The end of aviation?
It's hard to know exactly when oil prices are going to go way up, and it's hard to know at what point we will finally put some kind of price on carbon emissions.
When either happens, the effect on aviation will be major. There's no reason to believe either is particularly imminent, but they seem inevitable, barring some kind of completely unforeseen technological advance, which is possible. The price of flying could be multiplied by a huge factor.
Brad Plumer's article of a few weeks ago explores -- without jumping too hard to absolute conclusions -- what he calls "the end of aviation."