Hydrogen bomb?  

Nick Kristof's oddly titled article on the possibilities of hydrogen powered cars puts a more positive spin on things. But he only briefly mentions the problem of where the hydrogen might come from:

[...] getting the hydrogen can be a problem and can produce greenhouse gases. Hydrogen does not exist on its own but is locked up in water and fossil fuels. The goal is to use wind energy to pluck hydrogen from water in the ocean, but in the near term it's more likely that the hydrogen will come from natural gas.