If the cost to remove carbon was between $30 and $90 a ton, that would be roughly the same as other emission reduction measures used to trim energy consumption in buildings, automobiles and appliances, the report said.

However, removing carbon roughly equal to one-fifth of annual US emissions would require nearly 148 million acres -- an area the size of Texas -- and cost more than $7 billion each year, the study said.

"When and if a mandatory domestic greenhouse gas reduction program is established in the United States, a carefully designed carbon sequestration program really ought to be included in a cost-effective portfolio of compliant strategies for the country," said Robert Stavins, a Harvard University economist who co-authored the report.

Stavins and another researcher, Kenneth Richards from Indiana University, said carbon sequestration would become more attractive in the United States as current voluntary practices to cut emissions eventually become mandatory through action from Congress or the White House.

Most carbon dioxide in the atmosphere comes from burning fossil fuels such as coal and oil. The United States is the world's biggest emitter of the greenhouse gas.

The Pew report cautioned that while carbon sequestration is a promising tool to reduce global warming, a large-scale plan has many unanswered economic, political and social questions.

The 40-page report, which reviewed and extrapolated on earlier studies, said it was vital for the US government to make the technology enticing to private landowners, especially early on when the program would require a significant amount of capital and land. Such incentives could include special payments or tax credits.

The United States produces an estimated 5.8 billion tons of carbon dioxide annually, according to the US Energy Department. By 2050, as much as 250 billion tons of carbon could be captured from the atmosphere and stored in soil or underground geological formations, such as abandoned oil wells, the government said.

The Pew report said several factors could affect the success of carbon sequestration projects, including alternative uses for the land and the development of long-term methods to track carbon removal.