Aviation, Air Pollution, and Climate Change

Updated April 26, 2024

Aviation, Air Pollution, and Climate Change

Some Members of Congress have expressed interest in

addressing air pollution emissions, greenhouse gas (GHG)

emissions, and the climate change effects from domestic

and international aviation. Recent legislative proposals

would provide for sustainable fuel mandates, incentives for

airport efficiency improvements, and GHG emission

targets, among other requirements.

Emissions from Aircraft

The U.S. Environmental Protection Agency (EPA)

estimates that transportation—including passenger cars and

light trucks, heavy-duty trucks, buses, trains, ships, and

aircraft—accounted for 37% of carbon dioxide (CO2, the

principal GHG) emissions in 2021. While CO2 emissions

from passenger cars and light trucks exceed those from

aircraft in the United States, CO2 emissions from aviation

are currently experiencing a faster rate of growth. All

aircraft, including military, commercial, and privately

chartered, accounted for 11% of the U.S. transportation

sector’s CO2 emissions and 4% of all U.S. CO2 emissions in

2021. Commercial aircraft, including those operated by

passenger and all-cargo airlines, accounted for 7% of

transportation sector and 3% of all emissions. These

estimates include emissions from U.S. domestic flights and

emissions from international flights departing the United

States, referred to as “international bunkering.”

In the United States, aggregate CO2 emissions from aircraft

have fluctuated due to changes in technology, the economy,

travel frequency, and military activity, among other

reasons. However, since the global financial crisis in 2009,

aggregate CO2 emissions from all aircraft types have grown

steadily, increasing by almost 22% between 2009 and 2019.

This increase makes aircraft one of the faster-growing

sources of CO2 emissions in the U.S. transportation sector

over the past decade. This trend was affected, at least

temporarily, by reduced air travel in 2020 and 2021 due to

Coronavirus Disease 2019 (COVID-19).

The effects of aircraft emissions on the atmosphere are

complex, reflecting differing altitudes, geography, time

horizons, and environmental conditions. Research has

shown that in addition to CO2 emissions, other factors

increase the climate change impacts of aviation. These

factors include the contribution of aircraft emissions to

ozone production; the formation of water condensation

trails and cirrus clouds; the emission of various gases and

particles, including water vapor, nitrous oxides, sulfates,

and particulates from jet fuel combustion; and the high

altitude location of the bulk of these emissions. In

examining the warming and cooling influences of these

factors, the United Nations’ Intergovernmental Panel on

Climate Change estimated aviation’s total climate change

impact could be from two to four times that of its past CO2

emissions alone.

Aside from GHG emissions, aircraft engines emit a number

of criteria—or common—pollutants, including nitrogen

oxides, carbon monoxide, oxides of sulfur, unburned or

partially combusted hydrocarbons (also known as volatile

organic compounds [VOCs]), particulates, and other trace

compounds. A subset of the VOCs and particulates are

considered hazardous air pollutants.

Emission Reduction Strategies

In an effort to reduce emissions from the aviation sector,

the U.S. government, other nations, and international

organizations have worked together with the aviation

industry toward improving technologies, increasing the

efficient use of aircraft and airport infrastructure, adopting

appropriate economic incentives, and setting standards.

Aircraft Emission Standards: Domestic Process

In the United States, in accordance with Clean Air Act

(CAA) Section 231 (42 U.S.C. §7571), EPA sets emission

levels for specified pollutants, as promulgated in 40 C.F.R.

Part 87, “Control of Air Pollution from Aircraft and

Aircraft Engines.” EPA sets standards for Federal Aviation

Administration (FAA)-certified aircraft according to the

amount of thrust generated by their engines. Aircraft

emission standards currently exist for fuel venting, and

engine hydrocarbons, carbon monoxide, and nitrogen

oxides. In 2021, EPA promulgated standards for CO2

emissions from aircraft engines. In 2022, EPA finalized

standards for particulate emissions from certain classes of

engines used by civil subsonic jet aircraft (87 FR 72312). In

2023, EPA finalized an endangerment finding for lead

pollution from gasoline-powered, piston-engine aircraft (88

FR 72372). With this final determination, EPA is required

to propose and promulgate regulatory standards for lead

emissions from aircraft engines.

The standard-setting language under CAA Section 231 is

similar to the statutory language for other mobile sources in

the CAA (e.g., cars, trucks, buses). However, compared to

other mobile sources, EPA must meet additional

requirements in setting emission standards for aircraft and

aircraft engines: (1) the EPA Administrator must consult

with the Administrator of the FAA and the Secretary of the

U.S. Department of Transportation (DOT) in developing

emission standards; (2) the EPA Administrator cannot

change standards if doing so would “significantly increase

noise and adversely affect safety”; and (3) the President

may disapprove any such standards if the DOT Secretary

finds that they “would create a hazard to aircraft safety.”

CAA Section 232 requires the FAA to enforce the standards

at the time an engine is certified for emissions under 14

C.F.R. Part 34, “Fuel Venting and Exhaust Emission

Requirements for Turbine Engine Powered Airplanes.”

Since compliance with the federal standards is determined

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Aviation, Air Pollution, and Climate Change

at engine certification, there are no operational emissions

regulations for aircraft.

Aircraft Emission Standards: International Process

Due to the global nature of the aircraft manufacturing

industry and its customer base, EPA has generally regulated

emissions from aircraft only after the United States has

negotiated an international agreement through the

International Civil Aviation Organization (ICAO). ICAO is

a United Nations specialized agency established in 1944 to

manage the administration and governance of the

Convention on International Civil Aviation (the Chicago

Convention). ICAO has 193 member states, including the

United States. ICAO addresses civil aviation (i.e., all

nonmilitary, private, and commercial aviation).

ICAO’s activities regarding environmental protection focus

on issues that could benefit most from an industry-wide

coordinated approach—for example, aircraft noise and

engine emissions. ICAO has no direct regulatory or

enforcement authority. After member states agree to a

negotiated set of international standards, they implement

these standards through their own domestic laws and

regulatory processes. Typically, ICAO’s international

standards for pollutants from aircraft, unlike EPA’s

regulations for the same pollutants from on-road vehicles,

have consistently avoided technology-forcing requirements.

For example, the most recent ICAO standards for nitrogen

oxides essentially ratified what the principal aircraft

manufacturers had already achieved.

Greenhouse Gas Emission Reduction Strategies

CO2 Emission Standards

Since 2010, ICAO has negotiated with the aviation industry

and selected stakeholders to develop international CO2

emission standards for aircraft engines. A delegation of

EPA and FAA representatives have participated in ICAO’s

process. In March 2017, ICAO adopted international CO2

standards for commercial aircraft engines to begin in 2020.

The ICAO standards represent the world’s first global

design certification measure governing CO2 emissions for

any industry sector. The standards apply to newly

developed civil aircraft designs phased-in between January

1, 2020, and January 1, 2023, and to in-production aircraft

after January 1, 2028. They do not apply to alreadymanufactured aircraft that are currently in use. CO2

emissions targets vary by aircraft type and are set as a

function of the aircraft’s maximum takeoff weight.

In accordance with the ICAO negotiations and the CAA,

EPA issued a finding that GHG emissions (including CO2

emissions) from civil aircraft contribute to the pollution that

causes climate change and endangers U.S. public health and

welfare (81 FR 54422). EPA’s endangerment finding, under

Section 231 of the CAA, laid the necessary foundation for

adoption and implementation of CO2 standards for U.S.

aircraft, in consultation with FAA. On January 11, 2021,

EPA promulgated GHG emission standards for aircraft

engines equivalent to the CO2 standards adopted by the

ICAO (86 FR 2136). The standards cover U.S. subsonic jet

and propeller-driven aircraft above certain takeoff weights.

Upon EPA’s promulgation of the rule, CAA Section 232

requires the FAA to issue regulations to enforce the

standards and apply such standards when certifying the

engines of U.S. aircraft manufacturers (87 FR 36076). EPA

stated that the standards would make domestically

manufactured aircraft engines competitive in the global

marketplace; however, the agency also acknowledged that

the rule likely would not spur any emissions reductions

from U.S. aircraft manufacturers beyond their current

trends.

Market-Based Mechanisms

In October 2016, ICAO also agreed on a framework for

offsetting future carbon emissions from aviation—referred

to as the Market-Based Mechanism, or MBM. ICAO

member states agreed to implement a “Carbon Offsetting

and Reduction Scheme for International Aviation

(CORSIA) to address any annual increase in total CO2

emissions from international civil aviation (i.e. civil

aviation flights that depart in one country and arrive in a

different country) above the 2020 levels, taking into

account special circumstances and respective capabilities.”

CORSIA relies on the use of emissions units from carbon

markets to offset the amount of CO2 emissions that cannot

be reduced through the use of sustainable aviation fuels or

technological and operational improvements. CORSIA

began in 2021. Compliance was to be measured against a

baseline of CO2 emissions defined as the average from all

international civil aviation in 2019 and 2020. However, due

to the effects of the Coronavirus Disease 2019 (COVID-19)

pandemic on international air travel in 2020, ICAO adopted

a baseline based solely on 2019 emissions for a three-year

pilot phase, and a baseline of 85% of 2019 emissions for the

period 2024-2035.

Participation in CORSIA is voluntary through 2026. The

U.S. aviation industry agreed to participate during ICAO

negotiations. To fulfill the U.S. commitments under the

Chicago Convention with respect to the MBM, FAA

implemented the CORSIA Monitoring, Reporting, and

Verification Program in 2019 (84 FR 9412). Whether and

what additional authorities are required by EPA and FAA to

comply with CORSIA’s mandatory trading scheme

beginning in 2027 is under consideration.

Other Reduction Strategies

Beyond federal and international CO2 emission standards

for aircraft engines, other policy options are available to

reduce GHGs from the aviation sector. These include (1)

taxes or fees on fuel or its carbon content; (2) incentives or

mandates to use sustainable aviation fuels or fuel

alternatives; (3) incentives to modernize air traffic control

systems (see CRS In Focus IF11420, Aircraft Noise and Air

Traffic Control Modernization); and (4) ground-based

measures aimed at reducing GHG emissions from

nonaircraft operations at airports. EPA and FAA administer

several initiatives in operations and research, and

collaborate at the national and international levels, in

support of many of these policies.

Richard K. Lattanzio, Specialist in Environmental Policy

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IF11696

Aviation, Air Pollution, and Climate Change

Disclaimer

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