Before long, the airlines of the United States may be flying in environmentally friendlier skies -- whether they like it or not.
The European Union, which has taken several steps to address climate-change concerns, is preparing to crack down on greenhouse gas emissions by all airlines that do business in Europe, imposing cap-and-trade rules designed to encourage emissions reductions for commercial aircraft that serve the region. The European Parliament is scheduled to take its first vote on the plan this week.
U.S. carriers and the Bush administration don't like the proposal -- the White House has already called it a violation of postwar aviation agreements -- but they're unlikely to do anything that might jeopardize access to the lucrative European market.
The upshot is that airlines, which have been overlooked in much of the debate over climate change, will probably become one of the first test beds for a broader system of carbon restrictions in the United States. That's because Europe is likely to impose rules on them before Congress acts on any climate-change legislation that would affect the United States in a broad fashion.
"If airlines had to do it and it ended up not being a huge burden, that would be a very valuable lesson," said an economist with ties to the aviation industry who for that reason asked not to be identified. "We're already moving down that pathway."
The Federal Aviation Administration, in fact, is in partnership with airlines, aircraft manufacturers, airports, oil companies and universities on a Commercial Aviation Alternative Fuels Initiative. Representatives met in Washington last week to see how they might accelerate the development of fuels that would produce fewer emissions.
The aviation industry is responsible for about 3.5 percent of the greenhouse gas emissions and other agents, such as water vapor from hot exhausts, that can trap solar heat and contribute to global warming, according to the U.N.'s Intergovernmental Panel on Climate Change. That amount is small compared with automobile emissions but still substantial.
"That's about the same size of emissions as a medium-sized country, say Canada or the U.K.," said Annie Petsonk, international counsel for the advocacy group Environmental Defense. "If aviation were its own country, we would look to it and expect it to step up to the plate, to participate in capping and cutting emissions."
But airline travel is increasing, as is its effect on climate. World airports recorded 4.4 billion passengers in 2006 and expect the total to reach nine billion by 2025, according to the trade group Airports Council International.
"The concern is more, not what the impact is right now but what will the impact be 20 years from now, after many countries have put into place policies to try to reduce greenhouse gas emissions" for other industries, said Donald J. Wuebbles, director of the University of Illinois' School of Earth, Society and Environment. "At that point, aviation's percentage may have risen dramatically."
The U.N. panel estimates that by 2050, aviation could contribute up to 15 percent of the factors that lead to global climate change. The industry contends that its contribution would be about 5 percent.
Governments in several countries concerned about global warming have begun to assess aviation's impact. The European Union has been considering whether and how to add airlines to its existing cap-and-trade system, under which companies must meet emissions limits or buy carbon credits from those that do more than meet the standards.
The European Commission -- the EU's executive body -- proposed that European air carriers be brought under the plan by 2011, and international carriers by 2012.
The United States, Australia and China have balked at the EU plan and are girding for a trade fight, but the proposal expected to emerge from the European Parliament is even stricter and would extend the restrictions to foreign airlines at the same time as European carriers.
The airline industry, long concerned with fuel costs, says the market already provides all the motivation it needs to be environmentally friendly, because more efficient engines require less fuel. The industry also argues that the EU's plan could impose significant costs on companies that are struggling.
An analysis by the investment firm Lehman Brothers said the EU plan could increase the cost of fuel and might force airlines to fly less overall. But Lehman also noted that the plan could spur fuel-saving technologies and more efficient operating procedures.
With the public becoming more attuned to climate change and, perhaps, aviation's role in it, some airlines, like their cousins in the automotive industry, have already made moves to show that they are paying attention. Delta Air Lines, for instance, has started a carbon offset program: In exchange for a few extra dollars on a passenger's ticket price, Delta will plant trees along the Gulf Coast.
And this summer the Air Transport Association, the group that lobbies for the largest U.S. airlines, created a new position: vice president for environmental affairs, filled by aviation lawyer Nancy Young.
"We have huge market incentives to minimize our greenhouse gas emissions. They're directly related to fuel burn," she said. "We're not embarrassed that our economic interests and our environmental interests line up."
Young said the industry is focused on reducing pollutants by using more efficient engines. She said that since 1978 the industry as a whole has improved its fuel efficiency by 103 percent and that all the major U.S. airlines have committed to an additional 30 percent improvement by 2025.
Historically, fuel efficiency in aircraft has been achieved primarily by building lighter airframes with new metals and composite materials and by tweaking engines to burn hotter and as a result use less fuel.
But there are questions about whether jet engines, basically refinements of 50-year-old designs, can be made much more fuel efficient than they are already, or efficient enough to keep up with aviation's projected rate of growth and new emissions standards. Improvements now are mostly incremental, with no big breakthroughs.
"There are technological limits, yes," Young said. "That's part of our concern, we're so fuel efficient already. We're going to get better, but we have to invest a lot of money to buy new aircraft."
Young said the industry probably would not be able to reduce its emissions quickly enough to comply with the proposed EU caps. Instead, companies would have to spend money on carbon credits that would otherwise be used to purchase more efficient technology.
Aircraft manufacturers, spurred by airlines' intense desire to be more efficient, have rolled out new designs such as the Boeing 787, which uses 20 percent less fuel than planes of comparable size, mostly because of the use of lightweight composite materials in its fuselage.
But new planes are expensive, and engine improvements can take a long time to show up in an airline's fleet. According to Lehman Brothers, it takes 10 to 15 years at minimum for an aircraft to be replaced.
Also, pressure to save money on fuel doesn't always yield the most environmental benefits, said a Senate Democratic aide knowledgeable on the issue. The addition of biofuels to kerosene jet fuel, for instance, would make it much cleaner-burning but no cheaper.
"Biofuels could have a real emissions benefit, but . . . there's no cost advantage," the aide said. "So there's very little driving airlines to go into biofuels right now."
Some are, however. Virgin Atlantic and Air New Zealand have expressed interest in using biofuels. And the Air Transport Association participates in the Commercial Aviation Alternative Fuels Initiative, a government-industry partnership spearheaded by the Massachusetts Institute of Technology.
But there are no large-scale research efforts under way, said Wuebbles. The Air Force is interested in fuel supplements, but mainly to reduce dependence on foreign oil rather than to cut emissions. The Air Force has said it wants its fleet to fly on just 50 percent petroleum by 2010. Also, its primary focus is on synthetic additives that could emit as much carbon dioxide as regular jet fuel.
The biggest hurdle in developing alternative fuels might be weight. Ethanol is heavier than kerosene and contains less energy per gallon, so a plane would have to carry more.
The U.N. panel acknowledged such challenges in its 2007 report, saying, "There would not appear to be any practical alternatives to kerosene-based fuels for commercial jet aircraft for the next several decades."
One way for airlines and government agencies to pare both fuel consumption and emissions would be to reduce traffic congestion in the air and on airport runways. The industry says such steps should be taken before imposing cap-and-trade restrictions.
Modern-day air traffic control is based on 1950s technology that requires aircraft to fly between radar beacons. The FAA is in the early stages of moving to a satellite-based air traffic control system that would allow aircraft to fly in a straighter line, saving time and fuel.
Then there are tarmac delays that leave planes idling at terminal gates or on taxiways, burning fuel. According to the International Air Transport Association, global carbon dioxide emissions could be cut by 12 percent if air traffic control systems were more efficient.
Although Europe is moving forward on greenhouse gas emission controls, no congressional action affecting aircraft or emissions generally is expected during the remaining year of the Bush administration.
Still, Sen. Frank J. Lautenberg, a New Jersey Democrat, is developing a proposal that would place aviation under a cap-and-trade system, although it has not been introduced. On Nov. 1, a Senate subcommittee approved a bill that would require electric utilities, transportation companies and manufacturers to reduce their greenhouse gas emissions, but that would affect aviation only indirectly, mainly through fuel costs.
Subcommittee approval was hard-won, however, and the bill's future is uncertain.
Ken Button, director of George Mason University's Center for Transportation Policy, Operations and Logistics and an expert in international aviation, said cap-and-trade proposals such as the one the EU wants to institute are a good idea and that such a system is largely the reason why tetraethyl lead was forced out of gasoline in the 1970s. He suggested that cap and trade, if implemented properly, could work the same way with greenhouse gases.
"Markets certainly do work, providing that everything is included in the market. The problem of course is that damage from greenhouse gases is not something in the market," Button said. "The cap-and-trade system tries to bring it into the market. Cap and trade is going to have less impact on a good airline than a bad airline."