The United States has enough deep saline aquifers to store a century's worth of carbon dioxide emissions from its coal-fired power plants, a study shows.

While efforts to reduce greenhouse gases have focused on sources of clean energy, such as wind or solar power, "one thing that's not going away is coal" because it's such a cheap and widely available source of power, Ruben Juanes of the Massachusetts Institute of Technology said.

Some researchers have proposed systems for capturing emissions from the burning of fossil fuels such as coal, then compressing and storing the waste in deep geological formations, an approach dubbed carbon capture and storage.

While deep saline aquifers -- at more than half a mile below the surface safely below the freshwater sources used for human consumption and agriculture -- are attractive storage possibilities, the capacity of U.S. aquifers has been the subject of much debate.

The MIT researchers used computer modeling to estimate the capacity of the available aquifers across the country, which they say is enough for at least a century's worth of carbon capture and storage.

Though questions remain about the economics, it should be a part of any greenhouse gas reduction proposals, the researchers said.

"I really think CCS has a role to play," Juanes said. "It's not an ultimate salvation, it's a bridge, but it may be essential because it can really address the emissions from coal and natural gas."