According to the Post:
The proposal -- which comes in response to a 2007 Supreme Court decision ordering EPA to consider whether carbon dioxide and other greenhouse gases should be regulated under the Clean Air Act -- could lay the groundwork for nationwide measures to limit such emissions. It reverses one of the Bush administration's landmark environmental decisions: In July 2008 then-EPA administrator Stephen Johnson rejected his scientific and technical staff's recommendation and announced the agency would seek months of further public comment on the threat posed by global warming pollution.
Some environmentalists have expressed optimism over this news. Frank O’Donnell, who heads the public watchdog group Clean Air Watch, told the Post that “it will set the stage for the first-ever national limits on global warming pollution.”
The EPA has yet to comment on the situation.