A new assessment report finalized in September 2005 by the Intergovernmental Panel on Climate Change (IPCC) concludes that capturing and storing the carbon dioxide (CO2) produced by power plants and factories before it enters the atmosphere could play a major role in minimizing climate change.

"While the most important solutions to climate change will remain energy efficiency and cleaner energy sources, this new report demonstrates that capturing and storing carbon dioxide can supplement these other efforts," said Executive Director Klaus T?pfer of the United Nations Environment Programme (UNEP).

"Since emissions of carbon dioxide - the most important cause of climate change - continue to rise in many parts of the world, it is vital that we exploit every available option for reducing their impact on the global climate. CO2 capture and storage can clearly play a supporting role," said Secretary-General Michel Jarraud of the World Meteorological Organization (WMO).

According to a number of studies, carbon dioxide capture and storage technologies (known as CCS) could lower the costs of mitigating climate change over the next 100 years by 30% or more. In addition, capture and storage of CO2 in geological formations could account for 15 - 55% of all emission reductions (equal to 220 to 2,200 billion tonnes (Gt) of CO2) needed between now and 2100 for stabilizing greenhouse gas concentrations in the atmosphere.

Many components of carbon dioxide capture and storage technology are already mature, including several applications of CO2 capture, pipelines and gas injection into geological formations. Three CCS projects are already in operation, in Algeria, Canada and the North Sea off the Norwegian coast. CO2 capture from large-scale power plants will require further demonstration over the coming years and decades. Other possible applications, such as ocean storage or fixing CO2 in stable carbonates, are still in a research phase.

The potential of capture and storage could be limited by several important non-technology constraints. In particular, unless governments adopt climate change policies that put a cost on emitting CO2, there will be no incentive to use these technologies.

Furthermore, while the available storage capacity in geological reservoirs is "likely" to be sufficient, the true amount is yet uncertain. This is particularly so in some regions that are experiencing rapid economic growth, such as South and East Asia.

Because CCS process requires energy, its adoption may increase the use of fossil fuels. For the same level of electricity production, a power plant with CO2 capture would require 10-40 % more energy than a plant without capture.

Under current conditions, producing electricity costs about US$0.04 - 0.06 / kWh (kilo-watt hour). Adopting today's CCS technologies would raise this cost by an estimated US$0.01 - 0.05 / kWh. The future costs of CCS could decline due to technological advances and economies of scale - perhaps by 20-30% over the next decade, assuming sustained R&D and deployment. On the other hand, rising oil prices could influence CCS costs. The report finds that such estimates for the current and future costs of CCS have significant uncertainties.

For CCS systems to contribute to lowering emissions from power generation - the sector with by far the greatest potential for this technology - the price of carbon dioxide reductions would have to exceed $25-30/tCO2 (ton of CO2) over the lifetime of the project (in 2002 dollars). CCS could play a role in emissions trading or the Kyoto mechanisms, but a methodology to account for emissions reductions may need further elaboration.

The most economically feasible storage options for CO2 are geological formations, particularly given the experience already gained by the oil and gas industry. Fortunately, a large proportion of existing power plants and other "point sources" lie within 300 km of areas that potentially contain storage reservoirs, such as oil and gas fields, unminable coal beds and deep saline water-bearing formations.

Technologies for injecting captured CO2 into the oceans may also have potential, but they are still in the research phase and have not undergone full-scale testing. They involve releasing CO2 into the ocean water column via a fixed pipeline or a moving ship, or depositing it onto the deep sea-floor at depths below 3,000 m where CO2 is denser than water. There are concerns regarding the impact such technologies could have on ocean life and it is known that marine organisms could can be harmed. Although the long-term environmental implications of changing the ocean chemistry in this way are unclear, the oceans could become significantly acidified if CO2 injection occurred on a large scale.

Technologies for storing CO2 virtually permanently by converting it into inorganic mineral carbonates are also in the research phase, and certain applications have been demonstrated on a small scale. The energy requirements for this technology, however, are still unfavorable and would need to be further improved before it could become a real option. Using captured CO2 for chemical processes in industry is technically possible but has hardly any potential for net reduction of CO2 emissions.

As important as technology and cost issues are health, safety, environmental and legal concerns, would also need to be addressed to ensure public support. Potential risks include leakage from capture, transport and injection (comparable to the risk in similar existing industrial operations) and slow leaks from storage sites (a low risk if reservoirs are carefully selected and best available technologies are used). A key legal issue would be how international law would treat CO2 injection activities in international seas.

The "IPCC Special Report on Carbon Dioxide Capture and Storage" report, written by 100 experts from over 30 countries and reviewed by many experts and governments, is posted at www.ipcc.ch