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Aviation and the Global Atmosphere Aviation and the Golbal Atmosphere. Aircraft engines (also) directly emit soot and metal particles. Liquid aerosol precursors include water vapor, oxidized sulfur in various forms, chemi-ions (charged molecules), nitrogen oxides, and unburned hydrocarbons. Executive Summary | Full IPCC Report

Source: United States General Accountability Office, Washington, D.C. 20548. Resources, Community, and Economic Development Division. February 18, 2000 Report to The Honorable James L. Oberstar, Ranking Democratic Member Committee on Transportation and Infrastructure, House of Representatives

Abstract

Aviation and the environment

Aviation's effects on the global atmosphere are potentially significant and expected to grow

This report is based on our review of current research and interviews with experts in the aviation, scientific, and environmental communities on issues related to aviation and global warming. In particular, we relied on a recent report on aviation and the earth's atmosphere issued by the Intergovernmental Panel on Climate Change under the auspices of the United Nations. Although we did not independently evaluate the research in this report, it was reviewed by over 150 experts worldwide and is generally considered the most comprehensive and up-to-date information on the subject.

According to data from a 1999 report of the Intergovernmental Panel on Climate Change, global aviation contributed about 145 million metric tons of carbon in 1996, or about 2.4 percent of all human-generated carbon emissions—an amount roughly equivalent to the total carbon emissions of Canada.

Aircraft emissions are potentially significant for several reasons:

Jet aircraft are the primary source of human emissions deposited directly into the upper atmosphere. The Intergovernmental Panel on Climate Change and experts noted that some of these emissions have a greater warming effect than they would have if they were released in equal amounts at the surface—by, for example, automobiles.
Carbon dioxide is relatively well understood and is the main focus of international concern. According to the Intergovernmental Panel on Climate Change, it survives in the atmosphere for about 100 years and contributes to warming the earth. Moreover, as noted, global aviation’s carbon dioxide emissions (measured in million metric tons of carbon) are roughly equivalent to the carbon emissions of certain industrialized countries.
Carbon dioxide emissions combined with other gases and particles emitted by jet aircraft-including water vapor, nitrogen oxide and nitrogen dioxide (collectively termed NOx), and soot and sulfate—could have two to four times as great an effect on the atmosphere as carbon dioxide alone. According to the Intergovernmental Panel on Climate Change the atmospheric effects of these combined emissions will require further scientific study.
The Intergovernmental Panel on Climate Change recently concluded that the increase in aviation emissions attributable to a growing demand for air travel would not be fully offset by reductions in emissions achieved through technological improvements alone.

The IPCC experts agree on the types of emissions from jet aircraft that may contribute to a warming of the earth’s surface but know more about the impact of carbon dioxide than of the other emissions. Jet aircraft deposit most of their emissions at cruise altitudes, primarily in the troposphere – altering concentrations of greenhouse gases directly by emitting carbon dioxide and indirectly by emitting NOx. In addition, emissions of water vapor and soot and sulfate particles have both direct and indirect effects.

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