As pollution bad guys go, carbon dioxide may be the media darling, but trying to capture it and lock it away could allow other repeat offenders to go free.

Power plant emissions that cause acid rain, water pollution and destruction of the ozone layer may actually be made worse by capturing the CO₂ and pumping it deep underground, a new study reported online and in an upcoming International Journal of Greenhouse Gas Control suggests.

This increase of other emissions is largely because collecting and burying CO₂ — a process called carbon sequestration — requires additional energy, new equipment and new chemical reactions at the plants. And using current technology, meeting all of these requirements releases extra pollutants.

“Other studies mostly just look at one aspect, the carbon capture,” says study coauthor Joris Koornneef, an environmental scientist at Utrecht University in the Netherlands. “This is a first step in trying to quantify the [environmental] trade-offs.”

Captured CO₂ must be compressed to about 100 times atmospheric pressure (which takes energy), transported to a suitable underground reservoir (which takes energy) and pumped into the ground (which takes energy). A coal-fired power plant that sequesters its CO₂ must burn about 30 percent more coal than conventional plants to cover these energy needs. And that extra coal must first be mined (which has environmental effects) and transported to the plant (which takes fuel) — the list goes on and on.

Even with this extra burden, a CO₂-burying plant emits between 71 and 78 percent less CO₂ than a normal coal-fired plant for each unit of usable electricity produced, Koornneef and his colleagues report. But when the researchers factored in all the “cradle to grave” pollution of a CO₂-burying plant, emissions of acid rain-causing gases like nitrogen oxides and sulfur oxides were up to 40 percent greater than the total cradle-to-grave emissions of a modern plant that doesn’t capture its CO₂.

If the mining, transportation and other supporting technologies become greener in the future, the pollution penalty for carbon sequestration would be reduced, the researchers note.

“The decision to substantially reduce greenhouse gas emissions is going to be intertwined with decisions about how to deal with these other emissions,” comments Jim Dooley, an expert in carbon sequestration at the Joint Global Change Research Institute in College Park, Md., and one of the lead authors for a major 2005 report on carbon sequestration by the Intergovernmental Panel on Climate Change. That IPCC study concluded that nearly all properly buried CO₂ would probably remain underground for centuries.

“People are turning their attention to this, which is great,” Dooley adds, referring to the environmental costs of sequestration.

At the time that IPCC scientists were writing the 2005 report, “everyone was thinking what are the environmental benefits of [carbon capture], not so much the environmental costs,” comments Ken Caldeira, an ecologist at the Carnegie Institution for Science in Stanford, Calif., and another lead author of the IPCC report. “The costs people talked about were mostly economic costs.”

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