The aviation industry’s part in the battle over global warming is heating up fast.

Pilloried as a high-profile generator of greenhouse gases, commercial aviation is increasingly being targeted by legislators on both sides of the Atlantic for mandatory carbon-trading schemes and limits on aircraft emissions — even though airlines say they are already dramatically cutting emissions and painting their operations green.

The need to reduce aircraft emissions is gaining a sense of urgency as the sheer volume of air travel overwhelms gains in cleaner, quieter aircraft. Although modern aircraft are much more eco-friendly than their predecessors, the number of airliners in the sky is growing constantly.

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While commercial aviation accounts for just 2 percent of global carbon emissions, that percentage will grow to 3 percent in coming years, according to number-crunchers at the International Air Transport Association.

Last month, the European Parliament voted to impose a cap-and-trade scheme on airlines flying to the European Union, starting in 2011.

The proposal is bitterly opposed by the United States; the Bush administration regards mandatory limits as violations of international treaties and champions market-driven solutions to global warming.

State and Senate initiatives

Nevertheless, on Wednesday, five states and several non-governmental organizations filed a petition with the Environmental Protection Agency, asking the EPA to impose reductions on aircraft emissions.

That same day, the Senate agreed to consider a bill sponsored by Senators Joseph Lieberman and John Warner that would impose a schedule for cutting U.S. aircraft emissions — part of a much broader bill to reduce American greenhouse gases.

None of these proposals has yet become law, and perhaps none will. But all point in the same direction: toward greater scrutiny of aviation, especially in Europe, where consumers, regulators and airlines themselves have taken the lead on climate-change issues.

"Europeans are definitely spinning out a lot more policies than we are in the U.S.," said Nancy Young, vice president for environmental affairs at the Air Transport Association, the U.S. airline trade group. “We have this voluntary approach in the U.S. right now; they have a mandatory approach in Europe. The focus on aviation in Europe has gotten out of proportion."

U.S. airlines say they do care

Young said the perception that U.S. carriers don’t care about cleaning up their environmental act is simply untrue.

"Our airlines improved fuel efficiency 103 percent from 1978 to 2006. Fuel burn is directly related to carbon dioxide, the leading greenhouse gas. To have that kind of achievement — it didn't just happen," said Young.

She added that U.S. carriers continue to improve performance by attaching winglets to make aircraft more aerodynamic, removing weight from planes, researching alternative fuels and buying more-efficient new aircraft.

U.S. carriers, which suffered $40 billion in losses from 2001 to 2005, and have only fitfully returned to profit, operate aging fleets.

By contrast, Lufthansa, the profitable German carrier, will spend $12 billion for new aircraft over the next several years, according to Karlheinz Haag, Lufthansa's head of environmental issues.

More efficient aircraft burn less fuel — an important edge when the price of a barrel of crude oil is pushing $100.

"Only an economically strong company can invest in sustainability," said Haag.

Innovation trumps regulation, airlines argue

Airlines and their trade associations argue that innovation trumps regulation when it comes to going green.

The International Air Transport Association (IATA), a trade group for 270 of the world's airlines, holds that building more-efficient aircraft, integrating Europe's 20-odd national air traffic control systems into a streamlined "single European sky" and adoption by the U.S. of a GPS-based "next generation" air traffic control system to replace the present outmoded radar-based system are essential for improving aviation’s environmental record.

IATA opposes the EU plan to impose a trading-emission scheme, said Steve Lott, a spokesman for IATA in Washington, D.C.

"If we are going to have emissions trading, the system must be global. One region or one country can't solve the problem. We're working through the International Civil Aviation Organization to come up with a global balance."

In the absence of global standards, individual airlines are trying out a variety of ideas, from landing their aircraft differently to allowing passengers to purchase carbon offsets.

Continuous-descent approaches

Scandinavian Airlines System has been experimenting with a program called continuous-descent approaches — basically, continually reducing power on aircraft as they descend to land.

The European carrier has operated 2,000 "green" landings in Stockholm the last few years, according to SAS spokesman Tom Fredo, who said the method can save up to 5 percent of an aircraft's fuel, thus reducing carbon emissions and cutting expenses.

Last year SAS followed British Airways in allowing passengers to calculate the amount of carbon produced by their flights and funnel donations to a third-party company to fund green projects such as tree-planting.

BA, which launched the voluntary program on its web site in late 2005, hasn't disclosed how many customers have used it or how much they have spent.

But carbon offsets offer a feel-good factor to air travelers that technological fixes don't.

This year, two major American carriers, Delta Air Lines and Continental Airlines, started similar programs.

Still, that approach likely has limits, said industry analyst Henry Harteveldt, of Forrester Research.

"Consumers probably feel it's the company's responsibility to address the environmental impacts of their industry, not theirs," he said.

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