Rising costs have prompted new fears for one of the central planks of the Scottish Government's strategy for cutting climate pollution.
Scottish ministers want to keep burning coal in power stations by developing technology to capture and store the carbon dioxide they belch out. But new evidence from Norway suggests that this could cost nearly three times more than expected.
This comes on top of recent expert reports casting doubt on the feasibility of carbon capture and storage (CCS) - the great green hope of the energy industry. But technology is strongly defended by its backers in Scotland.
One of Norway's flagship CCS projects is run by the state-owned gas company, Gassco. But it has revealed that the estimated costs have rocketed from £0.4 billion in 2007 to £1.2bn now.
"The CCS costs are big and higher than we initially thought," said Sigve Apeland from Gassco. The company is trying to capture, transport and store 1.1 million tonnes of carbon dioxide a year from the Naturkraft gas-fired power plant at Kårstø.
Gassco told the environment company, ENDS, that the escalating costs were mostly due to the difficulties of actually capturing the carbon. It is a process that absorbs a lot of energy, which makes it expensive.
"This is only one example, but these kind of cost increases could kill off the prospect of having full-scale carbon capture working any time soon," said Dr Richard Dixon, director of WWF Scotland.
There is a pioneering scheme aimed at developing CCS at the Longannet coal-fired power station in Fife, run by ScottishPower. Both the Conservative and Labour parties have promised four CCS plants, but neither has said when.
A report from two universities in Texas has argued that the difficulties in storing carbon deep underground have been hugely underestimated. It concluded that burial was "a profoundly non-feasible option for the management of carbon dioxide emissions".
Patrick Harvie, the Green MSP, said: "The doubts about carbon capture and storage are growing week by week, and it looks increasingly like an impractical and unaffordable technology.
"It is wildly irresponsible to use the mere hope of a viable CCS option as an excuse for new coal plants, as both Labour and SNP governments have been doing."
The Scottish Government has backed plans to build a new coal-fired power station at Hunterston in north Ayrshire. But it is insisting that the plant starts up with one-fifth of its carbon being captured and stored.
Stuart Haszeldine, the ScottishPower CCS professor at the University of Edinburgh, pointed out that costs in Norway were always high. As CCS projects were developed, they would benefit from the economics of scale, he argued.
"It's entirely to be expected that the cost of capture will be extremely high for the first 10 or so projects in Europe," he said. "That is why these need support by national governments, as commercial companies cannot afford such expensive experiments."
According to Professor Haszeldine, the experience gained from experimental plants would as much as half the cost of subsequent plants.
For ScottishPower, which is owned by the Spanish energy company Iberdrola, the point of its prototype CCS plant at Longannet was to find ways of reducing costs. "That is key to the future of CCS, being able to capture CO2 effectively and efficiently without it being cost-prohibitive to ourselves or consumers," said a company spokesman.