IPCC on carbon storage: two cheers.

An emerging technology for helping to address climate change is carbon capture and storage (CCS), in which the heat-trapping carbon in fossil fuels is stripped out, either before or after combustion, and then injected into a reservoir. CCS is controversial for several reasons, but proponents argue that fossil fuels will retain a significant share of the global energy budget for some time under any transition scenario and that CCS would mitigate their climate effects.

Now the authoritative Intergovernmental Panel on Climate Change (IPCC) has released an assessment of the technical and economic potential of CCS, and the results are mixed. In general, the IPCC concludes that by 2050 CCS could sequester 20-40 percent of global carbon dioxide emissions from large point sources (such as power plants and factories), and that it could enable the reduction of carbon emissions from vehicles as well if they were driven by hydrogen or electricity made from CCS-treated fossil fuels.

On the other hand, the report estimates that use of CCS would raise electricity costs by 1 to 5 cents per kilowatthour, depending on the fuel, location, and other variables, even with new generating plants that incorporated CCS technology from the start. Retrofitting it to older plants would reduce efficiencies and raise costs even more. The usefulness of the geological storage options--oil and gas fields, unminable coal beds, and saline formations--hinges on their proximity to major point sources of emissions, an issue that has not been studied extensively. The ocean options present concerns, too. The carbon dioxide may be dissolved in the water or injected on to the sea floor below 3,000 meters, at which depth it is denser than water and is expected to form stable carbon pools. But dissolving it in ocean waters makes them significantly more acidic, and the ecological effects of these options are not fully understood. Neither are leakage rates, because of limited experience with carbon storage. Finally, while the various pieces of a CCS system may work to one extent or another, there is little experience in combining them into an integrated whole.

The entire report may be viewed and downloaded from the IPCC website (www.ipcc.ch).

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