Back to earth: Scientists are seeing the logic in returning carbon to whence it came.
Drilling activities at Firstenergy's R.E. Burger plant near Shadyside, Ohio

The big idea: Finding ways to pull the by-products of energy consumption out of the air and put them where they can't hurt us. For now, policymakers and scientists use the generic term "carbon sequestration" to describe the process of removing greenhouse gasses from the air. But there are few ways to do this.

The most obvious one is to plant trees (which pull CO2 from the air during photosynthesis), and this is now what many organizations do to be "carbon neutral." But it turns out that forests only sequester carbon when they are expanding, and that only works in the tropics, where regulations are hard to enforce. The oceans also absorb some CO2, but too much tends to acidify water.

So California has taken the unusual step of looking at sinking the stuff underground.

"There is ample space in the subsurface for storage of all of the CO2 we could envision producing," says Larry Myer, a 30-year veteran of geology research with Lawrence Berkeley National Laboratory.

Myer heads a group of researchers experimenting with turning CO2 in the air into a liquid and dropping it into spongy rock layers under the Central Valley. He says the technology to bury greenhouse gasses already exists theoretically.

"We basically have the technological know-how to do this," he says.

What's next: Putting carbon back into the ground is a lot like taking it out: You need a precise picture of the geology under your feet. And from what we know, California is a perfect place to do it. In the Central Valley, there are wide areas of porous sandstone capped by an impermeable shale lid. Myer and his team are working on early experiments to sink about 3,000 tons of liquid carbon dioxide 3,000 feet underground.

There are some concerns. For instance, what will happen when you shove all that CO2 underground? If it's not put in the right place, could it pop right back up? Then there is the expense of trapping and sinking it. Even under the best technological circumstances, Myer says, it may be decades before the political and economic infrastructure is there.