The weight of airplanes could be decreased by using composite materials, for example, or replacing heavy wiring with lighter fiber optics. Some of these advances have already been incorporated into new airplanes. Airbus’s A380 and Boeing’s 787, for example, are expected to reduce fuel consumption by something like 17 percent to 20 percent. Beyond 2020, the industry could employ more radical designs. It could abandon the ubiquitous tube-and-wing design of airplanes, for example, in favor of something called the blended wing. The entire airplane would essentially be a wing, increasing the amount of lift it generates and reducing fuel consumption by perhaps 25 percent. Such a design has been considered for many decades but has yet to be used for commercial aircraft, although a variant was used for the military’s B-2 bomber.
Improving flight logistics could shave another 8 percent off fuel consumption by 2020. With cooperation from governments, it may be possible for planes to fly more direct routes. Better air traffic control technologies could also reduce the amount of fuel planes waste idling on the runway or waiting to land.
Finally, advanced biofuels could decrease carbon emissions by about 5 percent by 2020, according to aviation industry estimates. The contribution from biofuels is highly uncertain, however, and existing biofuels–ethanol and biodiesel–won’t work in today’s airplanes for a variety of reasons. Ethanol simply doesn’t store enough energy, and it introduces safety concerns because it’s much easier to ignite than jet fuel. Biodiesel would require heating at cold temperatures, and, more important, it breaks down at high temperatures, says James Hileman, associate director of the Partnership for Air Transportation Noise and Emissions Reduction. That leaves only advanced biofuels, such as hydrocarbons that are almost identical to jet fuel and can be made by refining oils produced by algae. But so far these are very expensive and available only in small quantities. In the distant future, alternative fuels such as liquefied hydrogen might help, but large obstacles remain, including the difficulty of storing liquid hydrogen on an airplane.
There are many possibilities for reducing emissions, but even the aviation industry acknowledges they won’t be adequate to meet its goals. The industry will likely exceed its emissions cap by 90 million tons of carbon dioxide in 2025, says Quentin Browell, assistant director for environmental issues in aviation at the International Air Transport Association, the group that announced the emissions goals. To make up for this, it will have to purchase offsets–essentially paying other industries to reduce emissions.