"A lot will depend on the next few years," said Chizmeshya, whose group has received $1 million in federal funds in the past five years.
Many power plant executives and conservationists instead favor biological sequestration by growing trees or changing farming practices. Trees and other plants absorb carbon naturally, but they release it again when they are cut down or burned.
Some scientists favor "carbon sequestration" using trees, which absorb carbon dioxide, as in a project underway along the Neches River in Texas.
In the past four years, utility executives, eager to show they are countering their industry's contribution to global warming, have teamed up with environmental nonprofits to buy land that serves simultaneously as a carbon sink and protected wildlife habitat.
Twenty-five U.S. energy companies have committed $3 million to establish six biological carbon sequestration projects in Arkansas, Louisiana and Mississippi through a group called PowerTree Carbon Co. The consortium aims to plant enough trees to capture more than 2 million tons of carbon dioxide from the atmosphere.
American Electric Power (AEP) has spent $24 million on such projects, restoring a bottomland hardwood forest in central Louisiana in collaboration with the Virginia-based Conservation Fund and buying timber rights in Bolivia with the Nature Conservancy.
"It's something the public can identify with," said AEP's eco-asset manager Gary Kaster, who also heads PowerTree.
Last month, the Pew Center on Global Climate Change issued a study by two environmental economists suggesting that the United States could offset a third of its annual carbon emissions by planting trees, at a cost of between $30 to $90 per ton. Under this scenario, the nation could meet half of the requirements mandated under the Kyoto global-warming treaty, which the United States rejected, for $7.2 billion a year.
Harvard University economist Robert Stavins, a co-author of the Pew study, said this approach, while expensive, is comparable in cost to options such as fuel switching or greater energy efficiency.
"It's something to look at right now, rather than a long-term solution," Stavins said, adding that over time it will become cheaper to use alternatives to fossil fuels.
Scientists are also exploring liquefying carbon dioxide and pumping it into saltwater aquifers half a mile beneath the surface: The Norwegians are already storing CO
under the North Sea, and similar potential reservoirs exist in the Midwest and elsewhere.
Detractors say all these efforts are wrongheaded. Each one has potential liabilities, they say: Mineral sequestration requires unearthing massive amounts of rock to produce the final carbonate, and biological sequestration only works until the trees are disposed of or burned.
"To balance out a rainforest in Bolivia with a coal-fired plant in Ohio is not a fair trade," said Kert Davies, research director at Greenpeace USA. "Meaningful greenhouse-gas cuts are what we should be investing the big bucks in now."
But with the administration and utility officials firmly opposed to mandatory CO
restrictions, many scientists say they feel the need to explore even somewhat far-fetched technological possibilities.
"We have so much fossil energy and it's so cheap, the temptation to use it will be there for a very long time," said Klaus Lachner, a Columbia University physicist who has been working with an Arizona entrepreneur on a scheme to capture carbon from the air and store it. "If we think we already have a problem, we've just scratched the surface."