Recently, I attended an event organised by Airbus which included a film about their vision of aviation in 2050 followed by a question and answer session with their VP for Engineering in the UK, Neil Scott.  A strong theme that I took away from the event was maintaining air transport as fossil fuels become scarce and expensive through the use of oceanic algae farmed and harvested to generate biofuels.  This could be a good solution but we will need to consider the environmental impact of the massive level of ocean agriculture required to supply our airline system.  Airbus propose a more balanced, diverse approach to sourcing biofuel in this short video on their website: http://videos.airbus.com/channel/iLyROoafYvHb.html; so perhaps I took away the wrong message from the event I attended.

[Photo from http://cleantechnica.com/2010/07/20/holy-sustainble-cow-ordinary-algae-can-double-as-biofuel-and-cattle-feed-too/%5D