Most of us are unlikely to be flying around in solar-powered aircraft any time soon—that’s a privilege reserved for people like Bertrand Piccard and André Borschberg, who are flying the Solar Impulse 2 around the world. Piccard last month completed the trans-Pacific portion of the journey.

Unfortunately, writes Brad Plumer at Vox, the 17,000 solar cells crammed into Solar Impulse 2’s jumbo-jet-sized wings can carry only a single pilot at speeds of 43 mph. A carbon-fuel-powered Boeing 747-400 can carry 400 people at 570 mph.

Nevertheless, air travel can be made greener, Plumer writes. The easiest approach is through incremental improvements in current technology. He notes that the 787 Dreamliner is 20% more efficient than the 767, and today’s U.S. commercial airline fleet emits one-third the CO₂ per passenger mile vs. 1970.

In addition to improving the efficiency of new aircraft joining the commercial fleet (through lighter weight composites and blended winglets, for example), Plumer writes that the industry can take additional steps, such as optimizing routes and air-traffic management and aggressively retrofitting existing aircraft.

Citing a 2015 Nature Climate Change paper by Andreas Schäfer, Antony Evans, Tom Reynolds, and Lynnette Dray, Plumer notes that many of these measures would pay for themselves if oil were above $50 per barrel. Conversely, retiring inefficient planes before the end of their 25-year service life would make financial sense only if oil were above $100 per barrel.

More dramatic, Plumer notes, would be the adoption of biofuels and radical new wing designs.

Read the complete article here, where Plumer provides many more details and links to additional reading on the topic.