Air travel's impact on Earth' climate

Because they are released so high in the atmosphere, emissions from airplanes have greater relative effects upon air quality than do emissions from ground vehicles. The extent of those emissions’ effects upon Earth’s climate is a much studied and hotly debated issue.

Background

Powered flight was introduced in 1903, when Wilbur Wright and Orville Wright conducted the first short flight at Kill Devil Hills, North Carolina. The first thirty-five years of powered flight had minimal impacts upon Earth’s climate. The advent of widespread aerial cargo and passenger service in the late 1930s and early 1940’s arguably marks the first significant influence upon Earth’s climate by aircraft. However, beginning in the 1960s, air travel’s impact became much more pronounced, as jet aircraft were introduced. The effects of air travel were increased in 1978, when the United States deregulated the airline industry, resulting in a significant increase in the annual number of jet aircraft flights.

Air Travel Growth Rate

Since 1960, air travel has grown by approximately 4.5 percent per year. A mode of transportation once regarded as available only to the wealthy quickly became the preferred, affordable method of long-distance travel. With this rapid growth has come a proportionate increase in the impact that air travel has on Earth’s environment and climate. It is expected that air travel will continue to grow at a similar rate during the twenty-first century. This significant anticipated growth suggests that substantial progress must be made in limiting the negative effects that air travel has on the environment.

Impact of Air Travel on Earth’s Climate

Aircraft engines emit gases and particulates into the upper and lower stratosphere. These gases modify atmospheric composition, resulting in either increases or decreases in radiative forcing. Water vapor and emissions result in positive radiative forcing. In addition, sulfur and soot emitted by aircraft engines combine with water to form trails, commonly called contrails, resulting in further positive radiative forcing. Both processes warm the climate. In 2024, air travel accounted for roughly 2.5 percent of global carbon emissions. Scientists estimated that air travel has been responsible for roughly 4 percent of global warming.

Impact of Air Travel on Earth’s Ozone Layer

Ozone, a greenhouse gas, absorbs ultraviolet radiation. The majority of this absorption occurs in the stratosphere. A wide variety of human interactions with the environment deplete ozone in the atmosphere. Subsonic aircraft engines emit nitrogen oxides in the troposphere and lower that increase ozone, reducing the amount of ultraviolet radiation reaching Earth’s surface. Supersonic aircraft, flying higher in the stratosphere, have an opposite effect, depleting ozone at those higher altitudes.

Best estimates are that net air-travel-related comprises approximately 3.5 percent of total human atmospheric radiative forcing. Most air travel is conducted by subsonic aircraft operating in the upper troposphere and lower stratosphere. However, significant research and development is under way to introduce supersonic and hypersonic aircraft into the air transportation fleet. If this occurs, much of the ozone-depletion offset generated by subsonic aircraft would be negated by ozone-depleting supersonic aircraft operating primarily in the stratosphere.

Interestingly, a disproportionate amount of positive radiative forcing occurs in the delicate upper portion of the Northern Hemisphere as a result of the high volume of jet aircraft traffic in that region. Increases in atmospheric temperatures in the polar region have a potentially significant effect on rising ocean levels resulting from polar-cap and glacial-ice melting.

Reducing Air Travel Impacts

A number of options exist to reduce air travel’s impact upon the environment. Rises in petroleum-based fuel prices reduce the impact of air travel on the environment by making air travel less cost-effective and reducing the demand for flights. In addition, airlines are striving to work worldwide with air traffic control organizations to reduce ground holds and increase flight efficiency through more direct routing and highly planned, efficient descents from altitude.

Technological advances in jet-engine design and efficiency also offer great promise for reducing environmental impacts. State-of-the-art turbine engines, utilized on most new transport aircraft, are much more efficient than older versions. Finally, a basic solution to reduce air travel’s impact upon the environment is to reduce the need to travel at all. Modern computing technologies, including high-quality video conferencing, make possible complex online meetings. These meetings can be held with participants located throughout the world, reducing the need for business travel.

Context

Air travel is growing at a brisk rate; it has an impact upon global warming, but there are mitigation measures available. It remains unclear, however, to what extent governments, aircraft manufacturers, and airline companies will institute such mitigation measures. Research and development of greener aircraft technologies is an expensive and time-consuming venture. As with all ventures, governments and companies must attempt to strike a compromise between the environmental impacts of aviation and economic factors related to technological innovation. The long-term availability of aircraft fuel and the will of airlines and aircraft manufacturers to adopt green technologies remain unclear.

Key Concepts

• aircraft emissions: gases and particulate matter expelled from aircraft engines
• greenhouse effect: an atmospheric warming phenomenon by which certain gases act like glass in a greenhouse, allowing the transmission of ultraviolet solar radiation but trapping infrared terrestrial radiation
• greenhouse gases (GHGs): gases that tend to hold heat within the atmosphere and contribute to the greenhouse effect
• ozone: a greenhouse gas that absorbs ultraviolet radiation
• radiative forcing: a change in the balance between incoming and outgoing radiation that increases or decreases overall energy balance
• stratosphere: the atmospheric region just above the that extends up to about 50 kilometers
• troposphere: the lowest layer of the atmosphere, in which storms and almost all clouds occur, extending from the ground up to between 8 and 15 kilometers in height

Bibliography

Dokken, David J., et al. Special Report on Aviation and the Global Atmosphere. Geneva, Switzerland: World Meteorological Organization, Intergovernmental Panel on International Climate Change, 1999.

General Accounting Office, U.S. Aviation and the Environment: Aviation’s Effects on the Global Atmosphere Are Potentially Significant and Expected to Grow. Washington, D.C.: Author, 2000.

Ritchie, Hannah. "What Share of Global CO₂Emissions Come From Aviation?" Our World in Data, 8 Apr. 2024, ourworldindata.org/global-aviation-emissions. Accessed 13 Dec. 2024.