BioEd Online

Sequestering carbon dioxide from industrial power plants could be important in reducing the threat of climate change, but not until the middle of this century.

So says a report released on 26 September by the Intergovernmental Panel on Climate Change (IPCC). It details emerging technologies designed to deal with the carbon dioxide emitted from sources such as power plants. The tools would capture the gas, compress it and store it somewhere, maybe underground, in the ocean or inside rocks. This would reduce the amount of greenhouse gas entering the atmosphere, and help to combat global warming.

There has been great interest in such projects, but it has been unclear exactly how much they could help the planet, or at what cost.

Number crunch

The report's authors say that, given expected technical limitations, 20-40% of global fossil-fuel emissions could be captured and squirrelled away by 2050. This could account for some 15-55% of all efforts to reduce greenhouse emissions in the coming century.

A new power plant fitted with the proper equipment, for example, could emit 80-90% less carbon dioxide than a normal plant, even taking into account the energy used to spirit away the emissions. Retrofitting existing plants with this technology produces less striking results.

But today's price is relatively large. Applying this technology to electricity production under 2002 conditions would increase electricity generation costs by 1-5 US cents a kilowatt hour. That is a big hike, given that a typical coal plant produces electricity at a cost of 4-5 cents per kilowatt hour.

Down under

Where would the captured carbon dioxide be stored? The report says that, at the moment, injecting it into emptied oil reserves more than 800 metres beneath the ground is a leading option. Three industrial projects to store the gas underground are already under way, in Norway, Canada and Algeria.

Scientists estimate we could stash some 2,000 billion tonnes of carbon dioxide underground using current technologies. Energy production and other activities, including making cement and refining oil, currently produce about 14 billion tonnes of carbon dioxide each year.

Other less developed options for carbon dioxide storage include pumping the gas into the sea, where it might dissolve, or locking it up in minerals. The gas might even be used in industry.

But IPCC scientists emphasize that putting carbon dioxide into the ocean increases the water's acidity, and the broad impact of this on marine ecosystems remains unclear.

Environmental groups stress that carbon capture and storage technologies will not have a significant effect for decades. "It will simply not be ready in time to provide us with the huge near-term emissions cuts that we need in order to avoid catastrophic climate change," says Gabriela von Goerne, a climate expert for Greenpeace, the international conservation group based in Amsterdam.