This is no idle pursuit. Airlines are one of the fastest-growing carbon polluters around; air traffic could double by 2025. And as Dennis Gaffney details in "Fly the Eco-Friendly Skies", it's a tremendously complicated problem to solve. Any alternative biofuel needs to pack the same energy punch as today's jet fuel, needs to be able to be made in abundance, and needs to not freeze at high altitude. Says James Hileman, a research engineer at the Massachusetts Institute of Technology, "If you're a kid and you're thinking, 'OK, what can I do to save the world?' Well, the one way you can save the world is to find new, growable sources of fuel."