Researchers at Audi are making synthetic diesel fuel using only water and air. Miracle? No. Science. http://money.cnn.com/2015/04/28/technology/audi-diesel-air-w...
Using water, air and large amounts of heat. (Where does that heat come from? Many possibilities, but currently from fossil fuels.)
First, the researchers heat up steam to very high temperatures to break it down into hydrogen and oxygen. This process requires temperatures of over 800 degrees Celsius (1,472 Fahrenheit) and is powered by green energy such as solar or wind power.