Aviation is a notoriously difficult sector to decarbonize. So as Melissa plans a family trip, she wrestles with her options. Which flights emit the least carbon? How well do offsets work? Should we even be flying at all? Melissa and colleague Kirsten Smith task producer Daniel Woldorff with calling up airlines to look for answers.  Engineer Alejandra Uranga imagines airplanes in a net-zero future. Melissa and Alejandra cover electric planes, sustainable aviation fuel, hydrogen and more. Guests: Alejandra Uranga is an Assistant Professor of Aerospace and Mechanical Engineering at USC. Kirsten Smith is a Research Associate at Columbia University's Center on Global Energy Policy. Daniel Woldorff is a producer for The Big Switch. The Big Switch is produced by Columbia University's Center on Global Energy Policy in partnership with Post Script Media. This episode was produced by Daniel Woldorff and Alexandria Herr. Theme music and mixing by Sean Marquand. A special thanks to Natalie Volk, Kirsten Smith and Kyu Lee. Our executive editor was Stephen Lacey.