As energy prices soar and global warming awareness grows, more Americans are buying hybrid cars, outfitting their homes with low-energy light bulbs and worrying about the distance their food travels from farm to plate. But when it comes to air travel, how many pay attention to the jet fuel their flights consume and the carbon emissions those planes generate?
Though aviation represents only 3 percent of global greenhouse gas emissions, that share is likely to rise as air traffic grows - the Federal Aviation Administration says commercial flights in the U.S. alone will increase 60 percent by 2030. Passenger jets are about a third more fuel-efficient today than those built 40 years ago, and their design continues to improve. But worldwide traffic growth is projected to outstrip efficiency improvements, leading to an increase of carbon dioxide emissions from aviation of 3 percent to 4 percent per year, according to the 2007 report of the U.N. Intergovernmental Panel on Climate Change.
Adding to concerns is the nature of aircraft emissions. Because nitrous oxide pollutants are discharged at such high altitudes, damage to the ozone layer is amplified and the cloud-like contrails formed have an additional heat-trapping effect.
Together, those factors may bring new regulatory and economic pressures on airlines.
"Going forward, climate change could be the most significant challenge facing aviation," said Daniel K. Elwell, the FAA's assistant administrator for aviation policy, planning and the environment. "We could run up against environmental limits to aviation growth before we run into actual concrete infrastructure limits at airports."
Already, the European Union is pushing for international airlines to pay for the carbon gases they produce. The move has tensions simmering across the Atlantic. Europe's nascent cap-and-trade system would be expanded to limit the amount of carbon dioxide airlines could release, saddling them with extra costs if they exceed those caps and allowing them to sell off credits if fuel consumption is reduced.
But the method for regulating aviation emissions is complicated, because the pollutants are largely produced outside neat national borders.
Major U.S. airlines, represented by the Air Transport Association, have balked at any regulation proposal. With oil pushing the $130-a-barrel mark, the carriers argue that jet fuel prices - their largest expense - act as a carbon tax, providing all the incentive they need to conserve.
The federal government also maintains that Europe's unilateral plan could violate international aviation treaties.
Regardless, the next U.S. president will face mounting pressure to adopt cap-and-trade legislation that includes aviation. Recently, the Senate killed the proposed Lieberman-Warner Climate Security Act, which would have forced refineries to pay for the carbon dioxide emitted in fuel production, a cost they would likely have passed on to airlines and other petroleum-dependent industries.
"The notion that any substantial sector can be excused is unlikely," said Jonathan Pershing, a U.S. and international climate change policy expert at the World Resources Institute, a Washington-based environmental think tank. "Aviation emissions are growing faster than any other transportation sector and ultimately will account for as much 5 percent of global emissions unless those are accounted for or curtailed. It's bigger than steel."
Rising fuel prices have forced airlines to enact conservation measures that have the side benefit of curbing emissions. In March, Southwest Airlines started flying at slower speeds, a remedy Northwest Airlines and JetBlue Airways also employ. Slowing down adds just minutes to flying times but could save Southwest 18 million gallons of jet fuel this year, said a company spokeswoman, Whitney Eichinger.
Southwest also uses its now-iconic curved winglets to reduce drag on its newer Boeing 737-700s and some of its older 737-300s. Other airlines, including AirTran Airways, have installed the winglets, creating fuel savings of 3 to 4 percent on an average 737-700 flight, the Air Transport Association said.
Anything airlines can do to limit the idling of aircraft engines on the taxiway helps. American Airlines has its aircraft taxi on one engine whenever possible and, similar to Southwest and AirTran, uses ground power instead of the plane's unit to provide electricity and air conditioning at many gates.
Financially strapped airlines such as American, Delta and United plan to retire some aging, gas-draining planes. But the economic slowdown also means carriers have delayed or canceled the delivery of new, more fuel-efficient planes.
Commercial service on Boeing's new 787 jetliners won't debut until the third quarter of 2009, a delivery date pushed back three times. The 787 is the first jumbo jet to be built primarily of lighter carbon-fiber composites, requiring 20 percent less fuel than a comparable aluminum-bodied plane, Boeing says. So far, few of the orders for the 787 jetliners are from U.S. carriers.Until Congress upgrades the nation's 1950s-era air traffic control system to fully support satellite navigation, airlines have less motivation to purchase newly outfitted planes, said Elwell of the FAA.
Planes will be able to fly closer together on more direct routes under the system, reducing fuel burn. Improvements have already come as the required vertical distance between planes flying in the stratosphere was halved to 1,000 feet in 2005, he said. The FAA also opened up new routes recently over the Atlantic Ocean to allow planes to fly more efficient trips from New York to the Caribbean.
The satellite technology would also reduce emissions and noise generated during arrivals, by allowing aircraft to remain at higher altitudes longer and use less power as they descend toward a destination, according to a recent Government Accountability Office report. Overall, full implementation of the new "NextGen" air traffic control system could reduce aviation emissions up to 12 percent by 2025, according to the FAA.
Alternative fuels to jet kerosene aren't yet a viable solution. But the race is on. Plane maker Airbus and manufacturer Honeywell International Inc. recently said they are developing an algae-based biofuel that could power nearly a third of commercial aircraft worldwide by 2030.
Virgin Atlantic earned bragging rights in February with the world's first biofuel-powered commercial flight, a passenger-less jumbo jet partially fueled on an edible cocktail of coconut and babassu nut oil. In 2009, Continental Airlines and Boeing are scheduled to make the first U.S. commercial test, using a more advanced blend of biofuels.
In the meantime, what's a green-minded traveler to do? Take more efficient rail or bus transportation for short-haul trips. Pay for nonstop flights, as extra take-offs and landings guzzle fuel. But don't pay for business class. The more people packed into coach, the more efficient the flight.
On a trip from Baltimore to New York City, flying would generate twice as many carbon emissions as driving in a compact car, according to NativeEnergy.com, which handles carbon offsets. But a longer flight to Boston would generate .079 tons of CO2, compared to .101 tons CO2 from the drive.
You can pay a carbon-offsetting group to reduce emissions equal to the amount a trip generates. The money helps fund wind farms or solar panel installations, for example. Some airlines even allow customers to purchase offsets as they book tickets online.
Silver Spring-based Carbonfund.org has a new partnership with JetBlue to sell offsets directly to its passengers.
"Airlines understand that theirs is an industry where it's a lot more difficult to reduce carbon," said Eric Carlson, Carbonfund.org's founder and a former Environmental Protection Agency employee. "They realize that their consumers want green options, and that there are things they can do to reduce their emissions, and then they want to offer the opportunity to offset the rest."
But since the offset industry is unregulated, it's difficult for consumers to determine which organizations live up to their claims.
Nor is any voluntary program likely to account for all the pollutants generated by such a huge industry.
"Offsets are not the overall solution," said Pershing. "Ultimately we have to figure out how to reduce emissions in aviation - not let aviation pay for somebody else to reduce emissions."