Each year, the U.S. releases more than 1.6 million metric tons of heat-absorbing greenhouse gases into the atmosphere. Of this amount, about 81 percent comes from the combustion of fossil fuels ? oil, coal, and natural gas.

So far the government has focused on decreasing emissions as the solution to reducing atmospheric CO₂ levels. But now the Department of Energy is investigating the feasibility of carbon sequestration ? disposing of the CO₂ after it is produced. The idea of carbon sequestration isn’t new, but the DOE is just beginning to take it seriously. This year the department is spending $29 million to study the process.

An ambitious and controversial project is the proposed CO₂ Ocean Sequestration Experiment. In this project, researchers will extract CO₂ from power plant exhaust and convert it to liquid. They will then pump 40 to 60 tonnes of the liquid into the ocean bottom off the coast of Hawaii. Designed to minimize impact on the environment, the experiment will take place in water more than 3,000 feet deep and will run for about 40 hours over a two-week period. It is scheduled for the summer of 2001.

How else might we dispose of all this unwanted CO₂? Possibilities include the following:

• Piping it into oil fields. This would help extract oil by thinning it and causing small globs to swell and join together. A similar technique is already used to obtain oil, but it uses as little CO₂ as possible. In this case the goal would be to inject as much CO₂ as possible.
• Injecting it into coal seams too deep to mine. Methane molecules cling to coal, but CO₂molecules dislodge them and take their place. If this technique worked, disposing of CO₂ would yield a new source of natural gas.
• Pumping it deep underground. The U.S. is rich in deposits of briny water, not suitable for drinking. CO₂ could be injected 2,000 feet or more beneath these deposits. If encased in rock, the gas would theoretically remain underground forever.

Some environmental groups have objected to carbon sequestration on the grounds that it will remove incentive to use fossil fuels more efficiently and expand use of alternative energy sources. The Energy Department responds that it will continue to encourage businesses and consumers to find ways to reduce greenhouse gas emissions. But adding the extra step of removing existing emissions may be necessary to meet long-term air quality goals.

All of these methods have yet to be studied in depth, and it could be decades before they are put into practice. A primary obstacle is cost, particularly the cost of extracting CO₂ from smokestacks. The government hopes to develop a process that will increase consumer electric bills by no more than 2 to 5 percent.

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