The EPA has failed "to put stringent controls on aircraft emissions," says William Becker, the group's executive director. In its court filing, the EPA says it meets international law by adopting standards that "are at least as stringent" as ICAO's.
Unlike European governments, the FAA doesn't see an immediate threat. "Compared to other sources of emissions, aviation represents a relatively small source" of air pollutants and greenhouse gases, the FAA said in response to USA TODAY questions. "Cars and trucks generate seven times the amount of emissions that aviation produces."
American Airlines, the world's No. 1 carrier, would not comment, referring all questions about its planes' emissions to the Air Transport Association, the main trade group representing U.S. carriers. The ATA says U.S. airlines reduced greenhouse gas emissions by improving fuel efficiency 23% since 2000 and 70% in the past 30 years.
"Our record demonstrates that we are committed to managing our growth responsibly," says John Meenan, executive vice president.
But those gains don't offset the effect of more travel, scientists say.
More-efficient engines and fuel savings from improved flow of air traffic "will not fully offset the effects of the increased emissions resulting from the projected growth of aviation," the 1999 scientific report by the U.N. concluded.
Jet manufacturer Boeing says it's working with engine manufacturers to develop more environmentally friendly engines. Technological advances, says Bill Glover, Boeing's director of environmental performance, could reduce the amount of carbon dioxide and other pollutants emitted from jet engines.
Whether climate concerns will require limits on the growth in aviation is not for his company to decide, he says. "There's great economic value in aviation," says Glover. "Society has to decide where to cut emissions and how to retain the lifestyle we enjoy."
Nobody sees easy solutions for reducing aircraft emissions. Wuebbles, the Illinois professor, says more money for research is part of the answer.
Piers Forster, a professor at the University of Leeds in England, suggests putting additional taxes on jet fuel, using alternative fuels and redesigning aircraft. Britain's Royal Commission on Environmental Pollution says high-speed rail could replace short-haul flights.
Boeing is studying new fuel-cell technology that can power an aircraft and reduce emissions by combining hydrogen and oxygen to produce electricity. Such technology may be 10 years away, says Glover. Until then, "Our role is to keep building the most efficient, best airplanes on the planet."
Other possible solutions
Some other areas where solutions may lie:
*Jet engines. The most modern engines on new jets have reduced carbon dioxide emissions, but they've increased nitrogen oxide emissions. A 2003 report by the Government Accountability Office estimates that some new engines emit at least 40% more nitrogen oxides than older engines they're replacing. NASA is developing technology that would permit Boeing 737 and Airbus A320 jets, in 2018, to burn 25% less fuel and reduce nitrogen oxide emissions by 80%.
*Airports. Environmentalists and some European lawmakers and government agencies say airports should not be allowed to expand to accommodate more flights. The FAA disagrees. "Providing sufficient airfield capacity increases the efficiency of operations and tends to reduce, rather than increase, emissions," the FAA said.
U.S. airports are not going to lose business and halt runway or terminal expansion plans because planes are emitting pollutants, says Dick Marchi, senior vice president of Airport Council International-North America. Instead, the federal government "needs to adopt more aggressive standards on emissions," he says.
Virgin Atlantic Chairman Richard Branson, an activist for moving aggressively against global warming, favors constructing jet parking bays closer to runways and using tugs to tow them.
University of North Carolina professor John Kasarda, who consulted in the design of airports in Detroit, Bangkok, Brazil and the Philippines, says a new approach to airport design could reduce emissions.
He said he sees merit in an untried design by Illinois inventor Jim Starry, who conceived the design while flying back to the USA from England in the early 1980s.
Clouds of ice formed in the trails of jet exhaust trap heat and prevent the earth from cooling.
Aviation is going green from ticketing to takeoff by modernizing equipment, reducing fuel consumption and exploring new technologies.
Aviation expert Mike Boyd said he thought high-profile announcements by airlines are akin to building a firebreak to show the industry is taking some action.