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Last summer, more than 1,000 environmentalists in the U.K. staged a weeklong protest in a "Climate Camp" at Heathrow Airport, where about 70 people were arrested. Their immediate purpose was to block a planned expansion of Heathrow, but the protests highlighted a growing complaint in Europe—that the ride to global-warming catastrophe is being fueled not only by coal-fired power plants and SUVs, but also by the ever-rising number of commercial jets. Now governments are starting to listen. In November, the European Parliament voted to bring airlines flying within or into Europe into their carbon-trading scheme, forcing them to reduce their carbon emissions by 10 percent by 2011 or buy carbon credits on the open market. Then, in December, the protests crossed the Atlantic: California joined four other states and New York City in a petition asking the Environmental Protection Agency to regulate carbon emissions from airlines. "We want the EPA to take their head out of the sand," said California Attorney General Jerry Brown at the press conference announcing the petition.

Although the aviation industry claims that it generates only 2 percent of global CO2 emissions, it's one of the fastest-growing carbon polluters around. The Federal Aviation Administration predicts that passenger levels will double in 10 years and perhaps triple by 2025. In 2004, air traffic grew at a rate of 14 percent, faster than at any time in the past quarter-century. All those extra miles in the air translate into more jet fuel, and every pound of jet fuel releases three pounds of carbon into the upper atmosphere.

The auto industry, braced for the regulations to come, plans to reduce its carbon footprint using a combination of hybrid technology and alternative fuels. But lowering the emissions of a jumbo jet is a more complicated proposition than slapping an electric motor behind the gas tank. The airlines argue that the high price of oil already compels them to burn as little fuel as possible. That defense might not prevent future regulations, though. And so airlines are trying to engineer their way to a low-carbon future.

The Fuel Question

The most visible crusader against airline carbon emissions has been, paradoxically, a billionaire airline owner. Richard Branson, the chairman of Virgin Atlantic Airways, has committed to spending all the profit from his trains and airlines over the next decade—an estimated $3 billion—on fighting global warming. Step one in that program is the Virgin Green Fund, a venture-capital effort that invests in alternative-energy companies.

Virgin Atlantic is also collaborating with Boeing research into biofuels, which generate less net carbon because the crops they're made from consume carbon as they grow. The two companies, along with engine maker General Electric, have planned a demonstration flight for early this year that will "move biofuels forward and disprove the naysayers," according to Dave Daggett, Boeing's technology leader for energy and emissions. The 747 used for the demonstration will power one of its four engines with a mix of 20 percent biofuel combined with traditional jet fuel. The 10-year goal of the program is to fly with a mix that is as much as 50 percent biodiesel.