Reducing Carbon Dioxide Emissions From Aircraft

How significant a source of emissions is air travel?

Aircraft are a rapidly growing emissions source within the transportation sector, which is second only to the power sector as a source of U.S. carbon dioxide emissions. In 2013, aircraft were responsible for about 3 percent of total U.S. carbon dioxide emissions and nearly 9 percent of carbon dioxide emissions from the U.S. transportation sector. Commercial air travel accounted for most of the aircraft carbon dioxide emissions, with military and general aviation making up the rest.

From 1990 to 2013, U.S. carbon dioxide emissions from domestic commercial flights grew 4 percent. Recent studies estimate that U.S. aircraft emissions will increase substantially in the next 20 years. Moreover, airplanes remain the single largest source of carbon dioxide emissions within the U.S. transportation sector that is not yet subject to greenhouse gas regulations.

U.S. aviation is part of the increasingly interconnected global aviation sector, which makes up about 2 percent of global carbon dioxide emissions but is one of the fastest growing sources. From 1990 to 2010, global aircraft carbon dioxide emissions grew about 40 percent. If global aviation were a country, it would rank as the seventh largest carbon dioxide emitter, and U.S. aircraft emissions are 29 percent of all global aircraft emissions. Absent new policies, global aircraft emissions are projected to triple by 2050.


Figure 1: 2013 U.S. carbon dioxide emission, by sector and transportation source

The transportation sector is responsible for more than one-third of U.S. carbon dioxide emissions. Aircraft are responsible for nearly 9 percent of U.S. transportation sector carbon dioxide emissions.

Source: U.S. Environmental Protection Agency (EPA), Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2013 (Washington, DC: U.S. Environmental Protection Agency, 2015),

What is the status of regulation?

In 2012, the DC District Court ruled that the U.S. Environmental Protection Agency (EPA) is required under the Clean Air Act to determine whether greenhouse gas emissions from aircraft cause or contribute to air pollution, which may reasonably be anticipated to endanger public health or welfare. An endangerment finding would trigger regulation under the Clean Air Act.

On July 25, 2016, EPA issued the final endangerment finding under section 231(a)(2)(A) of the Clean Air Act for aviation emissions. This finalizes the process following the proposed endangerment finding issued on June 10, 2015. The final finding builds on the previous 2009 endangerment finding for light-duty vehicles and found greenhouse gas emissions from aircraft engines used in certain types of aircraft are responsible for contributing to climate change, which threatens public health and welfare.

Covered aircraft are those subject to international carbon dioxide emission standards, subsonic jet aircraft — ranging from smaller jet aircraft such as the Cessna Citation II to larger jet aircraft such as the Boeing 747 — and subsonic turboprop aircraft — e.g., Bombardier Q400. The proposed endangerment finding will receive public comment before a final endangerment finding may be issued. 

How does EPA action fit with global action?

Unlike stationary sources, such as power plants, and many mobile sources, such as cars, aircraft frequently travel between jurisdictions with different environmental laws and standards. As such, the United Nations' International Civil Aviation Organization (ICAO) serves as a global forum to develop policies and standards for the global industry, including a comprehensive set of measures to address greenhouse gas emissions.

In 2010, industry’s goal of carbon neutral growth from 2020 onwards was formally adopted by ICAO. Within the sector, the key pathways to reduce emissions are improvements in aircraft technology, improvements in operations and infrastructure, and further use of aviation biofuels.
In addition, ICAO agreed at its 38th Assembly in 2013 to develop a Global Market-Based Mechanism (GMBM) that allows emission reductions occurring outside the aviation sector to be used to meet its goals. At the 39th ICAO Assembly in October 2016, ICAO formally adopted a resolution establishing the GMBM as an offsetting mechanism available to airlines to offset their growth in emissions from 2020 onwards. A Global Market Based Mechanism Task Force is currently working to establish the technical details of what types of offsets will be permittewd in the GMBM, and will conclude their work no later than 2018. ICAO adopted additional measures, including a CO2 standard that will be phased in for new aircraft design to continue improvements in energy efficiency.
Traditionally, both the EPA and the Federal Aviation Administration (FAA) have worked within the ICAO process to establish international emission standards and related requirements for other pollutants. Under this approach, international emission standards are first adopted by ICAO, and EPA subsequently initiates rulemaking under section 231 of the Clean Air Act to establish domestic standards equivalent to international standards where appropriate. Both EPA and FAA expect to take a similar approach in promulgating future domestic aircraft greenhouse gas standards for covered aircraft.

What are the next steps?

The endangerment finding does not create any regulation in of itself and does not prejudge what future EPA standards for aircraft engines will be. Nevertheless, the final endangerment finding triggers EPA’s duty under the CAA to enact emissions standards applicable to GHG emissions from the classes of aircraft engines included in the endangerment finding. EPA can then proceed with developing regulatory standards, including a CO2 standard based from the agreed standard adopted by ICAO in October 2016.