Concern has been expressed in recent years over the contribution of aircraft to GHG emissions. Some airlines have gotten favorable publicity for experimenting with bio-derived fuels. But, what if aircraft were to target reducing fuel consumption by half, or more. That will require some radical rethinking about aircraft design. If you have an interest in some of the serious redesigns being discussed, then you will enjoy the following article: http://www.economist.com/node/18329444.