Aviation may be the last technical frontier where it’s tough to find replacements for carbon-intensive technologies—even in principle. Biofuels can help, but they, too, still have large carbon footprints, some even worse than oil.
Meet Solar Impulse, the first plane to fly 24 hours without fuel other than light from the sun. Last night it completed a flight from Switzerland to Spain. Next up: Morocco. And in a couple years, if everything goes according to plan, it will circle the globe.
We are still a ways off from coming close to making any of this commercial. But if I had some spare change and had to decide between blowing it onto a fossil-fueled blastoff into outer space or on a solar mission around the globe, my money would be on the sun.