The United States unveiled plans on Tuesday to bury climate-warming carbon dioxide emissions deep underground to keep the greenhouse gas from further heating up the atmosphere.

The burial process, known as carbon capture and storage or geologic sequestration, has long been part of the Bush administration's strategy to combat climate change without imposing any economy-wide limit on carbon emissions.

But this is the first time the US government has proposed requirements on how to do it. No federal rule is expected until late 2010 at the earliest, according to Benjamin Grumbles of the Environmental Protection Agency.