioxide removal methods.{{cite news | url=https://www.flightglobal.com/airlines/carbon-removal-a-necessity-for-aviation-to-reach-net-zero-emissions-ipcc-report/152566.article | title=Carbon removal 'a necessity' for aviation to reach net-zero emissions: IPCC report | author=Lewis Harper | date=22 March 2023 | work=FlightGlobal}}

On 29 March 2003, during a Senate hearing, hydrogen propulsion proponents like ZeroAvia or Universal Hydrogen bemoaned that the incumbents like GE Aerospace or Boeing were supporting sustainable aviation fuel (SAF) because it does not require major changes to existing infrastructure.{{cite news | url=https://www.flightglobal.com/engines/us-aerospace-leaders-disagree-on-best-path-to-net-zero-carbon-emissions/152699.article | title=US aerospace leaders disagree on best path to 'net-zero' carbon emissions | author=Jon Hemmerdinger | date=30 March 2023 | work=FlightGlobal | access-date=31 March 2023 | archive-date=30 March 2023 | archive-url=https://web.archive.org/web/20230330223152/https://www.flightglobal.com/engines/us-aerospace-leaders-disagree-on-best-path-to-net-zero-carbon-emissions/152699.article | url-status=live}}

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.{{cite web | url=https://drive.google.com/file/d/1wUwc3XCdwS4zfOTKbUdBtXBwKKHuahgR/view | title=Bridging the Gap to 2050 – How to Decarbonize Aviation Faster With Today's Technologies | work=Sustainable Aviation Lab GmbH | publisher=Hamburg Investment and Development Bank | date=April 2023 | access-date=28 April 2023 | archive-date=28 April 2023 | archive-url=https://web.archive.org/web/20230428085554/https://drive.google.com/file/d/1wUwc3XCdwS4zfOTKbUdBtXBwKKHuahgR/view | url-status=live}}

The airline industry faces a significant climate challenge due to the scarcity of clean fuel options, exemplified by the recent establishment of LanzaJet Inc.'s $200 million facility in Georgia, the first to convert ethanol into jet engine-compatible fuel, with an annual production target of 9 million gallons of sustainable aviation fuel (SAF). This volume, however, is minuscule compared to the global demand, as evidenced by the world's airlines consuming 90 billion gallons of jet fuel last year, and even major airlines like IAG SA (parent company of British Airways) using only 0.66% of their total fuel consumption as SAF, with a goal to increase this to 10% by 2030. Incentives such as the $1.75 per gallon SAF credit offered by the US Inflation Reduction Act, set to expire in 2027, aim to boost SAF usage, while L.E.K. Consulting forecasts that alcohol-to-jet technology will become the dominant source of SAF by the mid-next decade. Meanwhile, emerging technologies like e-kerosene, though potentially reducing climate impacts significantly, face economic challenges as they cost nearly seven times more than traditional jet fuel, and the future of 45 proposed power-to-liquids plants in Europe remains uncertain, according to Transport & Environment.{{Cite news | date=2024-04-11 | title=The Airline Industry's Biggest Climate Challenge: A Lack of Clean Fuel | url=https://www.bloomberg.com/news/articles/2024-04-11/united-british-airways-search-for-sustainable-aviation-fuel-to-reach-net-zero | access-date=2024-04-15 | work=Bloomberg.com | language=en | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014824/https://www.bloomberg.com/news/articles/2024-04-11/united-british-airways-search-for-sustainable-aviation-fuel-to-reach-net-zero | url-status=live}}

= Technology improvements =

== Electric aircraft ==

File:Pipistrel Velis Electro sn003 LJAJ left.jpg was the first type certificated electric aircraft on 10 June 2020.]]

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.{{cite news | author=Philip E. Ross | date=1 Jun 2018 | title=Hybrid Electric Airliners Will Cut Emissions—and Noise | work=IEEE Spectrum | url=https://spectrum.ieee.org/hybrid-electric-airliners-will-cut-emissionsand-noise | access-date=31 July 2024 | archive-date=4 March 2024 | archive-url=https://web.archive.org/web/20240304075513/https://spectrum.ieee.org/hybrid-electric-airliners-will-cut-emissionsand-noise | url-status=live}} 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 6,555 Wh/kg of fuel: a {{#expr:6545/145round0}}:1 ratio.{{cite news | author=Bjorn Fehrm | date=June 30, 2017 | title=Bjorn's Corner: Electric aircraft | work=Leeham | url=https://leehamnews.com/2017/06/30/bjorns-corner-electric-aircraft/ | access-date=24 November 2020 | archive-date=28 July 2023 | archive-url=https://web.archive.org/web/20230728215158/https://leehamnews.com/2017/06/30/bjorns-corner-electric-aircraft/ | url-status=live}} For Collins Aerospace, this 1:50 ratio forbids electric propulsion for long-range aircraft.{{cite news | author=Paul Seidenman | date=Jan 10, 2019 | title=How Batteries Need To Develop To Match Jet Fuel | work=Aviation Week Network | url=https://www.mro-network.com/engines-engine-systems/how-batteries-need-develop-match-jet-fuel | access-date=24 November 2020 | archive-date=19 April 2019 | archive-url=https://web.archive.org/web/20190419070640/https://www.mro-network.com/engines-engine-systems/how-batteries-need-develop-match-jet-fuel | url-status=live}} By November 2019, the German Aerospace Center estimated large electric planes could be available by 2040. Large, long-haul aircraft are unlikely to become electric before 2070 or within the 21st century, whilst smaller aircraft can be electrified.{{Cite news | author=Chris Baraniuk | date=18 June 2020 | title=The largest electric plane ever to fly | work=Future Planet | publisher=BBC | url=https://www.bbc.com/future/article/20200617-the-largest-electric-plane-ever-to-fly | access-date=18 October 2020 | archive-date=5 September 2023 | archive-url=https://web.archive.org/web/20230905230153/https://www.bbc.com/future/article/20200617-the-largest-electric-plane-ever-to-fly | url-status=live}} 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.{{cite news | author=Kerry Reals | date=7 January 2019 | title=Don't count on technology to save us | work=Flightglobal | url=https://www.flightglobal.com/news/articles/analysis-dont-count-on-technology-to-save-us-454396/ | access-date=20 October 2020 | archive-date=25 April 2019 | archive-url=https://web.archive.org/web/20190425132458/https://www.flightglobal.com/news/articles/analysis-dont-count-on-technology-to-save-us-454396/ | url-status=live}} 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. This would greatly reduce the value of the existing fleet of aircraft, however.

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.

== Hydrogen-powered aircraft ==

In 2020, Airbus unveiled liquid-hydrogen-powered aircraft concepts as zero-emissions airliners, poised for 2035.{{cite news | url=https://aviationweek.com/aerospace/manufacturing-supply-chain/boeing-moves-forward-airbus-a321xlr-competitor-plan | title=Boeing Moves Forward With Airbus A321XLR-Competitor Plan | author=Guy Norris | date=February 4, 2021 | work=Aviation Week | access-date=4 February 2021 | archive-date=26 March 2023 | archive-url=https://web.archive.org/web/20230326221630/https://aviationweek.com/aerospace/manufacturing-supply-chain/boeing-moves-forward-airbus-a321xlr-competitor-plan | url-status=live}}

Aviation, like industrial processes that cannot be electrified, could use primarily Hydrogen-based fuel.{{cite press release | url=https://www.pik-potsdam.de/en/news/latest-news/hydrogen-instead-of-electrification-potentials-and-risks-for-climate-targets | title=Hydrogen instead of electrification? Potentials and risks for climate targets | date=6 May 2021 | publisher=Potsdam Institute for Climate Impact Research | access-date=12 May 2021 | archive-date=30 May 2023 | archive-url=https://web.archive.org/web/20230530205909/https://www.pik-potsdam.de/en/news/latest-news/hydrogen-instead-of-electrification-potentials-and-risks-for-climate-targets | url-status=live}}

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. A short-range aircraft (< {{cvt|2,000|km|nmi|disp=comma}}) 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 (> {{cvt|7,000|km|nmi|disp=comma}}) also with H₂ turbines could reduce climate impact by 40–50% for a 40–50% additional cost. Research and development would be required, in aircraft technology and into hydrogen infrastructure, regulations and certification standards.{{Cite report | title=Hydrogen-powered aviation | url=https://cleansky.paddlecms.net/sites/default/files/2021-10/20200507_Hydrogen-Powered-Aviation-report.pdf | date=May 2020 | publisher=EU Clean Sky 2 and Fuel Cells and Hydrogen 2 Joint Undertakings | access-date=6 December 2022 | archive-date=5 May 2022 | archive-url=https://web.archive.org/web/20220505211324/https://cleansky.paddlecms.net/sites/default/files/2021-10/20200507_Hydrogen-Powered-Aviation-report.pdf | url-status=live}}

== Sustainable aviation fuels (SAF) ==

== 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.

Those could be reduced to €20–270 per ton of {{CO2}} in 2050, but maybe not early enough to replace fossil fuels.

Climate policies could bear the risk of e-fuel uncertain availability, and Hydrogen and e-fuels may be prioritised when direct electrification is inaccessible.{{cite journal | title=Potential and risks of hydrogen-based e-fuels in climate change mitigation | journal=Nature Climate Change | date=6 May 2021 | volume=11 | issue=5 | page=384 | doi=10.1038/s41558-021-01032-7 | bibcode=2021NatCC..11..384U | s2cid=233876615 | url=https://www.nature.com/articles/s41558-021-01032-7 | url-access=subscription | last1=Ueckerdt | first1=Falko | last2=Bauer | first2=Christian | last3=Dirnaichner | first3=Alois | last4=Everall | first4=Jordan | last5=Sacchi | first5=Romain | last6=Luderer | first6=Gunnar | display-authors=1 | others=(Potsdam Institute for Climate Impact Research) | access-date=12 May 2021 | archive-date=12 September 2023 | archive-url=https://web.archive.org/web/20230912223142/https://www.nature.com/articles/s41558-021-01032-7 | url-status=live}}

== Aircraft with lower design speed and altitude ==

According to a research project focusing on short to medium range passenger aircraft, design for subsonic instead of transonic speed (about 15% less speed) would save 21% of fuel compared to an aircraft of conventional design speed and similar characteristics in terms of size, range and expected general technology improvements. The lower mach number and turboprop instead of turbofan propulsion leads to lower flight altitude with a disproportionately high reduction in Non-CO₂ emissions. Thus, over 60% climate impact reduction can be potentially achieved by such advanced turboprop aircraft compared to current short to medium range passenger aircraft, yet before switching to synthetic fuels. {{cite web |url= https://drive.google.com/file/d/1AHme_5PLwQZliwaksKzahgU2GeOS6jei/view |title= EXACT Results - How Slow Should We Go - DLR Presentation for Safe Landing |publisher= Georgi Atanasov |access-date= 2025-01-01 |archive-url= https://web.archive.org/web/20250101155327/https://drive.google.com/file/d/1AHme_5PLwQZliwaksKzahgU2GeOS6jei/view |archive-date= 2025-01-01 }}{{Cite web |title=Short Medium Range Turboprop-Powered Aircraft as an Enabler for Low Climate Impact |url=https://elib.dlr.de/148094/1/Short-Range_Turboprop.pdf/ |access-date=2025-01-01 |publisher= G. Atanasov, D. Silberhorn, P. Wassink, Dr. J. Hartmann, E. Prenzel, S. Wöhler, Dr. N. Dzikus, B. Fröhler, Dr. T. Zill, Dr. B. Nagel; DLR - Deutsches Zentrum für Luft- und Raumfahrt}}

= Reducing air travel =

File:Annual air transport consumption in the UK by income quintile, 1920–2019.jpg

File:Global distribution of aviation fuel use.jpg

{{Excerpt|Air travel demand reduction|Significance to global air travel emissions reduction|hat=no}}

== Measures ==

File:Taiwan High Speed Rail (0291).JPG in 2007]]

The {{abbr|ICCT|International Council on Clean Transportation}} estimates that 3% of the global population take regular flights.

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.{{Cite journal | author=Stefan Gössling | title=The global scale, distribution and growth of aviation: Implications for climate change | date=November 2020 | journal=Global Environmental Change | volume=65 | doi=10.1016/j.gloenvcha.2020.102194 | pmid=36777089 | pmc=9900393 | s2cid=228984718 | doi-access=free | bibcode=2020GEC....6502194G}}

File:Per-capita-co2-aviation-adjusted.svg

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.{{Cite web | title=2021–2022 EIB Climate Survey, part 2 of 3: Shopping for a new car? Most Europeans say they will opt for hybrid or electric | url=https://www.eib.org/en/surveys/climate-survey/4th-climate-survey/hybrid-electric-petrol-cars-flying-holidays-climate.htm | date=22 March 2022 | publisher=European Investment Bank | access-date=5 April 2022 | archive-date=13 April 2023 | archive-url=https://web.archive.org/web/20230413031533/https://www.eib.org/en/surveys/climate-survey/4th-climate-survey/hybrid-electric-petrol-cars-flying-holidays-climate.htm | url-status=live}}

;Short-haul flight ban

: {{#section:Short-haul flight ban|summary}}

;Flight shame

: In Sweden the concept of "flight shame" or "flygskam" has been cited as a cause of falling air travel.{{cite news | url=https://www.telegraph.co.uk/travel/news/is-swedens-flight-shame-movement-dampening-demand-for-air-travel/ | title=Is Sweden's 'flight shame' movement dampening demand for air travel? | first=Gavin | last=Haines | date=31 May 2019 | access-date=1 June 2019 | via=www.telegraph.co.uk | newspaper=The Daily Telegraph | archive-date=12 May 2023 | archive-url=https://web.archive.org/web/20230512205140/https://www.telegraph.co.uk/travel/news/is-swedens-flight-shame-movement-dampening-demand-for-air-travel/ | url-status=live}} 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.{{cite news | url=https://www.flightglobal.com/news/articles/flight-shaming-is-changing-the-face-of-travel-460329/ | title='Flight shaming' is changing the face of travel | date=6 Sep 2019 | author=Kerry Reals | work=Flightglobal | access-date=8 September 2019 | archive-date=15 September 2019 | archive-url=https://web.archive.org/web/20190915233056/https://www.flightglobal.com/news/articles/flight-shaming-is-changing-the-face-of-travel-460329/ | url-status=live}} 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.{{cite news | url=https://www.flightglobal.com/strategy/flight-shame-a-factor-in-swedish-traffic-decline/136087.article | title='Flight shame' a factor in Swedish traffic decline | date=10 January 2020 | work=Flightglobal | access-date=11 January 2020 | archive-date=28 November 2022 | archive-url=https://web.archive.org/web/20221128231958/https://www.flightglobal.com/strategy/flight-shame-a-factor-in-swedish-traffic-decline/136087.article | url-status=live}}

; 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."{{cite journal | last1=Fuso Nerini | first1=Francesco | display-authors=etal | title=Personal carbon allowances revisited | journal=Nature Sustainability | date=16 August 2021 | volume=4 | issue=12 | pages=1025–1031 | doi=10.1038/s41893-021-00756-w | s2cid=237101457 | doi-access=free | bibcode=2021NatSu...4.1025F}}{{cite news | title=Pandemic and digitalization set stage for revival of a cast-off idea: Personal carbon allowances | url=https://phys.org/news/2021-08-pandemic-digitalization-stage-revival-cast-off.html | work=phys.org | date=August 16, 2021 | access-date=27 February 2023 | archive-date=6 November 2023 | archive-url=https://web.archive.org/web/20231106034011/https://phys.org/news/2021-08-pandemic-digitalization-stage-revival-cast-off.html | url-status=live}}{{cite news | title=Opinion: We Need Cap-and-Trade For Individuals As Well As Companies | url=https://www.bloomberg.com/opinion/articles/2021-08-25/personal-cap-and-trade-do-you-know-what-your-carbon-allowance-is | date=25 Aug 2021 | agency=Bloomberg | access-date=28 February 2023 | archive-date=24 December 2022 | archive-url=https://web.archive.org/web/20221224205029/https://www.bloomberg.com/opinion/articles/2021-08-25/personal-cap-and-trade-do-you-know-what-your-carbon-allowance-is | url-status=live}}{{excessive citations inline|reason=the original study is sufficient, the others are just paraphrasing it|date=February 2023}} Everyone would have a share of allowed carbon emissions and would need to trade further emissions allowances.{{cite news | title=How personal carbon allowances can help normal people fight climate change | url=https://www.popsci.com/environment/personal-carbon-allowance/ | work=Popular Science | date=28 August 2021 | access-date=27 February 2023 | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014825/https://www.popsci.com/environment/personal-carbon-allowance/ | url-status=live}}{{importance inline|reason=paraphrasing the previous definition|date=February 2023}} An alternative would be rationing everyone's flights: an "individual cap on air travel, that people can trade with each other".{{cite news | last1=Sodha | first1=Sonia | title=Opinion: A radical way to cut emissions – ration everyone's flights | url=https://www.theguardian.com/commentisfree/2018/may/09/cut-emissions-flights-air-travel-flying | work=The Guardian | date=9 May 2018 | access-date=27 February 2023 | archive-date=21 August 2024 | archive-url=https://web.archive.org/web/20240821014825/https://www.theguardian.com/commentisfree/2018/may/09/cut-emissions-flights-air-travel-flying | url-status=live}}

= Economic measures =

== Emissions trading ==

File:EUA future real price.pdf]]

ICAO has endorsed emissions trading to reduce aviation {{CO2}} emission, guidelines were to be presented to the 2007 ICAO Assembly.{{cite press release | url=https://www.icao.int/secretariat/SecretaryGeneral/aviation_day/2005/pio200512_e.pdf | title=International Civil Aviation Day calls for the greening of aviation | date=30 November 2005 | publisher=ICAO | access-date=21 November 2020 | archive-date=29 May 2017 | archive-url=https://web.archive.org/web/20170529191253/https://www.icao.int/secretariat/SecretaryGeneral/aviation_day/2005/pio200512_e.pdf | url-status=live}} 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.{{cite report | url=https://ec.europa.eu/clima/sites/clima/files/transport/aviation/docs/report_publ_cons_en.pdf | publisher=European Commission | title=Reducing the Climate Change Impact of Aviation | year=2005 | access-date=21 November 2020 | archive-date=11 August 2021 | archive-url=https://web.archive.org/web/20210811040209/https://ec.europa.eu/clima/sites/clima/files/transport/aviation/docs/report_publ_cons_en.pdf | url-status=live}}{{cite press release | title=Climate change: Commission proposes bringing air transport into EU Emissions Trading Scheme | publisher=European Commission | date=2006-12-20 | url=https://ec.europa.eu/commission/presscorner/detail/en/IP_06_1862 | access-date=20 November 2020 | archive-date=22 May 2023 | archive-url=https://web.archive.org/web/20230522101936/https://ec.europa.eu/commission/presscorner/detail/en/IP_06_1862 | url-status=live}} 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.{{cite report | author=Lee, D. | display-authors=etal | year=2013 | url=http://www.cate.mmu.ac.uk/wp-content/uploads/Bridging_the_aviation_emissions_gap_010313.pdf | title=Bridging the aviation CO₂ emissions gap: why emissions trading is needed | publisher=Centre for Aviation, Transport and the Environment | access-date=4 March 2013 | archive-date=30 May 2013 | archive-url=https://web.archive.org/web/20130530181212/http://www.cate.mmu.ac.uk/wp-content/uploads/Bridging_the_aviation_emissions_gap_010313.pdf | url-status=dead}}

== 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.{{Cite news | url=https://www.reuters.com/article/us-climate-change-eu-flights-idUSKBN20X2RA | title=Ban short-haul flights for climate? In EU poll 62% say yes | author=Kate Abnett | work=Reuters | date=10 March 2020 | access-date=20 October 2020 | archive-date=24 December 2022 | archive-url=https://web.archive.org/web/20221224002805/https://www.reuters.com/article/us-climate-change-eu-flights-idUSKBN20X2RA | url-status=live}}

Aviation taxation could reflect all its external costs and could be included in an emissions trading scheme.{{cite web | url=http://www.verifavia.com/bases/ressource_pdf/122/AQ-ICF-2006-Impact-on-allowances.pdf | title=Including Aviation into the EU ETS: Impact on EU allowance prices | author=ICF Consulting | date=1 February 2006 | access-date=15 October 2014 | archive-date=4 May 2015 | archive-url=https://web.archive.org/web/20150504023059/http://www.verifavia.com/bases/ressource_pdf/122/AQ-ICF-2006-Impact-on-allowances.pdf | url-status=live}}

International aviation emissions escaped international regulation until the ICAO triennial conference in 2016 agreed on the CORSIA offset scheme.{{Cite web | url=https://www.icao.int/environmental-protection/CORSIA/Documents/Resolution_A39_3.pdf | publisher=ICAO | title=Resolution A39-3: Consolidated statement of continuing ICAO policies and practices related to environmental protection – Global Market-based Measure (MBM) scheme | date=15 February 2019 | access-date=15 February 2019 | archive-date=30 September 2019 | archive-url=https://web.archive.org/web/20190930185709/https://www.icao.int/environmental-protection/CORSIA/Documents/Resolution_A39_3.pdf | url-status=live}}

Due to low or nonexistent taxes on aviation fuel, air travel has a competitive advantage over other transportation modes.{{cite web | url=https://www.euractiv.com/section/transport/news/study-aviation-tax-breaks-cost-eu-states-39-billion-a-year/ | title=Study: Aviation tax breaks cost EU states €39 billion a year | date=25 July 2013 | website=euractiv | access-date=18 January 2019 | archive-date=25 April 2019 | archive-url=https://web.archive.org/web/20190425132454/https://www.euractiv.com/section/transport/news/study-aviation-tax-breaks-cost-eu-states-39-billion-a-year/ | url-status=live}}{{cite news | url=https://www.transportenvironment.org/press/eu-governments-miss-out-%E2%82%AC39bn-year-due-aviation%E2%80%99s-tax-breaks | title=EU governments miss out on up to €39bn a year due to aviation's tax breaks | work=Transport and Environment | date=July 24, 2013 | access-date=18 January 2019 | archive-date=25 April 2019 | archive-url=https://web.archive.org/web/20190425132456/https://www.transportenvironment.org/press/eu-governments-miss-out-%E2%82%AC39bn-year-due-aviation%E2%80%99s-tax-breaks | url-status=dead}}

= Carbon offsetting =

File:Windmill D1 (Thornton Bank).jpg.]]

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. More than 90% of rainforest offset credits certified by Verra's Verified Carbon Standard may not represent genuine carbon reductions.{{cite news | last1=Greenfield | first1=Patrick | title=Revealed: more than 90% of rainforest carbon offsets by biggest certifier are worthless, analysis shows | url=https://www.theguardian.com/environment/2023/jan/18/revealed-forest-carbon-offsets-biggest-provider-worthless-verra-aoe | work=The Guardian | date=18 January 2023 | archive-date=14 February 2023 | archive-url=https://web.archive.org/web/20230214230413/https://www.theguardian.com/environment/2023/jan/18/revealed-forest-carbon-offsets-biggest-provider-worthless-verra-aoe | url-status=live}}

== 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,{{cite web | title=British Airways Carbon Offset Programme | publisher=British Airways | url=http://www.britishairways.com/travel/csr-your-footprint/public/en_gb | access-date=2010-05-02 | archive-date=24 April 2012 | archive-url=https://web.archive.org/web/20120424080053/http://www.britishairways.com/travel/csr-your-footprint/public/en_gb | url-status=live}} Continental Airlines,{{cite web | title=Continental Airlines Carbon Offset Programme | publisher=Continental Airlines | url=http://www.continental.com/web/en-US/content/company/globalcitizenship/offset.aspx | access-date=2010-05-02 | archive-url=https://web.archive.org/web/20120302194628/http://www.continental.com/web/en-US/content/company/globalcitizenship/offset.aspx | archive-date=2012-03-02}}{{cite news | title=Continental Airlines Carbon Offset Schemes | publisher=Bloomberg | url=http://www.businessweek.com/bwdaily/dnflash/content/mar2008/db20080321_437700.htm | archive-url=https://web.archive.org/web/20080328063137/http://www.businessweek.com/bwdaily/dnflash/content/mar2008/db20080321_437700.htm | archive-date=28 March 2008 | access-date=2010-05-02}} easyJet,;{{cite web | title=easyJet Carbon Offset Programme | publisher=easyJet | url=http://www.easyjet.com/EN/Environment/index.shtml | access-date=2010-05-02 | archive-date=4 October 2012 | archive-url=https://web.archive.org/web/20121004053825/http://www.easyjet.com/EN/Environment/index.shtml | url-status=dead}} and also Air Canada, Air New Zealand, Delta Air Lines, Emirates Airlines, Gulf Air, Jetstar, Lufthansa, Qantas, United Airlines and Virgin Australia.{{Cite web | url=https://www.conserve-energy-future.com/airlines-that-offer-carbon-offset-programs.php | title=11 Airlines That Offer Carbon Offset Programs | access-date=18 October 2020 | archive-date=28 May 2023 | archive-url=https://web.archive.org/web/20230528131753/https://www.conserve-energy-future.com/airlines-that-offer-carbon-offset-programs.php | url-status=live}} Consumers can also purchase offsets on the individual market. There are certification standards for these,{{Cite web | url=https://www.nytimes.com/2019/07/24/climate/nyt-climate-newsletter-carbon-offsets.html | title=How to Buy Carbon Offsets | website=The New York Times | access-date=18 October 2020 | archive-date=11 August 2023 | archive-url=https://web.archive.org/web/20230811010900/https://www.nytimes.com/2019/07/24/climate/nyt-climate-newsletter-carbon-offsets.html | url-status=live}}{{subscription required}} including the Gold Standard{{Cite web | url=https://www.goldstandard.org/ | title=The Gold Standard | access-date=18 October 2020 | archive-date=25 September 2023 | archive-url=https://web.archive.org/web/20230925060331/https://www.goldstandard.org/ | url-status=live}} and the Green-e.{{Cite web | url=https://www.green-e.org/certified-resources/carbon-offsets | title=Find Green-e Certified Carbon Offsets | access-date=18 October 2020 | archive-date=4 July 2023 | archive-url=https://web.archive.org/web/20230704224644/https://www.green-e.org/certified-resources/carbon-offsets | url-status=live}}

== 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. 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.

Their position is that emissions in problematic sectors, like aviation, should be offset by greenhouse gas removal, carbon capture and storage and reforestation.

The UK will include international aviation and shipping in their carbon budgets and hopes other countries will too.{{Cite web | title=UK to include aviation in carbon emissions targets | url=https://centreforaviation.com/analysis/reports/uk-to-include-aviation-in-carbon-emissions-targets-558310 | date=27 Apr 2021 | website=CAPA – Centre for Aviation | access-date=15 May 2021 | archive-date=1 June 2023 | archive-url=https://web.archive.org/web/20230601153428/https://centreforaviation.com/analysis/reports/uk-to-include-aviation-in-carbon-emissions-targets-558310 | url-status=live}}

== Airline offsets ==

Some airlines have been carbon-neutral like Costa Rican Nature Air,{{cite news | url=https://news.un.org/en/story/2008/11/282442-carbon-neutral-airline-gets-board-un-scheme-cut-greenhouse-gas-emissions | title=Carbon neutral airline gets on board UN scheme to cut greenhouse gas emissions | date=20 November 2008 | work=UN News | access-date=2 December 2020 | archive-date=7 April 2022 | archive-url=https://web.archive.org/web/20220407114453/https://news.un.org/en/story/2008/11/282442-carbon-neutral-airline-gets-board-un-scheme-cut-greenhouse-gas-emissions | url-status=live}} or claim to be, like Canadian Harbour Air Seaplanes.{{cite web | url=https://www.harbourair.com/about/corporate-responsibility/going-green/ | title=Corporate Responsibility > Going Green | publisher=Harbour Air | access-date=2 December 2020 | archive-date=7 May 2021 | archive-url=https://web.archive.org/web/20210507123709/https://www.harbourair.com/about/corporate-responsibility/going-green/ | url-status=live}} Long-haul low-cost venture Fly POP aims to be carbon neutral.{{cite press release | url=https://www.flypop.co.uk/16/301/flypop-plans-to-be-first-international-carbon-neutral-airline | title=flypop plans to be first international carbon-neutral airline | publisher=flypop | date=17 July 2019 | access-date=2 December 2020 | archive-date=26 November 2020 | archive-url=https://web.archive.org/web/20201126173230/https://www.flypop.co.uk/16/301/flypop-plans-to-be-first-international-carbon-neutral-airline | url-status=dead}}

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.{{cite press release | url=https://corporate.airfrance.com/en/news/air-france-proactively-offset-100-co2-emissions-its-domestic-flights-january-1st-2020 | title=Air France to proactively offset 100% of {{CO2}} emissions on its domestic flights as of January 1st, 2020 | date=1 October 2019 | publisher=Air France | access-date=3 January 2020 | archive-date=9 February 2023 | archive-url=https://web.archive.org/web/20230209042356/https://corporate.airfrance.com/en/news/air-france-proactively-offset-100-co2-emissions-its-domestic-flights-january-1st-2020 | url-status=dead}}

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 2019–2020 financial year.

Its {{CO2}} emissions were 77 g per passenger in its 2018–2019 financial year, down from 78.4 g the previous year.{{cite news | url=https://www.flightglobal.com/news/articles/easyjet-to-offset-carbon-emissions-across-whole-netw-462389/ | title=EasyJet to offset carbon emissions across whole network | date=19 Nov 2019 | author=David Kaminski-Morrow | work=Flightglobal | access-date=19 November 2019 | archive-date=28 November 2019 | archive-url=https://web.archive.org/web/20191128203530/https://www.flightglobal.com/news/articles/easyjet-to-offset-carbon-emissions-across-whole-netw-462389/ | url-status=live}}

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.{{cite news | url=https://www.flightglobal.com/ba-begins-offsetting-domestic-flight-emissions/135987.article | title=BA begins offsetting domestic flight emissions | date=3 January 2020 | work=Flightglobal | access-date=3 January 2020 | archive-date=3 January 2020 | archive-url=https://web.archive.org/web/20200103082900/https://www.flightglobal.com/ba-begins-offsetting-domestic-flight-emissions/135987.article | url-status=live}}

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.{{cite news | url=https://www.flightglobal.com/airlines/jetblue-to-be-first-major-us-airline-to-offset-all-emissions-from-domestic-flights/136007.article | title=JetBlue to be first major US airline to offset all emissions from domestic flights | author=Pilar Wolfsteller | date=6 January 2020 | work=Flightglobal | access-date=7 January 2020 | archive-date=6 June 2023 | archive-url=https://web.archive.org/web/20230606104520/https://www.flightglobal.com/airlines/jetblue-to-be-first-major-us-airline-to-offset-all-emissions-from-domestic-flights/136007.article | url-status=live}} In August 2020, JetBlue became entirely carbon-neutral for its U.S. domestic flights, using efficiency improvements and carbon offsets. Delta Air Lines pledged to do the same within ten years.{{cite news | url=https://www.cnn.com/2020/02/14/business/delta-carbon-neutral/index.html | title=Delta burns tons of jet fuel – but says it's on track to be carbon neutral. What? | date=Feb 14, 2020 | work=CNN | access-date=18 October 2020 | archive-date=20 June 2023 | archive-url=https://web.archive.org/web/20230620225747/https://www.cnn.com/2020/02/14/business/delta-carbon-neutral/index.html | url-status=live}}

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.{{cite news | url=https://www.flightglobal.com/strategy/united-to-invest-in-direct-air-capture-as-it-makes-2050-carbon-neutral-pledge/141542.article | title=United to invest in 'direct air capture' as it makes 2050 carbon-neutral pledge | author=Jon Hemmerdinger | date=10 December 2020 | work=Flightglobal | access-date=10 December 2020 | archive-date=29 May 2023 | archive-url=https://web.archive.org/web/20230529162756/https://www.flightglobal.com/strategy/united-to-invest-in-direct-air-capture-as-it-makes-2050-carbon-neutral-pledge/141542.article | url-status=live}}

= Air traffic management improvements =

File:European airways.svg 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%. 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.{{Cite book | last1=Crespo | first1=Daniel Calleja | last2=de Leon | first2=Pablo Mendes | date=2011 | title=Achieving the Single European Sky: Goals and Challenges | url=https://books.google.com/books?id=ktGflCyLQh0C | location=Alphen aan de Rijn | publisher=Kluwer Law International | pages=4–5 | isbn=978-90-411-3730-2}} By 2007, 12 million tons of {{CO2}} emissions per year were caused by the lack of a Single European Sky. 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.{{Cite news | url=https://www.euractiv.com/section/aviation/news/corona-crisis-and-brexit-boost-eu-air-traffic-reform-hopes/ | title=Corona-crisis and Brexit boost EU air traffic reform hopes | author=Sam Morgan | work=Euractiv | date=22 September 2020 | access-date=19 October 2020 | archive-date=22 December 2022 | archive-url=https://web.archive.org/web/20221222105754/https://www.euractiv.com/section/aviation/news/corona-crisis-and-brexit-boost-eu-air-traffic-reform-hopes/ | url-status=live}}

= Operations improvements =

File:Air traffic optimal climat-cost relation.jpg

; Non-{{CO2}} emissions

: Besides carbon dioxide, aviation produces nitrogen oxides ({{chem|N|O|x}}), particulates, unburned hydrocarbons (UHC) and contrails. Flight routes can be optimized: modelling {{CO2}}, {{chem|H|2|O}} and {{chem|N|O|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%.{{cite journal | journal=Atmospheric Environment | date=September 2014 | title=Reduction of the air traffic's contribution to climate change: A REACT4C case study | author=Volker Grewe | volume=94 | page=616 | doi=10.1016/j.atmosenv.2014.05.059 | bibcode=2014AtmEn..94..616G | display-authors=etal | doi-access=free}} A 2000 feet (~600 m) lower cruise altitude than the optimal altitude has a {{#expr:100-48.6/61.8*100round0}}% lower radiative forcing, while a 2000 feet higher cruise altitude {{#expr:67.4/61.8*100-100round0}}% higher radiative forcing.{{cite journal | doi=10.3390/aerospace8020036 | doi-access=free | title=Mitigation of Non-{{CO2}} Aviation's Climate Impact by Changing Cruise Altitudes | date=31 January 2021 | first1=Sigrun | last1=Matthes | others=(Deutsches Zentrum für Luft- und Raumfahrt) | last2=Lim | first2=Ling | last3=Burkhardt | first3=Ulrike | last4=Dahlmann | first4=Katrin | last5=Dietmüller | first5=Simone | last6=Grewe | first6=Volker | last7=Haslerud | first7=Amund S. | last8=Hendricks | first8=Johannes | last9=Owen | first9=Bethan|last10=Pitari|first10=Giovanni | last11=Righi | first11=Mattia | last12=Skowron | first12=Agnieszka | display-authors=1 | journal=Aerospace | volume=8 | issue=2 | page=36 | bibcode=2021Aeros...8...36M | hdl=10852/92624 | hdl-access=free}}

; Nitrogen oxides ({{chem|N|O|x}})

: As designers work to reduce {{chem|N|O|x}} emissions from jet engines, they fell by over 40% between 1997 and 2003.{{cite book | author=Rolls-Royce | title=The Jet Engine | isbn=0-902121-23-5 | year=1996 | publisher=Rolls-Royce}} Cruising at a {{cvt|2000|ft}} lower altitude could reduce {{chem|N|O|x}}-caused radiative forcing from 5 mW/m² to ~3 mW/m².{{cite journal | journal=Atmospheric Environment | date=October 2014 | title=Aircraft emission mitigation by changing route altitude: A multi-model estimate of aircraft NOx emission impact on {{chem|O|3}} photochemistry | author=Ole Amund Søvde | volume=95 | page=468 | doi=10.1016/j.atmosenv.2014.06.049 | bibcode=2014AtmEn..95..468S | display-authors=etal | doi-access=free}}

; 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.

; 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.

; 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%.{{cite journal | last1=Williams | first1=Victoria | display-authors=etal | title=Reducing the climate change impacts of aviation by restricting cruise altitudes | journal=Transportation Research Part D: Transport and Environment | date=November 2002 | volume=7 | issue=6 | pages=451–464 | doi=10.1016/S1361-9209(02)00013-5 | bibcode=2002EGSGA..27.1331W}} 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.{{cite journal | url=https://www.nature.com/articles/nature04877.epdf | date=15 June 2006 | title=The importance of the diurnal and annual cycle of air traffic for contrail radiative forcing | author=Nicola Stuber | display-authors=etal | journal=Nature | volume=441 | issue=7095 | pages=864–867 | doi=10.1038/nature04877 | pmid=16778887 | bibcode=2006Natur.441..864S | s2cid=4348401 | access-date=25 November 2020 | archive-date=8 March 2023 | archive-url=https://web.archive.org/web/20230308135742/https://www.nature.com/articles/nature04877.epdf | url-status=live}} As 2% of flights are responsible for 80% of contrail radiative forcing, changing a flight altitude by {{cvt|2000|ft}} to avoid high humidity for 1.7% of flights would reduce contrail formation by 59%.{{cite news | url=https://www.imperial.ac.uk/news/195294/small-altitude-changes-could-contrail-impact/ | title=Small altitude changes could cut contrail impact of flights by up to 59 per cent | author=Caroline Brogan | date=12 February 2020 | publisher=Imperial College | access-date=22 February 2020 | archive-date=20 July 2023 | archive-url=https://web.archive.org/web/20230720064610/https://www.imperial.ac.uk/news/195294/small-altitude-changes-could-contrail-impact/ | url-status=live}} DLR's ECLIF3 study, flying an Airbus A350, show sustainable aviation fuel reduces contrail ice-crystal formation by 56% and soot particle by 35%, maybe due to lower sulphur content, as well as low aromatic and naphthalene content.{{cite news | url=https://www.flightglobal.com/air-transport/a350-flights-with-100-saf-suggest-lower-soot-cuts-contrail-ice-formation/158676.article | title=A350 flights with 100% SAF suggest lower soot cuts contrail ice formation | author=David Kaminski-Morrow | date=6 June 2024 | work=Flightglobal | access-date=7 June 2024 | archive-date=7 June 2024 | archive-url=https://web.archive.org/web/20240607052840/https://www.flightglobal.com/air-transport/a350-flights-with-100-saf-suggest-lower-soot-cuts-contrail-ice-formation/158676.article | url-status=live}}

References

= Works cited =

{{cite book | author=IPCC | ref={{harvid|IPCC AR6 WG3|2022}} | editor-last1=Shukla | editor-first1=P.R. | editor-last2=Skea | editor-first2=J. | editor-last3=Slade | editor-first3=R. | editor-last4=Al Khourdajie | editor-first4=A. | display-editors=etal | url=https://www.ipcc.ch/report/ar6/wg3/ | title=Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change | publisher=Cambridge University Press | year=2022}}.

:Environmental impact of aviation

Climate change

= Factors =

= Volume =

= Per passenger =

= Evolution =

Noise

Water pollution

Air pollution

Private jet travel

Mitigation

= Technology improvements =

== Electric aircraft ==

== Hydrogen-powered aircraft ==

== Sustainable aviation fuels (SAF) ==

== Electrofuels (e-fuels) ==

== Aircraft with lower design speed and altitude ==

= Reducing air travel =

== Measures ==

= Economic measures =

== Emissions trading ==

== Taxation and subsidies ==

= Carbon offsetting =

== Consumer option ==

== National carbon budgets ==

== Airline offsets ==

= Air traffic management improvements =

= Operations improvements =

See also

References

= Works cited =

Further reading