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December 7, 2020
Aviation and Climate Change
Some Members of Congress have expressed an interest in
estimated aviation’s total climate change impact could be
addressing the greenhouse gas (GHG) emissions and
from two to four times that of its past CO2 emissions alone.
climate change effects from aviation. Proposed legislation
in the 116th Congress would provide for sustainable fuel
Figure 1. CO2 Emissions from U.S. Aircraft, 1990-2018
mandates, incentives for airport efficiency improvements,
and GHG emission targets, among other requirements. In
some instances, these provisions would be conditioned on
economic stimulus and other forms of public funding.
Greenhouse Gas 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 35% of carbon dioxide (CO2, the
principal GHG) emissions in 2018. While CO

2 emissions
Source: CRS, from EPA, “Inventory of U.S. Greenhouse Gas
from passenger cars and light trucks exceed those from
Emissions and Sinks, 1990-2018,” Table 3.13, April 13, 2020.
aircraft in the United States, CO2 emissions from aviation
are currently experiencing a faster rate of growth. All
Emission Reduction Strategies
aircraft, including military, commercial, and privately
chartered, accounted for 13% of the U.S. transportation
In an effort to reduce GHG emissions from the aviation
sector’s CO
sector, the U.S. government, other nations, and international
2 emissions and 5% of all U.S. CO2 emissions in
2018. Commercial aircraft, including those operated by
organizations have worked together with the aviation
passenger and all-cargo airlines, accounted for 11% of
industry toward improving technologies, increasing the
transportation sector and 4% of all emissions. These
efficient use of aircraft and airport infrastructure, and
estimates include emissions from U.S. domestic flights and
adopting appropriate economic incentives. Policies in place
emissions from international flights departing the United
or under consideration currently include voluntary,
States, referred to as “international bunkering.”
regulatory, and market-based options for aircraft, fuels, and
the aviation system as a whole.
In the United States, aggregate CO2 emissions from aircraft
1. Federal Aircraft Emission Standards
have fluctuated due to changes in technology, the economy,
travel frequency, and military activity, among other
In the United States, in accordance with Clean Air Act
reasons. However, since the global financial crisis in 2009,
(CAA) Section 231 (42 U.S.C. §7571), EPA sets emission
aggregate CO
levels for specified pollutants, as promulgated in 40 C.F.R.
2 emissions from all aircraft types have grown
steadily, increasing by almost 22% between 2009 and 2018
Part 87, “Control of Air Pollution from Aircraft and
(see Figure 1). This increase makes aircraft one of the
Aircraft Engines.” EPA sets standards for Federal Aviation
faster-growing sources of CO
Administration (FAA)-certified aircraft according to the
2 emissions in the U.S.
transportation sector over the past decade. This trend is
amount of thrust generated by their engines. Aircraft
likely to be affected, at least temporarily, by reduced air
emission standards currently exist for fuel venting, and
travel in 2020 due to the COVID-19 pandemic.
engine hydrocarbons, carbon monoxide, and nitrogen
oxides. In 2020, EPA proposed standards for CO2 emissions
The effects of aircraft emissions on the atmosphere are
from aircraft engines.
complex, reflecting differing altitudes, geography, time
horizons, and environmental conditions. Research has
The standard-setting language under CAA Section 231 is
shown that in addition to CO
similar to the statutory language for other mobile sources in
2 emissions, other factors
increase the climate change impacts of aviation. These
the CAA (e.g., cars, trucks, buses). However, compared to
factors include the contribution of aircraft emissions to
other mobile sources, EPA must meet additional
ozone production; the formation of condensation trails and
requirements in setting emission standards for aircraft and
cirrus clouds; the emission of various gases and particles,
aircraft engines: (1) the EPA Administrator must consult
including water vapor, nitrous oxides, sulfates, and
with the Administrator of the FAA and the Secretary of the
particulates from jet fuel combustion; and the high altitude
U.S. Department of Transportation (DOT) in developing
location of the bulk of these emissions. In examining the
emission standards; (2) the EPA Administrator cannot
warming and cooling influences of these factors, the United
change standards if doing so would “significantly increase
Nations’ Intergovernmental Panel on Climate Change
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.”

Aviation and Climate Change
CAA Section 232 requires the FAA to enforce the standards
the CO2 standards adopted by the ICAO (85 Federal
at the time an engine is certified for emissions under 14
Register 51556, August 20, 2020). The proposed standards
C.F.R. Part 34, “Fuel Venting and Exhaust Emission
would cover U.S. subsonic jet and propeller-driven aircraft
Requirements for Turbine Engine Powered Airplanes.”
above certain takeoff weights. Upon EPA’s promulgation of
Since compliance with the federal standards is determined
a final rule, CAA Section 232 requires the FAA to issue
at engine certification, there are no operational emissions
regulations to enforce the standards and apply such
regulations for aircraft.
standards when certifying the engines of U.S. aircraft
manufacturers. EPA stated that the standards would make
2. International Aircraft Emission Standards and
domestically manufactured aircraft engines competitive in
Market-Based Mechanisms
the global marketplace; however, the agency also
Due to the global nature of the aircraft manufacturing
acknowledged that the rule likely would not spur any
industry and its customer base, EPA has generally regulated
emissions reductions from U.S. aircraft manufacturers
emissions from aircraft only after the United States has
beyond their current trends.
negotiated an international agreement through the
International Civil Aviation Organization (ICAO). ICAO is
Market-Based Mechanisms
a United Nations specialized agency established in 1944 to
In October 2016, ICAO also agreed on a framework for
manage the administration and governance of the
offsetting future carbon emissions from aviation—referred
Convention on International Civil Aviation (the Chicago
to as the Market-Based Mechanism, or MBM. ICAO
Convention). ICAO has 193 member states, including the
member states agreed to implement a “Carbon Offsetting
United States. ICAO addresses civil aviation (i.e., all
and Reduction Scheme for International Aviation
nonmilitary, private, and commercial aviation). ICAO’s
(CORSIA) to address any annual increase in total CO2
activities regarding environmental protection focus on
emissions from international civil aviation (i.e. civil
issues that could benefit most from a worldwide
aviation flights that depart in one country and arrive in a
coordinated approach—for example, aircraft noise and
different country) above the 2020 levels, taking into
engine emissions. After member states agree to a negotiated
account special circumstances and respective capabilities.”
set of international standards, they implement these
CORSIA relies on the use of emissions units from carbon
standards through their own domestic laws and regulatory
markets to offset the amount of CO2 emissions that cannot
processes. ICAO has no direct regulatory or enforcement
be reduced through the use of sustainable aviation fuels or
authority. Typically, ICAO’s international standards for
technological and operational improvements. CORSIA is to
pollutants from aircraft, unlike EPA’s regulation of the
begin in 2021. Compliance was to be measured against a
same pollutants from on-road vehicles, have consistently
baseline of CO2 emissions defined as the average from all
avoided technology-forcing requirements. For example, the
international civil aviation in 2019 and 2020. However, due
most recent ICAO standards for nitrogen oxides essentially
to the effects of the COVID-19 pandemic on international
ratified what the principal aircraft manufacturers had
air travel in 2020, the ICAO adopted a baseline based solely
already achieved.
on 2019 emissions for a three-year pilot phase.
CO2 Emission Standards
Participation in CORSIA is voluntary for the next decade.
Since 2010, ICAO has negotiated with the aviation industry
The U.S. aviation industry agreed to participate during
and selected stakeholders to develop international CO2
ICAO negotiations. To fulfill the U.S. commitments under
emission standards for aircraft engines. A delegation of
the Chicago Convention with respect to the MBM, FAA
EPA and FAA representatives have participated in ICAO’s
implemented the CORSIA Monitoring, Reporting, and
process. In March 2017, ICAO adopted international CO2
Verification Program in 2019 (84 Federal Register 9412,
standards for commercial aircraft engines to begin in 2020.
March 14, 2019). Whether, and if so, when, ICAO member
The ICAO standards represent the world’s first global
states will adopt CORSIA as a standard is under
design certification measure governing CO2 emissions for
negotiation. At that point, one question would be whether
any industry sector. The standards apply to newly
EPA’s authority under CAA Section 231 to “issue proposed
developed civil aircraft designs phased-in between January
emission standards” is broad enough to include setting an
1, 2020, and January 1, 2023, and to in-production aircraft
offset/trading scheme to comply with CORSIA’s
after January 1, 2028. They do not apply to already-
manufactured aircraft that are currently in use. CO2
emissions targets vary by aircraft type and are set as a
3. Other Reductions Strategies
function of the aircraft’s maximum takeoff weight.
Beyond federal and international CO2 emission standards
for aircraft engines, other policy options are available to
In accordance with the ICAO negotiations and the CAA,
reduce GHGs from the aviation sector. These include (1)
EPA issued a finding that GHG emissions (including CO2
taxes on fuel or its carbon content; (2) mandates to use
emissions) from civil aircraft contribute to the pollution that
sustainable aviation fuels or fuel alternatives; (3) incentives
causes climate change and endangers U.S. public health and
to modernize air traffic control systems (see CRS In Focus
welfare (81 Federal Register 54422, August 15, 2016).
IF11420, Aircraft Noise and Air Traffic Control
EPA’s endangerment finding, under Section 231 of the
Modernization); and (4) ground-based measures aimed at
CAA, laid the necessary foundation for adoption and
reducing GHG emissions from nonaircraft operations at
implementation of CO2 standards for U.S. aircraft, in
airports. FAA and EPA administer several initiatives in
consultation with FAA. On August 20, 2020, EPA proposed
operations and research, and collaborate at the national and
GHG emission standards for aircraft engines equivalent to
international levels, in support of many of these policies.

Aviation and Climate Change

Richard K. Lattanzio, Specialist in Environmental Policy

This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to
congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress.
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