Carbon capture concerns raised

A new study claims there are unanswered questions about carbon sequestration and the impact of leakage on global warming.

Carbon sequestration or carbon capture and storage (CCS) is being promoted as a way to remove growing levels of carbon dioxide from the atmosphere.

Governments around the world are investing billions of dollars over the next decade developing carbon capture and storage systems to extract CO2 at power plants and other combustion sites and store it underground.

Prof. Gary Shaffer from the Danish Centre for Earth System Science examined a range of CCS methods to determine their effectiveness and long-term impacts.

Reporting in the journal Nature Geoscience, Shaffer says there are still questions over which sequestration process is best and which is least likely to leak carbon.

Fears for the future

"CCS has many potential advantages over other forms of climate geoengineering," says Shaffer.

"However, potential short and long-term problems with leakage from underground storage should not be taken lightly."

The study reveals leakage of sequestered CO2 could cause large-scale atmospheric warming, sea level rise and oxygen depletion, acidification and elevated CO2 concentrations in the ocean.

Shaffer says storing CO2 in the deep ocean is a bad idea because of the problems it creates for deepsea life by creating a "large dead zone." He adds that deep ocean stored CO2 would return to the atmosphere relatively quickly.

Geological storage of CO2 — either underground or below the ocean floor — may be more effective, but only if leakage can be kept down to one per cent or less per one thousand years.

Shaffer says any long-term leakage would need to be actively countered by re-sequestration, which would need to be carried out over many thousands of years.

Necessary approach

Dr Peter Cook, chief executive of the Co-operative Research Centre for Greenhouse Gas Technologies, says Shaffer's figures for geological sequestration mirrors the conclusions reached by the Intergovernmental Panel on Climate Change (IPCC).

Cook, who was involved with the IPCC study, says "as long as you have the right rocks to store the carbon in, then sequestration will do what nature does anyway in keeping CO2 out of the atmosphere."

"We have the Ottway Basin Project which has been going for two years. We've injected 65,000 tonnes there with no leakage," he says. "We compress the CO2 gas into a liquid and inject it into porous rocks below non porous strata, trapping it deep underground."

Cook says the study doesn't take into account the fact that CO2 stored underground becomes denser over time.

"It will actually sink further down rather than bubble up towards the surface," he says.

But Shaffer says society should be targeting the source of CO2 rather than relying on capture and storage.

"The dangers of carbon sequestration are real and the development of CCS should not be used as a way of justifying continued high fossil fuel emissions," he says. "We should greatly limit CO2 emissions in our time to reduce the need for massive carbon sequestration and thus reduce unwanted consequences."

Cook says under the current set of circumstances CCS will be needed.

"As long as we use fossil fuels geological sequestration will need to be part of the cycle."