Aviators Bertrand Piccard and Andre Borschberg recently completed a flight around the world powered solely by solar energy. The journey was a stunt, but organizers hope that it will inspire the world to think more conscientiously about the environment. As for aviation, many engineers are concerned that air travel is already very close to its peak efficiency, so there is very little room for improvement. With global demand for air travel on the rise, commercial air travel is poised to have a growing impact on the environment.