Sen. McConnell and Sen. Murkowski are misleading the public. Framing the EPA's regulation of greenhouse gasses as usurping Congressional authority is fully misleading and a flat out lie. Here's why...
Sen. Murkowski's Dirty Air Act, which would eliminate the EPA's ability to regulate greenhouse gasses, is claimed to be necessary because the EPA is allegedly overreaching in it's authority. Sen. McConnell has called it a "blatant power grab by the administration and the EPA." (AP story here). Sen. Murkowski claims that "You either support the Congress setting the policy on climate change or you support the EPA in their capacity as a regulatory agency setting policy," framing the debate as "elected officials (congress)" vs. "unelected officials".
The summary of Sen. Murkowski's argument is that the EPA, as an unelected body, does not have the congressional authority to regulate greenhouse gasses. This is wholly untrue.
The 1963 (and subsequently amended) Clean Air Act gives the authority to regulate anything that is considered a pollutant. In fact, the CAA requires the EPA, under threat of lawsuit from private citizens, to regulate any emission that would "threaten the public health and welfare of current and future generations." A 2007 ruling in Massachusetts v. EPA established that the greenhouse gasses did indeed fall under the definition of a pollutant under the CAA.
The short of it is simple: The authority to regulate greenhouse gasses was assigned to the EPA in 1963, under the Clean Air Act, by an elected body. The response to the claim that EPA regulation is overstepping it's authority is best refuted by the argument that, in truth, the attempt to forbid the EPA from enforcing the CAA is itself an attempt to circumvent the law, as established by Congress.
The CAA and subsequent amendments were passed by Congress and signed into law by the President. If Sen. Murkowski is worried about overstepping authority, she should be reminded that any attempt to circumvent implementation of the law would be unconstitutional unless done through a congressional act, signed by the President. Sen. McConnell's argument that EPA regulation is a "blatant power grab," and Sen. Murkowski's false argument that EPA regulation is somehow lacking in constitutional foundation and flies in the face of Congressional authority, are purely false and misleading.