Wired: How to Create Fuel Out Of Thin Air :

“A small British company has developed a process that uses air and electricity to create synthetic fuel. Yes, it’s slightly more complicated than that, but the result is what Air Fuel Synthesis is calling, after much consideration to the term, ‘carbon-neutral’ gasoline.
Here’s how it works: air blows up into a tower filled with a sodium hydroxide solution mist. After reacting with some of the sodium hydroxide, the carbon dioxide in the air forms sodium carbonate. The mixture gets pumped into a cell where it gets hit with an electric current, which releases more carbon dioxide, the excess of which is collected and stored for subsequent reaction.
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They plan to scale up slowly (a refinery in 15 years). However, play this out. Eventually we not only clean out all the CO2 we put into the atmosphere, we clean out all the CO2 animals exhale and plants inhale, killing all life everywhere. (Assuming we convert more to fuel than we burn). We can call this new threat Global Oxygenating.