Google's Project Fog Horn had the potential to slow impact of climate change by making fuel out of carbon dioxide (CO2) harvested from sea water. Such fuel would still produce carbon when burned, but it would not release new carbon. This would have in theory helped us to advance as a civilization.

Scientists have known for decades that it is theoretically possible to extract carbon from water and air and reuse it as fuel, but so far all the solutions have been too expensive and impractical. Google shut down project Fog Horn because they too just could not find an economical solution that would justify further investments.

Prometheus is not the first startup to take on the problem, but they seem to be the first to to make fuel-from-air cost effective.

They take water and carbon, and using a chemical reaction convert this mixture to alcohol. Then, and this is their secret sauce, instead of using a traditional thermal process which requires a lot of energy, Prometheus is converting this alcohol at room temperature, using electricity and a carbon nanotube membrane, yielding fuel at a much cheaper cost.

Note: This technical explanation to why Prometheus is able to do what Google has not comes from the Prometheus CEO's recent post on Hacker News

According to Dr. Julio Friedmann, a Columbia professor and a researcher who has spent two decades on this topic, we should try any technology that seems promising. So far, every company that wanted to compete with gasoline has failed. We don't know what will work, so we should be trying everything.