Coal-fired power plants are responsible for a third of the carbon dioxide that’s pumped into the atmosphere in the U.S.—that’s two gigatons. Naturally, a lot of folks are trying to think of something better to do with all that CO2 than spewing it into the air. One solution that’s been batted around by everyone from energy companies to environmentalists is carbon sequestration, a process that captures carbon dioxide before it’s emitted and sticks it somewhere where it won’t do any (or not much) harm. This involves separating the CO2 from other gases, compressing it into a liquid so it can be transported, and then injecting it into a contained location.

“We should be utilizing this technology with new coal plants from now on,” says George Peridas, a scientist with the Natural Resources Defense Council. Energy companies are also gung-ho on sequestration methods—not only because they help reduce their emissions, but also because many of these techniques will make it possible to harvest additional energy sources like methane. Here’s a quick primer on how some of these ideas work.

1) Coal Seams: Coal beds hold methane, which is commercially valuable as a natural gas. When CO2 is injected, it displaces the methane and pushes it out. Potential CO2 storage capacity: 120 gigatons.

2) Saline formations: Deep, salty pools of water lie below much of the U.S. This brine reacts with injected CO2, helping to keep it locked in place. Potential CO2 storage capacity: 3,200 gigatons.

3) Marine Algae: Scientists are experimenting with ways to lace oceans with iron particles to promote algae growth; ostensibly, the algae would consume CO2 before sinking to the bottom of the sea. So far, results don’t look promising.

4) Depleted oil and gas reservoirs: Liquefied CO2 injected into oil reserves mixes with the oil and makes it easier to sweep out. When pumped into natural-gas reservoirs, the excess pressure forces gas to the surface. Potential CO2 storage capacity: 80 gigatons.

5) Ocean sea bed: Theoretically, liquid CO2 could be injected deep below the ocean floor, where it would stay locked under the surface. No one has tested this scenario yet, however.

Story by Susan Cosier. This article originally appeared in Plenty in June 2007. This story was added to MNN.com in June 2009.

Copyright Environ Press 2007.