Aviation and the Environment

Aviation emissions are a potentially significant and growing percentage of greenhouse gases and other emissions that are thought to contribute to global warming. Aircraft emissions are potentially significant for several reasons. First, jet aircraft are the main source of human emissions deposited directly into the upper atmosphere, where they may have a greater warming effect than if they were released at the earth's surface. Second, carbon dioxide--the primary aircraft emission--is relatively well understood and is the main focus of international concern. For example, it survives in the atmosphere for nearly 100 years and contributes to global warming, according to the Intergovernmental Panel on Climate Change. The carbon dioxide emissions from worldwide aviation roughly equal those of some industrialized countries. Third, carbon dioxide emissions, combined with other gases and particles emitted by jet aircraft, could have two to four times as great an effect on the atmosphere as carbon dioxide alone. Fourth, the Intergovernmental Panel recently concluded that the rise in aviation emissions due to growing demand for air travel would not be fully offset by reductions in emissions achieved solely through technological improvements. Experts GAO interviewed, as well as the report of the Intergovernmental Panel, have cited several options for better understanding and mitigating the impact of aviation as the industry grows. These options include (1) continuing research to improve the scientific understanding of aviation's effects on the global atmosphere as a basis for guiding the development of aircraft and engine technology to reduce them, (2) promoting more efficient air traffic operations through the introduction of new technologies and procedures, and (3) expanding the use of regulatory and economic measures to encourage reductions in emissions.

GAO noted that: (1) aviation emissions comprise a potentially significant and growing percentage of human-generated greenhouse gases and other emissions that are thought to contribute to global warming; (2) the Intergovernmental Panel on Climate Change (IPCC) recently estimated that global aircraft emissions accounted for approximately 3.5 percent of the warming generated by human activities; (3) of the various emissions generated by aviation, scientists know a great deal about carbon dioxide, which is the primary aircraft emission, but less about the other emissions; (4) as a result, the scientific community has identified areas that need further study to enable them to more precisely estimate aviation's effects on the global atmosphere; (5) as for the contributions of U.S. aviation relative to other U.S. industrial sources, data from the Environmental Protection Agency show that in 1997, aviation accounted for about 3 percent of U.S. greenhouse gas emissions; (6) this compares with 23 percent for other transportation sources and 41 percent for other industrial sources; (7) global aviation emissions of carbon dioxide are a small percentage of carbon emissions worldwide, however, they are roughly equivalent to carbon emissions of certain industrialized countries; (8) according to data from a 1999 IPCC report, 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; (9) according to IPCC, aircraft emissions are potentially significant for several reasons: (a) jet aircraft are the primary source of human emissions deposited directly into the upper atmosphere; (b) carbon dioxide survives in the atmosphere for about 100 years and contributes to the warming of the earth; and (c) carbon dioxide emissions combined with other gases and particles emitted by jet aircraft could have 2 to 4 times as great an effect on the atmosphere as carbon dioxide alone; (10) IPCC recently concluded that the increase in aviation emissions would not be fully offset by reductions in emissions achieved through technological improvements alone; and (11) IPCC identified a range of options to better understand and mitigate aviation's impact as the industry grows, including: (a) continuing research of aviation's effects to guide the development of aircraft and engine technology to reduce these effects; (b) promoting more efficient air traffic operations; and (c) expanding the use of regulatory and economic measures to encourage reductions in emissions.