One ever-popular idea for reducing greenhouse-gas emissions from coal plants is to capture the CO2 at the smokestack and bury it underground. Up until now, the biggest hurdle here has always been cost: While burning coal is relatively cheap (that is, if you ignore the pollution, the coal ash spills, and the devastation wrought by mountaintop mining…), sequestering CO2 can be pretty pricey—pricier than efficiency and even a lot of renewable power options. But now it turns out there may be another problem. It could prove exceedingly difficult to find space to store all that carbon underground:

A new research paper from American academics is threatening to blow a hole in growing political support for carbon capture and storage as a weapon in the fight against global warming.

The document from [the University of Houston] claims that governments wanting to use CCS have overestimated its value and says it would take a reservoir the size of a small US state to hold the CO2 produced by one power station.

Previous modelling has hugely underestimated the space needed to store CO2 because it was based on the "totally erroneous" premise that the pressure feeding the carbon into the rock structures would be constant, argues Michael Economides, professor of chemical engineering at Houston, and his co-author Christene Ehlig-Economides, professor of energy engineering at Texas A&M University.

"It is like putting a bicycle pump up against a wall. It would be hard to inject CO2 into a closed system without eventually producing so much pressure that it fractured the rock and allowed the carbon to migrate to other zones and possibly escape to the surface," Economides said.

The paper concludes that CCS "is not a practical means to provide any substantive reduction in CO2 emissions, although it has been repeatedly presented as such by others."

As Tom Laskawy notes, there are currently about 600 coal-fired power plants currently operating in the United States. If just one station needs a reservoir "the size of a small U.S. state," well, things could start to get mighty crowded.