Aviation can go green, but not soon and not as comprehensively as ground-bound transport. As environmental advocates warn that flying makes an intolerably large contribution to climate change, the pace of progress in greening the sky may well lead travelers to question whether it’s ethical to fly at all. However,  promising developments with zero-emission, battery-powered electric engines are already happening in one area of aviation, involving trips of limited duration and distance. Now Everything we think of from solar panels, wind turbines, electric engines, high-storage batteries, hydrogen fuel cells is spurring green evolution. How Green can air travel be ?