The energy sector accounts for about one-third of all carbon emissions in the United States, according to the EPA. Trimming the pollution from that sector of the economy could be accomplished through a number of means, and the proposed rule would allow states to take advantage of many of them: Cap-and-trade, investment in alternative energy sources, and so on. EPA Administrator Gina McCarthy had previously hinted that the EPA would soon be proposing a "controversial" rule. However, she also said the rule would provide states with considerable flexibility in implementation.
The Clean Air Act of 1970, first signed into law by Richard Nixon and then amended twice, requires the EPA to regulate pollution that threatens public health and welfare. As the Supreme Court affirmed in a landmark 2007 ruling, it’s basically up to the EPA to decide what kinds of pollution meet that standard. In 2008, Stephen Johnson, who was then the EPA Administrator, formally told President Bush that the federal government is “compelled to act” on climate change. Bush ignored the recommendation. One year later, Lisa Jackson, Johnson’s successor, issued an official “endangerment finding” that greenhouse gases were trapping heat inside the earth’s atmosphere and causing temperatures to rise rise.... [T]he Obama Administration is carrying out the intent of Congress, as expressed in previously enacted legislation. This Congress is entitled to feel differently than its predecessors did. But to take away EPA's mandate to act, it would have to pass new legislation that supersedes the old. In other words, it would have to amend or repeal the Clean Air Act itself. That's not likely to happen.