Southern Co., a constant critic of federal attempts to regulate greenhouse gas emissions, must have seen the writing on the wall earlier this month when it promised to press ahead with a $2.8 billion power plant project in Mississippi. Its marquee "clean coal" project will convert lignite coal to gas and reduce carbon emissions that U.S. environmental regulators now plan to limit. Southern's determination to build a coal-to-gas plant despite high costs and regulatory hurdles comes as the Obama administration put an end to months of speculation about a U.S. EPA plan to combat power-sector emissions tied to climate change.