Berlin/Washington - It's one of the dirtiest forms of energy on the planet and a leading cause of global warming. But coal could, with a bit of luck and a lot of money, become the world climate's saving grace. Across the globe, scientists, politicians, environmentalists and investors are all asking themselves a key question: Just how real, and how viable, is CCS (carbon capture and storage) technology, and can it deliver "clean coal"?
As a fuel to supply the ever-growing demand for electricity, coal is as cheap as it comes - but it's also as dirty as it gets. Coal is responsible for about 40 per cent of the world's emissions of carbon dioxide (CO2), the greenhouse gas that is chiefly blamed for causing global warming, as well as being an air pollutant.
CCS technology promises coal without the carbon, by an industrial process that removes the CO2 either during or after combustion, and stores it underground rather than releasing it into the atmosphere.
As negotiators gather in Copenhagen from December 7-18 in an attempt to hammer out a new climate treaty, the debate over CCS is accelerating.
The problem is that commercially viable CCS is perhaps as much as 20 years away. Nevertheless, technological trials are already well underway.
At the coal-fired Mountaineer plant in West Virginia, American Electric Power has partnered with French power firm Alstom to install its chilled ammonia process technology - a method of separating CO2 - in a 20-megawatt portion of its 1,300-megawatt plant.
In Germany, utility Vattenfall opened the world's first CCS pilot plant in 2008, and hopes to open a 300-megawatt plant that would demonstrate the commercial viability of CCS technology by 2015.
CCS has divided the global environmental community. Some denounce it as a sham deployed by a coal industry desperate to avoid an inevitable shift towards cleaner energy sources. Others see it as the only way to clean up a fossil fuel that will inevitably remain part of the global energy mix for years to come.
"Coal is not clean and it's not going to be," said Sarah Forbes, who leads clean coal research at the World Resources Institute (WRI), an environmental group based in Washington. "But pragmatically, I'm not sure we can reach our climate goals without CCS."
Forbes said at least 20 larger-scale demonstration plants - at a cost of up to 1.5 billion dollars each - are needed around the world to see if the technology has any hope of succeeding.
US President Barack Obama seems to agree. The administration has restarted a public-private project in Illinois to build the world's first full-scale clean coal power plant, costing at least 1.5 billion dollars. Former president George W Bush withdrew state funding for the "FutureGen" plant in 2008 after five years of cost overruns.
Obama's fellow Democrats are also pushing for climate legislation in Congress that includes billions of dollars in incentives for the coal industry to clean up its act. This could sweeten the deal for lawmakers from coal-producing rural states.
Others believe the technology will never be viable. The Sierra Club, the oldest environmental organization in the US, has launched a multimillion dollar "Beyond Coal" campaign that ridicules CCS.
"The amount of resources that would be required to really clean up coal are so massive, and I think the results are still so uncertain, that my preference would be to see those resources invested in moving beyond coal," said Mary Anne Hitt, deputy director of the campaign.
Global advocacy group Greenpeace also says CCS will be too little, too late, to have any positive effects on the climate, and warns that spending money on the technology actually harms other prospects like wind and solar power. The group estimates the first commercial CCS plants won't be online before 2030.
"If you examine the interplay between CCS, renewables, energy efficiency and nuclear power, it's very much an either-or proposition," said Emily Rochon, Greenpeace's lead researcher on CCS. "The notion that you can have all the options on the table is false."
In Germany, serious regulatory and public relations challenges lie ahead for CCS. Berlin's attempt to adopt the European Union's CCS directive in 2009 failed, partly because of fears of where CO2 would end up being stored.
The technology ideally places captured CO2 in deep underground caverns or underneath the sea. Where underground storage sites have been suggested, public opposition has sprung up.
"With windmills, its 'NIMBY - Not In My Back Yard'," said Damian Mueller, spokesman for Vattenfall's CCS project. "With carbon storage, it's 'NUMBY - Not Under My Back Yard'."
Vattenfall would like to build and export its technology now being developed at Schwarze Pumpe, near the Czech Border - but is stuck because there is no long-term regulatory framework for CO2 storage.
The EU has made over 1 billion euros (1.5 billion dollars) available for research and development, but state money - to save both the climate and the coal industry - will undoubtedly be asked for, whatever Copenhagen throws up.
