Environmental impact of aviation

s produce gases, noise, and particulates from fossil fuel combustion, raising environmental concerns over both global impacts and their effects on local air quality.
Jet airliners contribute to climate change by emitting carbon dioxide, 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 alone, excluding induced cirrus cloud which remains poorly understood scientifically.
In 2018, global commercial operations generated 2.4% of all emissions.
Jet airliners became about 70% more fuel efficient between 1967 and 2007, and emissions per revenue ton-kilometer in 2018 were 47% of those in 1990. In 2018, emissions averaged 88 grams of 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- effects on climate from, particulates or contrails.
Aviation biofuel, emissions trading and carbon offsetting, part of the ICAO's CORSIA, can lower 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

Airplanes emit gases and atmospheric particulates, interacting among themselves and with the atmosphere.
While the main greenhouse gas emission from powered aircraft is, jet airliners contribute to climate change in four ways as they fly in the tropopause:
; Carbon dioxide
; Nitrogen oxides
File:Contrails.jpg|thumb|Contrails and cirrus clouds
; Contrails and cirrus clouds
; Particulates
In 1999, the IPCC estimated aviation's radiative forcing in 1992 to be 2.7 times that of 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, times the effect of 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 emissions alone, excluding induced cirrus clouds.
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. 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 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, represented 34.3 mW/m² of aviation's effective radiative forcing, with a high confidence level, 17.5 mW/m² with a low confidence level and contrail cirrus 57.4 mW/m², also with a low confidence level.
All factors combined represented 43.5 mW/m² excluding contrail cirrus and 101 mW/m² including them, 3.5% of the anthropogenic ERF of 2290 mW/m². Again, it must be remembered that the effect of 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 passengers per flight and 8.26 trillion RPKs, an average journey of, according to ICAO.
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.
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.
Between 1960 and 2018, RPKs increased from 109 to 8,269 billion.
In 1992, aircraft emissions represented 2% of all man-made emissions, having accumulated a little more than 1% of the total man-made increase over 50 years.
By 2015, aviation accounted for 2.5% of global emissions.
In 2018, global commercial operations emitted 918 million tonnes of, 2.4% of all emissions: 747 Mt for passenger transport and 171 Mt for freight operations.
Between 1960 and 2018, emissions increased 6.8 times from to 1,034 million tonnes per year.
Emissions from flights rose by 32% between 2013 and 2018.
Between 1990 and 2006, greenhouse gas emissions from aviation increased by 87% in the European Union.
In 2010, about 60% of aviation emissions came from international flights, which are outside the emission reduction targets of the Kyoto Protocol. 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.
In 1992, aircraft radiative forcing was estimated by the IPCC at 3.5% of the total man-made radiative forcing.

Per passenger

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.
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.
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.
The average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction of 1.3% with variable reduction rate.
By 2018, emissions per revenue ton-kilometer were more than halved compared to 1990, at 47%.
The aviation energy intensity went from 21.2 to 12.3 MJ/RTK between 2000 and 2019, a % reduction.
In 2018, emissions totalled 747 million tonnes for passenger transport, for 8.5 trillion revenue passenger kilometres, giving an average of 88 gram per RPK.
The UK's Department for calculate a long-haul flight release 102 g of per passenger kilometre, and 254 g of equivalent, including non-CO₂ greenhouse gas emissions, water vapor etc.; for a domestic flight in Britain.
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 emissions in half by 2050 relative to 2005.

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. 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 emissions budget would be entirely consumed by aviation emissions to keep the climate change temperature increase below 2 °C by mid-century. Given that growth projections indicate that aviation will generate 15% of global 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.
In 2013, the National Center for Atmospheric Science at the University of Reading forecast that increasing levels will result in a significant increase in in-flight turbulence experienced by transatlantic airline flights by the middle of the 21st century. 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.
Aviation emissions grow despite efficiency innovations to aircraft, powerplants and flight operations.
Air travel continue to grow.
In 2015, the Center for Biological Diversity estimated that aircraft could generate 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 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.
The International Energy Agency projects aviation share of global emissions may grow from 2.5% in 2019 to 3.5% by 2030.
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.
By 2050, aviation's negative effects on climate could be decreased by a 2% increase in fuel efficiency and a decrease in emissions, due to advanced aircraft technologies, operational procedures and renewable alternative fuels decreasing radiative forcing due to sulfate aerosol and black carbon.