deep-sea cure for climate change?

Environmental group Greenpeace said it was skeptical of the benefits and urged the development of less expensive and swifter solutions to global warming such as renewable energy and conservation.

"We have real questions about this technology. It is not something that currently works or is tested," said Chris Miller, a senior Greenpeace campaigner. "We have a relatively short amount of time to begin making pretty dramatic reductions in global warming pollutants."

Managing a carbon dioxide sequestration program could also cost hundreds of billions a year, scientists say.