[Below is the original script. But a few changes may have been made during the recording of this audio podcast.]

Coal is everywhere. It can be dirty and dangerous to wrest from the ground, but we're probably not going to run out of it anytime soon. And, unlike oil, the U.S. has a large domestic supply.

As a result, some have suggested that for "energy security" transforming coal into a liquid fuel alternative for cars might make sense. To do that, coal is mixed with oxygen and steam at high temperatures and pressure to produce a gas. This gas is then reacted in the presence of a catalyst to produce a synthetic oil.

Already, several industrial conversion plants exist, and the U.S. Air Force, for one, has used the resulting fuel to fly planes.

But there are two flaws with turning coal into oil, beyond its cost. First, it takes a lot of energy to loosen up the carbon bonds in coal. Second, all that energy use results in the emission of a lot of carbon dioxide—the most ubiquitous greenhouse gas causing climate change.

In the journal Science this week, chemical engineers suggest that incorporating hydrogen produced from solar, wind or nuclear-derived electricity into the process could eliminate this problem. Of course, it would take billions of dollars to do that and there might be a few better uses for that money, electricity or even hydrogen: advanced biofuels, electric cars or fuel cell vehicles.

After all, electric cars running on juice from coal-fired power plants use no foreign oil, less coal and even emit less CO2 overall than cars burning gasoline.

—David Biello