Fossil fuel burning wouldn't be so bad for the environment, were it not for all of the climate-changing carbon dioxide released in the process.
One solution could be to catch it before it escapes from a coal-burning power plant and lock it away underground. That may sound crazy -- and some say it is -- but carbon capture and storage (CCS) is moving closer to reality.
The U.S. Department of Energy announced earlier this month their funding -- to the tune of $126 million -- of two large-scale carbon storage projects in California and the Midwest. The DOE had previously announced $253.7 million in funding for four others.
"The announcement of these two projects, making a total of six, each with a minimum of a million tons [of CO2 injected underground], is a massive step forward," said Julio Friedmann of Lawrence Livermore National Laboratory in Livermore, Calif.
"It's been recognized for a while that there need to be many large-scale injections to learn what it is we need to learn," Friedmann said.
Companies have been injecting CO2 into the ground already, including in efforts to help force the last bits of oil out of oilfields, but the scale does not match what is needed to store CO2 from coal-fired plants.
"The next tier of questions include ones that really require a large, sustained injection," said Friedmann.
These projects will help researchers understand how the Earth's crust deforms as large volumes of CO2 are pumped underground, and which sites are the best for storing CO2, Friedmann said.
The Carbon Conundrum
Meanwhile, the Environmental Protection Agency is drafting regulations to address how sites for CO2 burial should be selected, managed and monitored and to address questions of who pays if something goes wrong. These will be released in July --- a fast track for rulemaking, sources said.
"Having the regulations established is going to be helpful in moving the technology forward," said Sarah Forbes of the World Resources Institute in Washington, D.C.
To Friedmann and Forbes, advancing the use of CCS is critical for addressing climate change.
"You have a new coal plant in China and India being built every single day," Forbes said. "The climate change problem is so big, and you can't address it without addressing coal."
"I've worked on analyses where I've said, 'Let's make wild assumptions about the progress of renewables and whether we still need CCS,' and I think the answer is we do," Forbes added.
But others disagree.
Emily Rochon of Greenpeace International in Amsterdam, Netherlands, said their calculations show emissions targets can be met through developing renewable energy sources and improving energy efficiency while phasing out coal.
"The problem with CCS is that it will completely derail efforts to get off coal," Rochon said. "It's not going to be any easier 30 years from now to make the transition to renewables. It's not going to be any faster. And by then, it's probably too late."
Rochon is the lead author on a Greenpeace report published earlier this month arguing against CCS.
Rochon points out that coal brings with it many environmental costs besides CO2: "Even if CCS can ameliorate CO2, we're still going to be blowing the tops off of mountains and dumping the tailings."
"One of the better articulated arguments against CCS is that it prolongs a coal economy and that there are big problems with the coal economy," Friedmann concedes. "There are just people who don't like coal. The best argument against that is, 'Are you prepared to triple the cost of electricity to fix the climate problem?' If you aren't, we need this option."
The Technology Is One Thing
Rochon also worries that industry's pledges to build plants that are "capture ready" -- suitable for installing equipment to capture CO2 once economics or regulations drive action -- provide no guarantee that the technology will ever be used.
Since CCS adds a large cost to coal combustion, there is little incentive for power plants to push forward until CO2 emissions cost something, said civil and environmental engineer Michael Celia, of Princeton University in Princeton, NJ.
"Right now we don't know if carbon is going to have a price and what that price may be," Celia said. "Until those are given much more certainty it's hard to imagine that much is going to go forward."
How It Works
Capturing CO2 from industrial processes can be done in a few ways. Most commonly the gas from combustion passes through a liquid containing amines that absorb the CO2.
The CO2 is then separated and compressed into a "supercritical fluid" that behaves much like a liquid. From there, the CO2 is transported to sequestration sites along pipelines. Some of these already exist for transporting CO2 for enhanced oil recovery, but widespread CCS would require a much bigger network.
The CO2 is injected at least a kilometer or so underground. At that depth, the temperature and pressure are high enough that the CO2 will remain in the supercritical, liquid-like state.
The key to making it stay down there is choosing the right site. The CO2 needs to be injected into porous rock layers that have room for it, but below impermeable layers that can act as a cap to keep the CO2 trapped beneath.
One of the concerns has been whether such sites may leak.
"I am not worried about leaks with proper regulation and siting," said Ken Caldeira of the Carnegie Institution of Washington in Stanford, Calif.
But, he adds, "The incentive to the industry will be to put the CO2 in the cheapest, easiest place, which may not be the best place. So it all depends on good regulation and enforcement."
Although the Greenpeace report cites sources saying CCS won't be practically available until 2030, others suggest that the reasons for the delay are political and regulatory, not technical.
"All of the major technologies needed for this are available. If there were a serious political will to make this happen, it could happen in the near term," Celia said.
But Rochon said such efforts would come at the cost of funding for renewables, which should be a higher priority.
"The concern with the cost of CCS is the fact that industry is asking the government to fund it and that therefore it takes away from funding for renewables," she said.
Friedmann, Forbes and Celia agree that efforts in renewables and efficiency are just as important, but, Celia said, "We need many solutions."
"There's been growing awareness that there really is a climate crisis," Friedmann added. "And we need to fire on all pistons quickly."