For Aviation's Greenhouse-Gas Emissions, It's Technology Versus Growth

Commercial aviation, faced with worldwide concerns about greenhouse gases and looming regulations to reduce them, can count on advances in technology that will help to clean up its operations to a substantial degree during the coming 20 years. But growth in air travel, both an enabler and a product of the burgeoning global economy, is likely to use up the environmental gains faster than they can be achieved.

The gains will come from aircraft and engine designers, particularly the latter, as they create and produce the next generations of commercial aircraft -- the Airbus A380 and the Boeing 787, both scheduled to enter service within a year; the A350, Airbus's forthcoming answer to the 787, which will lag by several years; and the airframe manufacturer's successors to their current single-aisle families, which probably won't reach airlines before the late 20-teens or the early 2020s.

Equally important to greenhouse-gas reduction, major improvements in air traffic management are in advanced stages of planning and early stages of development. The U.S. NextGen satellite-based air traffic management system, Europe's comparable Sesar ATM research program and adaptations worldwide are intended to increase the capacity of airspace systems to match the growth projected for aviation in the coming decades. In doing so, the ATM upgrades will, in many cases, shorten flight times.

Each of these initiatives will reduce the emission of greenhouse gases, because each will save fuel. In every case the driver is economic. Reducing fuel consumption cuts airline costs, an important goal at any time and a crucial one as oil prices continue to increase and fuel succeeds personnel as the highest cost category at most airlines. The moderation and stabilization of oil prices -- so optimistically predicted last winter -- hasn't happened. Indeed, they reached record highs this summer.

Although work to reduce fuel consumption is intended to boost airlines' bottom lines and the ATM initiatives grew out of the need to increase the capacity of national and regional airspace and airports, the environmental benefits of both promise to be enormous. The principal greenhouse gas produced from aircraft operations is carbon dioxide, and the weight of CO2 emissions from aircraft is considerably greater than the weight of the aviation fuel that creates them during combustion. Estimates from think tanks, academics, trade groups and individual companies suggest that unit fuel-burn reductions well into double-digit percentages can be attained in the coming 10-20 years from each of these two avenues.

The trouble for aviation is that growth in passenger and cargo traffic is likely to swallow up these unit reductions and cause an overall increase in CO2 tonnage during this same time frame.

Last winter, in its annual long-range forecast of U.S. airline activity, the FAA projected a 47.3% increase, to 5,750, in the number of mainline aircraft in the U.S. passenger fleet between 2005-20, reflecting 3% average annual growth. The increase among mainline-size cargo aircraft is similar in scale -- 48.1%, to 1,468, at 2.8% per year.

More to the point, the FAA estimated the increase in jet fuel consumption by airlines and general aviation aircraft, the latter including business jets, during the same period. For airlines in passenger and cargo service, the 15-year increase was 68.7%, combining 52.2% from domestic operations and 111.8% from international. Fuel consumption was estimated to nearly triple among general aviation aircraft, spurred by the development of the very light jet market.

The FAA fleet projections say nothing about the age of aircraft and the level of technology that will be applied to the emissions problem, but the fuel-consumption estimates suggest trouble. The latest market forecasts from Boeing and Airbus provide further insight and no comfort.

Boeing believes worldwide airline fleets will double in less than 20 years, to 36,400 aircraft from 18,200. The company estimates that the 2026 fleet will comprise 18,200 "growth" aircraft -- aircraft delivered during the forecast period to accommodate increases in demand for air travel -- plus 10,400 new deliveries to replace aircraft in today's fleet that will be retired, and 7,800 current aircraft that still will be in operation at the end of the century's first quarter. Using different years and aircraft sizes, Airbus draws similar conclusions. Of 27,307 aircraft estimated to be in worldwide fleets in 2025, 5,447 are flying today. For Boeing, 21.4% of the future fleet are holdovers from today; for Airbus, the share is 19.9% (see table).

These holdovers will offer no relief from greenhouse gases, except for modest gains from modifications like winglets. Furthermore, although the great majority of each manufacturer's estimated future fleets will be new-production aircraft, delivered during the forecast periods, most of the new deliveries figure to be single-aisle aircraft that are in production now, also with only modest improvements. These narrowbodies are the workhorses that network airlines operate on their hub-and-spoke routes, and that low-cost carriers use in their dense, mostly short-haul markets.

The aircraft that will enter service during the forecast period -- the A380, 787 and A350 -- are all widebodies, designed for long-haul routes. Replacements for the 737 and A320 figure to reach airline fleets toward the end of the projected periods, if then. So when Boeing estimates that 62% of 28,600 new aircraft will be single-aisle models, and when Airbus says the narrow-body share will be 70% of 21,860, they are saying that the great majority of deliveries will be of current designs, with no more than incremental upgrades. New deliveries during the next 15 years don't figure to produce quantum-leap emissions reductions.

ATM modernization might deliver more than aircraft designs in reducing fuel consumption during the next two decades -- if governments pursue it vigorously. After years of planning and technology development at relatively low cost and with relatively little payoff, the FAA foresees substantial spending increases for NextGen in the coming few years. Europe's concerns about global warming, greater than the U.S.'s, should propel Sesar, Eurocontrol's Single European Sky ATM Research program. But ATM modernization also depends on the ability and willingness of airlines to equip their aircraft, at considerable cost, for the improvements in store. ATM benefits to emissions reduction will be gradual.

As aviation grows in the coming years and consumes more fuel, it seems certain to become a part of emissions-trading systems being developed to control and eventually reduce the amount of greenhouse gases in the atmosphere. The European Union has such a system and intends to apply it to commercial aviation, starting in 2011. The International Civil Aviation Organization, meeting next month in Montreal, will consider plans to set up a global regime. As with noise years ago, Europe is ahead of the greenhouse-gas regulatory game, and airlines and manufacturers are counting on an ICAO system to reflect what they can attain technologically and affordably.

A fundamental issue in any emissions-trading concept will be the amount of emission "permits" allocated to aviation. In emissions trading, an allocation is based on an historic level of activity and the emissions associated with it, and reductions are imposed over time. Once an economic sector has used up its allocated permits, it must trade for more. In theory, industries that can reduce emissions relatively inexpensively do so and sell permits to industries whose costs are higher.

It isn't hard to make the case that aviation is the most carbon-efficient form of transportation, that it will cost aviation more than other industries to reduce its CO2 emissions, that aviation accounts for only 2-3% of current CO2 emissions and would remain a lesser contributor in an unregulated future, and that aviation's value to society and the world economy justify favorable treatment. But arguments like these are an unlikely source of relief -- aviation's visibility and its widely publicized customer-service failures make it a prominent political target.

Articles that follow in this special report explore these regulatory issues, the prospects for reduced CO2 emissions through aircraft and engine design, the potential contributions of modernizing air traffic management, experimentation with alternative fuels, and NASA's contributions to environmental research, and a longer-term initiative that would reduce greenhouse gases dramatically -- solar power from space. Also, because aircraft- and engine-design concepts for reducing carbon dioxide emissions are likely, sooner or later, to conflict with the aim of reducing aviation noise, we examine these questions also.