Friday, September 21, 2007

Potential For Carbon Sequestration In The U.S.

Sep 20: The Congressional Budget Office (CBO) released a report entitled, The Potential for Carbon Sequestration in the United States. The 32-page report was prepared at the request of the Chairman of the Subcommittee on Private Sector and Consumer Solutions to Global Warming and Wildlife Protection of the Senate Committee on Environment and Public Works -- Senator Joseph Lieberman (I-CT). The report examines the methods, technological potential, and possible costs of carbon sequestration in the United States. In accordance with CBO’s mandate to provide objective, impartial analysis, the paper makes no recommendations.

According to the report, human activity emits roughly 32 billion metric tons of carbon dioxide (CO2) -- the primary greenhouse gas -- into the atmosphere each year. Worldwide, about 80 percent of those emissions come from the combustion of oil, coal, natural gas, and other fossil fuels; the remaining 20 percent comes from deforestation. (Because plants take in CO2, removing them releases some or all of that carbon.) Currently, in any given year, the equivalent of about half of total CO2 emissions are absorbed by the world’s oceans, soil, and vegetation, which (together with the atmosphere and fossil carbon deposits) make up the
natural reservoirs through which carbon flows over time.

The other half of those emissions remain in the atmosphere, contributing to the rising atmospheric concentration of CO2 and the gradual warming of the Earth’s climate. Various analyses suggest that avoiding future climate related damage by starting to reduce the atmospheric concentration of CO2 would have greater benefits than costs. Options for doing that include not only curbing activities that generate emissions but also sequestering CO2 -- for example, by encouraging its absorption from the atmosphere into vegetation and soil (biological sequestration) and by trapping CO2 at power plants and industrial facilities before it is emitted and injecting it into underground storage sites (a process known as carbon dioxide capture and storage, or CCS).

The paper looks at the methods, potential scale, and possible costs of both types of carbon sequestration. It also examines the particular role that sequestration could play in the context of the full range of possible actions to mitigate greenhouse gas (GHG) emissions. The report indicates that biological sequestration faces implementation challenges, in part because it can be easily reversed by common natural disturbances, such as fires, or by changes in land use and management. Carbon dioxide capture and storage involves capturing CO2 emissions for long-term storage in geologic formations such as oil or natural gas fields, coal seams that cannot be mined economically, or deep saline formations. Such sites offer the potential for much larger and more secure storage than biological sequestration does. (Another possibility is to inject CO2 deep into the ocean, but that option raises significant ecological concerns.)

Studies estimate that biological sequestration has the technological potential to sequester about 40 billion to 60 billion metric tons of CO2 in the United States over the course of 50 years and another few tens of billions of tons over the following half-century. The total capacity for storing captured CO2 emissions in geologic formations is estimated at roughly 1.2 trillion to 3.6 trillion metric tons. Thus, the United States has the technological potential to offset roughly a decade’s worth of its current CO2 emissions through biological sequestration and a few hundred years’ worth of emissions through carbon dioxide capture and storage.

If a policy was established to limit the atmospheric concentration of CO2, it would effectively put a price on CO2 emissions -- with a corresponding value for CCS and perhaps also for biological sequestration. The specific details of the policy would determine the price. The range of recently debated policies and literature on the economic costs of reducing greenhouse-gas emissions suggest a CO2 price of about $5 to $65 per metric ton by 2020.

CO2 capture and storage, which has a fairly large technological potential, has not yet been demonstrated on the scale envisioned for mitigating CO2 emissions. It is also more costly than biological sequestration. Analysts estimate that the CO2 price would need to be in the range of $15 to $90 per metric ton (depending on the type of electricity plant at which the CO2 was captured) to cover the anticipated costs of CCS and exploit the full potential for geologic storage. That potential corresponds to several hundred years’ worth of CO2 emissions at current U.S. levels.

To refine estimates of the extent to which the United States might use carbon sequestration practices, those practices need to be considered in the context of a broader range of strategies for mitigating climate change. Other strategies include increasing the nation’s reliance on renewable or alternative sources of energy (including biofuels), using energy more efficiently, and reducing emissions of other greenhouse gases (such as methane and nitrous oxide). The relative importance of those different strategies is apt to vary over time with changes in the price for CO2. Analysis suggests that limits on CO2 emissions would be likely to spur an increasing, and relatively large, reliance on carbon dioxide capture and storage for some time. By contrast, the economic potential for biological sequestration would start to decline after some point.

Access the complete CBO report (click here). [*Climate]