By Paul Wehling

Air travel is often cited as a major source of emissions, and with good reason: while aviation only accounts for about three percent of US total emissions, modern jetliners burn a gallon of high-grade fuel every five seconds. Even after adjusting for passenger count, that’s a huge emissions footprint compared to almost all other forms of travel. 

So what to do about it? Many conversations in the climate community focus on decreasing the number of flights taken by individuals, but the feasibility of reducing passenger loads is questionable. For one, we live in an increasingly globalized, interconnected world where air travel has become an important tool for business, educational, and personal connection. Sure, some flights we take are probably unnecessary, but most offer real benefits over distanced communication. For another, even people who don’t personally fly are the beneficiaries of aviation: per day, there are over 5000 military flights and 2000 dedicated cargo flights in the US alone, not even counting the significant amount of cargo that scheduled passenger flights also carry. Indeed, aviation emissions may be set to climb with increasing global access and the reintroduction of passenger supersonic flight.

The good news is that plenty of technologies exist or are under development to change how we fly, and the aerospace industry has become increasingly aware of the need for sustainability in the last few years. From improving current technology to completely eliminating emissions, here are a few of the ideas under development:

1. Increased Engine Efficiency

The newest passenger airliners are already 80% more fuel efficient than the first long-range planes from the 1960s. This is due to a variety of improvements in aircraft design, most of which are thanks to innovations in materials. Better high-temperature alloys inside engines have led to direct improvements in efficiency: hotter engines can extract more power from fuel. The introduction of composite aircraft bodies have decreased the weight of planes, and the use of high-power computers in design has allowed for vast improvements in fuel combustion efficiency and aircraft aerodynamics.

More of these improvements are set to come with new engines and aircraft models, and this is where the industry is most willing to innovate. Unfortunately, efficiency increases are getting harder to realize, especially as engines are reaching the boundaries of what current materials can handle. New engines, for example, may feature active cooling of turbine blades to allow for more efficient operating temperatures, but such systems drastically increase the complexity and cost of engines. In addition, any improvements may take a while to be reflected in total emissions, since an airplane’s lifespan is often 30 years in a passenger role or more while flying cargo.

2. Electric Aviation

Recently, promises of all-electric planes have become feasible for the first time. The same advances in battery technology that have powered electric cars are being introduced to the aviation world, and some sectors could potentially be completely electrified. In these aircraft, electric motors provide thrust with propellers, replacing conventional combustion engines or even small jets. 

While we’ve already seen the first electric aircraft, though, the technology has hard limits. Electric aircraft still have much less endurance (and thus range) than gas-fed counterparts, although that may change with improving battery capacity. More seriously, propeller aircraft cannot match the speeds or altitudes of turbine-equipped aircraft, limiting chances for industry-wide electrification.

3. Biofuels

A real possibility for revolutionary sustainability comes from biofuels, termed Sustainable Aviation Fuel (SAF), and are the same concept as biofuels for automotive applications: fuel is synthesized from biomass, including corn, algae, or industrial and agricultural waste, with the idea that emissions released were neutralized as the biomass was growing. The advantage of the technology is that it requires relatively minimal adjustments to current engines.

SAF has recently seen a huge push, especially from the US government and Boeing, the largest US aircraft manufacturer. In the last year, manufacturers have progressed from merely accepting SAF as an additive to tests of 100% SAF-powered engines. That being said, SAF suffers from the same problems as all biofuels do, and the true environmental and climate footprint of SAF remains uncertain.

4. Hydrogen

European governments and aviation companies (notably Airbus) have made commitments to the implementation of hydrogen-based turbine engines. Using hydrogen as a fuel source is promising because it can be created electrically and combusts into steam. While probably the most sustainable option on this list, hydrogen has major problems, starting with the timeline, since it will require extensive changes to engine design. Airbus aims to produce its first zero-emission aircraft by 2035, so widespread adoption wouldn’t be feasible until 2050 at earliest. 

Hydrogen also faces other hurdles, most notably the fact that any hydrogen-fueled aircraft would have to carry cryogenic liquid hydrogen tanks, which have much lower density than current fuels. Ensuring safety may be difficult, which is part of why hydrogen is still a future concept.

Aviation has a sustainable path ahead with these and other technologies, but adoption timelines are longer than they might even appear at first glance since old technologies will linger unless regulated or forced out for at least 50 years after all new aircraft are sustainable. As with all climate problems, change is possible but needs to happen more rapidly than is currently underway. Next time you fly, check your airline’s sustainability policy: have they committed to adopting sustainable aircraft, and by when?